Title of Invention	A COMBINED TOROID/SHUNT DEVICE FOR DETECTING RESIDUAL CURRENT IN AN ELECTRICAL INSTALLATION
Abstract	A combined toroid/shunt device for detecting a residual current in an electrical installation comprising a plurality of conductors such as a live conductor 2 and a neutral conductor 3 is described. The device comprises a toroid means 1, 4 for detecting an AC residual current within a first range and a plurality of resistive shunts 6a to 6d for connection in respective ones of the plurality of conductors. A current detection means 5, 7, 13 responsive to current flowing in each of said shunts for detecting a DC residual current and/or an AC residual current within a second range is described. The first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between conductors up to a saturation level at which the toroid or electronic means associated means therewith becomes saturated. The second range includes an AC residual current of said saturation level.

Title of Invention

A COMBINED TOROID/SHUNT DEVICE FOR DETECTING RESIDUAL CURRENT IN AN ELECTRICAL INSTALLATION

Abstract

A combined toroid/shunt device for detecting a residual current in an electrical installation comprising a plurality of conductors such as a live conductor 2 and a neutral conductor 3 is described. The device comprises a toroid means 1, 4 for detecting an AC residual current within a first range and a plurality of resistive shunts 6a to 6d for connection in respective ones of the plurality of conductors. A current detection means 5, 7, 13 responsive to current flowing in each of said shunts for detecting a DC residual current and/or an AC residual current within a second range is described. The first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between conductors up to a saturation level at which the toroid or electronic means associated means therewith becomes saturated. The second range includes an AC residual current of said saturation level.

