JPH0576131A - Faint ground fault detector - Google Patents

Abstract

PURPOSE:To realize high sensitivity detection of deterioration of insulation of load machines connected with the distribution line in isolated neutral power supply system. CONSTITUTION:When a faint ground current flows through a main circuit cable 8 due to deterioration of the insulation of a load machine 9, the faint ground current is superposed on the imbalance component of ground charging current of the main circuit cable 8 on the secondary of a grounded current transformer 10. On the contrary, only the imbalance component of ground charging current of the main circuit cable 8 is detected through a grounded current transformer 11 provided for a sheath earth line 14. Consequently, outputs from the grounded current transformers 10, 11 are subjected to subtraction by means of a comparing/deciding unit 19 and only a faint ground fault current, caused by deterioration of insulation of the load machine 9, is detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fine ground fault detecting device for highly sensitively detecting a minute increase in leakage current in the insulation state of all electric devices connected to a power supply system, and more particularly to a non-grounded device. The present invention relates to a fine ground fault detection device suitable for detecting an insulation deterioration state of an electric device connected to a system power supply system.

[0002]

2. Description of the Related Art A power transformer, a load-side bus of the power transformer, an induction motor or the like which is a load device branched from the bus and connected through a circuit breaker, and these and the bus. In a non-grounded power supply system in which there are multiple distribution lines that are connected to the cable and grounded to the power supply side of the cable and are configured with a zero-phase current transformer for ground fault current detection, each load device The zero-fault current transformer (ZCT) detects the ground fault current due to the insulation deterioration, and isolates the load equipment with insulation deterioration from the power supply system to protect it. In this case, a cable penetration type ZCT is provided on the power source side of the distribution line to detect a minute ground fault current.

[0003]

On the other hand, in the above-mentioned conventional non-grounded power supply system, the ZCT for detecting the ground fault current is provided on the power transmission side of the cable to which the load device is connected. In this case, a cable having a relatively large capacitance to ground is unbalanced between the phases, and the sum of the charging currents to ground does not become zero, and the unbalanced portion apparently flows as a ground fault current. Has occurred on the secondary side of.

This apparent ground fault current is on the order of amperes depending on the size of the cable used and the length of the cable, and the ground fault detection sensitivity is set to a value higher than this unbalanced current value in order to avoid malfunction of the ground fault current detection. It has to be set, and it has been impossible to detect the minute ground fault current that occurs at the early stage of deterioration of the insulator.

In an ungrounded power supply system, the capacitance of the cable to ground is relatively large, and an unbalanced current is constantly flowing due to the unbalance between the phases of this value.

A minute leakage current caused by insulation deterioration of a value equal to or less than the unbalanced current value is absorbed in the unbalanced current in consideration of the phase difference of the unbalanced current and cannot be detected. Therefore, it could be detected only at the level above the maximum unbalanced current value. Therefore, the ground fault current cannot be detected with high sensitivity.

The present invention has been made in view of the above circumstances, and provides a fine ground fault detecting device capable of detecting with high sensitivity an insulation deterioration state of a load device or the like connected to a distribution line of an ungrounded power supply system. The purpose is to provide.

[0008]

A fine ground fault detecting device of the present invention is an ungrounded power supply system in which a load device is connected to a main circuit cable forming a plurality of distribution lines branched from a power supply side bus bar. , A first current detection means penetrating the main circuit cable for detecting a ground fault current, and an unbalanced portion of the ground charging current flowing through the main circuit cable penetrating the sheath ground wire of the main circuit cable. A second current detecting means for detecting and a determining means for determining the insulation deterioration state of the load device or the main circuit cable from a calculation result obtained by taking in the detection outputs of the first and second current detecting means and subtracting these detection outputs. And having.

Further, in the micro-ground fault detecting apparatus of the present invention, the judging means includes an amplitude limiting means for limiting the amplitude of the detection output of the second current detecting means to a predetermined level or less. It is characterized by being composed of.

[0010]

In the fine ground fault detecting device having the above-mentioned structure, when the load device suffers insulation deterioration, the unbalanced portion of the ground charging current flowing through the main circuit cable by the first detecting means and the load device superposed on it. Is detected, and the second current detecting means detects only the unbalanced portion of the ground charging current flowing in the main circuit cable. Furthermore, the detection outputs of the first and second current detection means are subtracted by the determination means. Therefore, the determining means detects only the fine ground fault current caused by the insulation deterioration of the load device.

