CN104035013A - 500 KV electromagnetic voltage transformer alternating-current frequency-doubling withstand voltage test circuit and method - Google Patents

Abstract

The invention discloses a 500 KV electromagnetic voltage transformer alternating-current frequency-doubling withstand voltage test circuit. The 500 KV electromagnetic voltage transformer alternating-current frequency-doubling withstand voltage test circuit comprises a variable-frequency power supply, an excitation transformer and a frequency-doubling withstand voltage circuit; the frequency-doubling withstand voltage circuit comprises a test reactor, a voltage divider, an electromagnetic voltage transformer and a stray capacitor; the voltage divider is formed by a high voltage arm capacitor and a low voltage arm capacitor through series connection; a variable-frequency output end of the variable-frequency power supply is connected onto a primary winding of the excitation transformer; the test reactor and the voltage divider are in parallel connection with two ends of a secondary winding of the excitation transformer respectively after being connected in series; ground connection is formed between the voltage divider and the secondary winding of the excitation transformer; the stray capacitor and a primary winding of the electromagnetic voltage transformer are in parallel connection with the voltage divider; the frequency-doubling withstand voltage circuit and the secondary winding of the excitation transformer form a test resonant circuit. The invention also discloses a test method of the test circuit. According to the 500 KV electromagnetic voltage transformer alternating-current frequency-doubling withstand voltage test circuit and method, the test voltage is applied to the primary winding of the electromagnetic voltage transformer and accordingly the problem that the capacity of the applied voltage from a second winding is insufficient is solved.

Description

A kind of 500kV electromagnetic potential transformer exchanges frequency multiplication withstand voltage test circuit and method

Technical field

The present invention relates to the alternating current withstand voltage test method of electromagnetic potential transformer, particularly for the conventional improvement that exchanges frequency multiplication induced over voltage withstand test system and method for 500kV electromagnetic potential transformer.

Background technology

According to the requirement of existing commissioning test code, electromagnetic potential transformer On-Site Testing has following 2 kinds of methods: the one, and power frequency withstand test (45～65Hz), to a winding head and the tail short circuit, apply over the ground power-frequency voltage, to check the insulation ability to bear of test specimen to Power frequency voltage rising.For the electromagnetic potential transformer of graded insulation, its winding end dielectric level is very low, only has about 5kV, and this makes the outer voltage of a winding when executing withstand test voltage value and moving well below equipment, is difficult to the insulation status of apparatus for checking.The 2nd, induced over voltage withstand test, a both winding end ground connection, makes winding head end method to end induced test voltage in Secondary Winding pressurization.This method both can have been examined the major insulation of electromagnetic potential transformer, and (winding over the ground, insulation between alternate and different electric pressure windings), also the minor insulation (between same winding layers, turn-to-turn and section insulation) that can examine voltage transformer (VT), therefore the electromagnetic potential transformer of graded insulation all adopts induced over voltage withstand test.When induced voltage test, excessive for preventing core sataration and exciting current, the frequency of trial voltage should be greater than rated frequency, generally electromagnetic potential transformer is adopted to frequency multiplication (100～300Hz) induced over voltage withstand test.For the higher PT of electric pressure, the capacity of mutual inductor Secondary Winding cannot meet testing requirements, in this way has certain limitation.

For 500kV electromagnetic potential transformer, because trial voltage is high, and the voltage transformer (VT) of the hot power-carrying limit value of Secondary Winding and low-voltage-grade is more or less the same, utilize the test method of Secondary Winding pressurization can in Secondary Winding, occur very large electric current Secondary Winding being caused to damage.Although the method that can take shunt reactor and multiple secondary windings in series to add, compensativity is difficult to control, once test product generation flashover or puncture, reactor will lose compensating action, be difficult to meet testing requirements.

