JP2012005193A - Leakage cutoff unit and leakage detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a leakage cutoff unit and a leakage detector capable of detecting leak current resulting from ground resistance by easy and inexpensive configuration, and maintaining an operation sensitivity actual value between rating sensitivity current and rating non-operation current in a three-phase three-line type electric circuit of one line grounding to which delta connection is performed.SOLUTION: In the leakage cutoff unit which operates to detect a resistance component of the leak current in the three-phase three-line type electric circuit 2 which is connected to a system power supply 1 to which the delta connection is performed and grounded by one line, a variable resistor 37 for cancellation is serially connected to a magnetic coupling part 34a which is magnetically coupled to a zero-phase current transformer 34 which is connected to a leakage detection part 33 between two lines of T phase and R phase which are non-ground of the three-phase three-line type electric circuit 2, and leak current Iresulting from ground capacitance 5 of the leak current Iwhich is detected by the zero-phase current transformer 34 is canceled by current proportional to current Iwhich flows to the variable resistor 37 for cancellation.

Description

  The present invention relates to an earth leakage circuit breaker and an earth leakage circuit that operate by detecting only a ground resistance component (non-inductive component) of a leakage current in a three-phase three-wire electric circuit connected to a delta-connected system power source and grounded on one line. The present invention relates to a detection device.

  In recent years, computers have been used in various areas of society, and the length of electric lines may become long when connecting devices due to the widespread use of intelligent buildings and factory automation (FA). is there. Due to the increase in the length of the electric line, the capacitance to ground (floating capacitance) increases, and troubles caused by this increase in the trend.

By the way, the leakage current includes the leakage current flowing through the above-described ground capacitance and the leakage current flowing through the ground resistance. In the earth leakage breaker and the earth leakage detection device, It is required to accurately detect only the leakage current that flows.
If the power supply is star-connected, its neutral point is grounded, and the ground capacitance of each phase is equal, the total vector value of the leakage current that flows out of the wire through the ground capacitance is zero, and the leakage current It does not affect the leakage current detection value for operating the circuit breaker or leakage detection device. However, in a three-phase three-wire electric circuit with a delta connection that is grounded on one line, the phase difference of the leakage current through the two-phase ground capacitance, which is a non-grounded phase, is 60 degrees. The leakage current detection value becomes a vector sum of this value and the leakage current due to the ground resistance to be detected originally.

Therefore, in a general earth leakage breaker and earth leakage detection device, it is desired that only the leakage current caused by the ground resistance can be detected by an effective and simple means.
Note that, for example, Patent Document 1 discloses a detection principle of leakage current caused by ground resistance in a delta-connected three-phase three-wire circuit that is grounded on one line. This prior art is based on the leakage current flowing through the ground line detected by the zero-phase current transformer (ZCT) and the one-phase reference potential that is a non-grounded phase, and only the leakage current due to ground resistance is determined by a predetermined arithmetic expression. In this case, the insulation state can be detected with a small error accuracy with respect to the settling current value even when a leakage current occurs in any electric circuit.

JP 2001-242205 A (paragraphs [0043] to [0051], FIG. 3 and the like)

  In the prior art according to Patent Document 1, it is necessary to perform complicated vector analysis in order to detect a resistive ground fault current, and there is a problem that the apparatus becomes large and expensive.

On the other hand, the test circuit of the earth leakage breaker is tested to ensure that the trip operation by the test button can be performed even if the rated inactive current on the load side, that is, the ground fault current that is 1/2 of the rated sensitivity current I _Δn flows. Generally, the current is set to 1.5 times or more than the rated sensitivity current I _Δn . Here, the rated sensitivity current I _Δn is a current (for example, 30 [mA]) at which the leakage breaker always detects a leakage when the leakage breaker exceeds this current, and the rated inoperative current is a leakage current. When the breaker is less than this current, it means a current (for example, 15 [mA]) that does not detect a leakage and does not perform a breaking operation.
However, this is not cured also take, only to have tested that it works with a value of more than 1.5 times the rated sensitivity current _I Δn, not to be subjected to operation verification at the rated sensitivity current _I Δn Is the actual situation.