Full Text	Measuring Devices This invention relates to measuring devices for electrical installations, and in particular to measuring devices including a current/voltage detection module for analysing current and voltage to facilitate, inter alia, a residual current detection and power consumption. A method of detecting for residual current may involve using a current transformer having primary windings through which, in the case of a single phase device, load current flows in opposite directions so that if the return current is different from the outwardly flowing current because of current leakage, an output current signal is induced in a secondary winding of the transformer. In the case of a multi-phase device, primary windings of the transformer are connected in all of the phase lines and the neutral line. In normal situations, when there is no current leakage, the net current induced in the secondary winding is zero and therefore no output is detected. These devices are subject to nuisance tripping arising from surges in the supply, switches in appliances and the like. Further problems arise because the transformer is designed to be sensitive to very small current imbalances caused by current leakage. With relatively large current leakage faults, the magnetic flux may cause the transformer core to become saturated and so fail to induce a current in the secondary winding. Alternatively, a large induced current may cause saturation of an amplifier in the electronic circuit which is used to process the induced current signal. Also, toroidal transformer devices may be insensitive to dc current leakage faults, such that the fault goes undetected and no trip occurs. Many electrical systems incorporate switching power supplies, for example ac to dc converters and inverters in motor speed control and start-up systems. In such systems the ac supply phases are switched electronically (for example with high voltage FETs) to provide rectified waveform signals. In such cases a current leakage fault may not induce sufficient current in the secondary winding to detect the fault. One method of determining power consumption is to measure the voltage across the power supply wires and the current flowing through them and then multiply the current by the voltage measurement to determine a power measurement. One approach is to use a shunt of known value connected in series with one of the wires and to measure the voltage across and current flowing through it. Power meters include a counter or clock for measuring the number of watt- hours consumed. The counter or clock is periodically read manually in order that the consumer can be billed for the quantity of electricity used. Shunt resistors could also be used to detect an imbalance in the current caused by a current leakage. However, to be useful on their own as a residual current detection safety device for tripping a circuit breaker, the shunt resistors would have to be extremely accurate. The current flowing through the shunts would need to be detected to an accuracy in the order of 1 to 10 mA in 100 A (105 to 10-4). This means that sophisticated and complex measurement circuitry would be needed to provide the required resolution as well as precise and stable shunt resistors having linear resistance characteristics. Conventionally, residual current devices and power consumption meters are separate discrete devices. The power consumption meter is usually located at the point of entry of the electricity supply into the premises and the residual current device is located within the consumer unit or fuse box from which the circuits to the premises are distributed. It is an aim of the present invention to devise a combined residual current and power measuring device which overcomes or at least alleviates these problems. It is a further aim of the invention to devise a combined residual current and power measuring device which is less bulky than conventional devices and operates to an improved degree of sophistication such as to facilitate remote monitoring of the electrical installation. According to a the present invention, there is provided a a combined toroid/shunt device as defined in claim 1. In an embodiment, the combined toroid/shunt device further comprises an electronic means associated with the toroid means for processing the current signal, the first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between the conductors up to a saturation level at which the toroid or electronic means associated therewith become saturated, and the second range includes AC residual currents above said saturation level. The combined toroid/shunt device may further comprise a processor means for generating a trip signal indicative of the presence of a residual current fault in dependence on said residual current signal and/or said current signal indicative of current detected in each of said shunts. Preferably, the processor means is operative for generating a current imbalance signal indicative of the residual current during real time from the residual current signal, and the trip signal is generated on the basis of a comparison of the current imbalance signal with a predetermined threshold criterion. More preferably, the combined toroid/shunt device further comprises a circuit breaker operative to break said AC supply in response to said trip signal. In another embodiment, a measuring device for an electrical installation comprises the combined toroid/shunt device. Here, the current detection means is responsive to current flowing in each of said conductors for generating a current signal indicative of the current detected in each of said conductors. The measuring device may further comprise a resistor detector means for connection between said neutral and live conductors for generating a voltage signal indicative of the voltage between said live and neutral conductors by measuring the voltage drop across the resistor means or a potentially divided portion thereof. Preferably the processor means is operative for generating an output signal derived from said current and voltage signals to facilitate determination of power consumption. The processor means of either the combine toroid/shunt device or the measuring device may also comprise a first analog to digital converter coupled to a secondary winding of the transformer for generating the residual current signal as a digital signal representative of the voltage sensed across the winding and/or the current in the winding. Preferably the device also comprises a second analog to digital converter coupled to the shunt resistor detector for generating digital signals representative of the current flowing through the neutral conductor and each of the at least one live conductors. More preferably, the second analog to digital converter is coupled to said resistor detector means for generating digital signals representative of the voltage between said neutral and live conductors. The first and/or the second analog to digital converter may include a multiplexer for selectively coupling two or more of said detector means and generating corresponding digital signals representative of the voltage or current detected. The combined toroid/shunt device or the measuring device may comprise a communication device for transmitting monitoring information to a remote station. It is evident that, in embodiments of the invention, the device is provided with two means for detecting a residual current. The toroidal transformer facilitates detection of a current imbalance between the neutral and live conductors, indicative of a residual current, from the voltage induced in the secondary winding. The toroidal transformer can detect a residual current of a very low level (10mA or less). The shunt detector facilitates detection of a current imbalance from a comparison of the current detected in the neutral and live conductors. The shunt detector may thereby facilitate detection of a residual current even when the residual current arises from a dc fault, not detectable by the transformer. The shunt detector may also facilitate detection of residual current in circumstances where the magnetic flux causes the transformer to saturate. It is evident that embodiments of the invention provide for an integral or combined power and residual current device. One advantage arising out of this is that the power meter, which is usually owned by the electricity supplier, may be owned by the user. Parameters relating to electricity usage and fault conditions are transmitted to a station monitored by the supplier for billing, diagnostic, consumption or service purposes. It is also apparent that a reduction in bulk relative to conventional power measuring and separate residual current devices is possible. This allows devices embodying the invention to be embedded in appliances to provide for trip avoidance, greater discrimination, failure indication and downstream monitoring. Sub-circuit metering may be effected particularly if the devices are networked, this enabling better discrimination and isolation of faults, tripping the sub-circuit first, before the main circuit trips. Further uses are envisaged such as providing warning data prior to tripping and use in building management systems. According to a related aspect, which is mentioned by way of background, there is provided a measuring device for an electrical installation comprising a plurality of conductors, the device comprising toroid means for detecting a residual current and power consumption means comprising a shunt detector means for generating a current signal indicative of current detected in at least one of said conductors and a resistor detector means for generating a voltage signal indicative of voltage across at least one pair of said conductors. In a preferred embodiment the electrical installation comprises an ac supply via a neutral conductor and a live conductor, said toroid means comprising a toroidal transformer detector for generating a residual current signal in response to a detected residual current in said electrical installation, and said resistor detector means is provided for connection between said neutral and live conductors to generate said voltage signal by measuring the voltage drop across the resistor detector means or a potentially divided portion thereof, the device further comprising a processor means for generating a trip signal indicative of the presence of a residual current fault in dependence on said residual current signal, thereby to facilitate operation of a circuit breaker to break said ac supply in response to said trip signal, and an output signal derived from said current and voltage signals to facilitate determination of power consumption. In another preferred embodiment, the ac supply may comprise a plurality of phases, each phase comprising a supply via a phase live conductor and said neutral conductor, wherein the shunt detector means comprises a respective shunt connected in series in each of said phase live conductors for providing a respective current signal indicative of the current flowing in the respective phase live conductor, and said resistor detector means comprises a respective resistor means connected between