Title of Invention	FUSE MONITORING SYSTEM FOR MONITORING STATUS OF CURRENT
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.

Title of Invention

FUSE MONITORING SYSTEM FOR MONITORING STATUS OF CURRENT

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.

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.

Documents:

http://ipindiaonline.gov.in/patentsearch/GrantedSearch/viewdoc.aspx?id=HefBFlpj4euVHqRKzaWpQg==&loc=wDBSZCsAt7zoiVrqcFJsRw==

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Patent Number

269582

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:

#	Inventor's Name	Inventor's Address
1	SEBASTIAN, SANJITH	SWITCHGEAR DESIGN & DEVELOPMENT CENTER, LARSEN & TOUBRO LIMITED, ELECTRICAL SECTOR-(EBG), POWAI WORKS(EAST), GATE NO. 7, SAKI VIHAR ROAD, MUMBAI 400072
2	PATNE, SWAPNAJA	SWITCHGEAR DESIGN & DEVELOPMENT CENTER, LARSEN & TOUBRO LIMITED, ELECTRICAL SECTOR-(EBG), POWAI WORKS(EAST), GATE NO. 7, SAKI VIHAR ROAD, MUMBAI 400072

PCT International Classification Number

H02H

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA