GB2288498A

GB2288498A - Circuit breaker

Info

Publication number: GB2288498A
Application number: GB9506478A
Authority: GB
Inventors: Hanns P Sailer; Esteban Santos; John James Dougherty
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1994-04-13
Filing date: 1995-03-30
Publication date: 1995-10-18
Anticipated expiration: 2015-03-30
Also published as: GB9506478D0; GB2288498B

Abstract

A circuit breaker controlled by an electric trip unit (6) (figure 1) is configured to perform overcurrent protection and either ground fault or alternative protection of the fourth conductor, depending upon whether the circuit is in a three phase and earth or three phase and neutral arrangement. The type of protection is user-selectable and is set during the electrical installation process. A selector circuit inputs either ground fault or 4-wire data from current transformers to the circuit breaker and a selection program in the trip unit (6) determines whether ground fault or 4-wire protection is required. <IMAGE>

Description

CIRCUIT BREAKER This invention relates to circuit breakers.

Present day trip units must be designed for either 3-wire plug ground fault applications or 4-wire applications. The application criteria for the two types of functions differ sufficiently that previous designs would have been prohibitively complex and costly had they tried to implement them together.

Ground fault functions require a vector summation of the current flowing through the three phases and the ground fault phase. The ground phase is not looked at separately.

The resultant vector sum is compared with a present threshold to determine if the trip unit is in a pickup condition. 4-wire functions treat each phase input as a separate signal. All standard over current functions are applied to the fourth phase. There is no ground fault calculation done for this application since it is not applicable. In addition, the 4-wire function provides various levels of protection for the fourth phase. Present devices use an external adjustment such as a rating plug to permit protection levels of 0% (no protection), 50% and 100%.

According to a first aspect of the present invention a circuit breaker comprises an electronic trip unit connectable with a current transformer, said trip circuit breaker having facility for providing overcurrent protection along with either ground fault wire circuits comprising: selector circuit means allowing ground fault and 4-wire protection to a protected electric circuit; current sensors connected with said selection circuit providing electrical circuit input from said protected electric circuit having means for determining whether ground fault or 4-wire circuit protection is selected; whereby the facility for overcurrent protection along with either ground fault or 4-wire circuit protection is provided.

The selector circuit may include jumpers and an A/D converter connecting with said trip unit with, preferably, a gain resistor connecting between the current sensors and the A/D converter.

The trip unit may, conveniently, comprise a microprocessor.

According to a second aspect of the present invention, a method of operating a circuit breaker comprises a method of operating a circuit breaker comprising the steps of: connecting current sensors with a multi-phase electric circuit to be protected and with an electronic trip unit; connecting a selector circuit allowing ground fault and 4wire protection to said current sensors; and adapting said selector circuit for either ground fault or 4-wire protection; whereby overcurrent protection along with either ground fault or 4-wire protection is provided.

The method may include the step of instructing said trip unit to provide either ground fault or 4-wire protection and, preferably, further include the steps of determining whether said selector circuit is connected for ground fault or 4-wire protection and providing visual indication of said ground fault or said 4-wire protection.

The apparatus and method of the present invention can combine all of the above described features into one programmer.

Embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, of which: Figure 1 is a schematic illustration of a circuit breaker according to the present invention; and Figure 2 is a flow chart of a method according to the present invention.

The schematic illustration in Figure 1 shows one exemplary hardware implementation of the present invention.

An external neutral or ground fault signal passes through a jumper 1 or bi-stable latch. The jumper 1 is user selectable whereas the latch is controlled by a microprocessor (not shown). Either the ground or the fourth neutral pole signal is selected to be applied to a signal CT 2. The output of the signal CT 2 is adjusted by a combination of a gain resistor 4 and a neutral or ground fault resistor 3 which is normally contained in the rating plug.

The conditioned analog signal is then converted to a digital value via an analog to digital converter 5.

Finally, the microprocessor reads the digital value and executes various protection algorithms using this value.

Figure 2 shows one software implementation for the hardware setup described in Figure 1.

The programmer powers up and begins at S1. The microprocessor reads various information from the nonvolatile RAM S2. One item that it reads is the option bit to determine if the apparatus is in 3 or 4-wire mode S3.

If it is in 3-wire mode then several setup routines are run. The hardware, if needed, is set for 3-wire mode 87. The ground fault algorithms are turned on S8 and the 4-wire algorithms are turned off 89. Alternatively, if it is in 4-wire mode, then the 4-wire algorithms are turned on S4 and S5 and the ground fault algorithms are turned off S6. The remaining protection functions S10 run whichever algorithms were selected above.

Providing a single unit to perform all of the above functions allows delay of final function selection until the actual field setup of the unit. This allows last minute modifications to the power system without causing delays. It also permits the operator to carry fewer spares since one unit can now support several different types of application.

Claims

CLAIMS:

1. A circuit breaker comprising: an electronic trip unit connectable with a current transformer, said trip circuit breaker having facility for providing overcurrent protection along with either ground fault wire circuits comprising: selector circuit means allowing ground fault and 4wire protection to a protected electric circuit; current sensors connected with said selection circuit providing electrical circuit input from said protected electric circuit having means for determining whether ground fault or 4-wire circuit protection is selected; whereby the facility for overcurrent protection along with either ground fault or 4-wire circuit protection is provided.

2. The circuit breaker of claim 1 wherein said selector circuit includes jumpers.

3. The circuit breaker of claim 1 including an A/D converter connecting with said trip unit.

4. The circuit breaker of claim 3 including a gain resistor connecting between said current sensors and said A/D converter.

5. The circuit breaker of claim 1 wherein said trip unit comprises a microprocessor.

6. A method of operating a circuit breaker comprising the steps of: connecting current sensors with a multi-phase electric circuit to be protected and with an electronic trip unit; connecting a selector circuit allowing ground fault and 4-wire protection to said current sensors; and adapting said selector circuit for either ground fault or 4-wire protection; whereby overcurrent protection along with either ground fault or 4-wire protection is provided.

7. The method of claim 6 including the step of instructing said trip unit to provide either ground fault or 4-wire protection.

8. The method of claim 7 further including the steps of determining whether said selector circuit is connected for ground fault or 4-wire protection and providing visual indication of said ground fault or said 4-wire protection.

9. A circuit breaker substantially as hereinbefore described with reference to the accompanying drawings.

10. A method of providing a circuit breaker with overcurrent protection substantially as hereinbefore described with reference to the accompanying drawings.