Alternating current excitation type partial discharge detector

Abstract

The utility model relates to the field of electric power, and discloses an AC excitation type partial discharge detector, which comprises a frequency converter, an isolation excitation transformer, a high-voltage switch device, an additional resonant inductor, a three-phase cable line transformer bank, a partial discharge sensor and a partial discharge data acquisition and analysis unit. The three-phase cable line transformer bank is formed by connecting a three-phase transformer Y-connection winding and a three-phase cable line, at least one winding of the three-phase transformer is connected or short-circuited, and the other end of the cable line is open-circuited and is not grounded; the frequency converter and the isolation exciting transformer are connected in series with the additional resonant inductor and the neutral point of the Y-connection winding of the three-phase transformer, and the other two phases need to be disconnected from the transformer winding only when a single-phase cable is connected. According to the utility model, transformer and cable line partial discharge detection can be carried out simultaneously, and line transformer group equipment detection time and cost are reduced.

Description

Technical Field

[0001] The utility model relates to the field of electric power, and specifically is an AC excitation type partial discharge detector. Background Art

[0002] Transformer partial discharge detection is generally used for factory testing of high-voltage oil-fired transformers and dry-type transformers. Non-electrical methods such as ultrasonic waves and chromatographic analysis are often used on site.

[0003] With the rapid development of new energy technologies such as wind power and photovoltaics and large-scale industrial enterprises, the connection method of medium and high voltage 35-66kV (cable) line transformer group has become a major connection method. Conventional preventive tests require the cables and transformers to be separated, which requires a large number of electrical isolation and safety measures.

[0004] In addition, since partial discharge detection is generally not used in the pre-test of transformers of 35-66kV and below, and the power grid generally adopts a neutral point non-effective grounding system, the overvoltage level is relatively high.

[0005] Therefore, the current test methods have problems such as poor effectiveness and complex operation. Utility Model Content

[0006] In order to overcome the above-mentioned deficiencies, the present invention provides an AC excitation type partial discharge detector.

[0007] The technical solution adopted by this utility model:

[0008] An AC excitation type partial discharge detector comprises a frequency converter, an isolation excitation transformer, a high voltage switch device, an additional resonant inductor, a three-phase cable line transformer group, a partial discharge sensor and a partial discharge data acquisition and analysis unit.

[0009] The three-phase cable line transformer group consists of a three-phase transformer with Y-connected windings connected to a three-phase cable line. At least one winding of the three-phase transformer is connected in a delta connection or short-circuited, and the other end of the cable line is open and not grounded.

[0010] The inverter and the isolated excitation transformer are connected in series with the additional resonant inductor and the neutral point of the Y-connected winding of the three-phase transformer. When only a single-phase cable is connected, the other two phases need to be disconnected from the transformer winding.

[0011] The high-voltage switching device is connected in series between the connection point between the isolation excitation transformer and the additional resonant inductor and the ground;

[0012] The partial discharge sensor is connected in series between the partial discharge data acquisition and analysis unit and the Y-connected winding of the three-phase transformer, and the current sensor and the voltage sensor are directly connected to the connection point and the ground.

[0013] The rated current of the isolation excitation transformer is greater than the test current. The test current refers to the test voltage and the distributed capacitance of the power cable, and a certain margin is left.

[0014] The inverter power is greater than the apparent power of the isolation excitation transformer, with a certain margin.

[0015] The output voltage of the isolation excitation transformer is determined by calculating the quality factor Q of the additional resonant inductance and the maximum resonant output voltage, with a certain margin; the input voltage of the isolation excitation transformer is determined according to the inverter and test power supply voltage.

[0016] High-voltage switchgear shall be mechanical switches or power electronic switches, and shall be able to withstand the highest test voltage and maximum impact current, and be closed and grounded at the peak point of the variable frequency AC.

[0017] The partial discharge sensor is three-phase or single-phase, and can adopt current type, such as HFCT high-frequency current sensor, or voltage type, such as coupling capacitor sensor. When using HFCT high-frequency current sensor, the open type is the best.

