SU750640A1 - Device for protecting converter from internal short circuitings - Google Patents

Description

(54) DEVICE FOR PROTECTION OF THE CONVERTER FROM INTERNAL SHORT CIRCUITS

one

The invention relates to the protection of rectifiers on uncontrolled ventilators used in ice melting schemes on high voltage direct current lines.

A device for protecting the converter from short circuits is known, which contains current sensors on current transformers, measuring and output units 1.

The disadvantage of this device is low sensitivity when saturation of current transformers and the need for detuning from the normal mode.

Closest to the present invention is a protection device for the converter against internal short circuits, comprising a current sensor, made on the current transformer, measuring and output units 2.

However, the known device has a low reliability.

The purpose of the invention is to increase reliability.

To achieve this goal, a transformer protection organ was used as a measuring body, containing a circuit comparing the magnitudes of the second harmonics in the positive and negative half-wave of the controlled current.

In case of internal short circuit, the form of the current in the intact phases of the rectifier practically coincides with the form of the aperiodic surge of the magnetizing current of the transformer, and the shape of the secondary current of the transformer is identical to the shape of the secondary surge, of the magnetizing current. The transformer protection meter has a high sensitivity to the even harmonics of the secondary current appearing in this mode, containing a comparison circuit of the second harmonic values in the positive and negative controlled-current half-wave, designed to block the current protectors of the transformers.

The drawing shows a diagram of the proposed device.

Claims (2)

20 The device contains an intermediate current transformer (PTT) 1, the primary winding of which flows around the secondary current of the protective current transformer. To the secondary winding of the POS 1, diodes 2 and 3 with adjustable polarity and adjustable resistances 4 and 5 are connected to series circuits — winding 6 — capacitor 7, winding 8 — capacitor 9. As inductors 6 and 8, chokes with open ferromagnetic cores are used. The voltage pulsations at the outputs of the rectifying bridges 10 and II connected to capacitors 7 and 9 are smoothed by parallel chains 12, 13 and 14, 15. The output voltage that is the difference of the signals corresponding to the content of the second harmonic in the half-waves of the secondary current of the current transformer , is formed on the resistance 16. The device can also be used to protect the rectifier from external short circuits, followed by the saturation of the protective current transformers. Claims of the converter protection device against internal short circuits, comprising a current sensor made on a current transformer, a measuring and output unit, characterized in that, in order to increase reliability, a transformer protection organ is used as a measuring body, containing a circuit comparing the second harmonic values in positive and negative half-wave of the controlled current. Sources of information taken into account in the examination 1. Semiconductor rectifiers. M., “Energie, 1967, p. 327, fig. 7-1. 2. Glukh E. M. and Zelenov V. E. Protection of semiconductor converters. M., “Energie, 1970, p. 117, fig. 5-5.