FORM 2
THE PATENTS ACT, 1970 (39 of 1970)
As amended by the Patents (Amendment) Act, 2005
&
The Patents Rules, 2003
As amended by the Patents (Amendment) Rules, 2006
COMPLETE SPECIFICATION
(See section 10 and rule 13)
TITLE OF THE INVENTION
Trip coil supervision circuit for a circuit breaker
APPLICANTS
Crompton Greaves Limited, CG House, Dr Annie Besant Road, Worli, Mumbai - 400 030, Maharashtra, India, an Indian Company
INVENTORS
Sanas Ashok Haribhau, Pandharkar Anjani Prasad, Khedkar Parag Prabhakar and Joshi Ulhas Neelkanth, all of Crompton Greaves Limited, A3 MIDC, Amabd Nashik, Maharashtra, India, all Indian nationals
PREAMBLE TO THE DESCRIPTION
The following specification particularly describes the invention and the manner in which it is to
be performed:

FIELD OF THE INVENTION
This invention relates to a trip coil supervision circuit for a circuit breaker.
BACKGROUND OF THE INVENTION
A circuit breaker is used in power supply and power distribution systems as a protective electrical switching device. A circuit breaker comprises a contact system having at least one fixed contact and at least one moving contact operatively connected to the fixed contact. The moving contact is connected to an operating mechanism through a movable electrode. In operation, a circuit breaker is connected to an electrical power source at the line side thereof and one or more electrical loads like electrical appliances, devices or equipments at the load side thereof. Under overload conditions, the circuit breaker trips and clears fault currents thereby preventing damage to the electrical load(s) and also accidents.
The operating mechanism of a circuit breaker comprises a closing circuit and a trip circuit. The closing circuit comprises a closing coil impregnated with a resin insulation and a plunger reciprocally disposed in the closing coil and operatively connected to a ratchet wheel through a closing trigger and a ratchet wheel holding latch. The closing circuit also comprises a closing spring for charging and discharging the ratchet wheel during closing and tripping of the circuit breaker. The trip circuit comprises a trip coil impregnated with a resin insulation and a plunger reciprocally disposed in the trip coil and operatively connected to the ratchet wheel through a trip trigger, trip holding latch and a ratchet powl. The trip circuit also comprises a trip spring for charging and discharging the ratchet wheel during closing and tripping of the circuit breaker.

Both the trip coil and closing coil are connected to separate DC sources. When the trip coil and closing coil are energised, the respective plungers move out of the coils due to the repulsive force of the electromagnetic field generated in the coils. On denergising the coils, the plungers move into the respective coils to their original positions. It is very critical and important that the trip coil is healthy and conducting to cause instant tripping of the circuit breaker. Any delay in tripping of the circuit breaker can cause damage to the electrical load(s) and also accidents.
The conductivity and health of a trip coil is monitored with the help of a trip coil supervision circuit comprising a trip relay connected in series with the trip coil through a normally closed contact and a normally open contact and a trip relay contact. In the open position of the circuit breaker if the trip coil is healthy and conducting, a current flows through the trip relay via the normally closed contact and closes the trip relay contact so as to indicate the healthy and conducting state of the trip coil. In the closed state of the circuit breaker, the normally open contact is closed. If the trip coil is healthy and conducting, a current flows through the trip relay via the closed normally open contact and closes the trip relay contact so as to indicate the healthy and conducting state of the trip coil.
Generally the circuit breaker manufacturer supplies the circuit breaker with the normally closed contact and normally open contact and two terminals for connecting the trip relay. The customer buys the trip relay and trip relay contact and connects the trip relay between the terminals. In such a case, there is a possibility of mismatch of ratings between the trip coil and trip coil relay. In case there is a mismatch between the ratings of the trip coil and trip relay, high currents will flow through the trip coil. This may cause malfunctioning of the trip coil and circuit breaker and

