JP3080307B2 - How to prevent accidents caused by earth leakage breakers - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for preventing a leakage accident of a ground fault circuit breaker. In particular, when any one of a plurality of grounded devices (hereinafter referred to as grounded devices) connected to a power supply via individual earth leakage breakers is grounded, a sound having parallel capacitance is provided. The present invention relates to a method for preventing a "receive accident", which is a phenomenon in which an earth leakage breaker of a device unnecessarily trips (trips).

[0002]

2. Description of the Related Art At research laboratories, factories and other facilities, an earth leakage circuit breaker (ELB) is attached to production equipment and other equipment to ensure early separation of a ground fault for safety and fire prevention. Often. FIG.
Distribution transformers (hereinafter sometimes referred to as transformers) Equipment 5A and 5B connected to 1A and 1B, respectively,
An example in which 4A and 4B are attached is shown. In this example, one device 5A
And the earth leakage circuit breaker 4A are housed in a grounded metal outer box 6A and connected to the output voltage Va of the low-voltage winding 2A of the single-phase transformer 1A via the corresponding wiring circuit breaker 8A of the production panel 12A. You. Similarly, the other device 1B and the earth leakage breaker 4B are also housed in the grounded metal outer box 6B, and output voltage Vb of the low voltage winding 2B of the transformer 1B via the corresponding wiring breaker 8B of the production panel 12B. Connected to.

[0003] The low-voltage windings 2A and 2B of the transformers 1A and 1B share a common system.
Ground resistance 3 (hereinafter sometimes referred to as system ground)
You. ) , And the outer casings 6A and 6B are also grounded via a common equipment grounding resistor 7 (hereinafter, also referred to as equipment grounding) . In the following description, the low-voltage winding 2
The grounded transformer 1 is referred to as a grounded transformer 1 .

[0004] The operation of the earth leakage breaker 4A is changed from the point 5f on the ungrounded side electric wire between the equipment 5A and the earth leakage breaker 4A to the outer box.
A case where a ground fault has occurred at point 6f on 6A will be described.

Referring to FIG. 6, before the occurrence of the ground fault, the secondary voltage Va of the transformer 1A substantially exists between the points 5f and 6f. However, the impedance Zta of the transformer 1A is
Assume that it is negligibly small compared to the internal impedance of the device 5A. According to Thevenin's theorem, when the secondary voltage Va of the transformer 1A is applied between the points 6f and 5f, the ground fault current Ig at this time is the ground resistance Rp of the equipment ground 7 and the ground resistance Rt of the system ground 3 It can be approximated as a current flowing through a series circuit consisting of However, it is assumed that the high-voltage distribution line 20 on the power supply side of the transformer 1A is a substantially infinite bus, and the impedance Zta of the transformer 1A is
Is negligibly small compared to the ground resistances Rt and Rp, and the internal impedance of the device 5A is extremely large compared to the ground resistances Rt and Rp. Here, the ground resistance is an electric resistance between the ground electrode and the ground. For example, ground resistance
Assuming that Rt and Rp are 3 (Ω) and 6 (Ω), respectively, and the secondary voltage Va of the transformer 1A is 105 (V), the ground fault current Ig is about 11.
6 (= 105 / (3 + 6)) (A).

[0006] For example, when the wiring circuit breaker 8A is for a device 5A having a large power of 1 (KW) or more, about 11.6
No trip occurs with the ground fault current Ig of (A). However, the ground fault current Ig is connected to the primary side of the zero-phase transformer 11A of the earth leakage breaker 4A.
Is added. The rated sensitivity current of the earth leakage circuit breaker 4 is defined by the primary side current of the zero-phase transformer 11, but if the rated sensitivity current of the earth leakage circuit breaker 4A in the example of FIG. , For a ground fault current of about 11.6 (A), the earth leakage breaker 4A surely trips.

As described above, if the earth leakage breaker 4 is used,
Even a ground fault current small enough to prevent the operation of the circuit breaker 8 for preventing overcurrent can be surely cut off, ensuring the safety of the equipment and preventing fire.

[0008]

However, when a ground fault circuit breaker is connected to each of a plurality of devices, when a ground fault occurs in a certain device, not only the ground fault circuit breaker of the device in which the ground fault occurred but also the A so-called “receipt accident” has arisen as a phenomenon that induces an undesired trip in an earth leakage breaker of a complicated device.

