JPH03230785A - Grounding state monitor for direct current motor - Google Patents

Abstract

PURPOSE:To enable a grounding section due to the poor insulation of an armature coil, to be certainly specified by arranging a means for detecting the rotational angle and grounding current of a DC motor periodically to be stored, and by a means for computing the DC component of the grounding current with the use of the function of the rotational angle. CONSTITUTION:Grounding current I detected by a grounding current detecting circuit 16 is normalized, and absolute grounding current Ia is obtained. The absolute grounding current is divided into AC component Ia(AC) and DC component. The DC component is detected, and its polarity is discriminated. In the mean time, the AC component Ia(AC) is rectified to be smoothed, and the effective value of the AC component Ia(AC) is obtained. In a memory 22, the rotational angle theta of a rotor and the AC component Ia(AC) are stored. According to the stored content, the rotational angle theta is converted to its corresponding electrical angle theta*. Besides, from a multiplier 25d, the output of AC component Ia(AC)Xcostheta* is generated, and from a multiplier 25e, the output of Ia(AC)Xsintheta* is generated, and they are separately smoothed. Then, ratio arithmetic is performed, on them, and on its arithmetic result, inverse tangent arithmetic is performed, and an electric angle thetaE at a grounding section is obtained.

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, the configuration of which is shown in a block diagram in FIG. 4, is known.

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

However, insulation deterioration in DC motors mainly progresses from the rotor (=armature) windings, the power supply circuit, commutative poles, compensation windings, etc., and the conventional devices described above It is possible to detect an increase in the rotation speed of the DC motor rotor, but the ground current from the rotor windings becomes an AC current synchronized with the rotation speed of the DC motor's rotor, and the DC current from the power supply circuit and stator section. When the ground current and the ground current are superimposed and their polarities are opposite to each other, the detection accuracy of the ground current is low.

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

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

FIG. 5 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, the DC motor 1, and the resistors 3a, 3b, and 3c are the same as in FIG. 4, so their explanation will be omitted. This detects the ground current by the voltage across the resistor 3c, and separates the DC component and AC component of the ground current into a DC component separation circuit 8 and an AC component separation circuit 9.
The separated components are separated by a polarity discrimination circuit 10.11.
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 becomes possible to estimate the approximate location.

[Problem to be solved by the invention]

However, with the conventional device disclosed in the above publication, it is possible to determine whether there is a defective insulation in the rotor, but it takes time to identify the faulty part of the defective insulation in the armature coil of the rotor, which consists of many unit coils. There is a possibility that it will take a lot of time to repair the failure.

The present invention has been made in view of the above circumstances, and provides a grounding condition monitoring device for a DC motor that can reliably identify the grounding site due to poor insulation of the armature coil of the rotor and can quickly respond to troubleshooting. The purpose is to provide.

[Means to solve the problem]

A grounding state monitoring device for a DC motor according to the present invention detects a grounding current of a DC motor and thereby monitors a grounding state, and periodically detects a rotation angle and a grounding current of the DC motor. and means for calculating the DC component of the ground current using a function of the rotation angle.

[Effect]

The rotation angle and ground current of the DC motor are periodically detected and stored. The DC component of the ground current is calculated using a function of the rotation angle.

The calculated DC component of the ground current is related to the electrical angle of the grounded portion of the rotor.

(Embodiment) The present invention will be described 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, 1 is a DC motor, and the DC motor 1 is connected to a power supply device 2 that generates DC current from AC current. Further, a rotary encoder 23 for detecting the rotation angle of the DC motor 1 is attached concentrically to the rotation shaft of the DC motor 1. Furthermore, a series circuit of ground current detection resistors 3a and 3b is connected in parallel with the DC motor 1, and its intermediate node is grounded via a resistor 3c.

The ground current I, which is the output of the ground current detection circuit 16 which measures the voltage across the resistor 3c and thereby detects the ground current, is the armature voltage detection circuit 1 which detects the voltage of the power supply circuit.
5 is applied to the ratio calculator 17 along with the power supply voltage ■, where the ground current I is divided by the power supply voltage V, 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 (1) is applied to an AC component separation circuit 19 and a DC component separation circuit 18, respectively, in order to separate it into an AC component and a DC component. Separated absolute ground current 1. The DC component of is detected by the DC component grounding current detector 6b and the polarity discriminator
0 and the ground current is detected and its polarity is determined.

On the other hand, the AC component of the separated absolute ground current (2) is stored in the memory 22 by the output from the rotary encoder 23, that is, in predetermined angle units of the rotation angle of the DC motor (1). Also, absolute ground current 1. is applied to the rectifier circuit 4, and the rectifier circuit 4 receives an absolute ground current l.

