JP3712886B2 - Leakage breaker and ground fault detection method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an earth leakage circuit breaker for detecting an earth leakage by a zero phase current transformer and a ground fault detection method, and more particularly to an earth leakage circuit breaker and a ground fault for preventing malfunction due to unbalance characteristics of the zero phase current transformer. It relates to the detection method.
[0002]
[Prior art]
FIG. 6 is a block diagram showing an internal circuit of a conventional earth leakage circuit breaker disclosed in, for example, Japanese Patent Application Laid-Open No. 09-093790.
In the figure, 1 is an AC circuit, 2 is a zero-phase current transformer, 3 is a leakage detection circuit, 4 is a switching element connected to the output terminal of the leakage detection circuit 3, 5 is an electromagnetic device driven by the switching element 4, 6 is a circuit breaker contact that cuts off the current in the AC circuit 1 by driving the electromagnetic device 5, 7 is an overcurrent detection processing circuit, and its internal configuration is for converting the negative voltage output detected in each phase into a positive voltage. It is formed by a level conversion circuit 8, an A / D conversion circuit 9 for converting the output of the level conversion circuit 8 into a digital signal, and a microcomputer (CPU) 10 for determining a time period by determining the current level and its magnitude. ing. Reference numeral 11 denotes a power supply circuit that supplies operating DC power of the leakage detection circuit 3 and the electromagnetic device 5.
[0003]
Reference numerals 21 to 23, 30, 41 to 44 form current detection means. Reference numerals 21, 22, and 23 denote current transformers that detect currents of respective phases of the AC circuit 1, and reference numeral 30 denotes current transformers 21, 22, and 23. This is a rectifier circuit that full-wave rectifies the secondary output of the first and second diodes, and is composed of diodes 31-38. Reference numerals 41 to 44 denote phase current detection resistors which output a voltage proportional to the current of each phase as a negative voltage across each resistor. Among these, the phase current detection resistor 44 detects a zero phase current, and determines whether or not the AC circuit 1 is grounded according to the value of the zero phase current.
[0004]
10a is an overcurrent trip signal output, which determines the level of the voltage of the phase current detection resistors 41 to 44 corresponding to each phase of the AC circuit 1, and is based on a predetermined level and time limit (duration greater than the predetermined level). An output to the switching element 4 is given. The switching element 4 is connected via diodes 12 and 13 so as to operate with either the overcurrent trip signal output 10a or the leakage detection signal 3a.
[0005]
10b is a lock signal output, and the output controls the transistor 14 to short-circuit the leakage detection output 3a so that the leakage detection signal 3a is not input to the switching element 4. The lock signal output 10b is output when the current of the AC circuit 1 is not less than a predetermined value and is not a ground fault, but this determination level is set to a value different from the determination level of the overcurrent trip signal.
[0006]
The signal input to the microcomputer 10 is processed according to the flowchart of FIG. The processing procedure will be described. First, it is determined whether or not the input signal from the A / D conversion circuit 9 is an input signal in the unbalanced region in the unbalanced region determining step 101. If YES, the phase current detection resistor 44 detects whether it is a ground fault or not. The ground fault current determination step 102 makes a determination based on the level of the input signal.
[0007]
If it is determined that there is no ground fault, a lock signal is output, the operation of the switching element 4 is blocked, and the breaker contact 6 is prevented from being opened due to an erroneous output of the leakage detection circuit 3. If the input signal is not a current in the unbalanced region, or if it is determined that a ground fault has occurred even if the input signal is in the unbalanced region, the lock signal 10b is not immediately output, and the leakage detection circuit 3 The output to the switching element 4 is not disturbed.
[0008]
[Problems to be solved by the invention]
The conventional earth leakage breaker is configured as described above, and the zero-phase current detected by the phase current detection resistor 44 passes the fixed threshold value in the ground fault current determination step 102 for determining whether or not there is a ground fault. The number of times was counted, and the determination was made based on the result.
Shows this determination content in FIG. 8, the sampling time: zero-phase current counts the number of passes through the fixed threshold (T1 to T6 e.g. 20 ms) within less than 4 times, it is determined that the ground fault, or 4 times If so, it is determined as normal three-phase energization.
[0009]
However, a characteristic difference occurs in the zero-phase current due to the difference in the arrangement of the inner conductors of the AC current paths 1 of the current transformers 21 to 23 and the current detection performance difference of the current transformers 21 to 23. For example, the sampling time T2 In this section, the number of times of passing through the fixed threshold value is 3 even though it is in a normal three-phase energized state, so it is determined that there is a ground fault, and the microcomputer 10 of the overcurrent detection processing circuit 7 locks the lock signal 10b. The lock release is performed so as not to output, and the leakage breaker malfunctions due to the leakage detection signal 3a of the leakage detection circuit 3.
[0010]
The present invention has been made to solve the above-described problems. For the purpose of obtaining an earth leakage circuit breaker that reliably determines whether or not a ground fault occurs when a current flows through the AC circuit 1, and that does not malfunction. Yes.
