A method for improving overvoltage suppression characteristics of valve type lightning arrester

Abstract

The present invention discloses a method for improving the overvoltage suppression characteristics of a valve type lightning arrester, comprising: first, calibrating the relationship characteristics between the leakage current of the device and the overvoltage, second, sampling the leakage current at all times to inversely calculate the system overvoltage, and predicting and evaluating characteristic parameters such as the overvoltage peak value and the maximum rate of change, and finally, triggering the series gap of the valve type lightning arrester to make the lightning arrester act in advance after the prediction result meets the set conditions. The present invention accurately and effectively improves the overvoltage suppression characteristics of the valve type lightning arrester, enhances the ability of the lightning arrester to protect the insulation safety of power equipment, and facilitates solving the insulation coordination problem between it and the protected equipment.

Description

Technical Field

[0001] The invention belongs to the field of electric power system electrical equipment, and in particular relates to a method for improving overvoltage suppression characteristics of a valve type lightning arrester. Background Art

[0002] As an effective means of protecting power systems from overvoltage, valve-type lightning arresters are widely used in the insulation protection of power equipment, which is of great significance to ensure the long-term stable and safe operation of power systems. Valve-type lightning arresters are composed of an air gap and a nonlinear resistor in series and installed in a sealed porcelain bottle. When overvoltage invades, the air gap is broken down, and the nonlinear resistor has a very small resistance value, which clamps the overvoltage within a lower amplitude range, thereby protecting the insulation safety of power equipment.

[0003] However, since the series air gap discharge in the valve type arrester is dispersed, it greatly affects its ability to deeply suppress overvoltage, and also causes insulation coordination problems between the arrester and the protected power equipment. At present, the controllable arrester technology proposed by Chinese scholars is to connect part of the valve plate of the conventional arrester in parallel with the controllable element, and directly short-circuit part of the valve plate of the arrester when overvoltage occurs, thereby improving the arrester's overvoltage suppression characteristics. This method requires changing the design structure of the arrester, and the control method is relatively complicated. Summary of the invention

[0004] In order to overcome the defects or shortcomings of the above-mentioned prior art, the present invention provides a method for improving the overvoltage suppression characteristics of a valve type lightning arrester, and fully improves its ability to deeply suppress overvoltage while ensuring reliable and effective operation of the lightning arrester.

[0005] The present invention is achieved by adopting the following technical solutions:

[0006] A method for improving the overvoltage suppression characteristics of a valve type lightning arrester comprises the following steps:

[0007] S100: Use a standard voltage generator to calibrate the relationship between overvoltage and leakage current;

[0008] S200: Constantly sample the system leakage current and reversely calculate the overvoltage based on the calibration results;

[0009] S300: Determine whether the overvoltage amplitude exceeds a set value;

[0010] If the overvoltage amplitude exceeds the set value, the peak value and maximum change rate characteristic parameters of the overvoltage are predicted based on the sampling results within a period of time. Otherwise, go to S200;

[0011] S400: Determine whether the characteristic parameter meets the set value;

[0012] If the characteristic parameter meets the set value, a conduction signal is quickly sent out to cause the gap to break down and the lightning arrester to operate. Otherwise, go to S200.

[0013] A further improvement of the present invention is that the amplitude of the standard voltage generator in S100 is adjustable within the range of 0 to the rated working voltage of the valve type arrester, and the upper limit of the frequency of the generated waveform is not less than 1 MHz;

[0014] The relationship between overvoltage and leakage current is characterized by the ratio of the system output quantity (i.e., the Laplace transform of the leakage current i) to the input quantity (i.e., the Laplace transform of the applied overvoltage u) under zero initial conditions, which is the transfer function of the entire system G(s) = I(s) / U(s).

[0015] A further improvement of the present invention is that in S200, the system leakage current i is sampled at all times, and the system overvoltage u is obtained according to the Laplace transform and the transfer function G(s) of the system.

[0016] A further improvement of the present invention is that the setting value u0 in S300 is selected to be higher than the voltage of the valve type arrester under normal working conditions to avoid false operation of the arrester. u0 is usually 1.1 to 1.2 times the voltage under normal working conditions.

[0017] A further improvement of the present invention is that after determining in S300 that the system overvoltage u is greater than the set value u0 at time t0, the subsequent overvoltage waveform can be accurately predicted at time t1 based on sampling results within a period of time.

[0018] A further improvement of the present invention is that the sampling time required for predicting the overvoltage waveform, i.e., the time length of t1-t0, can be adjusted and does not exceed 1.5 microseconds.