As a countermeasure to prevent the accidents, attempts have been made to reduce the sensitivity of the earth leakage breaker in a sound circuit. In order to prevent this, it is difficult to reliably prevent a "receipt accident" in a system that tends to increase the ground fault current, because if a leakage current more than the sensitivity of the dust flows in, it trips again. The problem remains. In addition, if the sensitivity is increased, even if a ground fault current below the sensitivity occurs in the circuit itself, the earth leakage breaker will not trip, so there is also a problem of lack of safety and certainty of fire prevention. is there.

[0010] Accordingly, an object of the present invention is to provide a method for preventing an accident of a leakage breaker by adjusting a grounding resistance of a transformer in order to solve the above problems.

[0011]

SUMMARY OF THE INVENTION In order to solve the problems of the prior art and achieve the above object, the present inventor has encountered an accident when a device has a parallel capacitance such as a noise filter. We paid attention to the facts. Referring to FIG. 5 again, an attempt is made to analyze a possible accident when capacitance (hereinafter, sometimes referred to as a noise filter) 9 is connected in parallel to device 5B.

The equipment 5B is connected to the secondary voltage Vb of the transformer 1B, which has a phase difference of 120 degrees from the secondary voltage Va of the transformer 1A, to the circuit breaker 8B for wiring.
And the earth leakage breaker 4B . As described above, the point 5f on the ungrounded power line of the device 5A is connected to the point 6f on the outer case.
When a ground fault accident occurs, the earth leakage breaker 4B of the healthy device 5B malfunctions as follows.

A ground fault occurs in the device 5A. The ground fault current Ig flows toward the equipment ground 7 through the ground wire or the floor in contact with the metal outer box 6A . Ground wires of equipment 5A and 5B and metal outer boxes 6A and 6B
It is electrically connected to a common equipment ground 7. Ground fault machine
In the outer box 6A of the device 5A, the sound voltage Va (before this
When the voltage Va) of the low voltage winding 2A of the transformer 1A is applied,
The voltage Va is also applied to the outer box 6B of the healthy device 5B. this
Therefore, part of the ground-fault current Ig is diverted. One shunt is ground current Ig _1, and the flow returns to V ₀ via the secondary winding 2A of the transformer 1A ground fault occurs side through the ground resistor Rp and earth resistance Rt strains ground 3 of equipment grounding 7. At this time, the earth leakage breaker 4A of the device 5A trips (healthy earth leakage trip). The other shunt Ig ₂ of the ground fault current Ig flows through the noise filter (parallel capacitance) 9 into the circuit of the healthy device 5B,
Back to V ₀ through the zero-phase transformer 11B of the secondary side and the secondary winding 2A of the secondary winding 2B and the ground fault generation side of the transformer 1A transformer 1B earth leakage breaker 4B. At this time, the primary-side current balance of the zero-phase transformer 11B of the earth leakage breaker 4B of the healthy device 5B is disrupted, and the earth leakage breaker 4B trips (earth leakage trip as a fault accident).

[0014] transformer 1A Referring to FIG. 7 showing, including the phase relationship between the secondary voltage Va and the secondary voltage Vb of the transformer 1B, the power supply line of the ground-fault current Ig ₂ flowing a noise filter 9 ungrounded component Ig ₂₂ of the ground side components Ig ₂₁ and the power supply line is approximately given by the following equation. Here, Zc is the impedance of the noise filter 9, and the impedance Ztb of the transformer 1B is so small as to be negligible and the internal impedance of the device 5B is sufficient compared to the ground resistance Rt of the system ground 3 and the ground resistance Rp of the device ground 7. It is assumed that the circuit of the device 5B can be regarded as open.

[0015]

[Formula 1] Ig_{twenty one}= Va / Zc ………………………………………… (1) Ig_{twenty two}= (Va-Vb) / Zc ……………………………… (2) Ig_Two= Ig_{twenty two}+ Ig_{twenty one}= (2Va-Vb) / Zc ……………………… (3) | 2Va−Vb | = ｛(2Va)^Two+ Vb^Two−2.2Va · 2Vb · cos (2π / 3)｝^1/2  = ｛(2Va)^Two+ Vb^Two＋ 2Va ・ Vb｝^1/2 …………… (4) where | Va | = | Vb | = 105 (V) Rt = 3 (Ω) Rp = 6 (Ω) Zc = 12,500 (Ω) (0.25μF, 50Hz) Then Ig_Two= {7.105 / 12500}^1/2 ≒ 22.2 (mA)

