JP2000139059A - Detector for dielectric breakdown of ac motor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely prevent complete grounding fault by estimating the time of grounding of an AC motor with accuracy without stopping the motor. SOLUTION: When an AC motor 12 is grounded, current in an earth wire 14 is supplied to a filter circuit 18 and DC components which indicate semi- grounding fault are extracted from the current. Then, the DC components are amplified by a current transformer and then are further amplified by a DC amplifier 22 and then are converted into a voltage signal. Then, a change in voltage based on the DC components is recorded in a recorder 24 to make it recognize the semi-grounding fault. The recorder 24 functioning as a recognizing section gives warning, for example, by emitting an alarm and quickly detects the semi-grounding fault before the complete grounding fault to detect abnormality in the AC motor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for detecting dielectric breakdown of an AC motor, and more particularly to a device for detecting dielectric breakdown of an AC motor based on a current flowing through a ground wire.

[0002]

2. Description of the Related Art Conventionally, in order to properly operate and use equipment such as an air compressor, it is necessary that an AC motor driving the equipment be operated in a good state. Although the AC motor has durability enough to withstand continuous use, the use of the AC motor for a long period of time may cause deterioration of the coil insulating layer and cause a ground fault (dielectric breakdown). If a ground fault occurs, the AC motor stops and leads to damage to the equipment on which the AC motor is driven. For example, it is necessary to prevent a ground fault in the AC motor. The overall life of the AC motor is set based on the life of each component, but this life varies individually depending on the use conditions and use environment of the AC motor. Therefore, it is necessary to regularly inspect each AC motor to predict the occurrence of a ground fault, and to perform processing such as repair and replacement before the AC motor is broken. An inspection performed at this time includes an insulation property test. This insulation characteristic test, when the DC motor is stopped, for example, there are insulation resistance measurement and tan δ measurement, capacitance measurement, AC current measurement, partial discharge measurement, etc.
Various tests are performed using individual measuring devices. Then, using the result, the measurer (inspector) predicts the time of the ground fault based on past experience and the like.

[0003]

However, as described above, the insulation characteristic test can be performed only when the AC motor is stopped, and it is necessary to stop the equipment driven by the AC motor, thereby reducing productivity. Inviting is not preferred. In addition, since the ground fault timing is determined by the measurer's experience based on the measurement results, it fluctuates depending on the operator, and the ground fault timing cannot be predicted with high accuracy. There is a problem that it cannot be performed at the optimal timing. If the AC motor is disassembled and inspected, the ground fault timing can be predicted with higher accuracy. Can not. Therefore, there is a problem that detection reliability for a ground fault that can occur in a short time is low. In addition,
Japanese Patent Application Laid-Open No. 61-262048 discloses a ground current detecting device for a DC motor, but it cannot predict a ground fault of an AC motor.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and has as its object to predict the ground fault time of an AC motor with high accuracy without stopping the AC motor. An object of the present invention is to provide an AC motor insulation breakdown detection device that can reliably prevent damage to related devices.

[0005]

To achieve the above object, a first aspect of the present invention is to connect a series connection to a ground line of an AC motor and to separate a DC component from a current flowing through the ground line. And an amplifier for amplifying the separated DC component, and a recognition unit for recognizing dielectric breakdown of the AC motor based on the amplified DC component.

[0006] The occurrence pattern of the ground fault in the AC motor includes a complete ground fault in which a complete insulation breakdown occurs in the coil portion and the AC motor stops, and a semi-ground fault (micro ground fault) which occurs before that as a precursor. There is. In the complete ground fault state, the current flowing through the ground wire has an AC component and a DC component,
In a semi-ground fault condition, only the DC component appears. According to the configuration, the DC component that slightly changes is extracted by the filter circuit, the DC component indicating the half ground fault is amplified by the amplifier, the recognition unit recognizes the half ground fault, and the AC motor is driven before the complete ground fault. And performs warning processing such as alarm output. As a result, it is possible to perform a treatment for a ground fault at an optimal timing before the AC motor and related devices are affected, thereby preventing breakage and the like. Note that a current transformer or the like is used as the amplifier, for example.

