Method for sub-synchronous current calculation and sub-synchronous over-current and divergent protection of generator

Abstract

A method for generator subsynchronous current calculation, subsynchronous over-current and divergence protection comprises: collecting a three-phrase current signal of a generator; converting the positive sequence and negative sequence components of the subsynchronous current of each mode into an equivalent industrial frequency negative sequence current, which is substituted into the original industrial frequency negative sequence over-current protection criterion of the generator, for judging definite time and inverse time protection; and at the same time judging whether the equivalent industrial frequency negative sequence over-current increases continuously, which constitutes the divergence protection criterion. The present invention can detect the multi-mode subsynchronous current in the armature current of the generator, and realize over-current protection and divergence protection of the subsynchronous current.

Description

technical field [0001] The present invention relates to the technical field of generator protection in power systems, more specifically to subsynchronous oscillation of turbogenerators, and to subsynchronous current detection, overcurrent protection, divergence protection methods and corresponding relays in generator armature currents protective or monitoring devices. Background technique [0002] Some large-scale thermal power plants are far away from the load center, and the capacity of the generator set is large, so long-distance power transmission is mostly used, and power electronic equipment such as series capacitor compensation and controllable series capacitor compensation are installed in the transmission line, and DC transmission is sometimes used. When the parameters of these units are compensated by capacitance or long-distance lines with no load, asynchronous self-excitation (abbreviated as asynchronous self-excitation) may occur, and the armature current in the...

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Problems solved by technology

In April 2008, during the test of SBF input in Tuoketuo Power Plant, the generator set had obvious asynchronous self-excitation, and the current showed a divergent trend, so that the generator set could not be connected to the grid normally.

Although this method is simple, it has obvious disadvantages: (1) It is not enough to extract the current of only one mode. When the actual unit is running, there may be subsynchronous currents of multiple modes at the same time, such as the generator of Tuoketuo Power Plant During asynchronous self-excitation, subsynchronous currents with two frequencies near 27Hz and 39Hz once appeared; (2) The setting of the protection setting value is set arbitrarily, lacking theoretical basis; (3) The protection function is single, only providing definite time limit overcurrent Protect

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