Summary of the invention

Respond to the problem of withstand voltage Secondary Winding off-capacity in order to solve 500kV PT, patent of the present invention has proposed a kind of withstand voltage test circuit that utilizes the resonance step-up device of configuration current-limiting reactor directly to apply 3 frequency multiplication trial voltages on winding of PT, and it can utilize capacitive divider directly to measure PT single test voltage.The method has well solved the problem that conventional methods brings, and can be good at meeting the frequency multiplication withstand voltage test condition of 500kV and above PT, has verified the insulating property of PT in transport and after installing.

To achieve these goals, the technical scheme that the present invention takes is:

A kind of 500kV electromagnetic potential transformer exchanges frequency multiplication withstand voltage test circuit, it comprises variable-frequency power sources VF, exciting transformer T and frequency multiplication voltage holding circuit, described frequency multiplication voltage holding circuit comprises test reactor L1, the voltage divider being composed in series by high-voltage arm capacitor C 1 and low-voltage arm capacitor C 2, electromagnetic potential transformer PT and the stray capacitance C3 being formed by the earth and test lead equivalence, wherein, the frequency conversion output terminal of variable-frequency power sources VF is connected to the armature winding of exciting transformer T, after described test reactor L1 and voltage divider series connection, be connected to the two ends of the secondary winding of exciting transformer T, and ground connection between the secondary winding of voltage divider and exciting transformer T, a winding of stray capacitance C3 and electromagnetic potential transformer PT is all connected in parallel with voltage divider, the secondary winding of described frequency multiplication voltage holding circuit and exciting transformer T forms test resonant tank.

Described frequency multiplication voltage holding circuit further comprises an over-pressure safety device MOAI, and described over-pressure safety device MOAI is connected to the two ends of the secondary winding of exciting transformer T, and described over-pressure safety device MOAI is lightning arrester or ball gap protective device.

The armature winding of described exciting transformer T is formed by a low pressure winding, and the secondary winding of described exciting transformer T is formed by two high pressure windings in series.

A winding of described electromagnetic potential transformer PT is equivalent to resistance R, inductance L and test product capacitor C 4, and described test product capacitor C 4 is connected in parallel with voltage divider, after described resistance R, inductance L series connection, is connected in parallel with test product capacitor C 4 again.

Described frequency multiplication voltage holding circuit is equivalent to test reactor L1, high-voltage arm capacitor C 1, stray capacitance C3 and test product capacitor C 4, wherein, the two ends that are parallel to the secondary winding of exciting transformer T after described test reactor L1,1 series connection of high-voltage arm capacitor C, described stray capacitance C3 and test product capacitor C 4 are all connected in parallel with high-voltage arm capacitor C 1.

Between described high-voltage arm capacitor C 1 and low-voltage arm capacitor C 2, be connected in the feedback end of variable-frequency power sources VF by a sampled signal line.

Simultaneously, respond to the problem of withstand voltage Secondary Winding off-capacity in order to solve 500kV PT, patent of the present invention has proposed a kind of withstand voltage test method that utilizes the resonance step-up device of configuration current-limiting reactor directly to apply 3 frequency multiplication trial voltages on winding of PT, and it can utilize capacitive divider directly to measure PT single test voltage.The method has well solved the problem that conventional methods brings, and can be good at meeting the frequency multiplication withstand voltage test condition of 500kV and above PT, has verified the insulating property of PT in transport and after installing.

To achieve these goals, the technical scheme that the present invention takes is:

Adopt above-mentioned 500kV electromagnetic potential transformer interchange frequency multiplication withstand voltage test circuit to exchange the method for frequency multiplication withstand voltage test, it comprises the following steps:

Step 1, obtain 500kV electromagnetic potential transformer electric parameter model according to in-site measurement and equipment delivery test data, technical parameter;

The resonant parameter of step 2, definite test resonant tank, it comprises the following steps:

The complete equivalent electrical circuit of step 21, definite test resonant tank:

