JPS61164475A - Rotor restriction detector for ac motor - Google Patents

Abstract

PURPOSE:To readily detect the restriction of a rotor by monitoring the current to discriminate whether the rotor is restricted or not. CONSTITUTION:An AC motor 1 is connected by operating/stopping breaker 2 with a power source. A current obtained by a current transformer 3 of current detecting means of the motor 1 is input to a rectifier 4, and further input to a microcomputer 6 through an A/D converter 5. The microcomputer 6 discriminates a power On signal to the motor, and when the signal is presented, the A/D-converter current value is monitored to detect the rotor restricted state when the motor is started asynchronously. Thus, whether the rotor is restricted is detected without mounting a mechanical rotation detector.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a rotor restraint detection device for an AC motor. Background and problems: The thermal withstand capacity when starting an AC motor differs depending on whether the rotor is constrained or not. This is because heat dissipation becomes poor.

Detection of rotor restraint C'-C Conventionally, a mechanical rotation detector 33 as shown in FIG. This is almost never the case.When this rotation detector 33 is not installed, the restraint maintenance at the time of starting the AC motor is performed by determining whether or not the starting current is flowing for longer than the allowable restraint time. If the starting time is longer than the allowable locking time (there was a problem that protection could not be achieved if there were two cases), or if the fc1 starting time did not exceed the allowable locking time (even if the start time was longer than the allowable locking time, protection could not be provided immediately after the power was turned on during locking). Therefore, the thermal resistance of the motor was designed to be larger than necessary in order to allow the motor to be restricted for longer than the starting time.

[Object of the Invention] The present invention provides a method for monitoring only current (
It is an object of the present invention to provide a rotor restraint detection device for an AC motor that can be performed by a user.

[Summary of the Invention] At the time of asynchronous starting of an AC motor (2, on the fixed side C, the AC component and the DC component are superimposed for a short time to form a starting current. When the rotor starts rotating, it rotates 5 times) The magnetic field interlinks with the DC magnetic field caused by the DC component (Y), and a voltage with a frequency corresponding to the rotor's rotational speed (2) is generated on the rotor side, causing a current to flow. , reverse (two stator side (two is,
A voltage is induced, and a starting current with a superimposed low-frequency alternating current component flows. This low-frequency alternating current component is generated when the rotor is locked (- is not superimposed. Therefore, the starting current waveform when one rotor is locked and when it is rotating is different, so by monitoring this waveform, it is possible to determine whether the rotor is locked or not. can.

From this point of view, the present invention uses a plurality of current transformers (2) to rectify the current detected by the rectifier circuit C; /
This is a rotor constraint detection device at the time of starting an AC motor, which monitors the D-converted rt4 current value (2), thereby detecting the rotor constraint state at the time of asynchronous start of the TA machine, and outputs a signal to the outside.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to drawing C.
In the figure (Y), the AC motor 1 is connected to the power supply through the breaker 2 (2) for starting and stopping the current.
The signal 7 is the power-on signal from the breaker 2 to the microcomputer 6, and the signal 8 is the breaker signal from the microcomputer 6. This is a power cutoff signal to the device 2.

The microcomputer 6C' starts the program at step 9, initializes the memory, etc. at step 10, and sets the parameter N at step 11.

In step 12, it is determined whether there is a power-on signal to the motor. If there is no signal, the determination in step 12 is repeated. If there is a signal, the sampling period (
Set timer 1). This f'L is the envelope shown in Figure 3.That waviness occurs during normal startup (- means that it appears within a few seconds after the power is turned on (- means that it appears, and vice versa). This is to set the period for determining that the rotor is restricted.

In step 14, the first three-phase current value is set to R + "B + T.
Read and set the sampling period (same period as the commercial frequency) in step 15 (timer 2) O step 1
Step 6 determines the elapsed time of timer 2, and if the time has not reached the set value (-), repeat step 16. If the time of timer 2 has reached the set value (-), the next current value is set in step 17. Read the current value IR ( read in step 18).
N) and IR(N-1), IR(N)>IR(N
-1), the envelope curves as shown in Figure 3, and the rotor is judged to have started rotating.
This program ends in step 21. In(N)≦
In the case of IR(N-1), the envelope is C2 monotonically decreasing as shown at 30 in FIG. 4, and the next step 19 is executed.

In step 19, l5(N) and l5(N-1) are compared,
If l5(N)>l5(N-1), the program ends in step 21, as in case I above.

If l5(N)≦l5(N-1), proceed to the next step 2
Execute o.

In step 20, compare IT(N) and IT(N-1),
If IT(N)>IT(N-1), the program is terminated at step 21, as in the case of the above-mentioned work R.

If I T (N)≦IT (N-1), the next step 22 is executed.

At step 22, the read data (three-phase current value) is updated, and at step %, the value of the parameter N is updated. At step A, the elapsed time of timer 1 is determined, and if the elapsed time is less than the set value C, steps 15 to 24 are repeated. timer 1
If the set value C is repeated twice for a period of time, the %'5 flow value decreases monotonically as shown by the envelope 3o in Fig. 4 (it is determined that the halo-trochanter is restrained, and a cutoff signal 8 is output in step 25. Step 2
6 ends this program.

In the embodiment of the present invention, a microcomputer 6 is used as the calculation means, but it is a hard logic.

Computing means based on ζU, such as a host computer, may be used.

[Effects of the Invention] Let me explain the above (2. According to the present invention (2), the following effects can be obtained.

(1) AC motor (2) It is possible to detect whether the rotor is restricted without installing an expensive mechanical rotation detector.

(2) Also when the starting time is longer than the allowable locking time.

Capable of restraint protection.

(3) Prompt protection is possible after the rotor is locked.

There is no need to design an allowable restraint time longer than the starting time,
A compact electric motor can be designed.

[Brief explanation of drawings]

Fig. 1 is a motor operation system diagram employing the present invention, Fig. 2 is a 70-chart showing the program of the present invention, Fig. 3 is a stator current waveform diagram when the rotor is not restrained, and Fig. 4 is a diagram of the stator current waveform when the rotor is not restrained. Stator current waveform diagram when the rotor is restrained, 5th
The figure is a diagram of a motor operation system equipped with a mechanical rotation detector. l... AC motor 2... Breaker 3... Current transformer 4... Rectifier circuit 5... A/D transformer 6... Microcomputer 7... Power on signal 8. ...Power cutoff signal 28...Envelope of starting current 30...Envelope of starting current 33...Mechanical rotation detector Representative Patent attorney Noriyuki Chika (and 1 other person) Figure 1, Figure 2 Figure 3 Figure 7, ) Figure 4 Figure 5

Claims (1)

[Claims] A plurality of current transformers that detect current supplied from a power source to an AC motor, a rectifier circuit that rectifies the secondary current of the current transformer, and a rectifier that rectifies the current rectified by this circuit. /D converting A/D
Rotor locking of an AC motor, which consists of a converter and a calculation means that uses the A/D converted output of the A/D converter to detect the rotor locking state at the time of asynchronous starting of the AC motor and outputs a signal to the outside. Detection device.