JPH10336874A - Overcurrent protection device in semiconductor circuit breaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To eliminate the unnecessary operation of overcurrent protection due to di/dt detection. SOLUTION: A device has a first overcurrent detection circuit 1 where an overcurrent is detected by a first overcurrent level that is determined by the amount of resistance of a semiconductor circuit, a second overcurrent detection circuit 2 where the overcurrent is detected by a second overcurrent detection circuit 2 that is obtained by subtracting the increment of a circuit break current being generated due to a device delay on the maximum di/dt to be predicted from the first overcurrent level, and a di/dt detection/level judgment circuit 3 where the di/dt level is compared with a specific set value. In this case, when the second overcurrent detection circuit 2 detects the covercurrent, the di/dt detection/level judgment circuit 3 breaks the semiconductor circuit breaker at a point in time when it is judged that the di/dt level is equal to or higher than the set value, thus eliminating an unnecessary operation in the case of circuit break only when the di/dt level is equal to or more than a set value. When the first overcurrent detection circuit 1 detects the overcurrent, the semiconductor circuit breaker is unconditionally breaks.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor circuit breaker used for a power supply system, and more particularly to an overcurrent protection device for a semiconductor circuit breaker that connects a power supply system to a private power generator.

[0002]

2. Description of the Related Art As shown in FIG. 2, an in-house power generation system connected to an electric power system operates to prevent a generator or a load device from being down due to an instantaneous voltage drop on the electric power system side.
Semiconductor breaker SS is connected in series with interconnection breaker 52B,
The instantaneous voltage drop detection circuit 11 detects an instantaneous voltage drop of the system, controls the semiconductor circuit breaker SS to be turned off via the interruption circuit 13, and instantaneously interrupts the interconnection.

[0003] Since the semiconductor circuit breaker SS used in the power system has a small overcurrent withstand capability, the semiconductor circuit breaker SS is provided with an overcurrent protection circuit 12 for detecting an overcurrent and controlling the semiconductor circuit breaker SS to turn off. As the overcurrent protection circuit, there are the following devices.

(1) As in general overcurrent protection, an overcurrent detection method in which a semiconductor circuit breaker is turned off when a detection current reaches a certain set value. The set value is determined by the tolerance of the semiconductor circuit breaker. (2) detecting a change in current (di / dt),
When the value is larger than the set value, the semiconductor circuit breaker is turned off di /
dt detection method.

In the overcurrent detection method (1), the semiconductor circuit breaker is turned off after the detection current reaches a set value.
When the di / dt value is large as in the case of a short circuit, a current larger than the set value is cut off due to the operation delay. Assuming that di / dt is ΔI and the operation delay is td, FIG.
As shown in (1), a current larger than the set value I _S by ΔI × td is cut off, which is inconvenient. Therefore, the di / dt detection method of (2) is used at present.

[0006]

The above-mentioned conventional (2) di
In the / dt detection method, not only in the event of a short circuit that must be protected but also when the current value is within the tolerance of the semiconductor circuit breaker, such as when a power factor compensation capacitor is turned on.
If the dt value is large, the semiconductor circuit breaker will be turned off.

The present invention has been made in view of such conventional problems, and has as its object the purpose of di.
An object of the present invention is to provide an overcurrent protection device for a semiconductor circuit breaker that can prevent unnecessary operation caused by overcurrent protection of the / dt detection method.

[0008]

According to the present invention, there is provided an overcurrent protection apparatus for a semiconductor circuit breaker, wherein a first overcurrent is detected at a first overcurrent level determined by a withstand voltage of the semiconductor circuit breaker. A detection circuit for detecting an overcurrent of the device passing current at a second overcurrent level obtained by subtracting an increase in a cutoff current caused by an operation delay of the device at a maximum di / dt expected from the first overcurrent level; A second overcurrent detecting circuit for detecting the di / dt of the device passing current and detecting the di / dt
Di / d for determining whether the level is equal to or higher than a predetermined set value
If the second overcurrent detection circuit detects an overcurrent, the di / dt detection / determination circuit shuts down when the di / dt level determines that the di / dt level is equal to or higher than a set value. When the first overcurrent detection circuit detects an overcurrent, the circuit is immediately unconditionally shut off.