After the AC component is full-wave rectified, it is applied to the smoothing circuit 5, and after being smoothed, it is applied to the AC component ground current detector 6a, where the effective value of the AC component is detected.

The alternating current component stored in the memory 22 in units of predetermined angles is input to the phase calculator 25, where it is processed as a sine wave function of the rotation angle, and the angle at which the alternating current component of the ground current is maximized is calculated.

FIG. 2 is a block diagram of the phase calculator 25. memory 2
2 (see FIG. 1), the rotation angle θ is input to the electrical angle converter 25a, and after being converted to the electrical angle θ1, the cos θ1 generator 25b and the sin θ9
The signal is input to the generator 25c. Also, the AC component 1a (AC) read from the memory 22 is transmitted to the multipliers 25d and 2.
5e. Multipliers 25d and 25e include co
Output cos θ1 and sin of s θ′ generator 25b
The output sin θ° of the θ0 generator 25c is input separately, and the multiplier 25d inputs the AC component I□AC) and cos θ
The multiplier 25e multiplies the AC component I a TAC
Multiply l by sin θ1. The multiplication results of the multipliers 25d and 25e are input to the smoothing circuits 25f and 25g separately and smoothed, and then both are sent to the ratio calculator 25.
input to h.

The ratio calculator 25h calculates tan θt by ratio calculation, and the calculation result is input to the jan-' calculator 25i, and the AC component 11□0. The electrical angle θ4゛ of the ground contact portion at which the maximum is calculated is calculated.

Next, the operation of the ground state monitoring device for a DC motor constructed as described above will be explained with reference to FIG. FIG. 3 is a waveform diagram of various parts when a ground current is generated in the armature coil of a DC motor at a position corresponding to, for example, a rotation angle of 45 degrees of the rotor. The horizontal axis is time t, and the vertical axis is absolute ground current 1. In Fig. 3(b), the DC component 1 a +DC), in Fig. 3(C) the alternating current component I a (ACI), in Fig. 3(d) the rotation angle θ, in Fig. 3(el) The electrical angle θ° is c in Figure 3 ('').
os θ5, I m fAcl in FIG. 3(g)
X cos θ9, - In Figure 3 (b), I n (AC
The current obtained by smoothing I X cos θ is shown in Figure 3 (i
) then III+AC) X5inθ.

In FIG. 3(j), the currents obtained by smoothing t□ac+X5in θ0 are shown, respectively.

Now, when the armature voltage is supplied from the power supply circuit 2 to the DC motor l to drive the DC motor l, the armature voltage is detected by the armature voltage detection circuit 15.

When a ground current is generated in the DC motor 1 in such a driving state, the ground current detection circuit 16 detects it.

The ground current I detected by the ground current detection circuit 16 is normalized by being divided by the armature voltage ■ detected by the armature voltage detection circuit 15 in the ratio calculator 17, and the absolute ground current 1 shown in No. 3111(a) is obtained. is obtained. This absolute ground current 1. has AC component 1 a (MCI and DC component 1 s tD
c+, and they are AC component separation circuit ll11
9 and the DC component separation circuit 18, and the AC component 1a TACl outputted by the AC component separation circuit 18 is as shown in FIG. 3(C), and the DC component 1a +DC outputted by the DC component separation circuit 18. ) is as shown in Figure 3(b). This DC component is detected by the DC component grounding current detector 6.
b is detected, and the polarity discriminator 20 discriminates its polarity.

Thereby, an insulation defect in the power supply and the stator is detected, and by determining the polarity, it is determined whether the insulation defect is on the positive side or the negative side of the power source.

On the other hand, alternating current component 1 a (AC) is rectified by rectifier circuit 4 and smoothed by smoothing circuit 5 to become alternating current component 1 * I
The effective value of AcI is obtained and given to the AC component ground current detector 6a, and the AC component ground current detector 6a determines whether or not the armature coil has poor insulation.

The memory 22 stores the rotation angle θ of the rotor shown in FIG. 3(d) detected by the encoder detector 25 and the alternating current component I II (AC) shown in FIG. 3(C). Depending on the stored contents, the electrical angle converter 25a in the phase calculator 25
The rotation angle θ is converted into an electrical angle θ1 corresponding to the rotation angle θ as shown in FIG. This electrical angle θ0 can be obtained by multiplying the rotation angle θ by the number of poles P of the DC motor 1 and dividing the product by 2. This is because the polar brushes of a DC motor form a pair of positive and negative brushes and are arranged point-symmetrically around the rotor, so that during one rotation of the rotor, an appropriate point on the rotor is Since it passes directly under the positive or negative pole P/2 times, electrically it can be considered to be rotating P/2. Also cos
The output of the θ9 generator 25b is cos shown in FIG. 3(f).
θ1, and the multiplier 25d converts it and the AC component 1a (A.

