Cable AC withstand voltage oscillation wave partial discharge testing system

At present, the management of power cable maintenance is mainly based on the items and testing cycles specified in the "Regulations for Handover and Preventive Testing of Power Equipment", and insulation performance tests are conducted regularly under power outage conditions. The frequency conversion series resonance test has become a widely used testing method in China due to its testing conditions being close to the operating conditions of the cable.

However, extensive experiments and experience have shown that the series resonance withstand voltage test cannot quantitatively evaluate the overall insulation state of the cable, and some high-voltage cables that have passed the series resonance withstand voltage test still experience discharge breakdown in the short term. After long-term research, experimentation, and practice on high-voltage cables, it is believed that partial discharge is a precursor to cable insulation faults, and effective detection of partial discharge is an important way to improve the level of cable condition maintenance.

The oscillation wave cable partial discharge diagnosis and positioning system (OWTS system for short) is a new method for "condition maintenance" of power cables. But this method first applies a direct current voltage to the XLPE cable, and uses the partial discharge under the condition of damping oscillation waves to diagnose and locate it; The DC withstand voltage test of XLPE cables is prone to charge accumulation, which can cause hidden damage to the cables and also generate false partial discharge signals. The use of this method is worth further exploration. Therefore, we have developed an AC attenuation damping oscillation wave partial discharge testing device, which uses an AC high voltage source. On the AC variable frequency series resonant withstand voltage device, a peak synchronization signal is added to stop the power output of the series resonant circuit at the peak, and at the same time, the high-voltage electronic switch is closed to form oscillation wave damping oscillation for cable partial discharge testing. It can reliably detect weak insulation defects in cables and cable joints, and accurately locate them. The entire system equipment is shown in the diagram. Depending on the customized content and batch by the user, there may be some changes in the appearance of the product.

This device can perform cable partial discharge measurement and positioning under damping oscillation wave conditions on site, as well as on-site cable handover and preventive series variable frequency resonant AC withstand voltage test according to current standards (regulations). It can be used for both purposes, greatly improving equipment efficiency.

Cable AC withstand voltage oscillation wave partial discharge testing system Performance and Characteristics

1) The method of using AC series resonant boost and oscillation wave to test partial discharge is combined with the equipment, and one set of equipment can complete both partial discharge test and AC withstand voltage test, making it a dual-use device. The communication withstand voltage test complies with existing regulations.

2) Suitable for handover testing of new cables (before commissioning) and preventive testing of old cables (after power outage).

3) Follow the IEC60270 standard to measure the local discharge of cables.

4) Measure the distance of cable discharge points.

5) Measure the position and total distance of cable joints.

6) The variable frequency host can automatically boost the voltage according to the relevant regulations of State Grid, and the laptop system can automatically collect data, which is simple and convenient.

7) The combination of hardware and software anti-interference technology can effectively remove external interference.

8) The software expert system displays parameters such as partial discharge waveform, discharge amount, and test voltage, and has functions such as real-time saving of test data, generation of test reports, and printing.

Cable AC withstand voltage oscillation wave partial discharge testing system Main technical parameters

Sample capacitance: ≤ 0.4uF

Maximum test voltage: AC 55kV

Damping oscillation wave frequency range: 30-300Hz

Frequency range for frequency conversion series resonance withstand voltage test: 30-300Hz

Partial discharge testing range: 10pC~20nC

Partial discharge positioning accuracy: 1%

Applicable cable specifications: voltage level of 35kV and below, flexible support for cables within 500m, 1000m, and 3000m (cross-section within 300mm2)

Components of the equipment:

1. High voltage cable partial discharge testing system software (laptop)

2. Variable frequency host (customized according to different capacities)

1) Output power: ≤ 15KW

2) Output frequency: 30Hz-300Hz

3) Frequency resolution: 0.1Hz

4) Input power supply: AC220V ± 10% or AC380V

3. Resonant reactor (customized according to different capacities)

1) Inductance: ≤ 9.8H

2) Working frequency: 30Hz-300Hz

3) Maximum test voltage: AC 28KV

4) Maximum test current: 8A

4. Specialized partial discharge data filtering and acquisition device

1) Sampling frequency: 125MHz

2) Storage depth: 64M

3) Software: Expert Diagnostic System

5. Partial discharge calibrator (50pC, 100pC, 200pC, 500pC, 1nC, 2nC)

6. Excitation transformer and oscillation wave generator