  Therefore, the problem to be solved by the present invention is that it is possible to detect a leakage current caused by ground resistance with a simple and inexpensive configuration in a one-phase grounded three-phase electric circuit with a delta connection, and the operation sensitivity capability value is determined. An object of the present invention is to provide a leakage breaker and a leakage detection device that can be maintained between a rated sensitivity current and a rated inoperative current.

In order to solve the above-described problem, the leakage breaker according to claim 1 operates by detecting a resistance component of leakage current in a three-phase three-wire electric circuit connected to a delta-connected system power source and grounded by one line. In the earth leakage breaker,
A variable resistor and a magnetic coupling unit that is magnetically coupled to a zero-phase current transformer connected to the leakage detection unit are connected in series between two ungrounded wires of the three-phase three-wire circuit.
Of the leakage current detected by the zero-phase current transformer, the leakage current caused by the ground capacitance of the three-phase three-wire circuit is canceled by a current proportional to the current flowing through the variable resistor.

  In the present invention, the two-phase ground capacitance, which is a non-grounded phase in a three-phase three-wire circuit, is generally substantially equal, and the leakage current due to these ground capacitances is opposite to the voltage between the two ungrounded phases. The focus is on the phase (180 degree phase difference). That is, a variable resistor and a magnetic coupling unit are connected in series between two ungrounded phases, and this magnetic coupling unit is circulated or penetrated through a zero-phase current transformer (hereinafter also referred to as ZCT) to be magnetically coupled. Thereby, the leakage current due to the ground capacitance is canceled by the current flowing through the variable resistor, and only the leakage current due to the ground resistance can be detected effectively.

  The earth leakage breaker according to claim 2 is the earth leakage breaker according to claim 1, wherein the earth leakage detection unit is provided between an ungrounded one line and a grounded one line in the three-phase three-wire electric circuit. A first test circuit having a first switch means for flowing a rated sensitivity current during the test of the second test, and a second test having a second switch means for flowing a rated inoperative current during the test of the leakage detection unit The circuit is connected in parallel with each other.

By using the first test circuit and the second test circuit, the earth leakage circuit breaker operates at the rated sensitivity current I _Δn and does not operate at the rated inoperative current (I _Δn / 2). , I _Δn > Electric leakage breaker operating level> (I _Δn / 2).

The leakage detection device according to claim 3 is a leakage detection device that detects a resistance component of leakage current in a three-phase three-wire circuit connected to a delta-connected system power supply and grounded on one line.
A variable resistor and a magnetic coupling unit that is magnetically coupled to a zero-phase current transformer connected to the leakage detection unit are connected in series between two ungrounded wires of the three-phase three-wire circuit.
Of the leakage current detected by the zero-phase current transformer, the leakage current due to the ground capacitance of the three-phase three-wire circuit is canceled by a current proportional to the current flowing through the variable resistor,
Means for displaying the level of leakage current is connected to the leakage detection unit.

According to the earth leakage circuit breaker of the present invention, the leakage current due to the ground capacitance is canceled by the simple configuration in which the variable resistor and the magnetic coupling unit are simply connected in series between the two phases which are non-grounded phases. Only the leakage current can be accurately detected and a predetermined interruption operation can be performed.
Further, according to the leakage detection device of the present invention, it is possible to accurately detect only the leakage current due to ground resistance based on the same principle as the leakage breaker, and also to confirm insulation performance and ground capacitance by displaying the leakage current level. It is possible to check the cancellation status of leakage current due to.

As described above, according to the present invention, it is possible to realize an I _0r operation compatible type earth leakage circuit breaker that detects only the leakage current due to ground resistance and blocks the circuit under measurement based on the detected value. Further, it is possible to provide a leakage detection device capable of displaying a leakage current level and outputting an alarm.

It is a lineblock diagram of an earth-leakage circuit breaker concerning a 1st embodiment of the present invention. It is a vector diagram which shows the voltage and electric current in FIG. It is a block diagram of the leak detection apparatus which concerns on 2nd Embodiment of this invention.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an earth leakage circuit breaker (referred to as an I _0r operation type earth leakage circuit breaker) according to a first embodiment of the present invention, and FIG. 2 is a vector diagram showing voltage and current in FIG.
In FIG. 1, 1 is a system power supply connected in delta connection, 2 is a three-phase three-wire circuit connected to the system power supply 1, and one of the circuits 2, for example, the S phase is grounded And In addition, a load (not shown) is connected to the electric circuit 2 via the leakage breaker 3 of the present embodiment.