According to 500kV electromagnetic potential transformer electric parameter model, a winding of electromagnetic potential transformer PT is equivalent to resistance R, inductance L and test product capacitor C 4, with the complete equivalent electrical circuit of test resonant tank, wherein, described test product capacitor C 4 is connected in parallel with voltage divider, after described resistance R, inductance L series connection, be connected in parallel with test product capacitor C 4 again, obtain testing the total capacitance C of resonant tank according to complete equivalent electrical circuit:

$C=C_4+C_3+\frac{C_1*C_2}{C_1+C_2}---\left(1\right)$

Voltage computing formula in this complete equivalent electrical circuit on electromagnetic potential transformer PT is:

$\mathrm{Upt}=U_{C4}=U_s\·\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}---\left(2\right)$

Under certain frequency, Upt/U _sabsolute value

$\left|\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}\right|---\left(3\right)$

While reaching maximal value, formula reach maximal value, Upt is issued to maximal value in this frequency simultaneously, produces resonance potential on test product;

Step 22, complete equivalent electrical circuit is simplified, thereby is formed short form test resonant tank:

Frequency multiplication voltage holding circuit is equivalent to test reactor L1, high-voltage arm capacitor C 1, stray capacitance C3 and test product capacitor C 4 to be simplified, wherein, after described test reactor L1, high-voltage arm capacitor C 1 series connection, be parallel to the two ends of the secondary winding of exciting transformer T, the test loop that described stray capacitance C3 and test product capacitor C 4 are all connected in parallel after simplification with high-voltage arm capacitor C 1 can be equivalent to test product capacitor C, stray capacitance C spuious with after 1 parallel connection of capacitive divider high-voltage arm capacitor C again with test reactor L1 and connect;

Total capacitance C '=C in short form test resonant tank ₃+ C ₄+ C ₁;

The condition of resonance of short form test resonant tank is: ω ²l ₁c '=1, resonance frequency

Calculate the inductance value of test reactor

Under trial voltage, flow through the electric current of reactor by U=2 π fIL ₁calculate, the capacity S of test reactor is determined by S=UI.

Variable-frequency power sources VF chooses

According to resonance frequency, choose the parameter of variable-frequency power sources VF by test PT and test reactor L1 capacity.

Exciting transformer T chooses

The capacity of exciting transformer T can obtain according to the quality factor q of series resonance system.

Obtain the output voltage U of exciting transformer T _output=U _test/ Q

With exciting transformer T capacity S _output=S/Q

Choosing of capacitive divider

The method that voltage measurement adopts capacitive divider directly to measure at high-pressure side, adopts three joint 250kV/3000pF capacitances in series to use as high-voltage arm.

According to above-mentioned theory, determine that 500kV electromagnetism voltage transformer (VT) frequency multiplication withstand voltage test series resonance test device parameter is as follows:

Variable-frequency power sources VF: frequency adjustable extent 20Hz～300Hz, rated output voltage: single-phase 0～400V is adjustable continuously.

Exciting transformer T: rated capacity 450kVA, frequency of operation 20Hz～300Hz, nominal transformation ratio 400V/40kV.

Test reactor L1: adopt 3 oil-immersed electric reactor series connection, oil-immersed electric reactor withstand voltage level 250kV/ separate unit, inductance value 150H/ separate unit.

High-voltage arm capacitor C 1: rated voltage 750kV/1000pF (point three joints, single-unit 250kV/3000pF).

The present invention is compared with conventional methods, and tool has the following advantages: apply trial voltage at winding of mutual inductor, avoided from the problem of Secondary Winding pressurization off-capacity.Trial voltage is measured and is adopted the method directly measured at high-pressure side of capacitive divider, has avoided the error causing due to capacitive rise effect during according to no-load voltage ratio conversion trial voltage from double measurement.Series resonance boosting mode has reduced the output power of test apparatus, and in the time that test product or testing equipment break down, test loop loses condition of resonance at once, and output voltage reduces, and has effectively suppressed fault progression.

