Currently, there is an increasing trend both internationally and domestically to replace the traditional oil-filled paper-insulated power cables with XLPE (cross-linked polyethylene) insulated power cables. However, due to the large capacity of the cables under test and limitations of testing equipment, DC withstand voltage tests are still commonly used before commissioning cross-linked cables. Recent research by many international and domestic institutions has shown that DC tests can cause varying degrees of damage to XLPE cables. Some research suggests that the structure of XLPE has the ability to store accumulated unipolar residual charges. If these residual charges are not effectively released after a DC test, the combination of these charges with peak AC voltage upon operation could potentially lead to cable breakdown. Domestic research indicates that during DC withstand voltage testing of cross-linked polyethylene cables, the actual electric field strength in the insulation can be up to 11 times higher than the operating electric field strength due to space charge effects. Even if a cross-linked polyethylene cable passes a DC test without breakdown, it can still suffer significant insulation damage. Moreover, since the distribution of the electric field under applied DC voltage differs from that under operational AC voltage, DC testing cannot accurately simulate the overvoltage conditions experienced by cables in service or effectively identify defects in the cables and their joints or installation techniques.

Therefore, non-DC methods for performing withstand voltage tests on cross-linked cables are gaining attention. Additionally, periodic AC withstand voltage tests are conducted on various large transformers and thermal and hydro generators. These tests require high-capacity equipment, often performed using resonance methods but must be carried out at power frequency or equivalent power frequency conditions. Equivalent power frequency conditions typically use a frequency range of 45-65 Hz, though many testing units require a 30-300 Hz test power supply for AC withstand voltage testing of such equipment. Another type of low-frequency device is the ultra-low frequency (0.1 Hz) withstand voltage tester, which has the disadvantage of difficulty in achieving very high voltages and has not gained widespread acceptance in the industry. Series resonance devices have quickly gained market recognition as they realistically simulate operational voltage application and can rapidly reveal the status of the tested equipment.

Our company's series of series resonance devices are primarily used for variable frequency AC withstand voltage tests on 10kV, 35kV, 66kV, 110kV, and 220kV cross-linked rubber power cables, 66kV, 110kV, and 220kV gas-insulated switchgear (GIS), and power frequency AC withstand voltage tests on hydro and thermal generators or power transformers. The basic principle involves using adjustable (30-300 Hz) series resonance test equipment to resonate with the capacitance of the item under test to generate an AC test voltage. Given the large capacitance of cables, conventional power frequency test transformers are heavy, bulky, and difficult to obtain large working current power supplies on-site, so series resonance AC withstand voltage test equipment is generally used instead. This significantly reduces the required input power capacity, weight, making them easier to use and transport. Early systems used tunable inductance series resonance devices (50 Hz), but suffered from poor automation levels and high noise. Modern systems mostly use variable frequency resonance, offering higher quality factors (Q values), automatic tuning, multiple protections, reduced noise, flexible combinations, and lightweight components.

Scope of Application

1. 35kV/300mm² Cable, 2000m
2. Test Type: AC Withstand Voltage Test
3. Capacitance: ≤0.38μF
4. Test Frequency: 30-300Hz