The earth leakage circuit breaker 3 includes a ZCT (zero phase current transformer) 34 for detecting a zero phase current in the electric circuit 2, a magnetic coupling portion 34 a having N turns and magnetically coupled around the ZCT 34 N times, A leakage detection unit 33 that amplifies the output and detects a level, and a blocking unit 31 and an overcurrent tripping unit 32 that are driven by the leakage detection unit 33 are provided.
One end of the magnetic coupling part 34 a is connected to the R-phase electric circuit 2 and the leakage detection part 33, and the other end is one end of each of the first and second test resistors 35 and 36 and the canceling variable resistor 37. It is connected to the. Further, the other ends of the test resistors 35 and 36 are connected to the S-phase circuit 2 via the first and second test buttons 38 and 39, and the other end of the canceling variable resistor 37 is connected to the T-phase circuit 2. It is connected to the.

That is, the magnetic coupling portion 34a is connected between the R-phase and T-phase electric circuits 2 that are non-grounded phases via the canceling variable resistor 37, and is connected to the R-phase electric circuit 2 that is the non-grounded phase and the ground phase. A series circuit of the first test resistor 35 and the first test button 38 and a series circuit of the second test resistor 36 and the second test button 39 are provided between the S-phase electric circuit 2 and They are connected to each other in parallel.
Here, the first and second test buttons 38 and 39 constitute the first and second switch means in the claims, and the series circuit of the first test resistor 35 and the first test button 38 is the first. The series circuit of the second test resistor 36 and the second test button 39 constitutes a second test circuit.

When the first test button 38 is turned on, a rated inoperative current (I _Δn / 2) flows between the R and S phases via the first test resistor 35, and the second test button 39 is turned on. The resistance values of the test resistors 35 and 36 are set so that the rated sensitivity current I _Δn flows between the R and S phases via the second test resistor 36.
In addition, in FIG. 1, 5 has shown the earth | ground electrostatic capacitance (floating capacitance) of the electric circuit 2 of each phase.

The operation of this embodiment will be described below.
Now, when a leakage occurs at the ground fault point F in FIG. 1, a leakage current I _C (= I _CR) via the ground capacitance 5 is _added to the leakage current I _0r caused by the ground resistance that should be detected by the leakage breaker. Since + I _CT ) is added, the ZCT 34 detects I ₀ = I _0r + I _C as a leakage current.
Note that these currents are vector quantities, but in the text of this specification, “·” indicating that the current I is a vector quantity is omitted for convenience.

However, the leakage current I _C by the earth capacitance 5 of the delta connection to the system power source 1 is grounded 1 line (S-phase ground in the illustrated example), the capacitance to ground of each phase path 2 is approximately equal for all As shown in FIG. 2, a 90-degree advance phase current I _CT with respect to the line voltage V _ST between the S phase and the T phase and a 90 phase against the reverse phase voltage (−V _RS ) of the line voltage V _RS between the R phase and the S phase. degrees proceeds be combined current of the phase current I _CR, the phase of the leakage current I _C is, T phase, the opposite phase to the line voltage V _TR of the R phase.

Therefore, the capacitance to ground 5 is reduced by a current I _TR (in the same phase as the line voltage V _TR ) flowing through the canceling variable resistor 37 inserted between the two electric paths 2 of the T phase and the R phase which are non-ground phases. It is possible to cancel the leakage current I _C caused by. In other words, if the canceling variable resistor 37 is adjusted so that I _TR × N = −I _C , the leakage current I ₀ to I _C detected by the ZCT 34 are canceled and only the leakage current I _0r caused by the ground resistance is obtained. It becomes possible to detect.

Whether or not the leakage current I _C caused by the ground capacitance 5 has been canceled is determined when the first test button 38 is turned on and the rated inoperative current (I _Δn / 2) flows, If the leakage detection unit 33 and the cutoff unit 31 perform a cutoff operation when the rated sensitivity current I _Δn flows when the second test button 39 is turned on without the cutoff operation of the unit 31, the operation level of the leakage breaker is ensured. It can be confirmed that I _Δn > operation level> (I _Δn / 2).

