Measurement and protection method and circuit for power frequency withstand voltage test

Abstract

The invention relates to a measurement and protection method and circuit for a power frequency withstand voltage test, and belongs to the technical field of power frequency withstand voltage test; the method comprises step S1, obtaining a voltage value U1 on a low voltage side of a test transformer and a leakage current I2 on a high voltage side; step S2, calculating a voltage value U actually borne by a test product; step S3, calculating an electrical gap withstand voltage value Uf; step S4, adjusting the electrical gap withstand voltage value to Uf; the circuit comprises a voltage sensor module Q1 arranged on a low voltage side of a test transformer T2, a current sensor module Q2 and an adjustable electrical gap F1 arranged on a high voltage side of the test transformer T2, a first proportional operation module LJ1, a second proportional operation module LJ2, a third vector sum operation module LJ3, and a fourth proportional operation module LJ4; the protection of test equipment and test products is achieved, and accidents are avoided.

Description

Technical Field

[0001] The invention relates to a measurement and protection method and a circuit for a power frequency withstand voltage test, belonging to the technical field of power frequency withstand voltage test. Background Art

[0002] AC withstand voltage test is the most direct method to identify the insulation strength of electrical equipment. It is of decisive significance for judging whether electrical equipment can be put into operation. It is also an important means to ensure the insulation level of equipment and avoid insulation accidents. AC withstand voltage test can fully reflect the actual situation of electrical equipment when it is running under AC voltage, and can effectively find insulation defects. When testing AC withstand voltage of distribution network electrical equipment, the test product is basically capacitive. The capacitive current of the test transformer under capacitive load will produce a voltage drop on the leakage reactance of the test transformer. At this time, if the voltage is not directly measured at both ends of the tested equipment, the measured value of the low-voltage side voltage of the test transformer is multiplied by the transformation ratio of the test transformer to convert it into the high-voltage side voltage. The output voltage of the test transformer will be higher than the voltage borne by the test product. This is the "capacitance rise phenomenon" in the withstand voltage test. It will make the voltage applied to the distribution network electrical equipment higher than the specified voltage, causing irreparable damage to the insulation strength of the electrical equipment.

[0003] Simplified circuit for withstand voltage test of distribution network electrical equipment Figure 1 As shown in the figure, in the test circuit, R is the DC resistance of the test transformer winding, L is the leakage inductance of the test transformer, C is the capacitance of the distribution network electrical equipment, and Us is the potential of the high-voltage winding of the test transformer. In this way, the entire test circuit forms an RCL series connection, and the voltage phases on C and L are 180 degrees opposite. The phasor diagram is shown in the figure below. Figure 2 As shown, the voltage Uc on the test piece is higher than the power supply potential Us, and the higher part is what we often call "capacitor rise voltage".

[0004] The existing power frequency withstand voltage test circuit diagram is as follows Figure 3 As shown, when this wiring method is used for power frequency withstand voltage test, the voltage of the test product is estimated by multiplying the voltage on the low voltage side of the test transformer by the voltage ratio. At this time, the calculated voltage is less than the voltage value actually borne by the two ends of the test product. During the power frequency withstand voltage test of the distribution network electrical equipment, a "capacitance rise phenomenon" will occur, causing the test equipment to withstand more than the standard withstand voltage value. This is because the distribution network electrical equipment in the test is generally capacitive. Therefore, when a small power frequency withstand voltage device is under a capacitive load, the capacitive current in the circuit will produce a voltage drop on the leakage reactance of the test transformer. The voltage on the low voltage side of the test transformer is measured, and then multiplied by the transformation ratio of the transformer to convert it into the high voltage side voltage. This is used as the voltage on the test product. The voltage applied to the test equipment will be higher than the output voltage of the test transformer. This is the so-called "capacitance rise phenomenon." Summary of the invention

[0005] The technical problem to be solved by the present invention is: to overcome the deficiencies of the prior art, to provide a measurement and protection method and circuit for a power frequency withstand voltage test, to calculate the actual voltage value borne by the test product, and at the same time to protect the test equipment and the test product to avoid accidents.