Brief description of the drawings

Fig. 1 is the circuit theory diagrams that 500kV electromagnetic potential transformer of the present invention exchanges frequency multiplication withstand voltage test circuit;

Fig. 2 is the complete equivalent electrical circuit of testing resonant tank in Fig. 1;

Fig. 3 is the simplified electrical circuit diagram of Fig. 2.

Embodiment

Below in conjunction with the drawings and specific embodiments, content of the present invention is described in further details.

Embodiment

Please refer to shown in Fig. 1, a kind of 500kV electromagnetic potential transformer exchanges frequency multiplication withstand voltage test circuit, it comprises variable-frequency power sources VF, exciting transformer T and frequency multiplication voltage holding circuit, described frequency multiplication voltage holding circuit comprises test reactor L1, the voltage divider being composed in series by high-voltage arm capacitor C 1 and low-voltage arm capacitor C 2 and stray capacitance C3 and electromagnetic potential transformer PT, wherein, stray capacitance C3 is that the earth and the test lead equivalence that this 500kV electromagnetic potential transformer exchanges in frequency multiplication withstand voltage test circuit forms, and is not in esse device.The frequency conversion output terminal of variable-frequency power sources VF is connected to the armature winding of exciting transformer T, after described test reactor L1 and voltage divider series connection, be connected to the two ends of the secondary winding of exciting transformer T, and ground connection between the secondary winding of voltage divider and exciting transformer T, a winding of stray capacitance C3 and electromagnetic potential transformer PT is all connected in parallel with voltage divider, and the secondary winding of described frequency multiplication voltage holding circuit and exciting transformer T forms test resonant tank.Stray capacitance (or claiming stray capacitance) C3 is not an in esse test element in this hookup, it can think the equivalent capacity being formed by test lead and peripheral conductor and the earth, it is the factor that must consider in test parameters computation process, in this explanation, for the condition of better rendering circuit resonance, introduce this concept of stray capacitance.

The report of SVS550/8 type voltage transformer (VT) winding delivery test and the site test results that provide according to Trench Germany GmbH, obtain winding end ground connection of overseas Chinese hometown current conversion station 500kV voltage transformer pt, high-pressure side electric capacity over the ground; The DC resistance of a winding of voltage transformer pt; The inductance value of a winding; The rated capacity of voltage transformer pt first and second winding and hot power-carrying, as shown in table 1.

Table 1SVS550/8 type voltage transformer (VT) winding parameter

As shown in Figure 2, according to the structure of above-mentioned parameter and Trench Germany GmbH SVS550/8 type voltage transformer (VT), winding of tested voltage transformer pt is equivalent to resistance R, inductance L and the series-parallel combination of capacitor C 4; Series resonance test device is equivalent to test reactor L1 and capacitive divider C1, C2 tandem compound; Complete equivalent electrical circuit also needs to consider the stray capacitance over the ground of test lead and grading ring.

According to resonant circuit theory, impedance when circuit resonance in loop is pure resistance character and reaches minimum value, and theoretical analysis is known: obtain test loop test product total capacitance C by complete equivalent electrical circuit:

$C=C_4+C_3+\frac{C_1*C_2}{C_1+C_2}---\left(4\right)$

Voltage computing formula in equivalent electrical circuit on test product is:

$\mathrm{Upt}=U_{C4}=U_s\·\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}---\left(5\right)$

Under certain frequency ω, Upt/U _sabsolute value:

$\left|\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}\right|---\left(6\right)$

While reaching maximal value, formula reach maximal value, Upt is issued to maximal value in this frequency simultaneously, produces resonance potential on test product.Wherein, C ₁, C ₂, C ₃, C ₄be respectively the capacitance of high-voltage arm capacitor C 1, low-voltage arm capacitor C 2, stray capacitance C3, test product capacitor C 4, U _c4for the magnitude of voltage at test product capacitor C 4 two ends, U _sfor the output voltage values of exciting transformer T secondary winding, the inductance value of test reactor L1 and inductance L is designated as respectively L ₁and L, the resistance of resistance R is designated as R.

