A protection method that is not affected by frequency during the start-up and shutdown of the unit

Abstract

A protection method that is not affected by frequency during the start-up and shutdown of a unit, comprising the following steps: Step 1: The protection device uses a fixed sampling frequency to collect sampling instantaneous values ​​of analog quantities related to start-stop protection, and the relevant analog quantities include three Phase current, three-phase current at the neutral point side, and zero-sequence voltage at the neutral point side; Step 2: The protection device judges according to the position of the grid-connected circuit breaker, the phase-to-phase voltage at the machine terminal, the frequency, the machine terminal current, and the position of the SFC contact. Whether to put into the start-stop protection; step 3: under the premise that the start-stop protection is put into use, use the heat accumulation criterion logic and the sampling value criterion logic to judge whether the protection action condition is satisfied; step 4: when any of the step 3 When a criterion satisfies the protection action condition, the protection action. This method has nothing to do with the signal frequency. This method is used for start-stop differential protection, start-stop zero-voltage protection, and low-frequency overcurrent protection, which can realize reliable and rapid protection in the process of variable frequency start-stop.

Description

technical field [0001] The invention belongs to the technical field of relay protection for electric power systems, and relates to a protection method suitable for the start-up and shutdown process of a unit that is not affected by frequency. Background technique [0002] There are many ways to start the unit. Generators are started by prime movers such as steam turbines and water turbines; gas turbines, pumped storage units, and large-scale condensers are preferably started by static frequency converters (SFC), and the frequency converters are used to generate variable-frequency AC power for the condensers. start up. Special protection needs to be configured during the start-stop process, such as start-stop differential protection and start-stop zero-voltage protection for responding to phase-to-phase short circuit and stator ground fault, and low-frequency overcurrent protection for responding to short-circuit faults. [0003] In the process of starting and stopping, the...

AI Technical Summary

Problems solved by technology

In addition, since the injection-type stator grounding protection is more and more used in the protection of generators and condensers, it injects a 20Hz low-frequency AC signal into the generator stator winding through an external power supply, which will cause the zero-sequence voltage on the neutral point side to contain 20Hz Signal

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