each of said phase live conductors and said neutral conductor, said processor being operative for generating signals representative of the voltage between each phase live conductor and said neutral conductor by measuring the voltage across each of said resistor means or potentially divided portions thereof. According to a second related aspect, which is mentioned by way of background, there is provided a measuring device for an electrical installation having an ac supply via a neutral conductor and at least one live conductor, the device comprising a toroidal transformer detector for generating a residual current signal in response to a detected residual current in said electrical installation, a shunt resistor detector for generating respective current signals indicative of current detected in said neutral conductor and each of said at least one live conductors, a processor means for generating a trip signal indicative of the presence of a residual current fault in dependence on said residual current signal and/or said respective current signals detected, and a circuit breaker operative to break said ac supply in response to said trip signal. In a preferred embodiment, for each of said at least one live conductors, the device may further comprise a resistor detector means for connection between said neutral and live conductors and operative for providing a signal representative of the voltage between said neutral and live conductors by measurement of the voltage drop across said resistor detector means or a potentially divided portion thereof. In an embodiment, the processor means comprises a first analog to digital converter coupled to a secondary winding of said transformer for generating said residual current signal as a digital signal representative of the voltage sensed across the winding and/or the current in the winding. The processor means may further comprise a second analog to digital converter coupled to the shunt resistor detector for generating digital signals representative of the current flowing through said neutral conductor and each of said at least one live conductors. The first and/or second analog to digital converter may also be coupled to said resistor detector means for generating digital signals representative of said voltage between said neutral and live conductors. Alternatively, the first and/or second analog to digital converters may include a multiplexer for selectively coupling two or more of said detector means and generating corresponding digital signals representative of the voltage or current detected. Each analog to digital converter may include a delta-sigma modulator. The processor means may include a microprocessor for receiving the digital signals from the first and second analog to digital converters for determining the power consumed by the electrical installation from the digital signals. The microprocessor may be further operative for generating a current imbalance signal indicative of the residual current during real time from the residual current signal. The microprocessor may be further operative for generating said current imbalance signal from a comparison of said current signals indicative of the current in said neutral and live conductors. The microprocessor may be further operative for generating said trip signal on the basis of a comparison of said current imbalance signal with a predetermined threshold criterion. The microprocessor may be yet further operative for analysing the residual current, current and voltage in order to detect one or more other conditions, including, overcurrent, arc fault, standing current leakage, and "True power" measurement from the phase angle (Power = Voltage * Current * Cosine (Phi)). The power consumption, together with the other operating conditions or events may be logged for future reference. This information is useful for diagnostic purposes. A temperature sensor may be provided to allow for compensation for temperature fluctuations in the shunts. The microprocessor may be calibrated to generate current and voltage signals taking into account the temperature of the shunts relative to a reference point. The microprocessor may be arranged to adjust the threshold of the residual current necessary to generate a trip signal if it learns that the residual current is caused by a standing leakage at the installation. The residual current detector function will therefore continue to operate as a safety device while minimising the possibility of nuisance tripping. For example, if there were a standing leakage of 10mA when the monitoring device is installed, the device would trip when the predetermined threshold is reached above the 10mA level rather than zero. A communication device may be provided for transmitting this information to a remote monitoring station. The invention will now be further described by way of example with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a combined power meter and residual current device embodying the present invention applied to a single phase electricity supply; Figure 2 is a block diagram of a combined power meter and residual current device embodying the present invention applied to a three phase electricity supply; and Figure 3 is a flow chart indicating an operating sequence for residual current detection in a device embodying the present invention. One structural configuration of a monitoring device embodying the present invention is shown in Figures 1 and 2. In a first aspect, Figure 1 shows a single phase device in which a toroidal transformer core 1 is coupled to live and neutral conductors 2 and 3 respectively of an ac mains supply. A secondary coil 4 is wrapped around the core 1 and coupled to a first analog to digital converter 5 for generating a digital output 01 representative of the imbalance current sensed by the toroidal transformer 1. A shunt detector means comprises a resistive shunt 6a provided in series with the mains neutral conductor 3. This may be of a resistive material such as manganin having a nominal resistance of 0.2ml; to a tolerance of less than 5%. Respective ends of the shunt 6a are connected to an analog to digital converter 7 which produces a digitised output 02 representative of the voltage drop across the shunt 6a. The voltage drop across shunt 6a provides a measure of the current flowing in the neutral conductor 3. A resistor detector means comprises a potential divider having resistors 8a, 8b, 9 connected between the mains live and neutral conductors 2, 3 respectively. The voltage between these conductors can be determined by measuring the voltage drop across the resistor 8a by connecting respective ends of the resistor 8a to the second analog to digital converter 7. The digitised output 02 contains the information on the voltage across the resistor 8a. A power supply unit 10 is provided for drawing power from the live and neutral mains conductors 2, 3 and for supplying controlled voltages to the analog to digital converters 5, 7 via isolation barriers 11, 12 and processor 13. A multi- plexer may be provided in each converter for providing to the processor, through the respective isolation barrier, signals representing both the current in the associated shunt and the voltage at one end of it. The processor 13 uses these signals to monitor the current in each shunt as well as the imbalance current sensed by the coil 4 of the toroidal transformer 1. In the event of a current imbalance exceeding a predetermined threshold, the processor generates a trip signal 03 which drives a solenoid actuator 14 for breaking or tripping respective conductors 2, 3 via a circuit breaker indicated schematically by switches 15 and 16 in Figure 1. The processor 13 is also provided with a Universal Asynchronous Receiver Transmitter (UART) 25 as a means for generating and transmitting an output signal in the form serial data communications 04. The processor 13 provides output signals based on the current and voltage signals detected. This may include a power consumption signal based on power calculated from the detected current and voltage signals together with a time derived from a signal from a clock generator 26 within the processor 13. Each one of the analog to digital converters comprises an analog to digital converter in the form of a delta-sigma modulator 17 which provides a high frequency one bit digital data stream. A temperature sensor 18 is provided so that the digitised output signals 01 and O2 are modified to compensate for temperature fluctuations. The modification may be effected by means of a calibration technique involving the use of a look up table (not shown). The temperature compensation may take the form of a polynomial fitted to calibration test results, the polynomial coefficients being stored in the look-up table. In a second aspect, also shown in Figure 1, the shunt detector means comprises a further shunt resistor 6b provided in series with the mains live conductor 2. Respective ends of the further shunt 6b are connected to analog to digital converter 5 such that digitised output 02 contains a digital signal representative of the voltage drop across the further shunt 6b. The voltage drop across further shunt 6b provides a measure of the current flowing in the live conductor 2. The processor 13 performs a comparison of the detected currents in the live and neutral conductors 2, 3 to detect a residual current. A residual current not detected by the toroidal transformer 1, for example a dc residual current or a saturating residual current, will be detected by the shunt detector, from which the processor 13 generates trip signal 03. The resistors 8a, 8b and 9 that comprise the resistor detector means provide an additional voltage signal by connecting respective ends of the resistor 8b to the first analog to digital converter 5. The digitised output Ol contains the information on the voltage across the resistor 8b. The resistors 8a, 8b, across which connections are made to provide the voltage signals, are precision resistors of relatively low ohmic value, while the intermediate resistor 9 has a relatively high ohmic value. The ratio of the voltages measured across precision resistors 8a 8b should remain constant. By monitoring this ratio, an independent reference is provided, so that if the ratio changes over time due to drift in the analog to digital converter 5 or its references, an adjustment can be made by software within processor 13 to correct the value of the measured voltage. Figure 2 shows a three phase arrangement in which features similar to those of Figure 1 have a same reference numeral. In this case, the ac supply has two additional live conductors 21, 22 for the second and third supply phases respectively. Two additional analog to digital converters 14, 15 are provided for the additional two phases. These generate outputs representative of the sensed current and voltage for the second and third phases respectively and supply these to the processor 13 via isolation barriers 19 and 20. In the arrangement of Figure 2, the shunt detector means comprises resistive shunt 6a in the mains neutral conductor 3, and resistive shunts 6b, 6c, 6d in each of the mains live conductors 2, 21, 22 