As shown in FIG. 5, this noise filter 9
Ground fault current Ig ₂ flowing is a zero-phase residual current, the primary current of the zero-phase transformer 11B earth leakage breaker 4B sound equipment 5B. The rated sensitivity current of earth leakage breaker 4B is
4B is defined as the primary current of the zero-phase transformer 11B that always trips. According to the standard of JIS C 8371 (1980), it is sufficient that the rated non-operating current is 50% or more of the rated sensitivity current, so that the rated sensitivity current of the earth leakage breaker 4B of FIG. ), When the primary current of the zero-phase transformer of the earth leakage breaker 4B of the circuit of the healthy equipment 5B reaches 22.2 (mA) at the time of the ground fault accident of the equipment 5A, the earth leakage breaker 4B gets a trip as an accident. It can happen.

From the above analysis, in order to prevent such an accident, as shown in FIGS.
The noise filter 9, those due to the grounding of other devices 5A
This occurs when the voltage Va of the ground fault device 5A is added to the healthy device 5B.
Finding that must be suppressed the ground fault current Ig ₂ is obtained. The present invention has been completed based on this finding.

Referring to the embodiment of FIG. 1, the method for preventing accidental leakage of the earth leakage breaker according to the present invention uses a system ground resistance 3.
Low-voltage windings 2A, 2B of multiple distribution transformers 1A, 1B grounded
Metal outer boxes 6A, 6B connected to earth leakage breakers 4A, 4B
Multiple devices 5A, housed respectively one device 5A is ground in 5B
When a ground fault occurs, the sound voltage Va before ground fault of the ground fault device 5A is
6A, 6B In the method of preventing the "leakage accident" that the earth leakage breaker 4B of the healthy device 5B having the parallel capacitance 9 in the plurality of devices 5A, 5B due to the addition to the Low voltage of transformer 1A connected to equipment 5A without capacitance 9
By inserting a grounding resistor 10A in series with the system grounding resistor 3 in the winding 2A , the device grounding resistor 6 and the system grounding resistor are inserted.
Due to the sum of anti-3 and the partial pressure of the grounding resistor 10A,
Suppresses the voltage applied to the outer box 6B of the healthy equipment 5B,
This is obtained by suppressing the current of the column capacitance 9 .

Preferably, the plurality of devices 5A and 5B are connected in parallel.
And grounding by connecting to the equipment grounding resistor (Rp), connecting the low voltage windings 2A and 2B of the plurality of transformers 1A and 1B in parallel to the system grounding resistor (Rt) and grounding , low-voltage transformer 1A connected to the device 10A not having parallel capacitances 9
The resistance Ra of the ground resistor 10A connected to the line 1B is made larger than the sum (Rp + Rt) of the equipment ground resistance Rp and the system ground resistance Rt. The grounding resistance Ra of the transformer and the equipment grounding resistance
When defining the resistance value of Rp, safety regulations and examples
For example, it is natural to comply with the technical standards for electrical equipment.
The resistance value must be determined within these specified ranges.
Of course, the choices should be limited to certain transformers or equipment.
It is not necessary to set, grounding of various transformers and other devices
Adjust the resistance balance within the range of the above regulations
By doing so, it is possible to prevent "getting accidents".

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to FIG. 1, the operation of an embodiment of a method for preventing a leakage breaker from being damaged according to the present invention will be described. In this embodiment, a ground resistor 10 is inserted on the ground side of the conventional transformer 1 shown in FIG. That is, the transformer
Ground resistor of resistance value (sometimes referred to as resistance) Ra for transformer 1A for common system ground 3 of 1A and 1B
10A is inserted, and a grounding resistor 10B having a resistance value Rb is inserted into the transformer 1B. The parallel capacitance 9 of the device 5B that can cause the accident is shown as a noise filter as in the conventional example, but the parallel capacitance 9 that can cause the accident is not limited to the noise filter. For example, if the ground capacitance of the line is very large, it is a parallel capacitance that may cause an accident.

In FIG. 2, the voltage Va ′ applied to the sum (Rt + Rp) of the two ground resistances at the time of the ground fault is obtained by adding the voltage Va applied to the device 5A before the ground fault to three resistors Rp, Rt, Ra (ground resistor). Ten
A), the voltage is divided by the following formula.
Given by (5). However, the resistance Rb of the grounding resistor 10B is
It is assumed to be negligibly small compared to the impedance of the parallel capacitance 9. In equation (5), voltage Va ′ is equal to voltage Va
, There is no phase difference between the two. Current Ig ₂ flowing in parallel capacitance 9 is obtained by the above formula (1) to (4) wherein the observation of the following (6) to (8).

