Title of Invention | FUSE MONITORING SYSTEM FOR MONITORING STATUS OF CURRENT |
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Abstract | The present invention relates to a monitoring system adapted to monitor electrical status and operating conditions of plurality of current limiting devices or fuses whereby detecting and individuaL1y monitoring conditions of each fuse. The fuse links (9, 10, 11) are connected in each phase of a multi-phase system. Plurality of sensor means (6, 7 and 8) are operatively connected across each of the phases of the multi phase system to output instantaneous condition of fuses (9, 10, 11) . ControL1er means (2) connected to said sensor means (6, 7 and 8) such that it gives desired output depending on the status of the current limiting device and indicator means (4) operatively connected to the controller means indicating the status of the fuses or individual fuse. |
Full Text | FIELD OF INVENTION The present invention relates to a monitoring system to monitor the electrical status of current limiting devices. More particularly, the invention relates to a monitoring system to individually monitor the electrical status of current limiting devices and avoid single phasing of fuses thereby protecting load connected to the power system from overload. The system of the present invention finds application in current limiting devices such as thermal fuses or positive temperature coefficient (PTC) resistors present in each phase of a multiphase system. BACKGROUND AND PRIOR ART Study of international market clearly indicates that in an industrial environment monitoring the status of fuses is very important since a fuse in bad condition may cause a single phasing condition, which is not desirable. Several companies have come up with products, which monitors the status of the fuse. But almost all of them give only master indication but do not provide the secondary information for individual fuse, like in which phase fuse has blown and many of these products require an external dc source for its functioning. US1984000646535 describes an online indicator connected across each fuse across an electrical circuit, which includes a LED, which is illuminated if its protected fuse blows. Groups of these online indicator can be connected via an 'OR' gate to provide master indicator. Opto- isolators are used to reduce standby current drain and to isolate online indicators and not as the voltage sense element as in the invention. These are intended for use in dc systems. DE3515773 refers to a device which monitors the operating condition of one or several fuse links, preferably low voltage power fuses and emits outwards a continuous current pulse both for the normal operation, i.e. low voltage power fuse intact, as also for the disturbance, i.e. the fuse burnt. According to the invention the device consists of a parallel stretch to the fuse link, which, in case of disturbance, independently of the voltage prevailing on the fuse, gives a constant current on the luminous diode of a photo-coupler, so that the switching transistor of the photo-coupler switches on to a transistor component. In the normal operation the voltage present on the fuse link is so low that the photo-coupler does not switch through. Depending upon the condition of the photo-coupler, the transistor component switches through a permanent pulse either for normal operation or for a disturbance, whereby the other continuous pulse is switched off. During this optionally 2 luminous diodes are switched on for direct indication on the fuse monitor device. In this case the problems lie in the varying mains conditions and in the disconnecting property of a fuse link. The network can display either AC voltage or DC voltage; in case of AC voltage (poly-phase AC) up to 660V, in case of DC voltage up to 440V. On the burning of a fuse, e.g. in case of poly- phase AC, as a consequence of counter-EMS of a large motor, but with secured parallel cables, the residual voltage on the fuse link can be very small in comparison with the mains voltage. On disconnecting the fuse link a short-lived switching voltage surge can occur, which is higher by a multiple that the mains voltage. DE-OS1933942 describes a switch arrangement for electronic switch monitoring specially designed for circuits for supply to several parallel connected, individually secured consumer devices or for converters with parallely connected valves. A diode equipped with a resistor-capacitor circuitry lies in series to that fuse link. The blocking voltage appearing during the load on the diode in the blocking direction with burnt-through fuse at the fuse stretch is used for switching a transistor located in the device. Its switching leads to the switching of a thyristor connecting an optical indication with a separate auxiliary voltage. DE-OS2533182 describes an arrangement for electronic fuse monitoring where the fuse links lie in parallel diode branches, through which a common consumer device is supplied. If one of the fuse links is released, then, due to the increased current, the other fuse links are released one after the other, whereby already the release of the first fuse link is recorded, since an resistor capacitor- member is parallely connected to