Further, when insulation deterioration occurs in the main circuit cable, the amplitude of the detection output of the detecting means of the second current detecting means is limited by the amplitude limiting means, so that the minute discharge current generated in the main circuit cable. Can be detected with high sensitivity, and therefore the insulation deterioration state occurring in the main circuit cable can be detected.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a non-grounded power supply system to which the present invention is applied. In the figure, a power transformer 1 is connected to a power source side bus bar 3 via a power receiving breaker 2. The power source side bus bar 3 is connected to a grounding type instrument transformer (GPT) 4, and the secondary side thereof is connected to a limiting connector 5 for determining the effective grounding current of the non-grounded power supply system.

A power supply terminal portion 7A is connected to the power supply side bus bar 3 through a power distribution breaker 6, and the power supply terminal portion 7 is provided.
The main circuit cable 8 is connected from A to the other power supply terminal 7B. Further, the load device 9 is connected to the power supply terminal 7B. The main circuit cable 8 has a grounded current transformer 10 for detecting a ground fault current of the load device 9, and the ground wire 14 of the main circuit cable 8 has a grounded current transformer having the same characteristics as the grounded current transformer 10. 11 is provided. Grounded current transformer 10, 1
The detection output of 1 is input to the comparison and determination device 19. As shown in FIG. 2, the comparison and determination device 19 includes an amplifier 20 that amplifies a secondary output of the grounded current transformer 10, an amplifier 21 that amplifies a secondary output of the grounded current transformer 11,
It comprises a comparator 22 for comparing the output signals of the amplifiers 20 and 21. In addition, each distribution line has a main circuit cable 8
Are arranged in different sizes and lengths.

By the way, generally, the ground charging current of each phase of the main circuit cable 8 becomes like vectors 12a, 12b, 12c as shown in the vector diagram of FIG. 4, and the vector composition of these is not completely zero. No, it remains like vector 13. The component represented by this vector 13 becomes an unbalanced current and is generated on the secondary side of the grounded current transformer 10 penetrating the main circuit cable 8 (FIG. 5 (a)). Therefore, in order to detect the ground fault current resulting from the insulation deterioration of the load device 9 connected to the main circuit cable 8, the detection level is set to the unbalanced current value of the ground charging current of the main circuit cable 8 (see FIG. 5).
(a)) The above setting must be made, and therefore the ground fault current could not be detected with high sensitivity.

In the present invention, in order to eliminate the influence of the unbalanced portion of the ground charging current, a current for detecting the unbalanced portion of the ground charging current which flows back to the ground through the sheath ground wire 14 of the main circuit cable 8. Grounding type current transformer 10 as detecting means
The grounding type current transformer 11 having the same characteristics as the above is provided.

In the above configuration, when the load device 9 and the main circuit cable 8 are not deteriorated in insulation, the grounded current transformers 10 and 11 have the same detection output (see FIG. 5 (a),
(b)), these detected outputs are subtracted by the comparator 22 via the amplifiers 20 and 21 in the comparison and determination device 19, and the output becomes zero (FIG. 5 (c)).

On the other hand, when the load device 9 is insulation-degraded and a minute ground fault current flows in the main circuit cable 8, the unbalanced portion of the ground charging current of the main circuit cable 8 is distributed to the secondary side of the grounded current transformer 10. A current in which a fine ground fault current is superimposed on the current flows (Fig. 6 (a)).
On the other hand, in the grounding type current transformer 11 provided on the sheath ground wire 14, only the unbalanced current of the charging current to ground of the main circuit cable 8 is detected (FIG. 6 (b)). As a result, the detection outputs of the grounded current transformers 10 and 11 are subtracted by the comparator 22,
The output signal of the comparator 22, that is, the output signal of the comparison and determination device 19 is as shown in FIG. 6C, and only the fine ground fault current due to the insulation deterioration of the load device 9 is detected.

