JPH0287988A - Grounding condition monitor for dc motor - Google Patents

Abstract

PURPOSE:To judge the grounding position accurately by detecting a peak AC component of ground current then detecting the rotary angle of a DC motor at that moment. CONSTITUTION:When ground current I is detected, it is divided by source voltage V through a ratio operating unit 17 thus producing an absolute ground current Ia. DC component is detected through a ground current DC component detector 6b and the polarity thereof is judged through a polarity judging unit 20. Consequently, defective insulation in a power source equipment and at the stator section is detected, then defective insulation at plus side or minus side is judged based on the polarity judgement. AC component is detected through a ground current AC component detector 6a and defective insulation of an armature coil is judged while simultaneously the rotary angle stored in a memory 25 is latched with peak detection pulse ON timing and displaced on a display 26. Since the DC motor 1 has four poles, the peak detection pulse appears at two positions of 45 deg. and 225 deg. during single rotation, where one of them represents the actual defective insulation ground position.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a device that detects the ground current of a DC motor used to drive a rolling mill, a conveying device, etc., and monitors the ground state.

[Conventional technology]

In rolling mills, large-sized DC motors are often used because of their speed control accuracy and simplicity.

When insulation failure occurs in the rotor coil of this DC motor, there is a risk of serious damage such as winding burnout. If a failure such as winding burnout occurs, it is difficult to replace the motor with a spare, especially in large DC motors, so the accident is often dealt with by on-site repair of the failed part. Therefore, in a DC motor, not only the presence or absence of ground current but also the early detection of the location where it occurs is a major factor in shortening the repair time and is also important in minimizing the effects of an accident.

2. Description of the Related Art Conventionally, as a device for measuring the insulation characteristics of a DC motor during operation, a ground current detection device whose configuration is shown in a block diagram in FIG. 3 is known.

A series circuit of resistors 3a and 3b for detecting ground current is connected in parallel to a DC motor 1 connected to a power supply circuit 2, a resistor 3C for detecting ground current is connected to that node, and the other end is grounded. Detect the voltage across the resistor 3C,
It is full-wave rectified by a rectifier circuit 4, smoothed by a smoothing circuit 5, and the effective value of the ground current is detected by a ground current detector 6.

However, insulation deterioration in DC motors mainly progresses from the rotor (-armature) windings, the power supply circuit, commutating poles, compensation windings, etc., and the conventional devices described above It is possible to detect when the power increases, but the ground current from the rotor windings becomes an alternating current synchronized with the rotation speed of the rotor of the DC motor, and the ground current from the DC power supply circuit and stator section. When the ground current is superimposed and the polarity thereof is opposite, the detection accuracy of the ground current is low.

Furthermore, the detected ground current changes depending on the magnitude of the power supply voltage, making detection at low voltages difficult.

As a solution to these problems, Japanese Patent Application Laid-Open No. 61262
There is one disclosed in Publication No. 048.

FIG. 4 is a block diagram showing the configuration of the ground current detection device disclosed in the publication. In the figure, the configurations of the power supply circuit 2, DC motor 1, and resistors 3a, 3b, and 3c are the same as those in FIG. 3, and therefore their explanations will be omitted. This detects the ground current by the voltage across the resistor 3c, separates its DC component and AC component by a DC component separation circuit 8 and an AC component separation circuit 9, and separates each component into polarity discrimination circuits 1o, ii. and a gate circuit 13.14, the polarity of each component is determined by a polarity determination circuit 10.11, each determination result is supplied to a coincidence detection circuit 12, which detects coincidence of polarities, and when the polarities coincide. A gate signal is given to the gate circuits 13 and 14 to detect the direct current component and the alternating current component. As a result, the ground current is detected only when the polarity of the DC component and the AC component match, improving detection accuracy and making it possible to distinguish the ground current from the rotor, power supply circuit, and stator. It became possible to estimate the approximate location.

[Problems to be Solved by the Invention] However, in the prior art disclosed in the above-mentioned publication, it is possible to determine whether there is an insulation failure in the rotor, but it is possible to determine whether there is a failure due to insulation failure in the armature coil of the rotor, which is made up of many coil pieces. It is not possible to identify the part, and it may take a lot of time to repair the failure using alternative parts.

This invention was made in view of the above circumstances, and its purpose is to accurately determine the grounding point by detecting the peak of the alternating current component of the grounding current and detecting the rotation angle of the DC motor at that time. The object of the present invention is to obtain a grounding condition monitoring device for a DC motor.

[Means to solve the problem]

A grounding state monitoring device for a DC motor according to the present invention is a grounding state monitoring device that detects a grounding current of a DC motor connected to a power supply circuit by dividing it into a DC component and an AC component, thereby monitoring a grounding state. Angle detection means for detecting a rotation angle of the DC motor, a peak detection circuit for detecting a peak of the AC component, and a peak angle detection means for detecting the rotation angle when the peak is detected. It is characterized by

[Effect]

In this invention, the AC component of the ground current is separated, the peak thereof is detected, the rotation angle of the DC motor is memorized, and the rotation angle when the peak is detected is detected. The ground contact position can be determined.

〔Example〕

The present invention will be explained below based on the drawings showing one embodiment thereof.