In FIG. 1, one end of the magnetic coupling portion 34 a is connected to the R-phase connection point “A” and one end of the canceling variable resistor 37 is connected to the T-phase connection point “RO”. One end of 34 a may be connected to the T-phase connection point “B”, and one end of the cancellation variable resistor 37 may be connected to the R-phase connection point “A”.
Even if the rated inactive current (I _Δn / 2) flows as a ground fault current due to insulation degradation on the load side and the like and does not operate at the rated sensitivity current I _Δn during the test, the first and second test buttons 38 , 39 can be pressed simultaneously, a test current of (1.5 × I _Δn ) can be passed, so that the test operation can be confirmed in the same manner as in the prior art.

Next, FIG. 3 is a configuration diagram of a leakage detecting apparatus according to the second embodiment of the present invention.
In FIG. 3, the leakage detection device 4 includes a leakage detection unit 41, a ZCT 42 that detects a zero-phase current in the electric circuit 2, and a magnetic coupling unit that is turned N times around the ZCT 42 and connected to the R-phase electric circuit 2. A / D conversion that performs A / D conversion on the analog signal output from the leakage detecting unit 41 and the canceling variable resistor 47 connected between the other end of the magnetic coupling unit 42a and the T-phase circuit 2 Unit 43, a level display unit 44 for displaying the level of the leakage current detection signal by its digital output signal, an alarm output unit 45 such as a relay for outputting an alarm when the level of the leakage current detection signal exceeds a set value, and And a contact 46.

In this embodiment, to offset the leakage current I _C by the capacitance to ground 5, it suffices to leakage current to be displayed is minimized by the level display unit 44 to adjust the offset variable resistor 47. When this leakage current is minimized, I _TR × N = −I _C holds, and the leakage current I ₀ detected by the ZCT 42 becomes only I _0r, and the leakage current I _C due to the ground capacitance 5 is canceled out. ing.
In the leakage detection unit 41, when the level of the detected leakage current I _0r exceeds the set value, the alarm output unit 45 is operated, the contact 46 is closed, and an alarm is output.

1: System power supply 2: Three-phase three-wire circuit 3: Earth leakage breaker 31: Breaker 32: Overcurrent tripping part 33: Earth leakage detector 34: ZCT
34a: Magnetic coupling unit 35, 36: Test resistor 37: Countering variable resistor 38, 39: Test button 4: Earth leakage detection device 41: Earth leakage detection unit 42: ZCT
42a: Magnetic coupling unit 43: A / D conversion unit 44: Level display unit 45: Alarm output unit 46: Contact 47: Variable resistance for cancellation 5: Ground capacitance (floating capacitance)

Claims (3)

In the earth leakage circuit breaker which operates by detecting the resistance component of the leakage current in the three-phase three-wire electric circuit connected to the delta-connected system power source and grounded by one line,
A variable resistor and a magnetic coupling unit that is magnetically coupled to a zero-phase current transformer connected to the leakage detection unit are connected in series between two ungrounded wires of the three-phase three-wire circuit.
Of the leakage current detected by the zero-phase current transformer, the leakage current caused by the ground capacitance of the three-phase three-wire circuit is canceled by a current proportional to the current flowing through the variable resistor. Earth leakage circuit breaker. In the earth leakage circuit breaker according to claim 1,
A first test having a first switch means for allowing a rated sensitivity current to flow between the ungrounded one wire and the grounded one wire in the three-phase three-wire electric circuit when the leakage detecting unit is tested. An earth leakage circuit breaker characterized in that a circuit and a second test circuit having a second switch means for causing a rated inoperative current to flow during a test of the earth leakage detector are connected in parallel to each other. In a leakage detection device for detecting a resistance component of leakage current in a three-phase three-wire circuit connected to a delta-connected system power source and grounded on one line,
A variable resistor and a magnetic coupling unit that is magnetically coupled to a zero-phase current transformer connected to the leakage detection unit are connected in series between two ungrounded wires of the three-phase three-wire circuit.
Of the leakage current detected by the zero-phase current transformer, the leakage current due to the ground capacitance of the three-phase three-wire circuit is canceled by a current proportional to the current flowing through the variable resistor,
A leakage detecting apparatus, wherein a means for displaying a leakage current level is connected to the leakage detecting section.

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