[Means for Solving the Problems]
[0011]
(1) An earth leakage breaker according to the present invention includes an earth leakage detection means for detecting an earth leakage current of an AC circuit by a zero-phase current transformer and outputting a leakage detection signal when the detected value reaches a predetermined level; and the AC circuit Overcurrent detection means for detecting the current flowing through each phase and outputting an overcurrent trip signal in accordance with the detected current level, the current value flowing through each detected phase, and the magnitude of this current value The ground fault determining means for outputting a lock signal is determined based on the comparison with the fluctuation threshold value derived in this case, and if it is not, the leakage detection signal is passed according to the lock signal. Alternatively, it includes a locking means for blocking, and an opening / closing means for interrupting the AC circuit in response to the leakage detection signal passing through the locking means or the overcurrent trip signal.
[0012]
(2) Further, the fluctuation threshold value is set between the maximum value P1 of the combined detection voltage detected during normal operation and the maximum value P2 of the combined detection voltage detected during ground fault.
[0013]
(3) The fluctuation threshold value is set in advance in the ground fault determination means.
[0014]
(4) The ground fault detection method according to the present invention is based on a comparison between a current flowing through each phase of the AC circuit and a fluctuation threshold derived according to the magnitude of the current flowing through each phase of the AC circuit. It is determined whether or not it is a ground fault.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1 FIG.
The block diagram showing the internal circuit of the earth leakage circuit breaker according to the first embodiment of the present invention is the same as the conventional one shown in FIG. 6, and the signal inputted to the microcomputer 10 is processed according to the flowchart of FIG.
[0016]
(1) First, it is determined whether or not the input signal from the A / D conversion circuit 9 is an input signal in the unbalanced region in the unbalanced region determining step 201.
(2) If the determination is YES, in the ground fault current determination step 202, it is determined whether or not there is a ground fault based on the combined phase current level of the input signal detected by the phase current detection resistor 44.
[0017]
(3) If the determination in step 202 is “NO” and it is determined that there is no ground fault, a lock signal is output in step 204, the operation of the switching element 4 is blocked, and the leakage detection circuit 3 is erroneously detected. The breaker contact 6 is prevented from being separated by the output.
(4) If the input signal is not an unbalanced region current in step 201, or if it is determined in step 202 that a ground fault has occurred even if the input signal is in the unbalanced region, step 203 So that the lock signal 10b is not output and the output of the leakage detection circuit 3 to the switching element 4 is not disturbed.
[0018]
(5) Next, in step 205, whether or not the current flowing through each phase detected by the current transformers 21 to 23 and calculated by the CPU 10 is equal to or higher than a predetermined level, or the leakage detection detected by the zero-phase current transformer 2 It is determined whether or not the current from the circuit 3 is equal to or higher than a predetermined level (overcurrent determination).
(6) If the determination result is NO (NO), return to Step 201.
[0019]
(7) If the determination result is YES and the overcurrent state continues to a predetermined time period in step 206, an overcurrent trip signal is output in step 207 and the AC circuit 1 is interrupted.
(8) If the predetermined time limit is not reached in step 206 even if there is an overcurrent,
Returning to step 201, the AC circuit 1 is not interrupted.
[0020]
FIG. 2 is a relationship diagram of the detection voltage (combined phase current) detected by the phase current detection resistor 44 and the fluctuation threshold value for determining whether or not there is a ground fault. The flowing current is detected by the current transformers 21 to 23, converted into data by the rectifier circuit 30, the phase current detection resistor 44, the level conversion circuit 8, and the A / D conversion circuit 9, and then input to the microcomputer 10 for calculation. Is required.
[0021]
FIG. 3 shows characteristics for determining the fluctuation threshold, and the combined phase detection voltage (peak value) with respect to the current peak value when the peak value of the current flowing in the AC circuit 1 is normal three-phase energization, The composite phase detection voltage (peak value) with respect to the current peak value when the AC circuit 1 is unipolar ground fault is measured for each earth leakage circuit breaker model, and the value between the two characteristic curves is the characteristic of the fluctuation threshold. It is a curve.
[0022]
The characteristic curve of the fluctuation threshold may be obtained for each type of earth leakage breaker and set on the memory of the CPU. However, for the sake of simplicity, the fluctuation threshold is represented by a broken line (linear function).
The following arithmetic expression is an approximate expression.
Fluctuation threshold = [K (Z−X) / 100] + Y −−−−− (1)
Where Z: current value (peak value) flowing through the AC circuit
K, X, Y: Fluctuation threshold coefficient (coefficient that varies according to the range of Z value)
[0023]
FIG. 4 shows an example of the relationship between the peak value of the current flowing through the AC circuit 1 and the fluctuation threshold value obtained by the calculation formula (1). Both the models A and B have variable threshold values approximated by two straight lines (broken lines).