Test resonant tank is simplified.

(1) measurement of PT electric capacity (test product capacitor C 4):

Be 150Hz in order to make to test resonance frequency, need test reactor and capacitive divider that coupling is suitable.The be put to the test wiring and around electric conductor coupling influence is larger of site test electric capacity, according to delivery test and field actual measurement results, the electric capacity C of separate unit PT ₄for 330pF is between 350pF.

(2) estimation of stray electrical capacity (stray capacitance C3)

Test lead and conductor coupling capacitance C ₃be about 200pF.

(3) simplification of the high and low pressure arm electric capacity of voltage divider (C1, C2)

Because voltage divider low-voltage arm capacitor C 2 is much larger than high-voltage arm capacitor C 1, therefore low-voltage arm capacitor C 2 and the rear electric capacity of high-voltage arm capacitor C 1 series connection approximate the electric capacity of high-voltage arm capacitor C 1.

(4) PT primary impedance (resistance R and inductance L)

The DC resistance of a winding of PT is about 160 kilo-ohms, according to the excitation curve estimating test voltage of mutual inductor next time the induction reactance R+j ω L of winding be far longer than capacitive reactance 1/j ω C ₄, in hookup, test product Main Current is crossed capacity current, therefore can ignore the inductance L in equivalent electrical circuit, the electric current of resistance R branch road.Can be reduced to circuit shown in Fig. 3 therefore test the complete equivalent electrical circuit of resonant tank in Fig. 2.

Total capacitance C '=C in short form test resonant tank ₃+ C ₄+ C ₁;

The condition of resonance of short form test resonant tank is: ω ²l ₁c '=1, resonance frequency

Calculate the inductance value of test reactor

Determine the capacitance C of the high-voltage arm capacitor C 1 of capacitive divider ₁.In the time that resonance frequency is 150Hz, calculate the inductance value of test reactor

The technical parameter providing according to testing equipment producer, according to the inductance value that calculates test reactor L1 is 450H, calculate the electric current that flows through this test reactor L1 under trial voltage by U=2 π fIL=544kV (544kV is the trial voltage requiring for 500kV PT commissioning test code) calculating, I=1.3A, therefore the capacity S of test reactor is determined by S=UI=707kVA.

Jumbo test reactor L1 like this, is not easy to transport.Therefore, test reactor L1 can be adopted multiple oil immersion epoxy overcoat reactor series connection obtain, in preferred embodiment of the present invention, can choose withstand voltage level 250kV, the oil immersion epoxy overcoat reactor of single-unit inductance value 150H, 3 joint series connection are used and substitute.

Frequency changing power device tuning range 20～300Hz that this programme adopts, the single-phase 0～400V of output voltage, Maximum Power Output 200kW.

The capacity of exciting transformer can obtain according to the quality factor q of series resonance system.The Q value of frequency conversion resonance experiment device is 50～130 at present.The output voltage that obtains thus exciting transformer is:

U _output=U _test/ Q=600/50=12kV (7)

The 600kV is here the ceiling voltage that may be raised in process of the test.In order to allow the design of instrument meet request for utilization, the ceiling voltage that must need by test designs.

Exciting transformer capacity is

S _output=S/Q=707/50=14.1kVA (8)

Become and can select the array mode that no-load voltage ratio is 400/40kV in this method excitation, as shown in Figure 1 (high pressure windings in series is used, short circuit X1 and A2, X2 ground connection).

The method that voltage measurement adopts capacitive divider directly to measure at high-pressure side, adopts three joint 250kV/3000pF capacitances in series to use as high-voltage arm.

The superpotential damage equipment producing when preventing that test product from puncturing or cause testing crew personal injury, should be equiped with lightning arrester or ball gap protective device at transformer high-voltage winding terminal.