respectively. It is noted that the voltage sensing connections to analog to digital converters 23 and 24 are made via resistor chains connected between each phase line and the neutral in a similar manner to the resistors 8a, 8b and 9 of Figure 1. In both Figure 1 and Figure 2, the processor 13 is programmed to carry out the necessary calculations to determine the existence of an imbalance. It is also programmed to determine the current and voltage in respect of each phase to a high degree of precision for a subsequent power measurement. These measurements may be analysed in order to detect one or more other operating conditions including arc fault, standing current leakage, True power measurement. This information is useful for diagnostic purposes. Referring to Figure 3, the operating procedure of a monitoring device includes certain functions that are performed by hardware components and others that are performed by a software program in the processor which comprises a micro-controller unit (MCU). At step 101 the power supply is activated. Various checks are performed by the hardware to ensure that the supply is not switched on in the presence of a large residual current. A power supply unit monitor 102 checks that the power supply is stable, if not the device waits until the supply is stable before proceeding to step 104 where a check is made that the clock in the MCU is stable. Once stability has been confirmed buy these checks the MCU is reset at step 107. If the checks at steps 103 and 104 do not confirm stability such that the MCU is reset within a predetermined time, then at step 105 a watchdog timeout 106 provides a signal to operate a solenoid at step 108 that isolates the power supply. Once the MCU has been reset, software in the MCU performs a calibration of the analog to digital converters at step 109. The calibration uses predetermined criteria so that the analog current and voltage signals measured are converted into digital signals representing the currents/voltages with the required precision. Operating standards to which residual current devices are required to comply are usually defined in terms of RMS current values. Therefore the processor calculates the RMS values of the voltages and currents detected. To evaluate an RMS value accurately, the calculation must be performed over a full signal cycle or an integer multiple of signal cycles. This may be done by using a known supply frequency, or by measuring the supply frequency, for example by performing a Fourier analysis on a sample of measured values. Alternatively the RMS calculation may be peformed over a specific time interval which contains an integer multiple of cycles for all rated operating frequencies. In either case, at step 110 the MCU must initialise the RMS values and timing means. A new RMS value can be calculated for each input waveform cycle or after each instantaneous measurement. The former method obtains a new RMS value every cycle and the latter after every measurement sample. The latter method is preferred as it gives a faster response time to any suddenly appearing residual current or overcurrent. In either case it takes at least 20ms (rated frequency = 50Hz) to obtain the first RMS value. This is a significant portion of the time allowed for tripping on power up in the presence of a residual current, so it may be advantageous to have a specific routine at power up which looks at instantaneous values rather than RMS. Many mains measurement systems sample at frequencies to include the 31sl harmonic. Allowing for operation up to 60Hz and a frequency tolerance of ±5 % gives a minimum sampling frequency of 3906Hz, so a sampling frequency of 4KHz is often used, and this would seem a good basis for initial design. However, to ensure an integer number of samples at both rated mains frequencies of 50Hz and 60Hz a sampling frequency of 3-9Khz or 4-2KHz is preferred. The MCU, at step 111, evaluates the currents and voltages from the detected signals, at step 112 calculates the residual current I>, and at step 113 calculates the RMS values. At steps 114 to 117 the MCU performs various calculations and comparisons for determining whether an unsafe condition in the form of a residual current or other predefined condition exists. In the presence of an unsafe condition a trip signal is generated so as to operate the solenoid at step 108 to isolate the supply. The calculations and comparisons performed will depend on the type of residual current device employed. For example the comparisons shown at steps 115 and 117 would only be suitable for use with a residual current operated circuit-breaker having over-current protection (RCBO). Examples of the parameters calculated by the MCU include the following: Primary Measurement Quantities Instantaneous line and neutral current at 4.2KHz, its, i2s, i3s and ins Instantaneous line voltage at 4.2KHz, v1, V2, & V3 Instantaneous Temperature at 4.2KHz T1, T2 T3 & Tn Instantaneous Residual Current at 4.2KHz (Toroid) i?t, Secondary Measurement Quantities The secondary measurement quantities calculated by the MCU are defined as follows:- Instantaneous current, i?s, where this is the sum of the currents in all four shunts (n denoting neutral shunt) Instantaneous line and neutral current squared, Instantaneous line voltage squared, v21,v22, &v23 Instantaneous power, p1, p2, p3: RMS residual current I?s (from shunts): where j is the index of the sample point within a whole cycle. RMS residual current I?1 (from Toroid): where j is the index of the sample point within a whole cycle. Total line and neutral current (from shunts) I1s,l2s,l3s and Ins : and similarly for I2s, I3s and Ins. RMS line voltage V1, V2 and V3: RMS real power P1, P2 and P3: RMS total power W1, W2 and W3 where W1 =I1s.V1 Phase angle for each line Fl, F2 and F3: In the definition of all secondary RMS quantities, N is the number of 4.2KHz output words in a line voltage cycle. N = 84 for 50Hz line frequency and N=70 for 60Hz. We Claim 1. A combined toroid/shunt device for detecting a residual current in an electrical installation having an AC supply and comprising a neutral conductor (3) and at least one live conductor (2, 21, 22), the device comprising: a toroid means (1, 4) for detecting an AC residual current lying within a first range and for generating a residual current signal in response thereto; a plurality of resistive shunts (6a-6d) for connection in respective ones of each of said conductors; and current detection means (5, 7, 13) responsive to current flowing in each of said shunts for generating a signal indicative of current detected in each of said shunts for detecting a DC residual current and/or an AC residual current lying within a second range. 2. The combined toroid/shunt device as claimed in claim 1, comprising an electronic means associated with the toroid means (1) for processing the current signal, wherein said first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between the conductors up to a saturation level at which the toroid or electronic means associated therewith become saturated, and the second range includes AC residual currents above said saturation level. 3. The combined toroid/shunt device as claimed in claim 2, comprising a processor means (13) for generating a trip signal indicative of the presence of a residual current fault in dependence on said residual current signal and/or said current signal indicative of current detected in each of said shunts (6a-6d). 4. The combined toroid/shunt device as claimed in claim 3, wherein said processor means is operative for generating a current imbalance signal indicative of the residual current during real time from the residual current signal, and where by said trip signal is generated on the basis of comparison of the current imbalance signal with a predetermined threshold criterion. 5. The combined toroid/shunt device as claimed in claim 3 or claim 4, comprising a circuit breaker (15, 16) operative to break said AC supply in response to said trip signal. 6. A measuring device for an electrical installation comprising the combined toroid/shunt device of any of claims 3 to 5, wherein said current detection means (5, 7, 13) is responsive to current flowing in each of said conductors (2, 3, 21, 22) for generating a current signal indicative of the current detected in each of said conductors. 7. The measuring device as claimed in claim 6, comprising a resistor detector means (8a, 8b, 9) for connection between said neutral (3) and live conductors (2, 21, 22) for generating a voltage signal indicative of the voltage between the said live and neutral conductors by measuring the voltage drop across the resistor means or a potentially divided portion thereof. 8. The measuring device as claimed in claim 7, wherein said processor means (13) is operative for generating an output signal derived from said current and voltage signals to facilitated determination of power consumption. 9. The combined toroid/shunt device as claimed in claim 3 or the measuring device of claim 7 or claim 8, wherein the processor means (13) comprise a first analog to digital converter (5) coupled to a secondary winding (4) of said transformer (1) for generating said residual current signal as a digital signal representative of the voltage sensed across the winding and/or the current in the winding. 10.The device as claimed in claim 9, comprising a second analog to digital converter (7) coupled to the shunt resistor detector for generating digital signals representative of the current flowing through said neutral conductor and each of said at least one live conductors. 11.The device as claimed in claim 10, wherein the second analog to digital converter (7) is coupled to said resistor detector means (8a, 8b, 9) for generating digital signals representative of the voltage between said neutral and live conductors. 12.The device as claimed in any of claims 9 to 11, wherein the first (4) and/or the second (7) analog to digital converter includes a multiplexer for selectively coupling two or more of said detector means and generating corresponding digital signals representative of the voltage or current detected. 13.The device as claimed in any preceding claim, comprising a communication device for transmitting monitoring information to a remote station. A combined toroid/shunt device for detecting a residual current in an electrical installation comprising a plurality of conductors such as a live conductor 2 and a neutral conductor 3 is described. The device comprises a toroid means 1, 4 for detecting an AC residual current within a first range and a plurality of resistive shunts 6a to 6d for connection in respective ones of the plurality of conductors. A current detection means 5, 7, 13 responsive to current flowing in each of said shunts for detecting a DC residual current and/or an AC residual current within a second range is described. The first range of AC residual current is an AC residual current resulting from earth leakage or cross-leakage between conductors up to a saturation level at which the toroid or electronic means associated means therewith becomes saturated. The second range includes an AC residual current of said saturation level.