may even burn and damage the trip coil. Therefore, the trip coil supervision circuit is not reliable. Besides, the cost of the circuit breaker is also increased because of the trip relay and trip relay contact. There is thus need for a trip coil supervision circuit for a circuit breaker, which is customer or user friendly, simple in construction, reliable and cost effective.
SUMMARY OF THE INVENTION
According to the invention there is provided a trip coil supervision circuit for a circuit breaker, wherein the circuit breaker comprises a trip coil (1) having a first terminal (2), a second terminal (3) -and a third terminal' (4), the first terminal being connected to me negative terminal of a DC source and the second terminal being connected to the positive terminal of the DC source through a pair of normally open contacts (5,6) and wherein the trip coil supervision circuit comprises a high resistor (7) embedded in the trip coil resin insulation and having one end thereof extending internally through the trip coil resin impregnation and connected to the trip coil and having the other end thereof connected to the third terminal of the trip coil and an indicator (8) connected to the other end of the high resistor and the positive terminal of the DC source.
According to the invention there is also provided a trip coil supervision circuit for a circuit breaker, wherein the circuit breaker comprises a trip coil (1) having a first terminal (2), a second terminal (3) and a third terminal (9), the first terminal being connected to the negative terminal of a DC source and the second terminal being connected to the positive terminal of the DC source through a pair of normally open contacts (5,6) and the trip coil supervision circuit comprises a high resistor (7) embedded in the trip coil resin insulation and having the ends connected to the third terminal (9), one end of the high resistor being connected to the trip coil

through a normally closed contact (10) and further connected between the normally open contacts (5,6) externally of the trip coil resin insulation and an indicator (8) connected to the other end of the high resistor and to the positive terminal of the DC source.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
Fig 1 is a circuit diagram of a trip coil supervision circuit according to an embodiment of the invention for a circuit breaker; and
Fig 2 is a trip coil supervision circuit according to another embodiment of the invention for a circuit breaker.
DETAILED DESCRIPTION OF THE DRAWINGS
As illustrated in Fig 1 of the accompanying drawings, 1 is a trip coil having a first terminal 2, a second terminal 3 and a third terminal 4. Terminal 2 is provided with a connector hole 2a for connecting terminal 2 to the negative terminal of a DC source. Terminal 3 is provided with a connector hole 3a for connecting the terminal 3 to the positive terminal of the DC source through a pair of normally open contacts 5 and 6. 7 is a high resistor embedded in the trip coil resin insulation (not shown). One end of the high resistor extends internally through the trip coil resin impregnation and is connected to the trip coil. The other end of the high resistor is connected to

the third terminal 4 of the trip coil through connector hole 4a provided in the terminal 4. 8 is an indicator connected to the other end of the high resistor and the positive terminal of the DC source.
In the case of Fig 2 of the accompanying drawings, the third terminal 9 comprises connector holes 9a and 9b at the ends thereof. The two ends of high resistor 7 are connected to terminal 9 through connector holes 9a and 9b. One end of the high resistor connected to terminal 9 through connector hole 9a is also connected to the trip coil through a normally closed contact 10 and further connected between the normally open contacts 5 and 6 externally of the trip coil resin impregnation. Indicator 8 is connected to the other end of the resistor through connector hole 9b and to the positive terminal of the DC source.
The resistance value of the high resistor depends on the rating of the circuit breaker. Preferably the resistance value of the high resistor is in the range of 5 to 25 kOhms. The indicator is preferably a Light Emitting Diode (LED) and / or a hooter. Figs 1 and 2 illustrate the trip coil supervision circuit in the open position of the circuit breaker. Contact 5 also forms a part of the trip circuit of the circuit breaker and contact 6 forms a part of the trip circuit. Contact 5 and contact 6 are closed in the usual manner at the time of closing the circuit breaker.
In the case of the trip coil supervision circuit of Fig 1 both in the open and closed conditions of the circuit breaker, a current flows through the high resistor and drives the indicator if the trip coil is conducting and healthy. As a result, the LED glows and if the indicator also comprises a hooter, the hooter raises an audio alarm to indicate the healthy and conducting state of the trip

