CN102156247A - Method for recognizing lightning interference by utilizing average sampling value of short-window inner polar wave - Google Patents

Abstract

The invention is a lightning interference identification method using the average sampling value of polar waves in a short window. The invention is as follows: after the protective element is started, the pole-line voltage and the pole-line current measured at the place where the protection is installed are used to obtain the pole-wave voltage according to the formula. In the short window, directly use the polar wave voltage sampling value and the steady-state polar line voltage sampling value, and calculate the ratio of the polar wave voltage to the steady-state operating polar line voltage, and identify the lightning impact interference according to the ratio. The sampling frequency of this method is 10kHz, the time window is 5ms, it is not affected by the control system, and the delay protection is at the millisecond level. This method can correctly identify the lightning interference within the entire length of the line. The method has good robustness, strong resistance to transition resistance, is not affected by interference, and has strong practicability. A large number of simulation results show that the invention has good effects.

Description

A Lightning Disturbance Recognition Method Using the Average Sampling Value of Polar Waves in a Short Window

technical field

The invention relates to the technical field of electric power system relay protection, in particular to a lightning interference identification method for ultra-high voltage direct current transmission using the average voltage average value of polar waves within a short window.

Background technique

Transmission line protection based on transient quantities should quickly identify faults and remove faults. But at the same time, traveling wave protection and transient protection will also face more high-frequency interference. Lightning shock is the most important interference factor. Lightning strike failure is the lightning interference of transient protection. The DC line protection using du/dt as the criterion of traveling wave protection is affected by lightning disturbance.

Contents of the invention

The object of the present invention is to provide a lightning interference identification method using the average sampling value of polar waves in a short window.

The essence of the pole wave of DC transmission line is the anti-traveling wave of the pole-line voltage. By making full use of the fault information contained in the transient quantity of the pole-wave voltage traveling wave and its unique advantages in characteristic expression, the UHVDC line protection system based on the pole-wave voltage is constructed. Lightning strikes interfere with identification elements. Concrete realization of the present invention carries out according to the following steps:

：(1) According to the pole line voltage and pole line current measured at the protection installation place, the pole wave voltage is calculated

:

 (j=+,-)                        (1)

(j=+,-) (1)

为极波波阻抗，

为极线电压，

为极线电流，+表示为正极线，-表示为负极线，n=1、2、3….N，N=50为采样序列长度，；In the formula,

is the polar wave impedance,

is the pole-to-line voltage,

is the pole line current, + means the positive line, - means the negative line, n=1, 2, 3... N , N= 50 is the length of the sampling sequence,;

(2) In the short window, the polar wave voltage sampling value is directly used to calculate the average value and normalize. Now, the ratio of the average polar wave voltage to the steady-state operating pole line voltage under lightning fault and lightning fault is defined as

                             (2)

(2)

为极波电压，

为稳态运行时极线电压；In the above formula,

is the pole wave voltage,

is the pole-to-line voltage during steady-state operation;

时雷击未故障，当

时雷击故障。(3) The discrimination criterion between non-fault due to lightning strike and fault due to lightning strike, when

When the lightning strike does not fail, when

Lightning strike failure.

Following is the design principle of the present invention:

1. The Principle of Polar Wave Transient Protection for DC Transmission Lines

The mathematical essence of the polar wave is the unbalanced voltage equation caused by the fault, and the physical essence is the voltage reverse traveling wave under the unipolar-ground transmission mode. Taking full advantage of the fault information contained in the polar wave voltage traveling wave transient and its unique advantages in characteristic expression, a lightning strike interference identification element for UHVDC line protection based on polar wave voltage is constructed.

2. Identification of Lightning Interference Based on Average Voltage in Short Window

When the lightning strike is not faulty, the polar wave voltage alternates around the zero axis; when the lightning strike is faulty, the faulty pole wave voltage is far away from the zero axis, and the non-faulty pole wave voltage is close to the zero axis. In the short window, the average value of non-fault polar wave voltage of lightning strike is much smaller than the average value of lightning strike fault. Use 800kV as the reference value for normalization, and calculate the average value of the polar wave voltage in the short window. When there is no fault, its mean value should be less than 1, while the mean value of lightning strike fault and common fault should be greater than 1.

为In the present invention, the sampling frequency is 10 kHz, the time window is selected as 5 ms , and the polar wave voltage sampling values are directly used to calculate the mean and normalize. Now define the ratio of the average pole wave voltage under lightning strike fault and lightning strike non-fault to the pole line voltage in steady state operation

for

                             (2)

(2)

为极波电压，

为稳态运行时极线电压；In the above formula,

is the pole wave voltage,

is the pole-to-line voltage during steady-state operation;

沿线分布如图 3所示。由图3及相关阐述可见：在全线范围内，雷击未故障时<1，雷击故障时

>1。为了提高判据裕度，雷击故障、雷击未故障的判据为若，雷击未故障，若

，雷击故障Traversing across the full length of the

The distribution along the line is shown in Figure 3. It can be seen from Figure 3 and related explanations: in the whole line range, when the lightning strike does not fail <1, when lightning strikes fault

>1. In order to improve the criterion margin, the criterion of lightning strike failure and lightning strike non-failure is as follows: , lightning does not fail, if

, lightning fault

Compared with the prior art, the present invention has the following advantages:

1. The sampling frequency of this method is 10kHz, the time window is 5ms, it is not affected by the control system, and the delay protection is at the millisecond level.

2. The method can correctly identify the lightning interference within the entire length of the line.

3. The method has good robustness, strong resistance to transition resistance, is not affected by interference, and has strong practicability. A large number of simulation results show that the invention has good effects.

Description of drawings

Figure 1 is the structural diagram of Yunguang ±800kV DC transmission system, and M in the figure is the protection installation place.

Figure 2 Pole wave waveform diagram, in which t/ms is time/millisecond, u /kV is voltage/kilovolt. (a) is the polar waveform diagram of lightning without fault; (b) is the polar waveform diagram of lightning fault.

Fig. 3 is a distribution diagram of the ratio λ of the pole wave voltage mean value to the pole line voltage in steady state operation in the whole line length range of the present invention.

Detailed ways

The simulation model is shown in Figure 1. The lightning strikes the positive line 100km away from the M terminal, which is a fault. The time window length is 5ms, and the sampling frequency is 10kHz.

(1) According to the DC voltage and DC current measured at the place where the protection is installed, the positive line wave voltage P ₁ ( k ) is obtained as

In the formula, Z _p is the pole wave impedance of the DC transmission line, u ₁ ( k ) is the positive DC voltage, i ₁ ( k ) is the positive DC current, u ₂ ( k ) is the negative DC voltage, and i ₂ ( k ) is the negative DC voltage DC current, k =1, 2, 3.... N , N is the length of the sampling sequence;

(2) According to the formula, calculate the ratio λ of the average value of the polar wave voltage to the steady-state operating polar line voltage

为极波电压，

为稳态运行时极线电压；In the formula,

is the pole wave voltage,

is the pole-to-line voltage during steady-state operation;

=0.8，判别为雷击未故障。(3) The ratio of the mean value of the pole wave voltage to the pole line voltage in steady state operation

=0.8, it is judged that the lightning strike is not faulty.

In the present invention, the simulation experiment shown in Fig. 1 is carried out using PSCAD simulation software to verify the criterion proposed in this paper. When the transition resistance is different, the ratio λ of the average value of the polar wave voltage to the steady-state operating polar line voltage is distributed along the line as shown in Figure 3.

Claims (1)

1. thunder and lightning interference identification method that utilizes the equal sampled value of utmost point popin in the short window is characterized in that carrying out according to the following steps:

(1) according to the protection installation place measure polar curve voltage, polar curve electric current,

Obtain utmost point wave voltage

:

?(j=+,-) (1)

In the formula,

Be the polar wave impedance,

Be polar curve voltage,

Be the polar curve electric current ,+be expressed as electrode line ,-be expressed as negative line, n=1,2,3 .... N, N=50 is sample sequence length;

(2) in short window, directly utilize utmost point wave voltage sampled value to average and normalization, now define lightning fault and the fault not of being struck by lightning under the ratio of utmost point wave voltage average and the polar curve voltage of steady-state operation be

(2)

In the following formula,

Be utmost point wave voltage,

Polar curve voltage during for steady-state operation;

(3) the not examination criterion of fault and lightning fault of being struck by lightning, when

The time the not fault of being struck by lightning, when

The time lightning fault.

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