According to above-mentioned theory, determine that test unit parameter is as follows:

Variable-frequency power sources VF: frequency adjustable extent 20Hz～300Hz, rated output voltage: single-phase 0～400V is adjustable continuously.

Exciting transformer T: rated capacity 450kVA, frequency of operation 20Hz～300Hz, nominal transformation ratio 400V/40kV.

Test reactor L1: adopt 3 oil-immersed electric reactor series connection, oil-immersed electric reactor withstand voltage level 250kV/ separate unit, inductance value 150H/ separate unit.

High-voltage arm capacitor C 1: rated voltage 750kV/1000pF (point three joints, single-unit 250kV/3000pF).

Carry out test connection by Fig. 1, regulate variable-frequency power sources output power to 2% when process of the test starts, frequency sweep finds resonance frequency, notes avoiding the interference of variable-frequency power sources due to the false tuning-points of 3 subharmonic generations.Find after resonance frequency, increase output power and make output voltage reach testing requirements, the variation of monitoring current and voltage in pressure-resistant time, once occur extremely, reducing at once output power or cutting off the electricity supply.Adopting said method is right ± the high-end converter power transformer feeder line of 800kV overseas Chinese hometown current conversion station side 500kV electromagnetic potential transformer and ± 500kV carried out repeatedly on-the-spot frequency multiplication withstand voltage test from western current conversion station 500kV electromagnetic potential transformer.

The present embodiment applies to:

1, ± 800kV overseas Chinese hometown current conversion station 500kV electromagnetic potential transformer frequency multiplication induced over voltage withstand test;

2, ± 500kV is from the induced over voltage withstand test of western current conversion station 500kV electromagnetic potential transformer frequency multiplication.

Although the present invention describes by specific embodiment, it will be appreciated by those skilled in the art that, without departing from the present invention, can also carry out various conversion and be equal to alternative the present invention.Therefore, the present invention is not limited to disclosed specific embodiment, and should comprise the whole embodiments that fall within the scope of the claims in the present invention.

Claims (7)

1. a 500kV electromagnetic potential transformer exchanges frequency multiplication withstand voltage test circuit, it is characterized in that, it comprises variable-frequency power sources VF, exciting transformer T and frequency multiplication voltage holding circuit, described frequency multiplication voltage holding circuit comprises test reactor L1, the voltage divider being composed in series by high-voltage arm capacitor C 1 and low-voltage arm capacitor C 2, electromagnetic potential transformer PT and the stray capacitance C3 being formed by the earth and test lead equivalence, wherein, the frequency conversion output terminal of variable-frequency power sources VF is connected to the armature winding of exciting transformer T, after described test reactor L1 and voltage divider series connection, be connected to the two ends of the secondary winding of exciting transformer T, and ground connection between the secondary winding of voltage divider and exciting transformer T, a winding of stray capacitance C3 and electromagnetic potential transformer PT is all connected in parallel with voltage divider, the secondary winding of described frequency multiplication voltage holding circuit and exciting transformer T forms test resonant tank.

2. 500kV electromagnetic potential transformer according to claim 1 exchanges frequency multiplication withstand voltage test circuit; it is characterized in that; described frequency multiplication voltage holding circuit further comprises a lightning arrester or ball gap protective device, and described lightning arrester or ball gap protective device are connected to the two ends of the secondary winding of exciting transformer T.

3. 500kV electromagnetic potential transformer according to claim 1 exchanges frequency multiplication withstand voltage test circuit, it is characterized in that, the armature winding of described exciting transformer T is formed by a low pressure winding, and the secondary winding of described exciting transformer T is formed by two high pressure windings in series.

4. exchange frequency multiplication withstand voltage test circuit according to the 500kV electromagnetic potential transformer described in claim 1-3 any one, it is characterized in that, a winding of described electromagnetic potential transformer PT is equivalent to resistance R, inductance L and test product capacitor C 4, described test product capacitor C 4 is connected in parallel with voltage divider, after described resistance R, inductance L series connection, is connected in parallel with test product capacitor C 4 again.