[0022]

[Equation 2] Va ′ = Va {(Rp + Rt) / (Ra + Rp + Rt)} ……………………… (5) Ig_{twenty one}= Va '/ Zc ………………………………………… (6) Ig_{twenty two}= (Va'-Vb) / Zc ………………………………… (7) Ig_Two= Ig_{twenty two}+ Ig_{twenty one}= (2Va'-Vb) / Zc ……………………… (8) | 2Va′−Vb | = ｛(2Va ′)^Two+ Vb^Two−2.2Va ′ · 2Vb · cos (2π / 3)｝^1/2  = ｛(2Va´)^Two+ Vb^Two＋ 2Va´ ・ Vb｝^1/2 ……… (9) where | Va | = | Vb | = 105 (V) Rt = 3 (Ω) Rp = 6 (Ω) Zc = 12,500 (Ω) (0.25 μF, 50 Hz) Ra = 25 ( Ω) Va '= 105 · (3 + 6) / (3 + 6 + 25) = 27.8 (V) Ig_Two＝ ｛4 ・ (27.8)^Two+105^Two＋2 ・ 105 ・ 27.8 ／ 12500｝
^1/2≒ 11.3 (mA)

As compared with the prior art of FIG. 5, in the case of FIG. 1, the primary current of the zero-phase transformer 11B of the earth leakage breaker 4B of the device 5B is reduced from 22.2 (mA) to 11.3 (mA). . When the rated sensitivity current of the earth leakage breaker 4B is 30 (mA), even if the ground fault current Ig ₂ of 11.3 (mA) flows as the primary current of the zero-phase transformer, such a ground fault current Ig ₂ is Since it is 50% or less of the rated sensitivity current, the earth leakage breaker 4B is not tripped.

As can be understood from the observation of the equations (5) to (9),
Resistance Rb of the ground resistor 10B of the ground side of the power transformer 1B circuits parallel capacitance 9 exists not related to the ground fault current Ig ₂ flowing parallel capacitance 9. Therefore, in order to prevent accidents, it is sufficient to insert the ground resistor 10A only on the ground side of the power transformer 1A connected to the device 5A having no parallel capacitance.

FIG. 3 shows a ground to be inserted when a bank IV is used to prevent accidents in an existing distribution facility having seven transformer banks I to VII and a ground resistance Rt of the system ground 3 of 3Ω. An example of the value of the resistor 10 is shown. However, the ground resistance Rp of the equipment ground 7 is 6Ω. In the example of FIG. 3, the grounding resistor 10 of 25Ω is also inserted in the bank IV, but the grounding resistor 10 of the bank IV may be omitted.

In the distribution facility shown in FIG. 3 after the grounding resistor 10 is inserted, the bank IV has a parallel capacitance 9 connected via the earth leakage breaker 4 similar to that in FIG. In this distribution facility, when a ground fault has occurred individually for all banks other than the bank IV, the primary current flowing to the zero-phase transformer 11 of the earth leakage breaker 4 due to the parallel capacitance 9 connected to the bank IV. The magnitude of the current Ig ₂ was estimated. The results are shown in Table 1 as “current Ig _{2 at the time of} ground fault”.

As is clear from Table 1, no matter which bank is ground fault, the bank IV under the above conditions
The ground current Ig ₂ of the ground fault circuit breaker 4 at the time of ground fault is 50% or less of the rated sensitivity current, and the ground fault circuit breaker 4 does not accidentally trip due to ground fault of another bank.

Thus, the object of the present invention is to provide a "method of preventing accidental leakage of the earth leakage breaker by adjusting the transformer ground resistance".

[0029]

[Embodiment] When a distribution facility is to be newly constructed or grounding repair work can be easily carried out, the transformer bank IV of the line to be prevented from accidents is directly grounded to the system ground 3, and the other banks I to The transformers III and V to VII are grounded to the system ground 3 via the common single grounding resistor 10, so that it is possible to take a so-called single-grounding type leakage protection. FIG. 4 shows an example of a distribution facility including the transformer banks I to VII in which such measures are taken. In this case, the ground resistance of system ground 3 is Rt
_B = 3Ω, and the resistance Re of the ground resistor 10 of the other bank
The synthetic ground resistance containing was (Rt _A + Re) = 20Ω or more.
This resistance value of the grounding resistor 10 is the ground resistance of the equipment ground 7
It was determined under the condition of Rp = 6Ω.

