High-credibility excitation inrush current braking method of transformer device

Abstract

The invention relates to a high reliable inrush current brake method for a transformer, which comprises the steps of sampling, calculating the three-phase differential current fundamental wave content and the second harmonic content of a current sampling point, setting and calculating a floating threshold, and carrying out differential starting judgment, the judgment of the change characteristics of the fundamental wave content and the judgment of the change characteristics of the ratio between second harmonic content and the fundamental wave content by a discriminant so as to determine reliable locking or immediate differential opening. On the basis of a traditional second harmonic braking principle, the method sets the floating threshold, tracks and masters the change characteristics of the fundamental wave and the second harmonic in a real-time manner, analyzes and judges the operation state of the transformer in time by utilizing the change characteristics of the fundamental wave and the second harmonic, solves the contradiction of the right and fast motion between the inrush current brake and differential protection in the current method and ensures the reliable brake of the transformer under the condition of the only existence of the inrush current and the right and fast motion of the transformer under the situation of any fault in the sample space. Meanwhile, the method reduces the value scope of the brake coefficient of the second harmonic and improves the sensitivity of inrush current brake.

Description

technical field

[0001] The invention relates to a differential protection method for a transformer, in particular to a highly reliable excitation inrush current braking method for a transformer. Background technique

[0002] 1.

[0003] Longitudinal differential protection is the main protection of electrical main equipment. It has high sensitivity and good selectivity, and has been successfully applied to main equipment such as generators, reactors, motors, and buses. However, transformer longitudinal differential protection has always been troubled by the problem of excitation inrush current. In the case of no-load closing of the transformer or removal of external faults, an excitation inrush current comparable to the internal short-circuit current will flow into the differential circuit, causing transformer differential protection. Malfunction. Therefore, in some non-internal fault transient processes (such as airdrops and external faults), it is necessary to detect the...

Examples

Embodiment 1

[0035] Example 1: Press figure 1 Steps shown, set the transformer rated current I n =5A; Differential current starting value I d.q =1A (differential current starting value I d.q Given by the user, the general range is 0.1 to 2.0 times the rated current of the transformer); the second harmonic braking coefficient k 2 =10%; the sampling frequency is 1600 points per second, that is, one cycle sampling 32 points, and the value of m is 1 / 2 of one cycle sampling 32 points, that is, m=16, and the reliability coefficient λ=1.0.

[0036] 1. AC sampling, obtain the current sampling value of each side of the transformer, and calculate the differential current including angle difference conversion to obtain the fundamental wave content of the three-phase differential current at the current sampling point n and three-phase differential current second harmonic content And judge the differential start-up: the three-phase differential current RMS waveform diagram when the high volta...

Embodiment 2

[0042] Example 2: Press figure 1 Steps shown, set the transformer rated current I n =5A, differential current starting value I d.q =1A; second harmonic braking coefficient k 2 =10%; the sampling frequency is 2400 points per second, that is, one cycle sampling 48 points, m value is 1 / 2 of one cycle sampling 48 points, i.e. m=24, setting reliability coefficient λ=0.8, setting Fixed threshold coefficient ε 1 and ε 2 The value of ε 1 = 5%, ε 2 = 5%.

[0043] 1. AC sampling, obtain the current sampling value of each side of the transformer, and calculate the differential current including angle difference conversion to obtain the fundamental wave content of the three-phase differential current at the current sampling point n and three-phase differential current second harmonic content And judge the differential start: when the internal ground fault of the A-phase winding on the high-voltage side of the transformer is air-dropped, the three-phase differential current R...

technical field

[0001] The invention relates to a differential protection method for a transformer, in particular to a highly reliable excitation inrush current braking method for a transformer. Background technique

[0002] 1.

[0003] Longitudinal differential protection is the main protection of electrical main equipment. It has high sensitivity and good selectivity, and has been successfully applied to main equipment such as generators, reactors, motors, and buses. However, transformer longitudinal differential protection has always been troubled by the problem of excitation inrush current. In the case of no-load closing of the transformer or removal of external faults, an excitation inrush current comparable to the internal short-circuit current will flow into the differential circuit, causing transformer differential protection. Malfunction. Therefore, in some non-internal fault transient processes (such as airdrops and external faults), it is necessary to detect the...

Examples

Embodiment 1

[0035] Example 1: Press figure 1 Steps shown, set the transformer rated current I n =5A; Differential current starting value I d.q =1A (differential current starting value I d.q Given by the user, the general range is 0.1 to 2.0 times the rated current of the transformer); the second harmonic braking coefficient k 2 =10%; the sampling frequency is 1600 points per second, that is, one cycle sampling 32 points, and the value of m is 1 / 2 of one cycle sampling 32 points, that is, m=16, and the reliability coefficient λ=1.0.

[0036] 1. AC sampling, obtain the current sampling value of each side of the transformer, and calculate the differential current including angle difference conversion to obtain the fundamental wave content of the three-phase differential current at the current sampling point n and three-phase differential current second harmonic content And judge the differential start-up: the three-phase differential current RMS waveform diagram when the high volta...

Embodiment 2

[0042] Example 2: Press figure 1 Steps shown, set the transformer rated current I n =5A, differential current starting value I d.q =1A; second harmonic braking coefficient k 2 =10%; the sampling frequency is 2400 points per second, that is, one cycle sampling 48 points, m value is 1 / 2 of one cycle sampling 48 points, i.e. m=24, setting reliability coefficient λ=0.8, setting Fixed threshold coefficient ε 1 and ε 2 The value of ε 1 = 5%, ε 2 = 5%.

[0043] 1. AC sampling, obtain the current sampling value of each side of the transformer, and calculate the differential current including angle difference conversion to obtain the fundamental wave content of the three-phase differential current at the current sampling point n and three-phase differential current second harmonic content And judge the differential start: when the internal ground fault of the A-phase winding on the high-voltage side of the transformer is air-dropped, the three-phase differential current R...

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