[0018] Beneficial effects of the utility model:

[0019] The utility model can simultaneously perform partial discharge detection on transformers and cable lines, thereby reducing the detection time and cost of line transformer group equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the principle diagram of the utility model;

[0021] Figure 2 This is the wiring diagram of the utility model. DETAILED DESCRIPTION

[0022] like Figure 1-2 Shown: An AC excitation partial discharge detector includes a frequency converter, an isolation excitation transformer, a high-voltage switching device, an additional resonant inductor, a three-phase cable line transformer group, a partial discharge sensor and a partial discharge data acquisition and analysis unit.

[0023] The three-phase cable line transformer group consists of a three-phase transformer with Y-connected windings connected to a three-phase cable line. At least one winding of the three-phase transformer is connected in a delta connection or short-circuited, and the other end of the cable line is open and not grounded.

[0024] The inverter and the isolated excitation transformer are connected in series with the additional resonant inductor and the neutral point of the Y-connected winding of the three-phase transformer. When only a single-phase cable is connected, the other two phases need to be disconnected from the transformer winding.

[0025] The high-voltage switching device is connected in series between the connection point between the isolation excitation transformer and the additional resonant inductor and the ground;

[0026] The partial discharge sensor is connected in series between the partial discharge data acquisition and analysis unit and the Y-connected winding of the three-phase transformer, and the current sensor and the voltage sensor are directly connected to the connection point and the ground.

[0027] The rated current of the isolation excitation transformer is greater than the test current. The test current refers to the test voltage and the distributed capacitance of the power cable, and a certain margin is left.

[0028] The inverter power is greater than the apparent power of the isolation excitation transformer, with a certain margin.

[0029] The output voltage of the isolation excitation transformer is determined by calculating the quality factor Q of the additional resonant inductance and the maximum resonant output voltage, with a certain margin; the input voltage of the isolation excitation transformer is determined according to the inverter and test power supply voltage.

[0030] High-voltage switchgear shall be mechanical switches or power electronic switches, and shall be able to withstand the highest test voltage and maximum impact current, and be closed and grounded at the peak point of the variable frequency AC.

[0031] The partial discharge sensor is three-phase or single-phase, and can adopt current type, such as HFCT high-frequency current sensor, or voltage type, such as coupling capacitor sensor. When using HFCT high-frequency current sensor, the open type is the best.

[0032] After adjusting the inverter output voltage and frequency to charge the three-phase transformer Y-connected winding and the three-phase cable line to a certain voltage value.

[0033] The inverter and high-voltage switching devices are closed, the connection points of the inverter, isolation excitation transformer and resonant inductor and the ground are short-circuited, the distributed capacitance and additional resonant inductance of the three-phase cable line, and the Y-connected winding of the three-phase transformer under test form LC oscillation, which stimulates partial discharge at the insulation defects.

[0034] The partial discharge sensor and partial discharge data acquisition and analysis unit collect high-frequency signals in the loop for analysis, and simultaneously detect partial discharges in transformers and cable lines.

[0035] Example:

[0036] Conduct AC withstand voltage or partial discharge tests on 4MW / 35kV wind turbine step-up transformers and collector cable line transformer groups.

[0037] Step-up dry-type transformer with a capacity of 5MVA, voltage of 37.5 / 3.3kV, connection group Y△-11, short-circuit impedance 7%; power cable with cross-linked polyethylene insulation and aluminum core, model YJLV 22 -26 / 25-3*70mm 2 , length 1000m.

[0038] YJLV 22-26 / 25-3*70mm 2 The distributed capacitance of power cable is about 125nF (single core).

[0039] Calculate transformer short-circuit impedance (single-phase (UN√3, SN÷3))

[0040]

[0041] Ignoring the resistance in the short-circuit impedance, the inductance value of the short-circuit impedance is approximately

[0042]

[0043] According to the frequency close to 50 / 60Hz, add the resonant inductance value

[0044]

[0045] Since the additional resonant inductance is much larger than the transformer short-circuit impedance, the oscillating wave voltage applied to the transformer winding is approximately equal to the voltage on the cable, which can effectively stimulate partial discharge at the insulation defects.