[0009]

FIG. 1 shows an overcurrent protection circuit of a semiconductor circuit breaker according to an embodiment. In Figure 1, 1 and 2 are compared with the set value I _S1 and I _S2 of the current, respectively, the first and second overcurrent detection circuit that outputs when the current is increased, the set value I _S1 conventional overcurrent are determined as detection method by tolerance of the semiconductor circuit breaker SS, set value I _S2 is I _S1
Set slightly lower. The set value I _S2 is obtained by calculating the increase in the breaking current caused by the operation delay of the semiconductor circuit breaker SS in the case of the expected maximum di / dt at the time of an accident from the set value I _S1 determined from the withstand capacity of the semiconductor circuit breaker SS. Shall be deducted.

Reference numeral 3 denotes a di / dt detection / level judgment circuit.
It comprises a di / dt detection circuit 31 and a level judgment circuit 32 which compares the detected di / dt value with a set value I _S3 and outputs when the di / dt value increases, and the set value I _S3.
Is the same as the set value of the conventional di / dt detection method.

Reference numeral 5 denotes an AND circuit for passing the output of the di / dt detection / level judgment circuit 3 on condition that the second overcurrent detection circuit 2 outputs an overcurrent detection, and 6 denotes a first overcurrent detection. The output of the circuit 1 or the signal of the AND circuit 5 is connected to the semiconductor circuit breaker S
This is a logical sum circuit to be output to the S cutoff circuit 13.

The operation of the overcurrent protection circuit will be described. Always, overcurrent detection circuits 1 and 2 and di / dt detection
In the level judgment circuit 3, the overcurrent and di of the semiconductor circuit breaker SS
/ Dt is monitored.

When an accident current flows through the semiconductor circuit breaker SS,
First, it reaches the lower overcurrent detection level (I _S2 ). At this time, the level of di / dt detected by the di / dt detection circuit 31 is determined by the level determination circuit 32. If the level is equal to or higher than the set value _IS3 , it is determined that protection is necessary at this time, and the logical product circuit The signal is output to the shutoff circuit 13 via the switches 5 and 6 to shut off and protect the semiconductor circuit breaker SS.

The overcurrent detection level (I
_S2 ) and the overcurrent detection circuit 2 outputs di / dt
Is small, the di / dt detection and level determination circuit 3 does not output, and therefore, is not output from the AND circuit 5. Also,
In this case, the increase in the cutoff current (FIG. 3) due to the operation delay is small, and the cutoff current does not reach the higher overcurrent detection level (I _S1 ). The circuit breaker SS is not unnecessarily shut off.

When the power factor compensating capacitor is turned on, even if the di / dt detection / level judgment circuit 3 outputs, the current in that case does not reach the lower overcurrent level (I _S2 ). Therefore, the output is not output from the AND circuit 5, and the semiconductor circuit breaker SS is not unnecessarily interrupted.

The overcurrent detection level (I
_{When S1} ) is reached, the overcurrent detection circuit 1 operates by judging that a short circuit has occurred, and unconditionally operates the cutoff circuit 13 via the OR circuit 6.
, To shut off and protect the semiconductor circuit breaker SS.

[0017]

Since the present invention is configured as described above, the following effects can be obtained.

(1) Even when di / dt is high as in the case of a short circuit, an increase in the breaking current due to the operation delay of the device can be prevented.

(2) di / d as when a capacitor is turned on
Unnecessary operation when t is high but the current value is low can be prevented.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a protection circuit configuration of a semiconductor circuit breaker according to an embodiment.

FIG. 2 is a block diagram showing a connection example of a semiconductor circuit breaker.

FIG. 3 is a diagram illustrating a current increase due to a device operation delay.

[Explanation of symbols]

 1, 2, overcurrent detection circuit 3, di / dt detection / level determination circuit 11, instantaneous voltage drop detection circuit 12, overcurrent protection circuit 13, interruption circuit SS, semiconductor circuit breaker 52B, interconnected circuit breaker

Claims (1)

[Claims] 1. A first overcurrent detection circuit for detecting an overcurrent of a device passing current at a first overcurrent level determined by a withstand voltage of a semiconductor circuit breaker, and detecting the overcurrent of the device passing current with the first overcurrent. A second overcurrent detection circuit for detecting at a second overcurrent level obtained by subtracting an increase in a breaking current caused by an operation delay of the device at the time of maximum di / dt expected from the level, and a di / dt of a device passing current. And a di / dt detection / level judgment circuit for judging whether or not the di / dt level is equal to or more than a predetermined set value. When the second overcurrent detection circuit detects an overcurrent, di / dt
A semiconductor device characterized in that when the dt detection / judgment circuit judges that the di / dt level is equal to or higher than a set value, the dt detection / judgment circuit shuts off the current. Circuit breaker overcurrent protection device.