Full Text

Measuring Devices
This invention relates to measuring devices for electrical installations, and in
particular to measuring devices including a current/voltage detection module for
analysing current and voltage to facilitate, inter alia, a residual current detection
and power consumption.
A method of detecting for residual current may involve using a current
transformer having primary windings through which, in the case of a single phase
device, load current flows in opposite directions so that if the return current is
different from the outwardly flowing current because of current leakage, an output
current signal is induced in a secondary winding of the transformer. In the case of
a multi-phase device, primary windings of the transformer are connected in all of
the phase lines and the neutral line. In normal situations, when there is no current
leakage, the net current induced in the secondary winding is zero and therefore no
output is detected. These devices are subject to nuisance tripping arising from
surges in the supply, switches in appliances and the like. Further problems arise
because the transformer is designed to be sensitive to very small current imbalances
caused by current leakage. With relatively large current leakage faults, the
magnetic flux may cause the transformer core to become saturated and so fail to
induce a current in the secondary winding. Alternatively, a large induced current
may cause saturation of an amplifier in the electronic circuit which is used to
process the induced current signal.
Also, toroidal transformer devices may be insensitive to dc current leakage
faults, such that the fault goes undetected and no trip occurs. Many electrical
systems incorporate switching power supplies, for example ac to dc converters and
inverters in motor speed control and start-up systems. In such systems the ac
supply phases are switched electronically (for example with high voltage FETs) to
provide rectified waveform signals. In such cases a current leakage fault may not
induce sufficient current in the secondary winding to detect the fault.
One method of determining power consumption is to measure the voltage
across the power supply wires and the current flowing through them and then
multiply the current by the voltage measurement to determine a power
measurement. One approach is to use a shunt of known value connected in series
with one of the wires and to measure the voltage across and current flowing through
it. Power meters include a counter or clock for measuring the number of watt-
hours consumed. The counter or clock is periodically read manually in order that
the consumer can be billed for the quantity of electricity used.
Shunt resistors could also be used to detect an imbalance in the current
caused by a current leakage. However, to be useful on their own as a residual
current detection safety device for tripping a circuit breaker, the shunt resistors
would have to be extremely accurate. The current flowing through the shunts
would need to be detected to an accuracy in the order of 1 to 10 mA in 100 A (105
to 10-4). This means that sophisticated and complex measurement circuitry would
be needed to provide the required resolution as well as precise and stable shunt
resistors having linear resistance characteristics.
Conventionally, residual current devices and power consumption meters are
separate discrete devices. The power consumption meter is usually located at the
point of entry of the electricity supply into the premises and the residual current
device is located within the consumer unit or fuse box from which the circuits to the
premises are distributed.
It is an aim of the present invention to devise a combined residual current
and power measuring device which overcomes or at least alleviates these problems.
It is a further aim of the invention to devise a combined residual current and power
measuring device which is less bulky than conventional devices and operates to an
improved degree of sophistication such as to facilitate remote monitoring of the
electrical installation.
According to a the present invention, there is provided a a combined
toroid/shunt device as defined in claim 1.
In an embodiment, the combined toroid/shunt device further comprises an
electronic means associated with the toroid means for processing the current signal,
the first range of AC residual current is an AC residual current resulting from earth
leakage or cross-leakage between the conductors up to a saturation level at which
the toroid or electronic means associated therewith become saturated, and the
second range includes AC residual currents above said saturation level.
The combined toroid/shunt device may further comprise a processor means
for generating a trip signal indicative of the presence of a residual current fault in
dependence on said residual current signal and/or said current signal indicative of
current detected in each of said shunts.
Preferably, the processor means is operative for generating a current
imbalance signal indicative of the residual current during real time from the residual
current signal, and the trip signal is generated on the basis of a comparison of the
current imbalance signal with a predetermined threshold criterion.
More preferably, the combined toroid/shunt device further comprises a circuit
breaker operative to break said AC supply in response to said trip signal.
In another embodiment, a measuring device for an electrical installation
comprises the combined toroid/shunt device. Here, the current detection means is
responsive to current flowing in each of said conductors for generating a current
signal indicative of the current detected in each of said conductors.
The measuring device may further comprise a resistor detector means for
connection between said neutral and live conductors for generating a voltage signal
indicative of the voltage between said live and neutral conductors by measuring the
voltage drop across the resistor means or a potentially divided portion thereof.
Preferably the processor means is operative for generating an output signal
derived from said current and voltage signals to facilitate determination of power
consumption.
The processor means of either the combine toroid/shunt device or the
measuring device may also comprise a first analog to digital converter coupled to a
secondary winding of the transformer for generating the residual current signal as a
digital signal representative of the voltage sensed across the winding and/or the
current in the winding.
Preferably the device also comprises a second analog to digital converter
coupled to the shunt resistor detector for generating digital signals representative of
the current flowing through the neutral conductor and each of the at least one live
conductors.
More preferably, the second analog to digital converter is coupled to said
resistor detector means for generating digital signals representative of the voltage
between said neutral and live conductors.
The first and/or the second analog to digital converter may include a
multiplexer for selectively coupling two or more of said detector means and
generating corresponding digital signals representative of the voltage or current
detected.
The combined toroid/shunt device or the measuring device may comprise a
communication device for transmitting monitoring information to a remote station.
It is evident that, in embodiments of the invention, the device is provided
with two means for detecting a residual current. The toroidal transformer facilitates
detection of a current imbalance between the neutral and live conductors, indicative
of a residual current, from the voltage induced in the secondary winding. The
toroidal transformer can detect a residual current of a very low level (10mA or
less). The shunt detector facilitates detection of a current imbalance from a
comparison of the current detected in the neutral and live conductors. The shunt
detector may thereby facilitate detection of a residual current even when the residual
current arises from a dc fault, not detectable by the transformer. The shunt detector
may also facilitate detection of residual current in circumstances where the magnetic
flux causes the transformer to saturate.
It is evident that embodiments of the invention provide for an integral or
combined power and residual current device. One advantage arising out of this is
that the power meter, which is usually owned by the electricity supplier, may be
owned by the user. Parameters relating to electricity usage and fault conditions are
transmitted to a station monitored by the supplier for billing, diagnostic,
