Marine differential protection method for anti-excitation inrush current transformer

Abstract

The present application relates to a kind of marine anti-excitation inrush transformer differential protection method, according to the current transformer ratio of transformer two sides and transformer ratio, the current amplitude of the base wave of current differential is calculated and the secondary harmonic assignment;Determine short-circuit voltage eigenvalue state;According to the result of preceding, execute excitation inrush identification algorithm, output excitation inrush lockout signal;When excitation inrush lockout signal is 1, lockout differential protection output, otherwise normal output differential protection action signal.The present application fills the blank of anti-excitation inrush technology of marine transformer differential protection;Improve the stability and reliability of ship power system operation, avoid large-scale power loss caused by transformer excitation inrush caused by differential protection.

Description

Technical Field

[0001] The present invention relates to the technical field of ship power system protection, and in particular to a differential protection method for a ship-used anti-excitation inrush current transformer. Background Art

[0002] Marine transformers are crucial components in a ship's power system, and their proper operation is crucial to the ship's safety. Differential protection is typically configured for marine transformers to ensure timely disconnection of the fault zone in the event of a transformer short circuit. However, the presence of magnetizing inrush currents poses a challenge to the proper operation of differential protection. Magnetizing inrush currents are high currents that occur during the transient process of voltage recovery after the transformer is switched on or after an external fault is cleared. These currents can reach 6-8 times the rated current. Identifying and suppressing magnetizing inrush currents is a research hotspot in marine differential protection. Current techniques for identifying magnetizing inrush currents in land-based power systems include methods based on harmonic content, waveform characteristics, magnetic flux characteristics, and equivalent currents. Research on differential protection algorithms to mitigate magnetizing inrush currents continues to advance, with new theories and technical approaches being proposed and validated to improve the reliability and safety of power systems. Summary of the Invention

[0003] Aiming at the problem of magnetizing inrush current identification, a differential protection method for marine anti-magnetizing inrush current transformer is proposed.

[0004] The technical solution of the present invention is: a differential protection method for a marine anti-excitation inrush current transformer, which specifically includes the following steps:

[0005] 1) Calculate the current differential current fundamental amplitude Idiff_mod and second harmonic assignment Idiff_mod2ci based on the current transformer ratio and transformer ratio on both sides of the transformer;

[0006] 2) Determine the status of the short-circuit voltage characteristic mark;

[0007] Take the maximum value of the three fundamental amplitudes of the three-phase line voltage and compare it with the three-phase short-circuit positive sequence voltage constant value U1_set. If the maximum value of the line voltage fundamental amplitude is less than the three-phase short-circuit positive sequence voltage constant value, then condition one is satisfied; if the negative sequence voltage amplitude U2_mod is greater than the 1 / 2 phase short-circuit negative sequence voltage constant value U2_set, then condition two is satisfied; if either condition one or two is satisfied, the short-circuit voltage flag is 1, otherwise it is 0;

[0008] 3) Based on the results of steps 1) and 2), the magnetizing inrush current identification algorithm is executed and the magnetizing inrush current blocking signal is output; A) When the magnetizing inrush current blocking enable is 0, the magnetizing inrush current identification is not executed and the magnetizing inrush current blocking signal is output as 0;

[0009] B) When the magnetizing inrush current blocking enable is 1, the following judgment is performed:

[0010] Condition 1: The amplitude of the second harmonic of the differential current Idiff_mod2ci> the amplitude of the fundamental wave of the differential current Idiff_mod×the harmonic coefficient;

[0011] Condition 2: The differential current fundamental amplitude Idiff_mod is greater than the ratio differential pickup value;

[0012] After 20ms when the above conditions are met at the same time, if the short-circuit voltage flag is 0 and there is no voltage transformer disconnection, the output excitation inrush current blocking signal is 1;

[0013] If condition 1 and condition 2 are not met at the same time, the output excitation inrush current blocking signal is 0 after 20ms.

[0014] 4) When the excitation inrush current blocking signal is 1, the differential protection output is blocked, otherwise the differential protection action signal is output normally.

[0015] Furthermore, the calculation method of the current differential current fundamental amplitude Idiff_mod and the second harmonic assignment Idiff_mod2ci in step 1) is as follows:

[0016] Assume that the primary rating of the current transformer used to collect current values ​​on the primary side of the transformer is ICT1, the primary rating of the current transformer used to collect current values ​​on the secondary side of the transformer is ICT2, the rated voltage of the transformer primary side is UH, the rated current of the transformer secondary side is UL, the current collection value of the transformer primary side is I local side, and the current collection value of the transformer secondary side is I opposite side.

[0017] Transformer conversion factor K1 = (UL / UH) × (ICT2 / ICT1)

[0018] Differential current sampling value Idiff=I local side + I opposite side × K1

[0019] The fundamental amplitude Idiff_mod and the second harmonic amplitude Idiff_mod2ci of the differential current are calculated using the discrete Fourier algorithm.

[0020] Furthermore, in step 2), the three-phase short-circuit positive sequence voltage constant U1_set is 0.5 times the rated line voltage, and the 1 / 2-phase short-circuit negative sequence voltage constant U2_set is 0.3 times the rated line voltage.

[0021] Furthermore, the harmonic coefficient in step 3) is a set value for protection, indicating that the proportion of the second harmonic in the differential current is greater than the set value of the fundamental amplitude proportion.

[0022] Further, the ratio differential starting value in step 3) is a setting value for protection, which is 0.3 times the branch rated current, indicating that the current differential current meets the action condition of differential protection.

[0023] The ship anti-magnetic inrush transformer differential protection method has the advantages that the ship anti-magnetic inrush transformer differential protection method fills the gap of the anti-magnetic inrush technology of the differential protection of the ship transformer, improves the stability and reliability of the ship power system operation, and avoids large-scale power loss caused by the differential protection due to the transformer magnetic inrush. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The short-circuit voltage flag discrimination graph of the present application;

[0025] Figure 2 The magnetic inrush identification algorithm logic graph of the present application. DETAILED DESCRIPTION

[0026] The present application will be described in detail below in combination with the drawings and specific embodiments. The present embodiment is implemented on the premise of the technical solution of the present application, and detailed implementation modes and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0027] The ship anti-magnetic inrush transformer differential protection method is comprehensively used for the harmonic content information and the short-circuit voltage characteristics, and the current magnetic inrush is comprehensively distinguished by using the characteristics of the high secondary harmonic content of the transformer magnetic inrush and combining the voltage characteristics during short-circuit, and then the differential protection output is locked, including the following steps:

[0028] 1. The transformer two-side current transformer ratio and the transformer ratio are used to calculate the current differential current fundamental amplitude and the secondary harmonic assignment value;

[0029] 2. The short-circuit voltage characteristic flag state is judged;

[0030] 3. The magnetic inrush identification algorithm is executed according to the results of steps 1 and 2, and the magnetic inrush locking signal is outputted;

[0031] 4. When the magnetic inrush locking signal is 1, the differential protection output is locked, otherwise the differential protection action signal is normally outputted.

[0032] The transformer two-side current transformer ratio and the transformer ratio are used to calculate the current differential current fundamental amplitude and the secondary harmonic assignment value:

[0033] Assume that the primary side rating of the current transformer used to collect current values ​​on the primary side of the transformer is ICT1, the primary side rating of the current transformer used to collect current values ​​on the secondary side of the transformer is ICT2, the rated voltage of the transformer primary is UH, the rated current of the transformer secondary is UL, the current collection value of the transformer primary is I local side, and the current collection value of the transformer secondary is I opposite side.

[0034] Transformer conversion factor K1 = (UL / UH) × (ICT2 / ICT1)

[0035] Differential current sampling value Idiff=I local side + I opposite side × K1

[0036] The fundamental amplitude Idiff_mod and the second harmonic amplitude Idiff_mod2ci of the differential current are calculated using the discrete Fourier algorithm.

[0037] according to Figure 1 Execute the status judgment of the short-circuit voltage flag: among them, Uab_mod, Ubc_mod, and Uca_mod are the three-phase line voltage fundamental amplitudes. The maximum value of the three is compared with the three-phase short-circuit positive-sequence voltage constant U1_set. If the maximum value of the line voltage fundamental amplitude is less than the three-phase short-circuit positive-sequence voltage constant, then condition one is met. When a three-phase short circuit occurs in the system, the fundamental amplitude of the three-phase line voltage will tend to 0. Therefore, when the maximum value of the three is less than the set value U1_set, it can be judged that there may be a three-phase short circuit fault; the negative-sequence voltage amplitude U2_mod is greater than the 1 / 2-phase short-circuit negative-sequence voltage constant U2_set, then condition two is met. When a two-phase short circuit occurs in the system, the voltage fault characteristic is the occurrence of negative-sequence voltage. Therefore, when the negative-sequence voltage amplitude is greater than the set value U2_set, it can be judged that there may be a two-phase short circuit fault; when any one of conditions one or two is met, the short-circuit voltage flag is 1, otherwise it is 0. The three-phase short-circuit positive sequence voltage constant U1_set can generally be taken as 0.5 times the rated line voltage, and the 1 / 2-phase short-circuit negative sequence voltage constant U2_set can generally be taken as 0.3 times the rated line voltage.

[0038] like Figure 2 Logic diagram of the excitation inrush current identification algorithm,

[0039] A) When the magnetizing inrush current blocking enable is 0, the magnetizing inrush current identification is not performed and the output magnetizing inrush current blocking signal is 0;

[0040] B) When the magnetizing inrush current blocking enable is 1, the following judgment is performed:

[0041] Condition 1: The differential current second harmonic amplitude Idiff_mod2ci > the differential current fundamental amplitude Idiff_mod × the harmonic coefficient. The harmonic coefficient is the protection setting value, generally 10%, indicating that the proportion of the second harmonic in the differential current is greater than the set value of the fundamental amplitude.