[0046] Check the factory test withstand voltage value of 35kV transformer. For dry-type transformer, 60kV and 80% voltage are 48.0kV respectively. The applied voltage for partial discharge of 35kV cable can be 1.7U0, and U0 is 26kV relative to the cable ground, i.e., AC effective value is 44.2kV, which is about 2.08 times of the operating phase voltage (1.05UN / √3). It can stimulate partial discharge of insulation defects and does not exceed the withstand voltage value of cable and dry-type transformer.

[0047] Taking into account the handover withstand voltage test, the maximum output voltage of the additional resonant inductor is U Max Take it as 52kV.

[0048] The additional resonant inductor rated current is based on the cable-to-ground distributed capacitance current at a reference oscillation wave of 50 Hz.

[0049] I C =3×2πfC×U Max =3×314×125×10 -9 ×52×10 3 =6.13A

[0050] Assuming the additional resonant inductor quality factor Q is 26, the output voltage of the isolation excitation transformer is

[0051]

[0052] Assuming the test power supply voltage is 380V, the input and output voltages of the inverter and the output voltage of the isolation excitation transformer are both 380V.

[0053] The rated power of the isolation excitation transformer and the inverter should be greater than

[0054] S min =U2×I C =2×6.13=12.3kVA,

[0055] AC test power supply current

[0056]

[0057] In order to reduce the wiring workload, it is recommended to use open HFCT as the partial discharge sensor, but the frequency range should be between 30k-3MH Z Maintain high sensitivity. When using a coupling capacitor voltage sensor, the capacitor withstand voltage must meet the requirements.

[0058] When testing with this method, attention should be paid to the transformer connection group. If there are other △-shaped windings, they can be tested directly. If there are no other △-shaped windings, one of the other Y-shaped windings needs to be short-circuited so that the Y-shaped winding being tested presents a short-circuit impedance.

[0059] When testing with this method, the three phases of the transformer and the three cores of the power cable can be measured simultaneously. If only one (two) phases (cores) need to be measured, the number of sensors can be reduced and the other cable cores can be disconnected, which will not be repeated here.

[0060] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this patent, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An AC excitation partial discharge detector, characterized in that: It includes frequency converter, isolation excitation transformer, high voltage switch device, additional resonant inductor, three-phase cable line transformer group, partial discharge sensor and partial discharge data acquisition and analysis unit; The three-phase cable line transformer group is composed of a three-phase transformer Y-connected winding and a three-phase cable line connected together, at least one winding of the three-phase transformer is connected in a delta connection or short circuit, and the other end of the cable line is open and not grounded; The frequency converter and the isolation excitation transformer are connected in series with the additional resonant inductor and the neutral point of the Y-connected winding of the three-phase transformer. When only a single-phase cable is connected, the other two phases need to be disconnected from the transformer winding. The high-voltage switch device is connected in series between the connection point between the isolation excitation transformer and the additional resonant inductor and the ground; The partial discharge sensor is connected in series between the partial discharge data acquisition and analysis unit and the Y-connected winding of the three-phase transformer, and the current sensor and the voltage sensor are directly connected to the connection point and the ground.

2. The AC excitation partial discharge detector according to claim 1, characterized in that: The rated current of the isolation excitation transformer is greater than the test current. The test current refers to the test voltage and the distributed capacitance of the power cable, and a certain margin is left.

3. The AC excitation partial discharge detector according to claim 1, characterized in that: The power of the frequency converter is greater than the apparent power of the isolation excitation transformer, with a certain margin.

4. The AC excitation partial discharge detector according to claim 1, characterized in that: The output voltage of the isolation excitation transformer is determined by calculating the quality factor Q of the additional resonant inductor and the maximum resonant output voltage, with a certain margin; the input voltage of the isolation excitation transformer is determined according to the inverter and the test power supply voltage.

5. The AC excitation partial discharge detector according to claim 1, characterized in that: The high-voltage switch device is a mechanical switch or a power electronic switch, and can withstand the highest voltage and maximum impact current of the test, and is closed and grounded at the peak point of the variable frequency AC.

6. The AC excitation partial discharge detector according to claim 1, characterized in that: The partial discharge sensor is three-phase or single-phase.

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