In order to achieve the above object, a second aspect of the present invention provides a detector for detecting a current flowing in a ground line based on a magnetic field fluctuation around the ground line of an AC motor, and a DC component from the current. It is characterized by including a filter circuit that separates and extracts, an amplifier that amplifies the separated DC component, and a recognition unit that recognizes insulation breakdown of the AC motor based on the amplified DC component.

Here, the detector is a clamp tester having a ring clamp surrounding a ground line and detecting a magnetic field fluctuation. According to this configuration, even when the AC motor is completely grounded, a large current does not directly flow into the circuit of the insulation breakdown detection device, so that the insulation breakdown detection device can be easily protected. Further, the ground fault can be detected without increasing the ground resistance of the AC motor.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention (hereinafter referred to as embodiments) will be described below with reference to the drawings. FIG. 1 is a conceptual diagram illustrating the configuration of a dielectric breakdown detection apparatus 10 according to the present embodiment. The insulation breakdown detecting device 10 is connected in series to a ground line 14 of an AC motor 12 and is connected to the ground line 1.
4 flows in. The dielectric breakdown detecting device 10 includes a diode circuit 16 for preventing a large current from flowing into the dielectric breakdown detecting device 10 when a complete ground fault occurs and causing a circuit breakage, and a DC component from the current flowing into the circuit. Filter circuit 18 for extracting only the current, a current transformer (DC-CT) as an amplifier for amplifying the DC component extracted by the filter circuit 18
20, a DC amplifier 22 for further amplifying the DC component amplified by the current transformer 20, changing the current signal to a voltage signal, recording the converted voltage signal, recognizing the change in the voltage signal, and outputting an alarm output. It includes a recorder 24 to perform.

The diode circuit 16 includes the AC motor 1
When a large current exceeding the non-operating voltage (for example, 2 to 3 V) is applied to the ground wire 14 due to the damage of the coil 2 or the like, a large current is prevented from flowing into the downstream circuit (the filter circuit 18 or the like). Work to make it.
That is, when a large current flows through the ground line 14, the current flows to the ground via the diode circuit 16, thereby preventing circuit breakdown of the insulation breakdown detection device 10.

When a ground fault occurs due to damage to the coil of the AC motor 12, etc., the ground wire 14
Is, for example, 100 mA or less. This state is called a semi-ground fault state. A semi-ground fault is a precursor to a complete ground fault in which the coil will completely break down, and has the potential for a complete ground fault in the near future (between weeks and months). Therefore, it is important for the maintenance of the entire equipment to quickly detect a semi-ground fault condition and to repair or replace the AC motor.

As described above, the ground wire 14 is connected in a semi-ground fault condition.
Current flowing through the ground line 14 is less than 100 mA.
Flows through the filter circuit 18 including the capacitor 18a and the resistor 18b without passing through the diode circuit 16. By the way, when a semi-ground fault occurs, in the current flowing through the ground line 14, a DC component appears before an AC component appears. Therefore, quick detection of a DC component is required for detecting a semi-ground fault state. The filter circuit 18 removes the AC component included in the current by flowing it to the ground by the operation of the capacitor 18a. As a result, only the DC component included in the current flows into the current transformer 20. At this time, the current transformer 2
A CT ratio of 0 is, for example, 10: 1, and amplifies a DC component. The amplified DC component is further amplified by the DC amplifier 22 and converted into a voltage signal, which is provided to a recorder (voltage recorder) 24. The recorder can function as a recognition unit that recognizes insulation breakdown of the AC motor. That is, a ground fault (semi-ground fault) can be recognized by detecting a voltage change based on the detected DC component.

When the recorder 24 detects a voltage change based on a DC component, it outputs an alarm or the like that warns that a semi-ground fault has been detected. As described above, by detecting the appearance of the DC component quickly, before a complete ground fault occurs,
Repair and replacement of the AC motor can be efficiently performed at an optimal timing, and it is possible to prevent the equipment connected to the AC motor from being affected.