[0006] The measurement and protection method of the power frequency withstand voltage test of the present invention, the circuit of the power frequency withstand voltage test includes an autovoltage regulator, a test transformer, and a test product connected in sequence, including the following steps:

[0007] Step S1, obtaining the voltage value U1 on the low voltage side and the leakage current I2 on the high voltage side of the test transformer;

[0008] Step S2, calculate the voltage value U actually borne by the test piece according to formula (1),

[0009] U=K1*U1+I2*X (1);

[0010] Step S3, calculate the electrical clearance withstand voltage value Uf according to formula (2),

[0011] Uf=n*U (2);

[0012] Step S4, adjusting the electrical gap withstand voltage value to Uf;

[0013] Where K1 is the test transformer ratio, X is the inherent leakage reactance of the test transformer, n is the ratio of the electrical clearance withstand voltage value to the voltage value U actually borne by the test object, and the maximum limit of Uf is the rated withstand voltage value of the test transformer.

[0014] K1*U1 is the converted voltage on the high-voltage side of the test transformer, and I2*X is the leakage reactance voltage value of the test transformer; the vector sum of the two is the actual voltage value U that the test object bears. The actual voltage value U that the test object bears is adjusted to avoid overvoltage damage to the test object. At the same time, the electrical gap is set with a maximum limit to prevent overvoltage from damaging the power frequency withstand voltage test device.

[0015] Preferably, n=1.1, so that the electrical gap withstand voltage value is 1.1 times the test sample voltage withstand value, thereby avoiding overvoltage damage to the test sample.

[0016] Preferably, an overcurrent relay and an overvoltage protection indicator light are connected between the autovoltage regulator and the power supply. When breakdown discharge occurs during the power frequency withstand voltage test, the overcurrent relay operates and the overvoltage protection indicator light is always on.

[0017] Prevent overvoltage generated during the power frequency withstand voltage test from damaging the power frequency withstand voltage test equipment and test products.

[0018] The power frequency withstand voltage test measurement and protection circuit of the present invention is used to perform the power frequency withstand voltage test measurement and protection method, including an autovoltage regulator T1, a test transformer T2, and a test product Cx connected in sequence, and also includes a voltage sensor module Q1 set on the low voltage side of the test transformer T2, a current sensor module Q2 and an adjustable electrical gap F1 set on the high voltage side of the test transformer T2, a first proportional operation module LJ1 connected to the voltage sensor module Q1, a second proportional operation module LJ2 connected to the current sensor module Q2, and a first proportional operation module LJ1 and a second proportional operation module LJ2 connected to the first proportional operation module LJ1 and the second proportional operation module Cx. a third vector sum operation module LJ3 connected to the operation module LJ2, a fourth direct proportional operation module LJ4 connected to the third vector sum operation module LJ3 and the adjustable electrical gap F1, the fourth direct proportional operation module LJ4 includes a fourth direct proportional operation unit, a maximum limit storage unit, a comparison unit and an output unit, the output of the fourth direct proportional operation unit is connected to the positive phase input end of the comparison unit, the maximum limit storage unit is connected to the negative phase of the positive phase input end of the comparison unit, the output of the fourth direct proportional operation unit, the maximum limit storage unit and the output end of the comparison unit are connected to the output unit; the adjustable electrical gap F1 is connected in parallel with the test piece Cx.

[0019] The voltage sensor module Q1 is used to obtain the voltage value U1 on the low-voltage side of the test transformer, the current sensor module Q2 is used to obtain the leakage current I2 on the high-voltage side, the first proportional operation module LJ1 is used to calculate the voltage on the high-voltage side of the test transformer T2, the second proportional operation module LJ2 is used to calculate the leakage reactance voltage value of the test transformer T2, the third vector sum operation module LJ3 is used to calculate the voltage value U actually borne by the test piece Cx, and the fourth proportional operation module LJ4 is used to calculate the withstand voltage value Uf of the electrical gap F1, and drive the electrical gap F1 plate to move so that the withstand voltage value of the electrical gap F1 is Uf. According to the voltage value U actually borne by the test piece Cx, the electrical gap F1 is adjusted to avoid overvoltage damage to the test piece Cx. The fourth proportional operation module LJ4 sets a maximum limit for the electrical gap F1 to prevent overvoltage from damaging the power frequency withstand voltage test device.

[0020] Preferably, it also includes an overcurrent relay KM1, the first normally closed contact of the overcurrent relay KM1 and the coil are connected in series to the input end of the autovoltage regulator T1, the second normally closed contact of the overcurrent relay KM1 is connected to the neutral end of the autovoltage regulator T1, the normally open contact of the overcurrent relay KM1 is connected to the overcurrent protection indicator light RS, the other end of the normally open contact of the overcurrent relay KM1 is connected to the other end of the first normally closed contact of the overcurrent relay KM1, and the other end of the overcurrent protection indicator light RS is connected to the other end of the second normally closed contact of the overcurrent relay KM1.

