Protection method for unbalanced excitation current in transformer no-load closing and non-saturation area

Abstract

The invention discloses an unbalance protection method for excitation current of a no-load switch-on unsaturated zone of a transformer. By using the method, when the degree of unbalancedness of three-phase current in the unsaturated zone is greater than a setting value Phd and a floating threshold, an exit is tripped, which shows that the interior of the transformer goes wrong. By using the unbalance protection method, the transformer cannot generate false-tripping during no-load switch-on; and simultaneously the transformer has high sensibility when being switched to a turn-to-turn short circuit without load, and faults can be quickly removed when the transformer is switched to the turn-to-turn fault, an inter-phase short circuit and a grounded short circuit without load so that the transformer is not influenced by excitation surge current.

Description

technical field [0001] The present invention relates to the technical field of power system transformer protection, and in particular relates to a transformer that can safely realize no false operation when the transformer is closed normally under no-load, no-load closing when inter-turn short-circuit, phase-phase short-circuit, and grounding short-circuit can have high performance. Sensitive, rapid and reliable protection method. Background technique [0002] The transformer is an important device in the power system, which realizes the conversion of energy and voltage in the power system. Therefore, the safe operation of the transformer is related to the safety and stability of the entire power system. At present, the protection of transformers at home and abroad mostly adopts the principle of ratio braking differential protection. [0003] With this protection method, the most serious problem facing the transformer is the excitation inrush current. In order to avoid mal...

AI Technical Summary

Problems solved by technology

However, when the second harmonic braking principle is used for protection, when the transformer is closed with no load, if the saturation magnetic density of the transformer is low, misoperation may still occur. However, when the principle of discontinuous angle is used for protection, when the current transformer is saturated, It will deform the inrush waveform and cause the discontinuity angle to disappear

When the transformer is switched on with no-load through a long line, due to the influence of the distributed capacitance of the line, the braking ratio of the second harmonic will be less than the fixed value, resulting in the malfunction of no-load switch-on

In addition, when these two principles are used for protection, the sensitivity is not high enough when the transformer is unloaded and inter-turn short circuit

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