[0024]
According to this arithmetic expression, the fluctuation threshold value is the maximum value P1 of the detection voltage detected by the phase current detection resistor 44 when normal, and the maximum value P2 of the detection voltage detected by the phase current detection resistor 44 when a ground fault occurs. Therefore, even if the value of the current flowing through the AC circuit 1 fluctuates or the performance difference between the current transformers 21 to 23 for detecting the current may cause a characteristic difference in the zero-phase current. When a ground fault occurs, the detection voltage detected by the phase current detection resistor 44 exceeds the set fluctuation threshold value, and a ground fault is determined. When the ground fault is normal, the detection voltage detected by the phase current detection resistor 44 is The set fluctuation threshold is not exceeded, and it is determined that it is normal (three-phase energization).
[0025]
In the above description, the current data flowing in the AC circuit 1 is continuously taken into the microcomputer 10 and the fluctuation threshold value is calculated and set by an arithmetic expression. If the relationship between the current data flowing in the electric circuit 1 and the fluctuation threshold value is obtained and stored as data in the memory in the microcomputer 10, the calculation time can be omitted and high-speed processing can be performed.
[0026]
As described above, according to the present invention, when a transient current flows through the AC circuit 1, it is possible to reliably determine whether there is a ground fault and to obtain a leakage breaker that does not malfunction.
[0027]
In addition, although the case where a ground fault was detected in the earth leakage breaker was described above, it can be used as a method for detecting a ground fault of a device in another AC circuit.
[0028]
Embodiment 2. FIG.
In Embodiment 1, the earth leakage breaker in the three-phase AC circuit is used. However, Embodiment 2 shows the case of the earth leakage breaker in the single-phase AC circuit.
FIG. 5 is a block diagram showing a circuit configuration of the leakage breaker according to the second embodiment.
In FIG. 5, the central circuit of the AC circuit 1 is omitted from the circuit of FIG. 6 of the first embodiment, and the current transformer 22, the diodes 33 and 34, and the phase current detection resistor 42 are omitted.
Since the operation is the same as that of the first embodiment, a description thereof will be omitted.
[0029]
【The invention's effect】
As described above, the earth leakage breaker and the ground fault detection method of the present invention have the effect of reliably determining whether a ground fault has occurred when a transient current flows through the AC circuit, and preventing malfunction or detection. is there.
[0030]
In addition, the ground fault detection method of the present invention has an effect of reliably determining whether or not there is a ground fault.
[Brief description of the drawings]
FIG. 1 is a flowchart showing an operation of an earth leakage circuit breaker according to Embodiment 1 of the present invention.
FIG. 2 is a relationship diagram between a detection voltage waveform and a variation threshold value in a phase current detection resistor according to Embodiment 1 of the present invention;
FIG. 3 is a characteristic diagram for deriving a variation threshold value according to the first embodiment of the present invention.
FIG. 4 is a diagram showing an example of a relationship between a current flowing through an AC circuit according to Embodiment 1 of the present invention and a fluctuation threshold obtained by an arithmetic expression.
FIG. 5 is a block diagram showing a circuit configuration of a leakage breaker according to Embodiment 2 of the present invention.
FIG. 6 is a block diagram showing a circuit configuration of the first embodiment of the present invention and a conventional earth leakage breaker.
FIG. 7 is a flowchart showing the operation of a conventional earth leakage circuit breaker.
FIG. 8 is a relationship diagram between a detection voltage waveform and a fixed threshold value in a conventional phase current detection resistor.
[Explanation of symbols]
1 AC circuit, 2 Zero-phase current transformer, 3 Earth leakage detection circuit,
3a earth leakage detection signal, 4 switching element, 5 electromagnetic device,
6 Circuit breaker contact 7 Overcurrent detection processing circuit, 8 level conversion circuit,
9 A / D conversion circuit, 10 microcomputer (CPU),
10a Overcurrent trip signal output, 10b Lock signal output,
11 power supply circuit 12, 13 diode, 14 transistor,
21, 22, 23 Current transformer, 30 Diode,
31, 32, 33, 34, 35, 36, 37, 38 diode,
41, 42, 43, 44 Phase current detection resistors.

Claims (4)

A leakage detecting means for detecting a leakage current of the AC circuit by a zero-phase current transformer and outputting a leakage detection signal when the detected value reaches a predetermined level;
Overcurrent detection means for detecting a current flowing in each phase of the AC circuit and outputting an overcurrent trip signal according to the detected current level;
Based on the comparison between the detected current value flowing through each phase and the fluctuation threshold value derived according to the magnitude of this current value, it is determined whether or not there is a ground fault. If not, a lock signal is output. A ground fault judging means for
Lock means for passing or blocking the leakage detection signal in response to the lock signal;
An earth leakage circuit breaker comprising: the leakage detecting signal that has passed through the locking means; or an opening / closing means that interrupts the AC circuit in response to the overcurrent trip signal.   2. The fluctuation threshold value is set to be intermediate between a maximum value P1 of a combined detection voltage detected at normal time and a maximum value P2 of a combined detection voltage detected at ground fault. Earth leakage circuit breaker.   3. The earth leakage circuit breaker according to claim 1, wherein the fluctuation threshold value is set in advance in the ground fault determination means.   Ground fault detection method for determining whether there is a ground fault based on a comparison between a current flowing in each phase of the AC circuit and a fluctuation threshold derived according to the magnitude of the current flowing in each phase of the AC circuit .

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