5. Test Voltage: 52kV

6. 35kV Busbar, Instrument Transformers, Insulators

7. Test Type: AC Withstand Voltage Test
8. Capacitance: ≤0.008μF
9. Test Frequency: 30-300Hz

10. Test Voltage: 85kV

11. 35kV Transformer

12. Test Type: AC Withstand Voltage Test
13. Capacitance: ≤0.02μF
14. Test Frequency: 45-65Hz

15. Test Voltage: 72kV

16. 10kV/400mm² Cable, 3000m

17. Test Type: AC Withstand Voltage Test
18. Capacitance: ≤1.26μF
19. Test Frequency: 30-300Hz
20. Test Voltage: 22kV

Main Performance and Parameters of the System

1. Power Supply Voltage: 380V±10%, 50Hz
2. Rated Capacity: 216KVA
3. Output Voltage: 108KV
4. Output Current: 2A, 4A, 6A
5. Output Voltage Waveform: Sine Wave
6. Waveform Distortion Rate: ≤0.5%
7. Continuous Operation Time: 60 minutes at rated output current
8. Output Frequency Range: 30～300Hz
9. Quality Factor (Q): ≥30
10. System Noise Level: ≤60dB
11. Measurement Accuracy: 1.0 grade
12. Frequency Resolution: 0.01Hz
13. Frequency Instability: ≤0.05%
14. Environmental Conditions:
    • Temperature: -25℃～+55℃
    • Relative Humidity: ≤90%
    • Altitude: ≤2000m
15. Operation Modes: Manual Test/Auto Tuning/Auto Test
16. Display: Large screen display indicating output voltage (RMS) and frequency
17. Parameter Setting: Capable of setting test voltage, time, and frequency range
18. Protection Features: Overvoltage, overcurrent, overheating protection
19. Flashover Protection: In case of flashover, the resonant circuit detunes, power supply stops immediately, and "Test Failed" is displayed with relevant information
20. Data Printing: Various data printing functions available

System Configuration and Specific Parameters

I. Variable Frequency Control Power Supply (20KW, 1 unit)

• a) Specialized variable frequency power supply for high-voltage withstand testing, integrated design, capable of frequency adjustment, voltage regulation, control, and protection.
• b) Rated Output Capacity: 20KW
• c) Power Supply: AC 380V, 50Hz
• d) Output Voltage: Adjustable from 0 to 500V
• e) Voltage Instability: ≤0.05%
• f) Maximum Output Current: 40A
• g) Output Waveform: Sine wave, waveform distortion rate: ≤0.5%
• h) Frequency Adjustment Range: 30～300Hz
• i) Frequency Adjustment Resolution: 0.001Hz
• j) Continuous Operation Time: >1 hour
• k) Noise Level: ≤60dB
• l) High-performance microcomputer controls voltage and frequency adjustments
• m) Equipped with dedicated leads and connectors for interfacing with other devices
• n) Protection: Overvoltage, overcurrent, overheating, discharge protection
• o) Display: Large screen showing output voltage (RMS), frequency, excitation current, excitation voltage, test time, etc.
• p) Parameter Setting: Capable of setting test voltage, time, frequency range, and various data printing functions
• q) Weight: 28Kg

II. Excitation Transformer (20KVA, 1 unit)

• a) Rated Capacity: 20KVA
• b) Input Voltage: 500V
• c) Output Voltage: 1.5KV, 3KV
• d) Operating Frequency Range: 30～300Hz
• e) Continuous Operation Time: >1 hour
• f) Voltage Ratio Measurement Error: <1%
• g) Structure: Dry-type, insulation heat resistance grade H, meets national standards for dry-type transformers; includes static shielding between high and low voltage windings and core, serves as both an excitation transformer and isolation transformer; built-in overvoltage protection to prevent breakdown and counterattack.
• h) Weight: 70Kg

III. High Voltage Reactor (DK-54/27, 4 units)

• a) Rated Capacity: 216KVA
• b) Rated Voltage: 27KV
• c) Rated Current: 2A
• d) Quality Factor (Q): Q≥30
• e) Structure: Dry-type
• f) Weight: 48Kg/unit
• g) Continuous Operation Time: ≥1 hour

IV. Capacitive Voltage Divider (TRF-110/0.002, 1 unit)

• a) Rated Voltage: 110KV
• b) Operating Frequency: 30～300Hz
• c) Voltage Division Ratio: 1000:1
• d) Voltage Division Ratio Error: ≤1%
• e) Measurement Accuracy: RMS 1.0 grade
• f) Dielectric Loss: tgδ≤0.5%
• g) Weight: 10Kg
• h) Consistent dielectric structure for high and low voltage arms, small temperature coefficient, minimal angular displacement, constant division ratio within 30-300Hz range