Regarding the distribution facility of FIG.
When an individual ground fault occurs in all the banks except the bank IV, the magnitude of the primary current flowing through the zero-phase transformer 11 of the earth leakage breaker 4 due to the parallel capacitance 9 connected to the bank IV is determined. Estimated. The results are shown in Table 2 as "simulation for countermeasures for earth leakage due to single grounding".

As is clear from Table 2, no matter which bank is grounded, the bank IV
The leakage current Ig ₂ of the earth leakage breaker 4 at the time of a ground fault is 50% or less of the rated sensitivity current, and the earth leakage breaker 4 does not get tripped as an accident.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

As described above in detail, the method for preventing accidents caused by the earth leakage breaker according to the present invention prevents the accidents caused by the selection of the grounding resistance of the power transformer, and has the following remarkable effects.

(A) It is sufficient to take only measures on the power transformer side, and it is possible to prevent an accident caused by the earth leakage breaker without changing the load equipment side. (B) It is possible to easily take measures to prevent accidents caused by leakage breakers in existing power distribution equipment. (C) In the newly installed power distribution equipment, it is possible to extremely easily and at a low cost to prevent an accident caused by an earth leakage breaker simply by selecting the resistance value of the grounding resistance of the power distribution transformer.

[Brief description of the drawings]

FIG. 1 is a circuit diagram of an embodiment of a method for preventing a leakage accident of a ground fault circuit breaker according to the present invention.

FIG. 2 is an equivalent circuit diagram showing a distribution of a ground fault current in the circuit of FIG.

FIG. 3 is a connection diagram of a distribution facility transformer bank embodying the present invention.

FIG. 4 is a connection diagram of another distribution facility transformer bank embodying the present invention.

FIG. 5 is a circuit diagram of an example of a distribution line for a conventional device.

FIG. 6 is an equivalent circuit diagram for calculating a ground fault current in the circuit of FIG. 5;

FIG. 7 is an equivalent circuit diagram showing a distribution of a ground fault current in the circuit of FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... (Distribution) transformer 2 ... Secondary winding 3 ... System earth resistance 4 ... Earth leakage breaker 5 ... Equipment 6 ... (Metal) outer box 7 ... Equipment earth resistance 8 ... Wiring circuit breaker 9 ... Parallel static Electric capacity (noise filter) 10… Grounding resistor 11… Zero phase transformer 12… Distribution board 20… High voltage distribution line

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H02H 3/16 H02B 3/00 H02H 9/08

Claims (3)

(57) [Claims] 1. A metal device connected to low voltage windings of a plurality of distribution transformers grounded by a system ground resistance via respective earth leakage breakers and grounded by a common equipment ground resistance.
One of the devices contained in the outer box is grounded
The sound voltage before ground fault of the ground fault device is
In the method for preventing the "leakage accident" in which the earth leakage breaker of a healthy device having parallel capacitance among the plurality of devices is tripped due to the addition of the transformer, the transformer connected to the device having no parallel capacitance is used. To the low- voltage winding of the
By inserting a grounding resistor in series with the
The sum of the earth resistance and the system earth resistance and the earth resistor
Applied to the outer box of the sound equipment during the ground fault.
A method for preventing a leakage fault interrupter from receiving an electric leakage breaker, which suppresses an excessive voltage and a current of a parallel capacitance at the time of the ground fault. 2. The method according to claim 1, wherein
Connect the multiple devices in parallel to the device ground resistance (Rp).
To ground, and connect the low- voltage windings of each transformer in parallel.
Contact <br/> was ground by connecting to the system ground resistance (Rt) in the column, the ground resistor of the resistor to be connected to the low voltage winding of the transformer connected to the equipment not having parallel capacitances ( Ra) is the sum of the system ground resistance Rp and the equipment ground resistance Rt (Rp +
Rt) A method to prevent accidents from receiving electric leakage breakers that are larger than Rt. 3. The method according to claim 2, wherein:
Low voltage of the transformer connected to the device having the parallel capacitance
Connect a grounding resistor to the winding in series with the system ground.
Got accident prevention method of earth leakage breaker to be.