[0019] A further improvement of the present invention is that the method used to predict the overvoltage waveform is nonlinear fitting, and the function form used for fitting is u=ae bt +ce dt , t is time, a, b, c, d are the parameters to be fitted, e is the natural base, or the time series model, grey prediction model or neural network model prediction algorithm is used.

[0020] A further improvement of the present invention is that when the system overvoltage u is less than the set value u0, the sampling rate of the sampling loop is low, the sampling frequency is 5M / s, and when the overvoltage u is greater than the set value u0, the sampling loop enters a high-speed sampling mode, the sampling frequency is 100M / s.

[0021] A further improvement of the present invention is that after the overvoltage waveform is predicted, the overvoltage peak value u needs to be calculated. p and maximum rate of change of overvoltage (du / dt) maxCharacteristic parameters; the selection of characteristic parameters is based on the type of power equipment to be protected. When the protected equipment is a transformer or reactor with windings, the maximum rate of change of overvoltage (du / dt) max Needs to be considered.

[0022] A further improvement of the present invention is that the setting value of the characteristic parameter in S400 is selected in full combination with the insulation tolerance characteristics of the protected power equipment.

[0023] Compared with the prior art, the present invention has at least the following beneficial technical effects:

[0024] 1. The present invention can effectively improve the overvoltage suppression characteristics of the valve type lightning arrester and enhance the overvoltage suppression capability of the lightning arrester by predicting the overvoltage characteristic parameters and triggering the series gap in advance.

[0025] 2. The present invention reduces the discharge dispersion of the series gap by increasing the circuit of the series gap, thereby reducing the complexity of insulation coordination between the valve-type lightning arrester and the protected power equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 A flow chart of a method for improving overvoltage suppression characteristics of a valve type lightning arrester provided by one embodiment of the present invention.

[0027] Figure 2 A working principle diagram for improving the overvoltage suppression characteristics of a valve-type lightning arrester provided in another embodiment of the present invention.

[0028] Figure 3 A structural diagram of a working circuit for improving the overvoltage suppression characteristics of a valve-type lightning arrester provided in another embodiment of the present invention. DETAILED DESCRIPTION

[0029] The following is combined with Figures 1 to 3 The technical scheme of the present invention is described in detail with the embodiments, but is not intended to limit the present invention.

[0030] In one embodiment, if Figure 1 As shown, a PT turn-to-turn short circuit online detection method based on Lissajous figures of the present invention comprises the following steps:

[0031] S100: Use a standard voltage generator to calibrate the relationship between overvoltage and leakage current;

[0032] S200: Constantly sample the system leakage current and reversely calculate the overvoltage based on the calibration results;

[0033] S300: Determine whether the overvoltage amplitude exceeds a set value;

[0034] S400: If the overvoltage amplitude exceeds the set value, the peak value, maximum change rate and other characteristic parameters of the overvoltage are predicted based on the sampling results within a period of time. Otherwise, go to S200;

[0035] S500: Determine whether the characteristic parameter meets the set value;

[0036] S600: If the characteristic parameter meets the set value, a conduction signal is quickly sent out to cause the gap to break down and the arrester to operate. Otherwise, go to S200.

[0037] In another embodiment, if Figure 2 As shown, when the valve type lightning arrester is subjected to overvoltage intrusion without adopting the technical solution of the present invention, when the overvoltage waveform intersects with the inherent volt-second characteristic curve of the series gap, the series gap is broken down at this moment (i.e., moment t3), thereby limiting the overvoltage, and the maximum overvoltage amplitude suffered by the protected power equipment is u3; after adopting the technical solution of the present invention, the system predicts the overvoltage waveform based on the data of the sampling stage, triggers the series gap to be turned on in advance (i.e., moment t2), so that the maximum overvoltage amplitude suffered by the protected power equipment is reduced from u3 to u2, thereby improving the overvoltage suppression characteristics of the lightning arrester.

[0038] In this embodiment, the key technology is to accurately predict the overvoltage waveform based on the sampled data. The method used to predict the overvoltage waveform is nonlinear fitting. The recommended fitting function is u=ae. bt +ce dt , t is time, a, b, c, d are parameters to be fitted respectively, e is the natural base, and prediction algorithms such as time series model, grey prediction model and neural network model can also be used. The corresponding model should be selected in combination with the degree of fit and the physical process of overvoltage.

[0039] It should be understood that the present technical solution will basically not cause misoperation of the arrester, because the setting value u0 is selected to be higher than the voltage of the valve-type arrester under normal working conditions, which fully avoids misoperation of the arrester. If misoperation occurs frequently, the value of u0 can continue to be increased, but it will affect the improvement effect of the arrester in suppressing overvoltage; secondly, the present solution will not cause the arrester to refuse to operate. When the hardware circuit or model fails to accurately predict the occurrence of overvoltage or other uncontrollable factors, and fails to trigger the series gap to conduct in time, then as the overvoltage amplitude increases, the arrester will operate when the overvoltage waveform intersects with the inherent volt-second characteristic of the series gap, which is equivalent to the effect when the present technical solution is not adopted.

