220kV Substation Cable AC Withstand Voltage Test Case Using Series Resonance System

In modern power transmission systems, 220kV high-voltage cables are widely used in urban substations and long-distance power delivery networks. Before commissioning, these cables must undergo strict AC withstand voltage testing to ensure insulation reliability and operational safety.

In this project, a utility company carried out on-site testing of newly installed 220kV XLPE power cables in a regional substation using a variable frequency series resonance test system.

The main challenges of this field test included:

• Large cable capacitance requiring high reactive power compensation
• Limited on-site power supply capacity
• Strict safety requirements for high-voltage testing
• Need for stable sinusoidal voltage waveform

Traditional test transformers were not suitable due to excessive power demand and bulky structure.

A variable frequency series resonance test system was selected for this project.

The system operates by tuning the frequency so that the inductive reactor resonates with the capacitive load of the cable system, allowing high voltage generation with minimal power input.

Key advantages in this case:

• Reduced power demand (resonant operation)
• Lightweight and portable configuration for field use
• Stable voltage output with low harmonic distortion
• Automatic resonance frequency tracking

The test system was connected with:

• Variable frequency power supply
• Excitation transformer
• High voltage reactor
• Capacitive voltage divider
• 220kV XLPE cable system

Proper grounding and safety barriers were installed before energizing.

The system performed automatic frequency scanning in the range of 20Hz–300Hz to locate the resonance point of the cable system.

Once resonance was detected, the system automatically locked the optimal frequency and stabilized the output waveform.

The voltage was gradually increased to the required withstand level while continuously monitoring:

• Voltage stability
• Current variation
• Insulation condition of the cable system

After successful testing:

• Voltage was reduced to zero
• System was shut down safely
• Cable was fully discharged before disconnection

The 220kV cable passed the AC withstand voltage test successfully. Key observations:

• Stable sinusoidal waveform throughout test
• No abnormal discharge or breakdown detected
• High measurement stability during full voltage hold period
• Safe operation under limited power supply conditions

• ✔ High efficiency in large-capacitance cable testing
• ✔ Reduced dependency on heavy power sources
• ✔ Safe operation even under insulation stress conditions
• ✔ Portable design suitable for field substation environment
• ✔ Excellent waveform quality (<1% distortion typical system performance)

This 220kV substation cable test demonstrates that variable frequency series resonance technology is an ideal solution for modern high-voltage field testing. It significantly improves efficiency, safety, and portability compared with traditional AC test systems.

With increasing power grid expansion and underground cable applications, this method is becoming the preferred solution for high-voltage commissioning projects.