each diode, through which the signaling device receives current during the blocking direction loading of the diode with burnt-through fuse link. A separate control voltage source is not necessary, since the required energy is taken from the capacitor of the RC-member. Since the diodes with their RC-member lie at the mains branches, an application during the supply to any arbitrary number of consumer devices or to consumer devices directly connected to an AC network or poly-phase AC network is not possible. DE-OS2831139 describes an arrangement for fuse monitoring possessing a luminous diode, which lies connected in series to a thermally controlled resistor and a resistance in parallel connecting to the thermally controlled resistor parallel to the fuse link. In this series circuit yet another bridge rectifier can be included so that then the luminous diode lies at the DC outlet of the bridge rectifier. With this arrangement the leading out of the continuous pulses for a remote signaling or remote control is not possible. An indication for the normal operation is eliminated. Since the thermally controlled resistor with parallel resistance must be matched to the balancing diode at maximum mains voltage in cold condition, of which the maximum permissible voltage lies under 5V, and which increases its resistance substantially on exceeding the pull-out current, in spite of the parallel resistance, a deployment of the arrangement is possible only in a limited mains voltage range. The luminous diode is also endangered by excess switching voltage. DE-OS 2851956 describes an arrangement for electronic fuse monitor possessing a parallel stretch to the fuse link, consisting of a rectifier diode, a glow lamp, a limiting resistance and of a luminous diode of a photo-coupler, which are connected in series. In case of burnt fuse the positive half-wave of the AC voltage present on fuse link is passed through the rectifier diode and after the response of the glow lamp over the luminous diode of the photo-coupler so that this one switches through and activates a relay with the help of an auxiliary voltage. During this a smoothing of the half-waves through a capacitor can take place. A lamp indication takes place through the glow lamp in case of a disturbance. The arrangement gives a high response voltage on burning of a fuse link due to the use of a glow lamp. It cannot be used in low voltage ranges or in case of secured parallel cables. However, besides the motor protection switch, till now it is the only arrangement, which is suitable for a remote signaling or remote control. US6492799 B1 describes measuring the voltage difference between the two star points formed from six resistor taps taken from the lines of three phase system. In normal case there will not be any voltage difference between these points and in an abnormal condition voltage difference between these star points is detected and appropriate indication is given. But this logic can be used for giving master indications only and cannot be used for giving information as to in which phase the fuse has blown. Thus there is a need to provide a monitoring system to individually monitor the electrical status of current limiting devices and avoid single phasing of fuses thereby protecting load connected to the power system from overload. The present inventors have found that the a monitoring system can be achieved comprising some sensor means in operative connection to desired control means in a manner that it is possible to individually monitor the electrical status of current limiting devices and avoid single phasing of fuses thereby protecting load connected to the power system from overload. Further monitoring can be done in both load and no-load condition. OBJECTS OF INVENTION Thus one object of the present invention is to provide a monitoring system for accurate monitoring the status of current limiting devices and individual monitoring fusion of a fuse detecting the fuse in which fault has occurred. Another object of the present invention is to provide a self-generating power supply unit in the device so that it can work without the help of any external dc power supply. Yet another object of the present invention is to provide monitoring within a wide range (220 to 690 V AC) of operating voltage. Yet one more object of the present invention is to provide protection to a motor or any multiphase load connected to the power system from overload which may occur due to single phasing caused by the fusion of a fuse in one of the phases of a multiphase system with the help of potential free contacts whose state is decided by the control electronics depending on the state of the current limiting device. Yet another object of the present invention is to provide monitoring operation in both load and no-load condition. Another object of the present invention is to provide fuse monitor system that can withstand high impulse voltages. The other object is to provide monitor system which can work in presence of reverse voltage through the load. SUMMARY OF INVENTION Thus according to one aspect of the present invention there is provided a monitoring system adapted to monitor electrical status and operating conditions of plurality of current limiting