[0040] In another embodiment, if Figure 3As shown, the working circuit for improving the overvoltage suppression characteristics of the valve-type lightning arrester includes a nonlinear resistor (1), a series gap (2), a measuring coil (3), a sampling circuit (4), a signal processing control circuit (5) and a trigger circuit (6). The series gap electrode contains an ignition needle. After a high-voltage pulse signal is applied to the ignition needle, the ignition needle discharges plasma to the electrode, thereby greatly reducing the breakdown voltage of the gap, ensuring that the lightning arrester can act in advance according to the trigger signal; the resolution of the measuring coil should be less than 10 microamperes; the sampling rate of the sampling circuit is programmable, and the maximum sampling rate is not less than 100M / s; the signal processing control circuit is a field programmable gate array (FPGA) module, which has the ability to process signals at high speed; the trigger circuit and the signal processing control circuit are isolated by an optical coupler to avoid introducing high voltage into the signal processing control circuit.

[0041] The above description is only a preferred embodiment of the present invention and should not be understood as limiting the scope of the present invention. It should be pointed out that a person skilled in the art can make several modifications and improvements without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A method for improving the overvoltage suppression characteristics of a valve type lightning arrester, characterized in that: The following steps are involved: S100: Use a standard voltage generator to calibrate the relationship between overvoltage and leakage current; the amplitude of the standard voltage generator is adjustable within the range of 0 to the rated working voltage of the valve-type arrester, and the upper limit of the generated waveform frequency is not less than 1MHz; the relationship between overvoltage and leakage current is the ratio of the Laplace transform of the system output quantity, i.e., the leakage current i, to the Laplace transform of the input quantity, i.e., the applied overvoltage u, under zero initial conditions, which is the transfer function of the entire system G(s)=I(s) / U(s); S200: sampling the system leakage current i at all times, and obtaining the system overvoltage u according to Laplace transform and the system transfer function G(s); S300: Determine whether the overvoltage amplitude exceeds a set value; If the overvoltage amplitude exceeds the set value, the peak value and maximum change rate characteristic parameters of the overvoltage are predicted based on the sampling results within a period of time. Otherwise, go to S200; The setting value u0 is selected to be higher than the voltage of the valve type arrester under normal working conditions to avoid malfunction of the arrester. u0 is usually 1.1 to 1.2 times the voltage under normal working conditions. After judging that the system overvoltage u is greater than the set value u0 at time t0, the subsequent overvoltage waveform can be accurately predicted at time t1 based on the sampling results within a period of time; S4 00: Determine whether the characteristic parameters meet the set values; If the characteristic parameter meets the set value, a conduction signal is quickly sent out to cause the gap to break down and the lightning arrester to operate. Otherwise, go to S200.

2. A method for improving the overvoltage suppression characteristics of a valve type lightning arrester according to claim 1, characterized in that: The sampling time required for predicting the overvoltage waveform, ie, the time length t1-t0, can be adjusted and does not exceed 1.5 microseconds.

3. A method for improving the overvoltage suppression characteristics of a valve type lightning arrester according to claim 2, characterized in that: The method used to predict the overvoltage waveform is nonlinear fitting, and the function form used for fitting is u=ae bt +ce dt , t is time, a, b, c, d are the parameters to be fitted, e is the natural base, or the time series model, grey prediction model or neural network model prediction algorithm is used.

4. A method for improving the overvoltage suppression characteristics of a valve type lightning arrester according to claim 3, characterized in that: When the system overvoltage u is less than the set value u0, the sampling rate of the sampling loop is low, and the sampling frequency is 5M / s. When the overvoltage u is greater than the set value u0, the sampling loop enters the high-speed sampling mode, and the sampling frequency is 100M / s.

5. A method for improving the overvoltage suppression characteristics of a valve type lightning arrester according to claim 4, characterized in that: After predicting the overvoltage waveform, it is necessary to calculate the overvoltage peak value u p and maximum rate of change of overvoltage (du / dt) max Characteristic parameters; the selection of characteristic parameters is based on the type of power equipment to be protected. When the protected equipment is a transformer or reactor with windings, the maximum rate of change of overvoltage (du / dt) max Needs to be considered.

6. A method for improving the overvoltage suppression characteristics of a valve type arrester according to claim 5, characterized in that: The setting value of the characteristic parameter in S400 is selected in full consideration of the insulation tolerance characteristics of the protected power equipment.

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