5. 500kV electromagnetic potential transformer according to claim 4 exchanges frequency multiplication withstand voltage test circuit, it is characterized in that, described frequency multiplication voltage holding circuit is equivalent to test reactor L1, high-voltage arm capacitor C 1, stray capacitance C3 and test product capacitor C 4, wherein, the two ends that are parallel to the secondary winding of exciting transformer T after described test reactor L1,1 series connection of high-voltage arm capacitor C, described stray capacitance C3 and test product capacitor C 4 are all connected in parallel with high-voltage arm capacitor C 1.

6. 500kV electromagnetic potential transformer according to claim 1 exchanges frequency multiplication withstand voltage test circuit, it is characterized in that, is connected in the feedback end of variable-frequency power sources VF between described high-voltage arm capacitor C 1 and low-voltage arm capacitor C 2 by a sampled signal line.

7. adopt 500kV electromagnetic potential transformer interchange frequency multiplication withstand voltage test circuit claimed in claim 1 to exchange the method for frequency multiplication withstand voltage test, it is characterized in that, it comprises the following steps:

Step 1, obtain 500kV electromagnetic potential transformer electric parameter model according to in-site measurement and equipment delivery test data, technical parameter;

The resonant parameter of step 2, definite test resonant tank, it comprises the following steps:

The complete equivalent electrical circuit of step 21, definite test resonant tank:

According to 500kV electromagnetic potential transformer electric parameter model, a winding of electromagnetic potential transformer PT is equivalent to resistance R, inductance L and test product capacitor C 4, with the complete equivalent electrical circuit of test resonant tank, wherein, described test product capacitor C 4 is connected in parallel with voltage divider, after described resistance R, inductance L series connection, be connected in parallel with test product capacitor C 4 again, obtain testing the total capacitance C of resonant tank according to complete equivalent electrical circuit:

$C=C_4+C_3+\frac{C_1*C_2}{C_1+C_2}---\left(1\right)$

Voltage computing formula in this complete equivalent electrical circuit on electromagnetic potential transformer PT is:

$\mathrm{Upt}=U_{C4}=U_s\·\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}---\left(2\right)$

Under certain frequency, Upt/U _sabsolute value

$\left|\frac{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}}{\frac{(R+\mathrm{j\ωL})\frac{1}{\mathrm{j\ωC}}}{R+\mathrm{j\ωL}+\frac{1}{\mathrm{j\ωC}}}+\mathrm{j\ω}{L}_1}\right|---\left(3\right)$

While reaching maximal value, formula reach maximal value, Upt is issued to maximal value in this frequency simultaneously, produces resonance potential on test product;

Step 22, complete equivalent electrical circuit is simplified, thereby is formed short form test resonant tank:

Frequency multiplication voltage holding circuit is equivalent to test reactor L1, high-voltage arm capacitor C 1, stray capacitance C3 and test product capacitor C 4 to be simplified, wherein, after described test reactor L1, high-voltage arm capacitor C 1 series connection, be parallel to the two ends of the secondary winding of exciting transformer T, the test loop that described stray capacitance C3 and test product capacitor C 4 are all connected in parallel after simplification with high-voltage arm capacitor C 1 can be equivalent to test product capacitor C, stray capacitance C spuious with after 1 parallel connection of capacitive divider high-voltage arm capacitor C again with test reactor L1 and connect;

Total capacitance C '=C in short form test resonant tank ₃+ C ₄+ C ₁;

The condition of resonance of short form test resonant tank is: ω ²l ₁c '=1, resonance frequency

Calculate the inductance value of test reactor

Under trial voltage, flow through the electric current of reactor by U=2 π fIL ₁calculate, the capacity S of test reactor is determined by S=UI.