coil. If the trip coil is not conducting and healthy, the indicator does not give any visual and/or audio indication thereby indicating the non-conducting and unhealthy condition of the trip coil.
In the case of the trip coil supervision circuit of Fig 2, when the circuit breaker is in the open condition, a current flows through the high resistor via the normally closed contact 9 and drives the indicator if the trip coil 1 is healthy and conducting. In the closed condition of the circuit breaker, both the contacts 5 and 6 will remain closed and a current flows through the high resistor via the closed normally open contact 6 and drives the indicator if the trip coil is conducting and healthy.
The trip coil supervision circuit of Fig 1 may be supplied to the customer with the indicator connected to the other end of the high resistor and positive terminal of the DC source. Alternatively the trip coil supervision circuit may be supplied to the customer without the indicator and the customer will have the flexibility to purchase his own indicator and connect it to the other end of the high resistor through connector hole 4a in the terminal 4. The trip coil supervision circuit of Fig 2 may be supplied to the customer with the normally closed contact 10 and indicator 8. Alternatively the trip coil supervision circuit may be supplied to the customer without the closed contact 10 and indicator 8 in which case the customer will have the flexibility to purchase the normally closed contact 10 and indicator 8 and connect the contact 10 to one end of the high resistor through hole 9a and to connect the indicator to the other end of the high resistor through hole 9b.

According to the invention both the trip relay and trip relay contact have been eliminated. As a result there is no need for the customer to buy and connect the trip relay and trip relay contact in the trip relay supervision circuit and there is no possibility of mismatch between the trip coil rating and trip relay rating. Malfunctioning of the trip coil and circuit breaker and damage to the trip coil are avoided and the trip coil supervision circuit is reliable. The trip relay supervision circuit of the invention gives both visual indication and if necessary audio indication indicating the state of health of the trip coil. As a result it is possible to monitor the health of the trip coil effectively and to take timely remedial action. It is customer or user friendly, simple in construction and cost effective.
Although the invention has been described with reference to specific embodiments, these embodiments are not to be understood in a limiting sense. There can be variations in the embodiments illustrated and there can be alternate embodiments of the invention. Such variations and alternate embodiments will become apparent to those skilled in the art upon reading the description relating to the above embodiments. Therefore, variations and alternate embodiments which are apparent and obvious to those skilled in the art are to be construed and understood to be within the scope of the invention.

We claim ;
1. A trip coil supervision circuit for a circuit breaker, wherein the circuit breaker comprises
a trip coil (1) having a first terminal (2), a second terminal (3) and a third terminal (4), the first terminal being connected to the negative terminal of a DC source and the second terminal being connected to the positive terminal of the DC source through a pair of normally open contacts (5,6) and wherein the trip coil supervision circuit comprises a high resistor (7) embedded in the trip coil resin insulation and having one end thereof extending internally through the trip coil resin impregnation and connected to the trip coil and having the other end thereof connected to the third terminal of the trip coil and an indicator (8) connected to the other end of the high resistor and the positive terminal of the DC source.
2. The trip coil supervision circuit as claimed in claim 1, wherein the third terminal (4) comprises a connector hole (4a) for connecting the other end of the high resistor (7) and the indicator.
3. The trip coil supervision circuit as claimed in claim 1 or 2, wherein the resistance of the high resistor (7) is 5 to 25 kOhms.
4. The trip coil supervision circuit as claimed in any one of claims 1 to 3, wherein the indicator (8) comprises a Light Emitting Diode (LED) and/or a hooter.
5. A trip coil supervision circuit for a circuit breaker, wherein the circuit breaker comprises a trip coil (1) having a first terminal (2), a second terminal (3) and a third terminal (9), the first

terminal being connected to the negative terminal of a DC source and the second terminal being connected to the positive terminal of the DC source through a pair of normally open contacts (5,6) and the trip coil supervision circuit comprises a high resistor (7) embedded in the trip coil resin insulation and having the ends connected to the third terminal (9), one end of the high resistor being connected to the trip coil through a normally closed contact (10) and further connected between the normally open contacts (5,6) externally of the trip coil resin insulation and an indicator (8) connected to the other end of the high resistor and to the positive terminal of the DC source.
6. The trip coil supervision circuit as claimed in claim 5, wherein the third terminal (9) comprises a connector hole (9a, 9b) at each end thereof, one connector hole (9a) for connecting one end of the high resistor (7) to the third terminal (9) and the connector hole (9b) for connecting the other end of the high resistor to the third terminal (9).
7. The trip coil supervision circuit as claimed in claim 5 or 6, wherein the resistance of the high resistor (7) is 5 to 25 kOhms.
8. The trip coil supervision circuit as claimed in any one of claims 5 to 7, wherein the indicator (8) comprises a Light Emitting Diode (LED) and/or a hooter.