devices or fuses whereby detecting and individually monitoring conditions of each fuse, wherein the said fuse links are connected in each phase of a multi-phase system and wherein from over said fuse links connecting means being provide in a manner so as to establish operative connection from power supply network to said fuse monitoring system, said fuse monitoring system comprising : (i) plurality of sensor means operatively connected across each of the phases of the multi phase system; wherein said sensor means being adapted to output instantaneous condition of each fuse of said plurality of fuses; (ii) controller means connected to said sensor means such that it gives desired output depending on the status of the current limiting device; and (iii) indicator means operatively connected to the controller means indicating the status of the fuses or individual fuse. DETAILED DESCRIPTION OF INVENTION The electronic fuse monitoring system of the present invention comprises plurality of identical sub system for each phase of the multi phase power system for voltage detection, and it individually monitors the condition of each fuse of the plurality of fuses connected in the phases. The said sub system comprises an output circuitry comprising plurality of voltage sensors adapted to output instantaneous condition of each fuse monitored by the fuse monitoring unit correlating with the individual distinguishing information. The said voltage sensors comprises opto-couplers having predetermined threshold level of voltage for its actuation thus influencing the state of control electronics depending on the voltage present across its input terminals. In normal conditions the input voltage to opto coupler is below the said threshold level and the indications corresponding to normal operation comes on. In case of an abnormal condition such as a blown fuse, the voltage across this fuse is above the threshold limit of the voltage and this actuates the opto coupler and thereby changes the state of the control circuit and thus indications corresponding to faulty condition in the system comes on. The sub system comprises multiphase power supply unit which powers the output circuitry and comprises transformer less one in which the input voltage is fed to rectifier means directly from the supply lines. The said rectifier means comprises three phase bridge rectifier provided with plurality of arms having upper arms and lower arms. The said lower arm comprises means for protecting the power supply unit and also regulating the output voltage of the rectifier. The said means comprises transient voltage surge suppressor diodes. Additionally, the output of the power supply unit is used to energize sensing logic circuitry and the potential free auxiliary relay contact system. The said logic circuitry comprises plurality of logic gates, which control the voltage in the system according to the need of operation. The fuse monitoring system comprises display module comprising plurality of indicator means adapted for visual indication of the status of the fuse links. The said indicator means comprises green LED showing the healthy status of all the three phases, indicating all the three fuses are intact, one orange LED indicating that a faulty condition like a blown fuse has occurred in the power system, three red LEDs corresponding to each phase in a multi phase system and the red LED corresponding to a particular phase comes on whenever the fuse corresponding to that phase blows. This provides information as to in which phase the fuse has blown, making its replacement much more convenient. The fuse monitor is also provided with a set of potential free contacts, which can be used for protection or remote indication purposes or can be used in protection schemes to disconnect the load during abnormal conditions in the power systems. During fusion of fuse link connected in line LI between the fuse terminals Fl and F2, the voltage appearing across the fuse in this fused condition is well above the threshold value of the opto coupler causing it to turn ON, thereby- causing the voltage across the zener diode connected to the output of the opto coupler to go down to zero. Thus one of the inputs to the NAND gate which receives its inputs from the out put side of the opto-couplers connected across each fuse link, goes low causing its output to go high. This causes the transistor having green LED in its collector to receive a high base drive causing it to go into saturation and this causes the voltage across the green LED to drop to zero thereby causing it to turn OFF, and the output of the NOT gate which is connected to the output of the said NAND gate goes low as the output of the NAND gate is high cutting of the base drive to the transistor which carries the orange LED in its collector thereby causing the orange LED to go ON indicating an abnormal condition in the system. Since the opto coupler has turned ON the transistor connected through the zener at the output of optocoupler doesn't receive any base drive causing it to work in the cut off region, thereby the red LED connected in the collector of this transistor and corresponding to the fuse link comes ON indicating that there is a fault in the fuse link. At the same time since the output of the said NAND gate is high the transistor receives a base drive through the resistor driving it into saturation causing the relay- to get energized and thus causing the auxiliary contacts of the relay to change over. Similarly during fusion of fuse links in lines L2 and L3 the red LEDs corresponding to those phases also comes ON indicating a fault in the corresponding phase. Similarly, during faults in more than one phase and fusion of more than one fuse links, the red LEDs corresponding to the phases having faulty fuse links comes ON. The orange LED also comes ON indicating an abnormal condition in the system. The power required for the entire circuit is supplied by the three phase bridge rectifier circuit. The lower arms of the bridge rectifier consist of Transient Voltage Suppressor Diodes which protects the circuit from the line side disturbances as well as regulates the voltage. The filtered output of the bridge rectifier supplies the voltage required to energize the relay in case of an abnormal condition. The voltage levels required for the ICs in the circuit are obtained by stepping down and regulating the outputs of the bridge rectifier using zener diodes. The system comprises balanced load system formed by plurality of resistors making it possible for the circuit of the system to monitor the status of the fuse even when the load is in disconnected condition. When the load is in disconnected condition the path for the flow of the current between the phases get completed through these resistors. The said fuse monitoring system consumes only very low power because of the use of low threshold optocouplers as voltage sensors. It also avoids the need for any external power supply because of the self generating power supply unit present in the device. The said fuse monitoring device gives the status of the current limiting device in each phase of a multiphase system and it can further be used for remote indication and protection purposes also. BRIEF DESCRIPTION OF ACCOMPANYING FIGURES Figure 1 illustrates schematic diagram for fuse monitoring system of the present invention. Figure 2 illustrates the circuit configuration of the fuse monitoring system of the present invention. DETAILED DESCRIPTION OF ACCOMPANYING FIGURES Referring to figure 1 it is realizable that the fuse monitor is connected across the terminals (F1) and (F2) of fuse link (9), (F3) and (F4) of fuse link (10) and (F5) and (F6) of fuse link (11) (also shown in figure 2) and that the circuitry consists of a built-in power supply unit (5), voltage sensing units (6,7 and 8), logic circuitry (2) and display module (4). The output of the power supply unit (5) energizes the sensing logic circuitry (2) and the potential free auxiliary relay contact system (3) . The voltage sensors (6,7 and 8) are connected across the fuse links (9,10 and 11) and continuously monitors the voltage across each of the said fuse links (9, 10 and 11) . The output of these voltage sensors (6, 7 and 8) depends on the condition of the fuse i.e, whether it is in good state or fused state. The output of the voltage sensors (6,7 and 8) is fed to the logic circuitry (2) which gives an output such that appropriate indications in the display module (4) comes ON indicating the status of the fuse links (9,10 and 11). The display module (4) comprises five LEDs (described in details in the description of figure 2). Figure 2 represents an embodiment of the fuse monitor for a three phase system and it lucidly indicates the circuit details. The lines (L1), (L2) and (L3) represents individual phases of three phase power supply system. Fuses (9), (10) and (11) are thermal fuses inserted into the lines (L1, L2 and L3) respectively for the protection of the system in case of an abnormal condition in the system. The fuse monitor is connected across the fuse terminals (F1) and (F2), (F3) and (F4), (F5) and (F6) corresponding to fuse links (9, 10 and 11) respectively. In this embodiment the voltage sensors (6, 7 and 8) connected across fuse links (9, 10 and 11) respectively are low threshold sensing opto couplers with ac to dc logic interface. These opto couplers (6, 7, and 8) are connected to the lines (L1, L2 and L3) respectively through high resistors (46) and (47), (48) and (49), (30) and (31) in that order. These resistors determine the operating voltage range of the fuse monitor by setting the threshold values for the opto couplers (6, 7 and 8). Whenever the fuses (9, 10 and 11) are in good condition the voltage across the fuses are below the threshold level of the voltage sensors (6, 7 and 8) and hence the opto coupler wiL1 be OFF and so the voltage Vcc applied to the optocouplers (6, 7 and 8) through (33, 43 and 52) appears across the zener diodes (34,39 and 55) causing them to operate in their breakdown region. NAND gate (14) which receives it's input from across the zeners (34, 39 and 55). Since the zeners (34,39 and 55) are operating in their breakdown region aL1 the inputs to the NAND gate (14) is high and forcing the output of the NAND gate (14) to remain low. This causes the transistors (25) to operate in the cut off region thereby causing the voltage Vcc to appear across the green LED (24) and thus it turns on indicating that aL1 