A Combination Blocking Method of Exciting Inrush Current Based on Waveform Symmetry
A technology of exciting inrush current and symmetrical waveform, applied in the direction of emergency protection circuit devices, electrical components, etc., can solve the problems of non-fault phase difference current waveform asymmetry, transformer differential protection misoperation, high sensitivity of differential protection, etc., to improve reliability and rapidity, avoiding false action or refusal to operate, and reliable performance
Active Publication Date: 2018-08-07
JIANGSU ELECTRIC POWER CO +2
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[0010] The differential protection of the split-phase blocking method has high sensitivity, but due to the different wiring methods of the high and low voltage sides of the transformer, the differential current has a Y / △ transformation relationship, and the differential current after transformation may have a symmetrical waveform of one phase, so it is easy to cause the transformer airdrop time difference The differential protection of the three-phase locking method has high reliability, but when the airdropped transformer is grounded in the area, due to the asymmetrical waveform of the non-fault phase difference current, it is easy to block the differential protection by mistake
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[0045] The present invention will be further described below in conjunction with the accompanying drawings.
[0046] Such as figure 1 As shown, a combined blocking method for excitation inrush current based on waveform symmetry includes the following steps,
[0047] S01, differential current calculation: collect the high, medium, and low side currents of the transformer, and filter the current sampled values (filter out the DC component) to calculate the differential current sampled value i d (t);
[0048] S02. Discrimination of the asymmetry of the differential current waveform at the current sampling time:
[0049] Respectively judge whether the current sampling time of A phase, B phase, C phase difference flow is symmetrical, the judgment formula is formula (1):
[0050]
[0051] where i d (t) is the differential flow sampling value at the current sampling moment, i d (t-π) is the sampling value of the differential current half cycle before the current sampling time...
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The invention discloses a combined blocking method for excitation inrush current based on waveform symmetry, comprising the following steps: S01, calculation of differential current; S02, discrimination of asymmetry of differential current waveform at the current sampling time; S03, discrimination of waveform asymmetry within cycle time; S04, Combination blocking logic: according to the asymmetry of the three-phase differential current waveforms obtained in step S03, phase A, phase B, and phase C, the differential protection is blocked by combination logic; the present invention fully considers the transformer excitation from the technical defects of the existing methods Various forms of inrush current waveforms and the influence of inrush current on short-circuit fault identification, combined with the inherent phase angle conversion characteristics of power transformers, a combined blocking method for inrush current is proposed. This method can efficiently distinguish inrush current and fault current, which is beneficial to Improve the reliability and rapidity of transformer differential protection.
Description
technical field [0001] The invention relates to the technical field of electric power system relay protection, in particular to a combined blocking method for excitation inrush current based on waveform symmetry. Background technique [0002] When the transformer is closed with no load, due to the transformer residual magnetism and the non-linearity of the iron core flux, an exciting inrush current with a large amplitude will be generated. [0003] Since the transformer excitation inrush current only exists on the airdrop side, that is, the differential current calculated by the differential protection of the transformer is the excitation inrush current, so when the excitation inrush current is greater than the differential protection threshold, if there is no correct inrush current identification and blocking method, it will cause differential protection. Misoperation. [0004] At present, the commonly used blocking methods for transformer excitation inrush current include...
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IPC IPC(8): H02H7/045
Inventor 王树刚陆钟华李培培马在权滕俊胡兵郭晓
Owner JIANGSU ELECTRIC POWER CO