consumption or service purposes. It is also apparent that a reduction in bulk
relative to conventional power measuring and separate residual current devices is
possible. This allows devices embodying the invention to be embedded in
appliances to provide for trip avoidance, greater discrimination, failure indication
and downstream monitoring. Sub-circuit metering may be effected particularly if
the devices are networked, this enabling better discrimination and isolation of
faults, tripping the sub-circuit first, before the main circuit trips. Further uses are
envisaged such as providing warning data prior to tripping and use in building
management systems.
According to a related aspect, which is mentioned by way of background,
there is provided a measuring device for an electrical installation comprising a
plurality of conductors, the device comprising toroid means for detecting a residual
current and power consumption means comprising a shunt detector means for
generating a current signal indicative of current detected in at least one of said
conductors and a resistor detector means for generating a voltage signal indicative
of voltage across at least one pair of said conductors.
In a preferred embodiment the electrical installation comprises an ac supply
via a neutral conductor and a live conductor, said toroid means comprising a
toroidal transformer detector for generating a residual current signal in response to
a detected residual current in said electrical installation, and said resistor detector
means is provided for connection between said neutral and live conductors to
generate said voltage signal by measuring the voltage drop across the resistor
detector means or a potentially divided portion thereof, the device further
comprising a processor means for generating a trip signal indicative of the presence
of a residual current fault in dependence on said residual current signal, thereby to
facilitate operation of a circuit breaker to break said ac supply in response to said
trip signal, and an output signal derived from said current and voltage signals to
facilitate determination of power consumption.
In another preferred embodiment, the ac supply may comprise a plurality of
phases, each phase comprising a supply via a phase live conductor and said neutral
conductor, wherein the shunt detector means comprises a respective shunt
connected in series in each of said phase live conductors for providing a respective
current signal indicative of the current flowing in the respective phase live
conductor, and said resistor detector means comprises a respective resistor means
connected between each of said phase live conductors and said neutral conductor,
said processor being operative for generating signals representative of the voltage
between each phase live conductor and said neutral conductor by measuring the
voltage across each of said resistor means or potentially divided portions thereof.
According to a second related aspect, which is mentioned by way of
background, there is provided a measuring device for an electrical installation
having an ac supply via a neutral conductor and at least one live conductor, the
device comprising a toroidal transformer detector for generating a residual current
signal in response to a detected residual current in said electrical installation, a
shunt resistor detector for generating respective current signals indicative of current
detected in said neutral conductor and each of said at least one live conductors, a
processor means for generating a trip signal indicative of the presence of a residual
current fault in dependence on said residual current signal and/or said respective
current signals detected, and a circuit breaker operative to break said ac supply in
response to said trip signal.
In a preferred embodiment, for each of said at least one live conductors, the
device may further comprise a resistor detector means for connection between said
neutral and live conductors and operative for providing a signal representative of
the voltage between said neutral and live conductors by measurement of the voltage
drop across said resistor detector means or a potentially divided portion thereof.
In an embodiment, the processor means comprises a first analog to digital
converter coupled to a secondary winding of said transformer for generating said
residual current signal as a digital signal representative of the voltage sensed across
the winding and/or the current in the winding.
The processor means may further comprise a second analog to digital
converter coupled to the shunt resistor detector for generating digital signals
representative of the current flowing through said neutral conductor and each of
said at least one live conductors.
The first and/or second analog to digital converter may also be coupled to
said resistor detector means for generating digital signals representative of said
voltage between said neutral and live conductors.
Alternatively, the first and/or second analog to digital converters may
include a multiplexer for selectively coupling two or more of said detector means
and generating corresponding digital signals representative of the voltage or current
detected.
Each analog to digital converter may include a delta-sigma modulator.
The processor means may include a microprocessor for receiving the digital
signals from the first and second analog to digital converters for determining the
power consumed by the electrical installation from the digital signals. The
microprocessor may be further operative for generating a current imbalance signal
indicative of the residual current during real time from the residual current signal.
The microprocessor may be further operative for generating said current imbalance
signal from a comparison of said current signals indicative of the current in said
neutral and live conductors. The microprocessor may be further operative for
generating said trip signal on the basis of a comparison of said current imbalance
signal with a predetermined threshold criterion.
The microprocessor may be yet further operative for analysing the residual
current, current and voltage in order to detect one or more other conditions,
including, overcurrent, arc fault, standing current leakage, and "True power"
measurement from the phase angle (Power = Voltage * Current * Cosine (Phi)).
The power consumption, together with the other operating conditions or events may
be logged for future reference. This information is useful for diagnostic purposes.
A temperature sensor may be provided to allow for compensation for
temperature fluctuations in the shunts. The microprocessor may be calibrated to
generate current and voltage signals taking into account the temperature of the
shunts relative to a reference point.
The microprocessor may be arranged to adjust the threshold of the residual
current necessary to generate a trip signal if it learns that the residual current is
caused by a standing leakage at the installation. The residual current detector
function will therefore continue to operate as a safety device while minimising the
possibility of nuisance tripping. For example, if there were a standing leakage of
10mA when the monitoring device is installed, the device would trip when the
predetermined threshold is reached above the 10mA level rather than zero.
A communication device may be provided for transmitting this information
to a remote monitoring station.
The invention will now be further described by way of example with
reference to the accompanying drawings, in which:
Figure 1 is a block diagram of a combined power meter and residual current
device embodying the present invention applied to a single phase electricity supply;
Figure 2 is a block diagram of a combined power meter and residual current
device embodying the present invention applied to a three phase electricity supply;
and
Figure 3 is a flow chart indicating an operating sequence for residual current
detection in a device embodying the present invention.
One structural configuration of a monitoring device embodying the present
invention is shown in Figures 1 and 2. In a first aspect, Figure 1 shows a single
phase device in which a toroidal transformer core 1 is coupled to live and neutral
conductors 2 and 3 respectively of an ac mains supply. A secondary coil 4 is
wrapped around the core 1 and coupled to a first analog to digital converter 5 for
generating a digital output 01 representative of the imbalance current sensed by the
toroidal transformer 1.
A shunt detector means comprises a resistive shunt 6a provided in series
with the mains neutral conductor 3. This may be of a resistive material such as