[0021] When breakdown discharge occurs in the circuit, the overcurrent relay KM1 operates to disconnect the main circuit to prevent damage to the test equipment; an overcurrent protection indicator light RS is further provided. When the overcurrent relay KM1 operates, the overcurrent protection indicator light RS is always on, indicating that breakdown has occurred in the test circuit.

[0022] Preferably, the power supply is connected to the overcurrent relay KM1 through the main power switch K1 for disconnecting the power supply.

[0023] Preferably, it also includes a digital voltmeter V connected to the third vector sum operation module LJ3, which is used to display the voltage value U actually borne by the test sample Cx, and prompt the voltage value U actually borne by the test sample Cx.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The measuring and protecting method for the power frequency withstand voltage test of the present invention calculates the actual withstand voltage value U of the test object during the power frequency withstand voltage test, adjusts the electrical gap to protect the test object, and avoids the occurrence of accidents.

[0026] The measurement and protection circuit of the power frequency withstand voltage test of the present invention obtains the actual withstand voltage value U of the test piece Cx during the power frequency withstand voltage test, adjusts the withstand voltage value of the electrical gap F1 to follow the change of the actual withstand voltage value U of the test piece Cx, thereby protecting the test piece Cx and avoiding accidents. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a simplified circuit for withstand voltage test of distribution network electrical equipment according to the present invention;

[0028] Figure 2 is the test loop phasor diagram of the present invention;

[0029] Figure 3 This is the circuit diagram of the small power frequency withstand voltage test of the present invention;

[0030] Figure 4 The invention discloses a measurement and protection circuit diagram for the power frequency withstand voltage test. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with the accompanying drawings:

[0032] Embodiment 1 The measurement and protection method of the power frequency withstand voltage test of the present invention, the circuit of the power frequency withstand voltage test includes an autovoltage regulator, a test transformer, and a test product connected in sequence, and includes the following steps:

[0033] Step S1, obtaining the voltage value U1 on the low voltage side and the leakage current I2 on the high voltage side of the test transformer;

[0034] Step S2, calculate the voltage value U actually borne by the test piece according to formula (1),

[0035] U=K1*U1+I2*X (1)

[0036] Step S3, calculate the electrical clearance withstand voltage value Uf according to formula (2),

[0037] Uf=n*U (2)

[0038] Step S4, adjusting the electrical gap withstand voltage value to Uf;

[0039] Where K1 is the test transformer ratio, X is the inherent leakage reactance of the test transformer, n is the ratio of the electrical clearance withstand voltage value to the voltage value U actually borne by the test object, and the maximum limit of Uf is the rated withstand voltage value of the test transformer.

[0040] K1*U1 is the converted voltage on the high-voltage side of the test transformer, and I2*X is the leakage reactance voltage value of the test transformer; the sum of the two is the voltage value U actually borne by the test object. The electrical clearance is adjusted according to the voltage value U actually borne by the test object to avoid overvoltage damage to the test object. The electrical clearance is set with a maximum limit to prevent the generated overvoltage from damaging the power frequency withstand voltage test device.

[0041] Preferably, n=1.1, so that the electrical gap withstand voltage value is 1.1 times the test sample voltage withstand value, thereby preventing the test sample from being damaged by overvoltage.

[0042] Preferably, an overcurrent relay and an overvoltage protection indicator light are connected between the autovoltage regulator and the power supply. When breakdown discharge occurs during the power frequency withstand voltage test, the overcurrent relay operates and the overvoltage protection indicator light is always on.

[0043] Prevent breakdown discharge during the power frequency withstand voltage test from damaging the power frequency withstand voltage test equipment and test products.

[0044] Example 2

[0045] like Figure 4As shown, the measurement and protection circuit of the power frequency withstand voltage test of the present invention is used to perform the measurement and protection method of the power frequency withstand voltage test, including an autovoltage regulator T1, a test transformer T2, and a test product Cx connected in sequence, and also includes a voltage sensor module Q1 set on the low-voltage side of the test transformer T2, a current sensor module Q2 and an adjustable electrical gap F1 set on the high-voltage side of the test transformer T2, a first proportional operation module LJ1 connected to the voltage sensor module Q1, a second proportional operation module LJ2 connected to the current sensor module Q2, and a first proportional operation module LJ1 and a second proportional operation module LJ2 connected to the first proportional operation module LJ1 and the second proportional operation module Cx. The third vector sum operation module LJ3 is connected to the sample operation module LJ2, and the fourth direct proportional operation module LJ4 is connected to the third vector sum operation module LJ3 and the adjustable electrical gap F1. The fourth direct proportional operation module LJ4 includes a fourth direct proportional operation unit, a maximum limit storage unit, a comparison unit and an output unit. The output of the fourth direct proportional operation unit is connected to the positive phase input terminal of the comparison unit, the maximum limit storage unit is connected to the negative phase of the positive phase input terminal of the comparison unit, and the output of the fourth direct proportional operation unit, the maximum limit storage unit and the comparison unit output are connected to the output unit; the adjustable electrical gap F1 is connected in parallel with the test piece Cx.