By multiplying by
Output cos θ゛. Furthermore, the multiplier 25e has sin
The sin θ° output from the θ1 generator 25c is multiplied by the AC component 1 a (AC) to output 1□ACI X5in θ゛ shown in FIG. 3(i), and I m (
A CI X Co3O4 and I a (AC) X5i
nθ1 is smoothed separately by the smoothing circuits 25f and 25g, and the DC components after each smoothing become as shown in FIG. The electrical angle θ1 of the grounding portion of the rotor is obtained and displayed on the display 26.

Here, the principle of determining the grounding site using the relational expression between the electrical angle θ1 and the AC component 1 a +AC) will be explained.

Assuming that there is a grounding point at a clockwise angle θ with respect to a suitable point on the rotor as a reference, if this grounding point is located directly below the positive pole of the DC motor, the absolute grounding current will be 1.
flows in one direction and reaches its maximum, and when located directly under the negative electrode, the absolute ground current (■) flows in the opposite direction, reaching its maximum.

Therefore, the absolute ground current 1. AC component 1 a +A
C) is I n +AC+ -1io Hcos(θ8-θE
”) ・(1) However, θ1−θ4 11° is given by representing the amplitude of the AC component.

Next, when the AC component l□AC) is multiplied by cos θ" l Sin θ" using multipliers 25d and 25e, I 1
liACI ' CO3θ = I no ' C03
(θ0 - θ is expressed as cos θ1...(2) I m (AC) 'Sjnθ''= I so Hc
os(θ1−θE”)・sinθ1...(3) is obtained.

These AC components are passed through smoothing circuits 25f and 25g, respectively.
Then + %5in2θ1 ・si'n θd] ・d θ1 , and + y2sin2θ8 θ1] ・d θ1 1.

becomes.

is passed through the ratio calculator 25h to find jan-'θ,
By inputting it to the jan-' calculation unit 25i, the electrical angle θt of the grounding portion is finally calculated by arctangent calculation. Therefore, it is possible to know the grounding portion of the rotor due to poor insulation from the electrical angle θ.

In this embodiment, the alternating current component 1. . , ), and Fig. 3 (
h) and (i), the output of the ratio calculator 25h is 11゜2 tanθ, == ■ (8), and the output of the jan"' calculator 25e is jan -'
(00) =90° (9). From this, it can be seen that grounding occurs at a portion of electrical angle θ1-90°.

If we know the electrical angle θE-90° of the grounding part in this way, the rotation angle θ of the rotor at the grounding part is +360°.
) -225°...(11)
It turns out that there are two points. As a result, if you stop the DC motor and manually check the unit armature coils of the rotor at rotation angles of 45° and 225°, you will be able to find the unit in which the ground current is occurring among the many armature coils. Armature coils can be known reliably in a short time.

In this embodiment, the ratio calculator 17 is used to compensate for changes in ground current due to changes in armature voltage, but the invention is not limited thereto.

Further, although a rotary encoder is used as the angle detecting means, it is not limited to a rotary encoder as long as it can detect the rotation angle of the rotating shaft of the DC motor.

Furthermore, although the memory stores the ground current in units of predetermined rotation angles of the DC motor, it may also store the ground current in units of predetermined time.

〔Effect of the invention〕

As detailed above, according to the present invention, the rotation angle of the DC motor and the ground current are periodically detected and stored, and the DC component of the ground current is calculated using a function of the rotation angle. The unit armature coil in which the ground current is occurring can be determined reliably in a short time, and the excellent effect of quickly responding to repair of the DC motor is achieved.

[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 block diagram of a phase calculator, and Fig. 3 shows insulation failure when the armature coil is at a rotation angle of 90°. FIG. 4 is a block diagram showing the configuration of a conventional ground current detection device, and FIG. 5 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 6a... AC component grounding current detector 6b... DC component grounding current detector 18... DC component separation circuit 19... AC component separation circuit 22. ...Memory 23...Rotary encoder 25...Phase calculator 26...Display unit

Claims (1)

[Claims] 1. A grounding condition monitoring device for detecting a grounding current of a DC motor and thereby monitoring a grounding condition, comprising: means for periodically detecting and storing the rotation angle and grounding current of the DC motor; 1. A grounding condition monitoring device for a DC motor, comprising: means for calculating a DC component of a grounding current using a function of a rotation angle.