manganin having a nominal resistance of 0.2ml; to a tolerance of less than 5%.
Respective ends of the shunt 6a are connected to an analog to digital converter 7
which produces a digitised output 02 representative of the voltage drop across the
shunt 6a. The voltage drop across shunt 6a provides a measure of the current
flowing in the neutral conductor 3.
A resistor detector means comprises a potential divider having resistors 8a,
8b, 9 connected between the mains live and neutral conductors 2, 3 respectively.
The voltage between these conductors can be determined by measuring the voltage
drop across the resistor 8a by connecting respective ends of the resistor 8a to the
second analog to digital converter 7. The digitised output 02 contains the
information on the voltage across the resistor 8a.
A power supply unit 10 is provided for drawing power from the live and
neutral mains conductors 2, 3 and for supplying controlled voltages to the analog to
digital converters 5, 7 via isolation barriers 11, 12 and processor 13. A multi-
plexer may be provided in each converter for providing to the processor, through
the respective isolation barrier, signals representing both the current in the
associated shunt and the voltage at one end of it. The processor 13 uses these
signals to monitor the current in each shunt as well as the imbalance current sensed
by the coil 4 of the toroidal transformer 1.
In the event of a current imbalance exceeding a predetermined threshold, the
processor generates a trip signal 03 which drives a solenoid actuator 14 for
breaking or tripping respective conductors 2, 3 via a circuit breaker indicated
schematically by switches 15 and 16 in Figure 1.
The processor 13 is also provided with a Universal Asynchronous Receiver
Transmitter (UART) 25 as a means for generating and transmitting an output signal
in the form serial data communications 04. The processor 13 provides output
signals based on the current and voltage signals detected. This may include a power
consumption signal based on power calculated from the detected current and voltage
signals together with a time derived from a signal from a clock generator 26 within
the processor 13.
Each one of the analog to digital converters comprises an analog to digital
converter in the form of a delta-sigma modulator 17 which provides a high
frequency one bit digital data stream. A temperature sensor 18 is provided so that
the digitised output signals 01 and O2 are modified to compensate for temperature
fluctuations. The modification may be effected by means of a calibration technique
involving the use of a look up table (not shown). The temperature compensation
may take the form of a polynomial fitted to calibration test results, the polynomial
coefficients being stored in the look-up table.
In a second aspect, also shown in Figure 1, the shunt detector means
comprises a further shunt resistor 6b provided in series with the mains live
conductor 2. Respective ends of the further shunt 6b are connected to analog to
digital converter 5 such that digitised output 02 contains a digital signal
representative of the voltage drop across the further shunt 6b. The voltage drop
across further shunt 6b provides a measure of the current flowing in the live
conductor 2. The processor 13 performs a comparison of the detected currents in
the live and neutral conductors 2, 3 to detect a residual current. A residual current
not detected by the toroidal transformer 1, for example a dc residual current or a
saturating residual current, will be detected by the shunt detector, from which the
processor 13 generates trip signal 03.
The resistors 8a, 8b and 9 that comprise the resistor detector means provide
an additional voltage signal by connecting respective ends of the resistor 8b to the
first analog to digital converter 5. The digitised output Ol contains the information
on the voltage across the resistor 8b. The resistors 8a, 8b, across which
connections are made to provide the voltage signals, are precision resistors of
relatively low ohmic value, while the intermediate resistor 9 has a relatively high
ohmic value. The ratio of the voltages measured across precision resistors 8a 8b
should remain constant. By monitoring this ratio, an independent reference is
provided, so that if the ratio changes over time due to drift in the analog to digital
converter 5 or its references, an adjustment can be made by software within
processor 13 to correct the value of the measured voltage.
Figure 2 shows a three phase arrangement in which features similar to those
of Figure 1 have a same reference numeral. In this case, the ac supply has two
additional live conductors 21, 22 for the second and third supply phases
respectively. Two additional analog to digital converters 14, 15 are provided for
the additional two phases. These generate outputs representative of the sensed
current and voltage for the second and third phases respectively and supply these to
the processor 13 via isolation barriers 19 and 20. In the arrangement of Figure 2,
the shunt detector means comprises resistive shunt 6a in the mains neutral conductor
3, and resistive shunts 6b, 6c, 6d in each of the mains live conductors 2, 21, 22
respectively. It is noted that the voltage sensing connections to analog to digital
converters 23 and 24 are made via resistor chains connected between each phase
line and the neutral in a similar manner to the resistors 8a, 8b and 9 of Figure 1.
In both Figure 1 and Figure 2, the processor 13 is programmed to carry out
the necessary calculations to determine the existence of an imbalance. It is also
programmed to determine the current and voltage in respect of each phase to a high
degree of precision for a subsequent power measurement. These measurements
may be analysed in order to detect one or more other operating conditions including
arc fault, standing current leakage, True power measurement. This information is
useful for diagnostic purposes.
Referring to Figure 3, the operating procedure of a monitoring device
includes certain functions that are performed by hardware components and others
that are performed by a software program in the processor which comprises a
micro-controller unit (MCU). At step 101 the power supply is activated. Various
checks are performed by the hardware to ensure that the supply is not switched on
in the presence of a large residual current. A power supply unit monitor 102
checks that the power supply is stable, if not the device waits until the supply is
stable before proceeding to step 104 where a check is made that the clock in the
MCU is stable. Once stability has been confirmed buy these checks the MCU is
reset at step 107. If the checks at steps 103 and 104 do not confirm stability such
that the MCU is reset within a predetermined time, then at step 105 a watchdog
timeout 106 provides a signal to operate a solenoid at step 108 that isolates the
power supply.
Once the MCU has been reset, software in the MCU performs a calibration
of the analog to digital converters at step 109. The calibration uses predetermined
criteria so that the analog current and voltage signals measured are converted into
digital signals representing the currents/voltages with the required precision.
Operating standards to which residual current devices are required to comply
are usually defined in terms of RMS current values. Therefore the processor
calculates the RMS values of the voltages and currents detected. To evaluate an
RMS value accurately, the calculation must be performed over a full signal cycle or
an integer multiple of signal cycles. This may be done by using a known supply
frequency, or by measuring the supply frequency, for example by performing a
Fourier analysis on a sample of measured values. Alternatively the RMS
calculation may be peformed over a specific time interval which contains an integer
multiple of cycles for all rated operating frequencies. In either case, at step 110 the
MCU must initialise the RMS values and timing means.
A new RMS value can be calculated for each input waveform cycle or after
each instantaneous measurement. The former method obtains a new RMS value
every cycle and the latter after every measurement sample. The latter method is
preferred as it gives a faster response time to any suddenly appearing residual
current or overcurrent. In either case it takes at least 20ms (rated frequency =
50Hz) to obtain the first RMS value. This is a significant portion of the time
allowed for tripping on power up in the presence of a residual current, so it may be
advantageous to have a specific routine at power up which looks at instantaneous
values rather than RMS.
Many mains measurement systems sample at frequencies to include the 31sl
