A Phase Selection Control Method Aiming at the No-load Transformer with Star Ungrounded Connection on the Primary Side and Its Remanence Effect

Abstract

The invention discloses a phase selection control method aimed at a zero-load transformer comprising a primary side employing star ungrounded connection and calculating the influence of residual magnetism of the zero-load transformer. A vacuum breaker, a current zero crossing detection circuit, a voltage zero crossing detection circuit and a control circuit are included. The method is characterized in that (a) when the breaker is opened, a phase B of the breaker is firstly disconnected when a current of the phase B crosses zero, then currents flowing through a phase A winding and a phase C winding of the transformer are of the same size and opposite directions, and when the two currents cross zero, a phase A and a phase C of the breaker are disconnected simultaneously, and phase angles of voltages of the two phases at the moment of disconnection are recorded; and (b) when the breaker is closed, the phase A and the phase C of the breaker are closed at the same time if the voltage phase angles of the two phases equal the voltage phase angles of last breaker opening, and the phase B of the breaker is closed when the voltage of the phase B reaches a peak value. The method can effectively inhibit inrush current of a closing moment of the zero-load transformer.

Description

technical field [0001] The invention relates to a phase selection control method for an unloaded transformer with a star-shaped ungrounded connection mode on the primary side and the influence of residual magnetism, and belongs to the field of vacuum circuit breakers. Background technique [0002] When the no-load transformer operates stably, the excitation current is very small, usually only 3%-8% of the rated current. However, when the transformer is in the moment of no-load closing, a transient current with an amplitude much higher than the rated current will be generated. This transient current is called an inrush current. The generation of inrush current has a certain impact on the power grid, and sometimes it will cause the upper relay protection device to malfunction and affect the stable operation of the power grid. In order to solve this problem, phase selection control technology can be used to accurately control the phase angle of the voltage when the circuit br...

AI Technical Summary

Problems solved by technology

[0003] Purpose of the invention: In order to overcome the deficiencies in the prior art, the present invention provides a phase selection control method aimed at the no-load transformer with a star-shaped ungrounded connection on the primary side and the influence of its residual magnetism, so as to solve the problem of no-load closing inrush current of the transformer oversized problem

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