JP2752218B2 - Protection device for secondary excitation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a speed control device for an induction motor,
The present invention relates to a secondary excitation device in which a cycloconverter and an overvoltage protection device are connected to a secondary winding of an induction motor.

(Prior Art) FIG. 2 shows a configuration of a speed control system of an induction motor using a cycloconverter. 1 is an AC bus for supplying AC power to the induction motor, 2 is a transformer for transforming the AC voltage of the AC bus 1 to a predetermined voltage, 3 is a circuit breaker connecting the AC bus 1 and the transformer 2, 4 is a transformer A cycloconverter for converting the AC power of (2) into an AC of a required frequency;
Is an induction motor position whose speed is controlled, and 6 is an overvoltage protection circuit that protects the cycloconverter 4 and the induction motor 5 from overvoltage generated on the secondary side of the induction motor.

In such a device, when the AC power supply connected to the AC bus 1 is interrupted or restored, an overvoltage occurs on the secondary side of the induction motor 5. For this reason, the secondary side of the induction motor 5 is short-circuited by the overvoltage protection circuit 6 to protect the cycloconverter 3 and the induction motor 5 from overvoltage. After the power is restored and the overvoltage is attenuated, the overvoltage protection circuit 6 is cut off and disconnected from the circuit, so that the operation of the induction motor 5 can be continued.

This method will be described in detail with reference to FIG. FIG. 3 focuses on one phase for simplification of the three-phase circuit of FIG. The same components as those in FIG. 2 are denoted by the same reference numerals. Reference numeral 6 denotes an overvoltage protection circuit, which includes a switch 6-1. Reference numeral 7 denotes a control circuit that controls on / off of the switch 6-1. Reference numeral 8 denotes a gate control circuit that performs gate control of the cycloconverter 4. 9 is 2 of the induction motor 5
This is a voltage detector that detects the voltage on the next side. Reference numeral 10 denotes a current detector for detecting the output current of the cycloconverter, and reference numeral 11 denotes a level detector for detecting whether or not the current detected by the current detector 10 is higher than a certain level.

When the AC voltage of the AC bus 1 is lost or restored, an overvoltage occurs on the secondary side of the induction motor 5. The overvoltage is detected by the voltage detector 9 or the power failure of the AC bus 1 is detected, and the control circuit 7 turns on the switch 6-1 and stops the cycloconverter 4. Thereby, the induction motor 5 and the cycloconverter 4 are protected from overvoltage.

Thereafter, the control circuit 7 detects that the power has been restored and the overvoltage has attenuated, and the switch 6-1 is shut off, the cycloconverter 4 is restarted, and the operation of the induction motor 5 can be continued.

(Problem to be Solved by the Invention) In the above-mentioned overvoltage protection circuit on the secondary side of the induction motor 5, turning on the switch 6-1 means short-circuiting the output of the cycloconverter 4, 4 enters an overcurrent state. Usually, when the output is short-circuited, the cycloconverter 4 is stopped, the circuit breaker 3 is opened, and the system is stopped.

Therefore, as described above, the cycloconverter 4 cannot be restarted after the AC bus 1 is restored and the operation cannot be continued, so that the system is stopped every time a power failure occurs, and the reliability of the system is reduced. Was.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the above-mentioned disadvantages of the prior art, to prevent the system from being stopped by an overcurrent that occurs during operation of the overvoltage protection circuit, and to continue the operation of the induction motor during operation of the overvoltage protection circuit. An object of the present invention is to provide a protection device for a device.

[Constitution of the Invention] (Means for Solving the Problems) In order to achieve the above object, the present invention provides a failure detection circuit that detects a failure based on an overcurrent detection signal and an off signal of an overvoltage protection circuit. Features.

(Operation) According to the present invention, if the overvoltage protection circuit is operating,
The system can be prevented from being stopped due to an overcurrent, the cycloconverter can be restarted, and the operation of the induction motor can be continued.

(Embodiment) FIG. 1 is a configuration diagram showing one embodiment of the present invention, and the same components as those in FIG. 3 are denoted by the same reference numerals.

A failure detection circuit 12 detects a failure based on an overcurrent detection signal from the level detector 11 and an off signal of the switch 6-1 from the control circuit 7.

As described above, the occurrence of overvoltage on the secondary side of the induction motor 5 is detected by the voltage detector 9 or the AC bus 1
And the control circuit 7 turns on the switch 6-1 and stops the cycloconverter 4.

In FIG. 1, the ON signal of the switch 6-1 is set to "1", input to the NT circuit 12-1, the overcurrent detection signal by the level detector 11 is set to "1", and the type in,
The open signal of the circuit breaker 3 is set to "1" and output from the AND circuit 12-2.

Now, the ON signal “1” of the switch 6-1 is set to the NT circuit
If the overcurrent detection signal “1” is input to the AND circuit 12-2, the output of the AND circuit 12-2 is “0”. Since it is "0", the circuit breaker 3 is not opened.

Therefore, as described above, the control circuit 7 detects that the power is restored and the overvoltage has attenuated, the switch 6-1 is cut off, the switch is disconnected, the cycloconverter 4 is restarted, and the operation of the induction motor is continued. be able to. Although the switch 6-1 has been described as a switch in FIG. 1, the same effect can be obtained by using a semiconductor switch such as a thyristor or a gate turn-off thyristor.

[Effects of the Invention] As described above, according to the present invention, the condition that the overvoltage protection circuit has a fixed difference is added to the fault detection due to the overcurrent. Since failure detection can be prevented, the cycloconverter can be restarted without stopping the system, and the operation of the induction motor can be continued, a highly reliable protection device for the secondary excitation device can be provided.

[Brief description of the drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, FIG. 2 is a block diagram showing a main circuit of a conventional device, and FIG. 3 is a block diagram showing one phase of the conventional device. 1 AC bus, 2 Transformer, 3 Breaker, 4 Cycloconverter, 5 Induction motor, 6 Overvoltage protection circuit, 6-1 Switch, 7 Control circuit 8 Gate control circuit 9 Voltage detector 10 Current detector 11 Level detector 12 Fault detector 12-1 NT circuit 12-2 AND circuit.

Claims (1)

(57) [Claims] 1. An induction motor whose primary winding is excited by an AC power supply, a cycloconverter that excites a secondary side of the induction motor, and an overvoltage protection circuit that prevents an overvoltage on the secondary side of the induction motor. In the secondary excitation device, a protection device for the secondary excitation device is provided which does not stop the failure due to the overcurrent of the secondary side of the cycloconverter during the operation of the overvoltage protection circuit. .