[0042] Condition two: the fundamental amplitude value of differential current Idiff_mod is greater than the ratio differential starting value, the ratio differential starting value is the set value of protection, generally 0.3 times the branch rated current, which indicates that the current differential current meets the action condition of differential protection.

[0043] After 20 ms when the above conditions are met simultaneously, if the short-circuit voltage flag is 0 and no voltage transformer disconnection occurs, the excitation inrush current blocking signal is 1;

[0044] If the conditions one and two are not met simultaneously after 20 ms, the excitation inrush current blocking signal is 0.

[0045] When the excitation inrush current blocking signal of any one of A, B and C three phases is 1, the three-phase differential protection output is blocked, otherwise the differential protection action signal is normally output.

[0046] The above-described embodiments only express the specific implementation of the present application, and the description is more specific and detailed, but it cannot be understood as the limitation of the scope of the patent. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A differential protection method for a marine anti-excitation inrush current transformer, characterized in that: The specific steps include: 1) Calculate the current differential current fundamental amplitude Idiff_mod and second harmonic amplitude Idiff_mod2ci based on the current transformer ratio and transformer ratio on both sides of the transformer; 2) Determine the status of the short-circuit voltage characteristic mark; Take the maximum value of the three fundamental amplitudes of the three-phase line voltage and compare it with the three-phase short-circuit positive sequence voltage set value U1_set. If the maximum value of the line voltage fundamental amplitude is less than the three-phase short-circuit positive sequence voltage set value, condition 1 is met; If the negative sequence voltage amplitude U2_mod is greater than the 1 / 2 phase short circuit negative sequence voltage set value U2_set, then condition 2 is met; if either condition 1 or condition 2 is met, the short circuit voltage flag is 1, otherwise it is 0; 3) Based on the results of steps 1) and 2), execute the magnetizing inrush current identification algorithm and output the magnetizing inrush current blocking signal; A) When the magnetizing inrush current blocking enable is 0, the magnetizing inrush current identification is not performed and the output magnetizing inrush current blocking signal is 0; B) When the magnetizing inrush current blocking enable is 1, the following judgment is performed: Condition 1: The amplitude of the differential current second harmonic Idiff_mod2ci> the amplitude of the differential current fundamental wave Idiff_mod × the harmonic coefficient; Condition 2: The differential current fundamental amplitude Idiff_mod is greater than the ratio differential pickup value; After 20ms when the above conditions are met at the same time, if the short-circuit voltage flag is 0 and there is no voltage transformer disconnection, the output excitation inrush current blocking signal is 1; If condition 1 and condition 2 are not met at the same time, the output excitation inrush current blocking signal is 0 after 20ms. 4) When the excitation inrush current blocking signal is 1, the differential protection output is blocked, otherwise the differential protection action signal is output normally.

2. The method for differential protection of a marine anti-excitation inrush current transformer according to claim 1, characterized in that: The calculation method of the current differential current fundamental amplitude Idiff_mod and second harmonic amplitude Idiff_mod2ci in step 1) is as follows: Assume that the primary rating of the current transformer used to collect current values ​​on the primary side of the transformer is ICT1, the primary rating of the current transformer used to collect current values ​​on the secondary side of the transformer is ICT2, the rated voltage of the transformer primary side is UH, the rated current of the transformer secondary side is UL, the current collection value of the transformer primary side is I local side, and the current collection value of the transformer secondary side is I opposite side. Transformer conversion factor K1 = (UL / UH) × (ICT2 / ICT1) Differential current sampling value Idiff=I local side + I opposite side × K1 The discrete Fourier transform algorithm is used to calculate the fundamental amplitude Idiff_mod and the second harmonic amplitude Idiff_mod2ci of the differential current.

3. The method for differential protection of a marine anti-excitation inrush current transformer according to claim 2, characterized in that: In the step 2), the three-phase short-circuit positive sequence voltage constant U1_set is 0.5 times the rated line voltage, and the 1 / 2-phase short-circuit negative sequence voltage constant U2_set is 0.3 times the rated line voltage.

4. The method for differential protection of a marine anti-excitation inrush current transformer according to claim 2 or 3, characterized in that: The harmonic coefficient in step 3) is the set value of the protection, indicating that the proportion of the second harmonic in the differential current is greater than the set value of the fundamental amplitude proportion.

5. The method for differential protection of a marine anti-excitation inrush current transformer according to claim 2 or 3, characterized in that: In step 3), the ratio differential starting value is the protection setting value, which is 0.3 times the branch rated current, indicating that the current differential current meets the action conditions of the differential protection.

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