Redundancy sampling calculation-based superposed square-wave voltage type rotor earth-fault protection method

Abstract

The invention relates to a redundancy sampling calculation-based superposed square-wave voltage type rotor earth-fault protection method, which uses two algorithms of different sampling data to calculate the resistance to the ground of a rotor of a generator and judges the one point rotor earth-fault when the two calculated resistances are smaller than a protective setting value so as to solve the problem of the duality of rotor earth-fault protection criterion of a large unit. When the two calculated resistances are greatly different, the rotor earth-fault protection is latched so as to improve the reliability of the rotor earth-fault protection. Meanwhile, the position of a rotor earth-fault point can be judged without directly accessing a rotor voltage. After the one point rotor earth-fault action, whether the second point rotor earth-fault happens is judged according to the change of the position of the rotor earth-fault point.

Description

technical field [0001] The patent of the invention relates to a voltage-type rotor grounding protection method, which belongs to the technical field of generator rotor grounding protection. Background technique [0002] At present, the rotor grounding protection of reactive generators commonly used in the industry mainly includes two types: injection type and non-injection type. [0003] Non-injection rotor ground protection includes ping-pong switching rotor ground protection and bridge-type rotor ground protection, but the biggest disadvantage of non-injection protection is that it only works when the generator is running normally and the rotor is under excitation voltage. This kind of protection cannot play a protective role during the process of starting and stopping the generator and when the generator is stopped. [0004] Injection rotor grounding protection mainly includes three types: superimposed AC voltage type, superimposed DC voltage type, and superimposed squar...

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Problems solved by technology

[0003] Non-injection rotor ground protection includes ping-pong switching rotor ground protection and bridge-type rotor ground protection, but the biggest disadvantage of non-injection protection is that it only works when the generator is running normally and the rotor is under excitation voltage. This kind of protection cannot play a protective role during the process of starting and stopping the generator and when the generator is stopped

The more and more widely used injection type rotor grounding protection is the superimposed square wave voltage type, which overcomes the shortcomings of the superimposed AC voltage type applied to large units with low sensitivity and the superimposed DC voltage type with different sensitivity at different grounding points, but in The application still has the following deficiencies: figure 1 It is a commonly used superimposed square wave rotor ground protection schematic diagram. The rotor ground resistance is calculated in real time by measuring the leakage current Im under two states of positive voltage and negative voltage. Since the rotor ground protection is difficult to double, when measuring the leakage current When the sampling circuit fails, it is very likely to cause the wrong action of the rotor grounding protection, and the dual CPU solution cannot solve the unreliability caused by the failure of a single sampling circuit

If the excitation voltage is not connected, this method cannot realize the two-point grounding protection of the rotor

Some manufacturers directly introduce the excitation voltage into the protection device in order to realize the two-point grounding protection of the rotor. However, when the large unit is strongly excited, the rotor voltage is as high as 1500V, which is very unsafe for the operation and maintenance of the device.

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