harmonic. Allowing for operation up to 60Hz and a frequency tolerance of ±5 %
gives a minimum sampling frequency of 3906Hz, so a sampling frequency of 4KHz
is often used, and this would seem a good basis for initial design. However, to
ensure an integer number of samples at both rated mains frequencies of 50Hz and
60Hz a sampling frequency of 3-9Khz or 4-2KHz is preferred.
The MCU, at step 111, evaluates the currents and voltages from the detected
signals, at step 112 calculates the residual current I>, and at step 113 calculates the
RMS values.
At steps 114 to 117 the MCU performs various calculations and comparisons
for determining whether an unsafe condition in the form of a residual current or
other predefined condition exists. In the presence of an unsafe condition a trip
signal is generated so as to operate the solenoid at step 108 to isolate the supply.
The calculations and comparisons performed will depend on the type of residual
current device employed. For example the comparisons shown at steps 115 and 117
would only be suitable for use with a residual current operated circuit-breaker
having over-current protection (RCBO).
Examples of the parameters calculated by the MCU include the following:
Primary Measurement Quantities
Instantaneous line and neutral current at 4.2KHz, its, i2s, i3s and ins
Instantaneous line voltage at 4.2KHz, v1, V2, & V3
Instantaneous Temperature at 4.2KHz T1, T2 T3 & Tn
Instantaneous Residual Current at 4.2KHz (Toroid) i?t,
Secondary Measurement Quantities
The secondary measurement quantities calculated by the MCU are defined as
follows:-
Instantaneous current, i?s, where this is the sum of the currents in all four
shunts (n denoting neutral shunt)
Instantaneous line and neutral current squared,
Instantaneous line voltage squared, v21,v22, &v23
Instantaneous power, p1, p2, p3:
RMS residual current I?s (from shunts):
where j is the index of the sample point within a whole cycle.
RMS residual current I?1 (from Toroid):
where j is the index of the sample point within a whole cycle.
Total line and neutral current (from shunts) I1s,l2s,l3s and Ins :
and similarly for I2s, I3s and Ins.
RMS line voltage V1, V2 and V3:
RMS real power P1, P2 and P3:
RMS total power W1, W2 and W3 where W1 =I1s.V1
Phase angle for each line Fl, F2 and F3:
In the definition of all secondary RMS quantities, N is the number of 4.2KHz
output words in a line voltage cycle. N = 84 for 50Hz line frequency and N=70 for
60Hz.
We Claim
1. A combined toroid/shunt device for detecting a residual current in an
electrical installation having an AC supply and comprising a neutral
conductor (3) and at least one live conductor (2, 21, 22), the device
comprising: a toroid means (1, 4) for detecting an AC residual current
lying within a first range and for generating a residual current signal in
response thereto; a plurality of resistive shunts (6a-6d) for connection in
respective ones of each of said conductors; and current detection means
(5, 7, 13) responsive to current flowing in each of said shunts for
generating a signal indicative of current detected in each of said shunts
for detecting a DC residual current and/or an AC residual current lying
within a second range.
2. The combined toroid/shunt device as claimed in claim 1, comprising an
electronic means associated with the toroid means (1) for processing the
current signal, wherein said first range of AC residual current is an AC
residual current resulting from earth leakage or cross-leakage between
the conductors up to a saturation level at which the toroid or electronic
means associated therewith become saturated, and the second range
includes AC residual currents above said saturation level.
3. The combined toroid/shunt device as claimed in claim 2, comprising a
processor means (13) for generating a trip signal indicative of the
presence of a residual current fault in dependence on said residual current
signal and/or said current signal indicative of current detected in each of
said shunts (6a-6d).
4. The combined toroid/shunt device as claimed in claim 3, wherein said
processor means is operative for generating a current imbalance signal
indicative of the residual current during real time from the residual current
signal, and where by said trip signal is generated on the basis of
comparison of the current imbalance signal with a predetermined
threshold criterion.
5. The combined toroid/shunt device as claimed in claim 3 or claim 4,
comprising a circuit breaker (15, 16) operative to break said AC supply in
response to said trip signal.
6. A measuring device for an electrical installation comprising the combined
toroid/shunt device of any of claims 3 to 5, wherein said current detection
means (5, 7, 13) is responsive to current flowing in each of said
conductors (2, 3, 21, 22) for generating a current signal indicative of the
current detected in each of said conductors.
7. The measuring device as claimed in claim 6, comprising a resistor detector
means (8a, 8b, 9) for connection between said neutral (3) and live
conductors (2, 21, 22) for generating a voltage signal indicative of the
voltage between the said live and neutral conductors by measuring the
voltage drop across the resistor means or a potentially divided portion
thereof.
8. The measuring device as claimed in claim 7, wherein said processor
means (13) is operative for generating an output signal derived from said
current and voltage signals to facilitated determination of power
consumption.
9. The combined toroid/shunt device as claimed in claim 3 or the measuring
device of claim 7 or claim 8, wherein the processor means (13) comprise a
first analog to digital converter (5) coupled to a secondary winding (4) of
said transformer (1) for generating said residual current signal as a digital
signal representative of the voltage sensed across the winding and/or the
current in the winding.
10.The device as claimed in claim 9, comprising a second analog to digital
converter (7) coupled to the shunt resistor detector for generating digital
signals representative of the current flowing through said neutral
conductor and each of said at least one live conductors.
11.The device as claimed in claim 10, wherein the second analog to digital
converter (7) is coupled to said resistor detector means (8a, 8b, 9) for
generating digital signals representative of the voltage between said
neutral and live conductors.
12.The device as claimed in any of claims 9 to 11, wherein the first (4)
and/or the second (7) analog to digital converter includes a multiplexer for
selectively coupling two or more of said detector means and generating
corresponding digital signals representative of the voltage or current
detected.
13.The device as claimed in any preceding claim, comprising a
communication device for transmitting monitoring information to a remote
station.
A combined toroid/shunt device for detecting a residual current in an electrical
installation comprising a plurality of conductors such as a live conductor 2 and a
neutral conductor 3 is described. The device comprises a toroid means 1, 4 for
detecting an AC residual current within a first range and a plurality of resistive
shunts 6a to 6d for connection in respective ones of the plurality of conductors.
A current detection means 5, 7, 13 responsive to current flowing in each of said
shunts for detecting a DC residual current and/or an AC residual current within a
second range is described. The first range of AC residual current is an AC
residual current resulting from earth leakage or cross-leakage between
conductors up to a saturation level at which the toroid or electronic means
associated means therewith becomes saturated. The second range includes an
AC residual current of said saturation level.

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Patent Number

223755

Indian Patent Application Number

00009/KOLNP/2004

PG Journal Number

39/2008

Publication Date

26-Sep-2008

Grant Date

23-Sep-2008

Date of Filing

02-Jan-2004

Name of Patentee

EATON ELECTRIC LIMITED.

Applicant Address

PO BOX 22, NORFOLK STREET, WORSLEY ROAD NORTH, WORSLEY, MANCHESTER, M28 3ET

Inventors:

#	Inventor's Name	Inventor's Address
1	MURRAY, MARTIN ANTHONY	47 PENRHOS ROAD, BANGOR, LL57 2AX
2	CROSIER, MARK DAVID	4 SUNRISE TERRACE, GORS AVENUE, HOLYHEAD, ISLE OF ANGLESEY, LL65 1PD
3	REEDER, BRIAN MARTIN	SAMONA LON CRECIST, TREARDDUR BAY, ISLE OF ANGLESEY LL65 2AZ

PCT International Classification Number

G01R 19/25

PCT International Application Number

PCT/GB02/02643

PCT International Filing date

2002-06-07

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	0113941.9	2001-06-08	U.K.