FIG. 2 is an explanatory diagram for explaining that only a DC component appears before an AC component appears when a semi-ground fault occurs. As is clear from the figure, in the case of a semi-ground fault,
Only a DC component appears, and in the case of a complete ground fault, a DC component and an AC component appear. In this embodiment, the recorder 2
4, only the DC component is displayed. However, an AC component detection circuit may be separately provided to display the DC component and the AC component in parallel as shown in FIG. in this case,
The occurrence of a semi-ground fault can be more clearly recognized. Further, since the level of the DC component (voltage indication) increases as the ground fault state progresses, the level of the ground fault may be displayed stepwise based on the level.

FIG. 3 shows another embodiment of the insulation breakdown detecting device. The insulation breakdown detecting device 26 shown in FIG. 3 has a detector 28 which is not connected to the ground line 14 of the AC motor 12 and is configured by a ring clamp 28a (having a through hole of, for example, φ40) for detecting a current flowing through the ground line 14. are doing.
The detector 28 detects a magnetic field that fluctuates due to a current flowing through the ground line 14 by a ring clamp 28 a that can be detachably disposed around the ground line 14, and supplies a current based on the magnetic field fluctuation to the filter circuit 18. Filter circuit 1
The configuration and operation after 8 are the same as those of the insulation breakdown detection device 10 shown in FIG. By using the detector 28 having the ring clamp 28a, the current flowing through the ground wire 14 of the AC motor 12 does not directly flow into the insulation breakdown detecting device 26. While being able to do surely,
Since a diode circuit for preventing overcurrent is not required, the configuration is simplified. Further, since the AC motor 12 can be easily attached to and detached from the AC motor 12, a plurality of AC motors 12 can be measured sequentially, so that the inspection efficiency is improved and the versatility is improved. Note that the filter circuit 18 of the insulation breakdown detecting device 26
FIG. 1 shows only one capacitor 18a,
Similarly to the above, two or more may be arranged as a spare at the time of failure.

Incidentally, in the case of a high-voltage motor, 1
Preferably, the resistance is within 0Ω. However, if the ground wire 14 and the insulation breakdown detecting device 10 are connected in series as shown in FIG. 1, the ground resistance may exceed 10Ω in the case of a high-voltage AC motor. However, as shown in FIG. 3, if the ring clamp 28a is used, the ground resistance can be suppressed to about 1Ω even in the case of a high-voltage AC motor.

[0017]

According to the present invention, a delicately changing DC component of the current flowing through the ground line of the AC motor is extracted by the filter circuit, and the DC component indicating a half ground fault is amplified by the amplifier. Can quickly and easily recognize a semi-ground fault based on the DC component and perform alarm processing such as alarm output while the AC motor is operating, so it can detect abnormalities in the AC motor and accurately detect a complete ground fault. Predictable and appropriate actions can be taken quickly.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram illustrating a configuration of a dielectric breakdown detection device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining that only a DC component appears before an AC component appears when a semi-ground fault occurs.

FIG. 3 is a conceptual diagram showing a configuration of another insulation breakdown detecting device according to an embodiment of the present invention.

[Explanation of symbols]

10 insulation breakdown detection device, 12 AC motor, 14 ground wire, 16 diode circuit, 18 filter circuit,
20 current transformers, 22 DC amplifiers, 24 recorders.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Osamu Iida 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation (72) Inventor Yoshinori Takeda 1 Toyota Town, Toyota City, Aichi Prefecture Inside Toyota Motor Corporation ( 72) Inventor Haruo Ban 118 Otemachi, Toyohashi City, Aichi Prefecture F-term in the Central Research Office of Soken Electric Co., Ltd. RR02 RR03 TT01 TT03 UA01

Claims (2)

[Claims] 1. An AC motor is connected in series to a ground wire of an AC motor,
A filter circuit that separates and extracts a DC component from the current flowing through the ground line; an amplifier that amplifies the separated DC component; and a recognition unit that recognizes insulation breakdown of the AC motor based on the amplified DC component. A dielectric breakdown detecting device for an AC motor, comprising: 2. A detector for detecting a current flowing in a ground line based on a magnetic field fluctuation around a ground line of an AC motor, a filter circuit for separating a DC component from the current and extracting the DC component, An AC motor insulation breakdown detection device, comprising: an amplifier to amplify; and a recognition unit that recognizes insulation breakdown of the AC motor based on the amplified DC component.