[0046] The voltage sensor module Q1 is used to obtain the voltage value U1 on the low-voltage side of the test transformer, the current sensor module Q2 is used to obtain the leakage current I2 on the high-voltage side, the first proportional operation module LJ1 is used to calculate the voltage on the high-voltage side of the test transformer T2, the second proportional operation module LJ2 is used to calculate the leakage reactance voltage value of the test transformer T2, the third vector sum operation module LJ3 is used to calculate the voltage value U actually borne by the test product Cx, and the fourth proportional operation module LJ4 is used to calculate the withstand voltage value Uf of the electrical gap F1, and drive the electrical gap F1 plate to move and adjust the withstand voltage value of the electrical gap F1 to Uf. According to the voltage value U actually borne by the test product Cx, the electrical gap F1 is adjusted to avoid overvoltage damage to the test product Cx. The maximum limit value of the electrical gap F1 is set by the fourth proportional operation module LJ4 to prevent the generated overvoltage from damaging the power frequency withstand voltage test device. Here, the maximum limit stored in the maximum limit storage unit is the rated withstand voltage value of the test transformer T2.

[0047] The measurement and protection circuit of the power frequency withstand voltage test described in the present invention also includes an overcurrent relay KM1, a first normally closed contact of the overcurrent relay KM1 and a coil are connected in series to an input end of the autovoltage regulator T1, a second normally closed contact of the overcurrent relay KM1 is connected to a neutral end of the autovoltage regulator T1, a normally open contact of the overcurrent relay KM1 is connected to an overcurrent protection indicator light RS, the other end of the normally open contact of the overcurrent relay KM1 is connected to the other end of the first normally closed contact of the overcurrent relay KM1, and the other end of the overcurrent protection indicator light RS is connected to the other end of the second normally closed contact of the overcurrent relay KM1.

[0048] When breakdown discharge occurs in the circuit, the overcurrent relay KM1 operates to disconnect the main circuit to prevent damage to the test device; an overcurrent protection indicator light RS is further provided. When the overcurrent relay KM1 operates, the overcurrent protection indicator light RS is always on, indicating that breakdown has occurred in the test circuit.

[0049] The power supply is connected to the overcurrent relay KM1 through the main power switch K1 to cut off the power supply.

[0050] The measurement and protection circuit of the power frequency withstand voltage test of the present invention further includes a digital voltmeter V connected to the third vector and operation module LJ3, which is used to display the voltage value U actually borne by the test sample Cx, and prompt the voltage value U actually borne by the test sample Cx.

[0051] The working principle of the protection circuit of the power frequency withstand voltage test of the present invention is as follows:

[0052] The voltage sensor module Q1 obtains the voltage value U1 on the low-voltage side of the test transformer, the current sensor module Q2 obtains the leakage current I2 on the high-voltage side, the first proportional operation module LJ1 calculates the voltage on the high-voltage side of the test transformer T2, the second proportional operation module LJ2 calculates the leakage reactance voltage value of the test transformer T2, the third vector sum operation module LJ3 calculates the voltage value U actually borne by the test piece Cx, the fourth proportional operation module LJ4 calculates the withstand voltage value Uf of the electrical gap F1, and drives the electrical gap F1 plate to move to adjust the withstand voltage value of the electrical gap F1 to Uf. According to the voltage value U actually borne by the test piece Cx, the electrical gap F1 is adjusted to avoid overvoltage damage to the test piece Cx. The fourth proportional operation module LJ4 sets a maximum limit for the electrical gap F1 to prevent the generated overvoltage from damaging the power frequency withstand voltage test device.