fuses are in a healthy condition. NOT gate (59) gives a high output as it receives its input from the low output of the NAND gate (14). This provides a base drive for the transistor (16) causing it to operate in the saturation region thereby causing the voltage across the orange LED (17) to drop to zero, causing it to remain OFF. Similarly as the opto- couplers (6,7 and 8) are in OFF condition transistors (35,40 and 56) receives base drive from the voltages through the resistors (33,43 and 52) causing it to go into saturation and thus the red LEDs (36,42 and 57) to remain OFF indicating healthy condition of aL1 the fuse links. The invention has been described in a preferred form only and many variations may be made in the invention which wiL1 stiL1 be comprised within its spirit. The invention is not limited to the details cited above. The components of the circuit used as described and iL1ustrated in the above description and the drawings do not restrict the scope of the invention. The structure thus conceived is susceptible of numerous modifications and variations, aL1 the details may furthermore be replaced with elements having technical equivalence. In practice the materials and dimensions may be any according to the requirements, which wiL1 stiL1 be comprised within its true spirit. WE CLAIM 1. A monitoring system adapted to monitor electrical status and operating conditions of plurality of current limiting devices or fuses whereby detecting and individuaL1y monitoring conditions of each fuse, wherein the said fuse links are connected in each phase of a multi-phase system and wherein from over said fuse links connecting means being provide in a manner so as to establish operative connection from power supply network to said fuse monitoring system, said fuse monitoring system comprising : (i) plurality of sensor means operatively connected across each of the phases of the multi phase system; wherein said sensor means being adapted to output instantaneous condition of each fuse of said plurality of fuses; (ii) controL1er means connected to said sensor means such that it gives desired output depending on the status of the current limiting device; and (iii) indicator means operatively connected to the controL1er means indicating the status of the fuses or individual fuse. 2. System as claimed in claim 1, wherein the sensor means comprises voltage sensors provided with opto-couplers having predetermined threshold level of voltage so as to influence thereby changing state of controL1er means corresponding to any faulty/abnormal condition in the system. 3. System as claimed in claims 1 and 2, wherein controL1er means comprises (i) diode means co-operatively connected with the opto-couplers; (ii) logic gate establishing and intermediate and reciprocatory relatiobship between the opto- coupler and the indicator means. 4. System as claimed in claim 3, wherein diode means comprises zener diode. 5. System as claimed in claims 3 and 4, wherein logic gate means comprise NAND gate adapted to receive output from the zener diode and reciprocating the said output to indicator means. 6. System as claimed in claim 1, wherein power supply network comprises three phase bridge rectifier. 7. System as claimed in claim 6, wherein power supply network further comprises diode means adapted to suppress transient voltage surge. 8. System as claimed in any preceding claims further comprising balanced load system adapted to monitor the status of the fuse even when the load is disconnected. 9. System as claimed in any preceding claims further comprising self generating power supply unit. 10. System as claimed in any preceding claims wherein voltage range of monitoring is from 220V to 690V AC. The present invention relates to a monitoring system adapted to monitor electrical status and operating conditions of plurality of current limiting devices or fuses whereby detecting and individuaL1y monitoring conditions of each fuse. The fuse links (9, 10, 11) are connected in each phase of a multi-phase system. Plurality of sensor means (6, 7 and 8) are operatively connected across each of the phases of the multi phase system to output instantaneous condition of fuses (9, 10, 11) . ControL1er means (2) connected to said sensor means (6, 7 and 8) such that it gives desired output depending on the status of the current limiting device and indicator means (4) operatively connected to the controller means indicating the status of the fuses or individual fuse. |
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Patent Number | 269582 | |||||||||
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Indian Patent Application Number | 913/KOL/2005 | |||||||||
PG Journal Number | 44/2015 | |||||||||
Publication Date | 30-Oct-2015 | |||||||||
Grant Date | 28-Oct-2015 | |||||||||
Date of Filing | 04-Oct-2005 | |||||||||
Name of Patentee | LARSEN & TOUBRO LIMITED | |||||||||
Applicant Address | L & T HOUSE, BALLARD ESTATE, MUMBAI | |||||||||
Inventors:
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PCT International Classification Number | H02H | |||||||||
PCT International Application Number | N/A | |||||||||
PCT International Filing date | ||||||||||
PCT Conventions:
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