A highly sensitive third harmonic voltage differential stator ground protection method

Abstract

The invention discloses a high-sensitive third harmonic voltage differential stator grounding protection method, comprising the following steps: acquiring Un (k), Us (k), UA (k), UB (k), UC (k); Calculated as shown in the descrption; calculate. DELTA U3n (t) and. DELTA U3s (t); According to deltaU 3n (t) and deltaU 3s (t), it is judged whether the zero-sequence voltage of the generator is broken or not, and the protection is blocked if the generator is broken. U3d, U3r, U3d 'and U3r' were calculated. When the zero-sequence voltage of the generator is not broken, whether the operation conditionis satisfied or not is judged according to U3d, U3r, U3d 'and U3r'. If yes, the protection operation is delayed. The invention has the beneficial effects that the insulation of the stator winding tothe ground is reduced slowly, the zero-sequence voltage loop of the generator is broken without misoperation, and the reliability of the generator is improved.

Description

technical field [0001] The invention belongs to the technical field of electric power system relay protection, and in particular relates to a highly sensitive third harmonic voltage differential stator grounding protection method capable of detecting the slow drop of stator insulation. Background technique [0002] Stator single-phase grounding is a relatively common fault in generators. If stator single-phase grounding occurs and is not dealt with in time, it may easily cause phase-to-phase short circuit or inter-turn short circuit, and even burn the iron core. There are many reasons for the single-phase grounding of the stator, including the leakage of the cooling water of the water-cooled generator, and the water will accelerate the insulation deterioration of the stator bar through hydrolysis caused by damp heat; the conductivity of the cooling water used by the water-cooled generator increases, resulting in The resistance to ground decreases; the cooling water in the st...

AI Technical Summary

Problems solved by technology

Fundamental zero-sequence voltage protection is simple and reliable, but there is a dead zone near the neutral point

There are many types of third harmonic voltage protection, all of which can respond to ground faults near the neutral point, but in the middle of the stator winding, the sensitivity is low and even there is a dead zone

The principle of amplitude ratio can respond to the ground fault near the neutral point, but the sensitivity is higher only near the neutral point, and there is a dead zone in the range from the middle of the stator winding to the machine end, and it is theoretically impossible to combine it with the principle of fundamental zero-sequence voltage. dead zone, but the sensitivity in the middle of the winding is still not ideal

The sensitivity of the third harmonic voltage differential stator grounding protection of the self-adjusting coefficient type is high, but when the insulation of the stator winding to the ground drops slowly, the differential coefficient gradually changes with the insulation state, so that the differential voltage is continuously cleared until the insulation is complete damaged, the protection may still fail to operate

In addition, because the third harmonic voltage protection is affected by the disconnection of the zero-sequence voltage circuit, there are many misoperations on site, and the reliability still needs to be improved.

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