FIG. 1 is a block diagram showing the configuration of a ground condition monitoring device for a DC motor according to the present invention. In the figure, the DC motor 1 has one pole and two poles, and the DC motor 1 is connected to a power supply device 2 that generates a DC current from an AC current. Further, a rotary encoder 23 is attached to the rotating shaft of the DC motor 1 to detect its rotation angle. Further, in parallel with the DC motor 1, resistors 3a and 3b for ground current detection are provided.
are connected in series, and a resistor 3c is attached to the intermediate node with the other end grounded.

In addition, the grounding section [
I is given to the ratio calculator 17 together with the power supply voltage ■ of the power supply circuit voltage detection circuit 15 that detects the voltage of the power supply circuit, where the ground current I is divided by the power supply voltage ■, and the absolute ground current 1. (=I/V) is obtained. This is done in order to compensate for the variation in the ground current I due to variation in the power supply voltage (2). The obtained absolute ground current ■ is connected to AC component separation circuit 1 in order to separate it into AC component and DC component.
1. They are respectively applied to the DC component separation circuit 1H. Separated absolute ground current 1. The DC component is given to a DC component ground current detector 61) and a polarity discriminator 20, where the ground current is detected and its polarity is discriminated.

- force-separated absolute ground current 1. The AC component of is given to the peak detection circuit 22 and the rectifier circuit 4. .

The peak detection circuit detects the peak of the AC component and outputs the peak detection pulse. Further, in the rectifier circuit 4, the AC component is full-wave rectified and provided to the smoothing circuit 5, where it is smoothed and the effective value of the AC component is detected by the AC component ground current detector 6a.

-):j+C+- The output from the encoder 23 is given to the encoder detection circuit 24, and the rotation angle of the rotating shaft of the DC motor 1 detected here is input to the memory 25.
By inputting the peak detection pulse to the memory 25, the rotation angle input manually at the timing when the peak detection pulse is turned on is latched.

The launched rotation angle is then given to the display 26,
The F1 rotation angle is displayed.

Next, the operation of the apparatus of the present invention constructed as follows will be explained.

FIG. 2 is a graph showing a waveform when a ground current is generated due to insulation failure in the armature coil at a portion corresponding to a rotation angle of 60 degrees of the rotating shaft, and the horizontal axis represents time.

The vertical axis shows the absolute ground current in Figure 2 (a) and the absolute ground current in Figure 2 (b).
) is the DC component, Figure 2 (C) is the AC component, Figure 2 (d)
is the peak detection pulse, and FIG. 2(e) is the rotation angle.

When the ground current I is detected, it is divided by the power supply voltage ■ by the ratio calculator 17 to obtain one absolute ground current (FIG. 2(a)). This includes an alternating current component and a direct current component, which are separated by each separation circuit 19, 18 (FIGS. 2(b) and (C)). The DC component is detected by a DC component ground current detection circuit 6b, and its polarity is determined by a polarity discriminator 20.

As a result, insulation defects in the power supply device and the stator section are detected, and by determining the polarity, insulation defects on the positive side or the negative side are determined.

On the other hand, the alternating current component is rectified and its effective value is detected by the alternating current component grounding current detector 6a, and an insulation defect in the armature coil is determined.
) is turned on, the rotation angle stored in the memory 25 is latched (FIG. 2(e)), and is displayed on the display 26.

Note that at this time, the peak detection pulse is
Since it is a scratch, it appears at two places in one rotation, 60° and 240'', and the actual grounding position of the insulation failure is somewhere between these positions.

Thereby, the grounding position can be detected accurately from among the coil pieces of a large number of armature coils.

In this embodiment, a ratio calculator is used to compensate for variations in ground current due to fluctuations in power supply voltage, but the present invention is not limited to this, and the ratio calculator may not be used.

Furthermore, although a rotary encoder was used as the angle detection means in this embodiment, the present invention is not limited to this.
The angle detection means may be of any type as long as it can detect the rotation angle of the rotating shaft of the DC motor.

[Effects of the Invention] As explained above, according to the present invention, insulation defects in the armature coil are resolved by separating the AC component of the ground current, detecting its peak, and detecting the rotation angle when the peak is detected. It has an equivalent effect of being able to accurately determine the contact point of the ground.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of a ground current monitoring device for a DC motor according to the present invention, FIG. 2 is a graph showing a case where the armature coil has poor insulation at a rotation angle of 60 degrees, and FIG.
The figure is a block diagram showing the configuration of a conventional ground current detection device.
FIG. 4 is a block diagram showing the configuration of a conventional ground current detection circuit disclosed in the publication. 1... DC motor 2... Power supply circuit 22... Peak detection circuit 23... Low reencoder 25...
Memory Patent Applicant Sumitomo Metal Industries Co., Ltd. Agent Patent Attorney Noboru Kono Condolence Diagram November 14, 1999

Claims (1)

[Scope of Claims] 1. A grounding condition monitoring device that detects the grounding current of a DC motor connected to a power supply circuit by dividing it into a DC component and an AC component, thereby monitoring the grounding condition, comprising: A direct current comprising: angle detection means for detecting an angle; a peak detection circuit for detecting a peak of the alternating current component; and a peak angle detection means for detecting the rotation angle when the peak is detected. Electric motor grounding condition monitoring device.