Claims

1. A measurement and protection method for a power frequency withstand voltage test, wherein the circuit of the power frequency withstand voltage test comprises an autovoltage regulator, a test transformer, and a test product connected in sequence, and is characterized in that: The steps include: Step S1, obtaining the voltage value U1 on the low voltage side and the leakage current I2 on the high voltage side of the test transformer; Step S2: Calculate the actual voltage value U that the test sample is subjected to according to formula (1). U = K1*U1+I2*X (1); Step S3, calculate the electrical clearance withstand voltage value Uf according to formula (2), Uf = n*U (2); Step S4, adjusting the electrical gap withstand voltage value to Uf; Where K1 is the test transformer ratio, X is the inherent leakage reactance of the test transformer, n is the ratio of the electrical clearance withstand voltage value to the voltage value U actually borne by the test object, and the maximum limit of Uf is the rated withstand voltage value of the test transformer.

2. The measurement and protection method for power frequency withstand voltage test according to claim 1 is characterized in that: n＝1 .1。 3. The measurement and protection method for power frequency withstand voltage test according to claim 2 is characterized in that: An overcurrent relay and an overvoltage protection indicator light are connected between the autovoltage regulator and the power supply. When a breakdown discharge occurs during the power frequency withstand voltage test, the overcurrent relay is activated and the overvoltage protection indicator light is always on.

4. A power frequency withstand voltage test measurement and protection circuit, used to perform the power frequency withstand voltage test measurement and protection method according to any one of claims 1 to 3, comprising an autovoltage regulator T1, a test transformer T2, and a test product Cx connected in sequence, characterized in that: It also includes a voltage sensor module Q1 set on the low-voltage side of the test transformer T2, a current sensor module Q2 and an adjustable electrical gap F1 set on the high-voltage side of the test transformer T2, a first proportional operation module LJ1 connected to the voltage sensor module Q1, a second proportional operation module LJ2 connected to the current sensor module Q2, a third vector sum operation module LJ3 connected to the first proportional operation module LJ1 and the second proportional operation module LJ2, and a fourth proportional operation module LJ4 connected to the third vector sum operation module LJ3 and the adjustable electrical gap F1. The fourth proportional operation module LJ4 includes a fourth proportional operation unit, a maximum limit storage unit, a comparison unit and an output unit. The output of the fourth proportional operation unit is connected to the positive phase input end of the comparison unit, the maximum limit storage unit is connected to the inverse phase of the positive phase input end of the comparison unit, and the output of the fourth proportional operation unit, the maximum limit storage unit, and the output end of the comparison unit are connected to the output unit; the adjustable electrical gap F1 is connected in parallel with the test product Cx; The voltage sensor module Q1 is used to obtain the voltage value U1 on the low-voltage side of the test transformer T2, the current sensor module Q2 is used to obtain the leakage current I2 on the high-voltage side of the test transformer T2, the first proportional operation module LJ1 is used to calculate the voltage on the high-voltage side of the test transformer T2, the second proportional operation module LJ2 is used to calculate the leakage reactance voltage value of the test transformer T2, the third vector sum operation module LJ3 is used to calculate the voltage value U actually borne by the test piece Cx, and the fourth proportional operation module LJ4 is used to calculate the withstand voltage value Uf of the electrical gap F1, drive the electrical gap F1 plate to move, so that the withstand voltage value of the electrical gap F1 is Uf; according to the voltage value U actually borne by the test piece Cx, the electrical gap F1 is adjusted to avoid overvoltage damage to the test piece Cx; the maximum limit of the electrical gap F1 is set by the fourth proportional operation module LJ4 to prevent overvoltage damage to the power frequency withstand voltage test device.

5. The measurement and protection circuit for power frequency withstand voltage test according to claim 4, characterized in that: It also includes an overcurrent relay KM1, a first normally closed contact of the overcurrent relay KM1 and a coil connected in series to an input end of the autovoltage regulator T1, a second normally closed contact of the overcurrent relay KM1 is connected to a neutral end of the autovoltage regulator T1, a normally open contact of the overcurrent relay KM1 is connected to an overvoltage protection indicator light RS, the other end of the normally open contact of the overcurrent relay KM1 is connected to the other end of the first normally closed contact of the overcurrent relay KM1, and the other end of the overvoltage protection indicator light RS is connected to the other end of the second normally closed contact of the overcurrent relay KM1.

6. The measurement and protection circuit for power frequency withstand voltage test according to claim 5, characterized in that: The power supply is connected to the overcurrent relay KM1 through the main power switch K1.

7. The measurement and protection circuit for power frequency withstand voltage test according to claim 4, characterized in that: It also includes a digital voltmeter V connected to the third vector and operation module LJ3.

Images