Next, another embodiment of the present invention will be described with reference to FIGS. In this embodiment, insulation deterioration occurring in the main circuit cable 8 can be detected. The present embodiment is different from the above-mentioned embodiment in the configuration that a limiter 24 is provided between the amplifier 21 and the comparator 22 of the comparison / determination device 19 as shown in FIG. 3, and other configurations are exactly the same. Therefore, duplicate description will be omitted. The limiter 24 is provided here because when the insulation deterioration occurs in the main circuit cable 8, the output of the grounded current transformer 10 increases, but it returns to the ground via the sheath ground wire 14 of the main circuit cable 8. Therefore, the output of the grounded current transformer 11 also increases, and the difference (fine ground fault current) cannot be detected. In the limiter 24, the amplitude of the output signal of the amplifier 21 is obtained by the unbalanced component current of the main circuit cable 8 or the load current 9 flowing in the normal state in which insulation deterioration does not occur in the main circuit cable 8. The value obtained by adding α to the level of the output signal of 21 is limited as the slice level.

In the above structure, when insulation deterioration occurs in the main circuit cable 8, the detection outputs of the grounded current transformers 10 and 11 are amplified to predetermined levels by the amplifiers 20 and 21, respectively, and the output signal of the amplifier 20 ( FIG. 7A shows the comparator 2
2 is input to one input terminal.

On the other hand, the output signal of the amplifier 21 is the limiter 2
4, the amplitude is limited when the level exceeds the slice level set in the limiter 24, and the output signal of the limiter 24 (FIG. 7B) is input to the other input terminal of the comparator 22. .. The output signal of the amplifier 20 and the output signal of the limiter 24 are subtracted in the comparator 22, and as a result, the signal shown in FIG. 7C is output from the comparator 22. Therefore, by detecting the output signal of the comparator 22, that is, the comparison / determination device 19, a minute discharge current generated in the main circuit cable 8 can be detected with high sensitivity.

[0021]

As described above, according to the micro-ground fault detecting device of the present invention, the load device is connected to the main circuit cable which forms a plurality of distribution lines branched from the power source side bus bar. In the system power supply system, a first current detection unit that penetrates the main circuit cable and detects a ground fault current;
Second current detection means provided to penetrate the sheath ground wire of the main circuit cable to detect an unbalanced portion of the ground charging current flowing in the main circuit cable, and the detection outputs of the first and second current detection means are fetched. Since the determination means for determining the insulation deterioration state of the load device or the main circuit cable from the calculation result obtained by subtracting these detection outputs is provided, the load device connected to the distribution line of the non-grounded power supply system, etc. It is possible to detect the insulation deterioration state of with high sensitivity.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a non-grounded power supply system to which the present invention is applied.

FIG. 2 is a block diagram showing a specific configuration of an embodiment of the comparison / determination device in FIG.

FIG. 3 is a block diagram showing a specific configuration of another embodiment of the comparison / determination device in FIG.

4 is a vector diagram showing an unbalanced current component flowing in the main circuit cable in FIG.

5 is an explanatory diagram showing the principle of removing an unbalanced current component flowing in the main circuit cable in FIG. 1. FIG.

FIG. 6 is an explanatory diagram showing a principle of detecting a state in which insulation of a load device in FIG. 1 is deteriorated.

FIG. 7 is an explanatory diagram showing the principle of detecting a state in which insulation of the main circuit cable in FIG. 1 has deteriorated.

[Explanation of symbols]

 1 power transformer 2 power receiving circuit breaker 3 power supply side bus bar 4 grounding type instrument transformer 6 power distribution circuit breaker 7A, 7B power supply terminal section 8 main circuit cable 9 load equipment 10, 11 grounding type transformer 14 sheath ground wire 19 comparison Judgment device 20, 21 Amplifier 22 Comparator 24 Limiter

Claims (2)

[Claims] 1. An ungrounded power supply system in which a load device is connected to a main circuit cable forming a plurality of distribution lines branched from a power source side bus bar, wherein a ground fault current is provided penetrating the main circuit cable. A first current detecting means for detecting an unbalanced portion, a second current detecting means for penetrating a sheath ground wire of the main circuit cable, and detecting an unbalanced portion of a ground charging current flowing in the main circuit cable; The detection output of the first and second current detection means is fetched,
A fine ground fault detecting device, comprising: a determining unit that determines an insulation deterioration state of the load device or the main circuit cable from a calculation result obtained by subtracting these detection outputs. 2. The determination means includes an amplitude limiting means for limiting the amplitude of the detection output of the second current detecting means to a predetermined level or less when the detection output is input. The fine ground fault detection device according to claim 1.