High voltage testers for high voltage cables ensure the reliability, safety and longevity of transmission and distribution systems. Various methods are used to assess insulation integrity, detect defects and verify performance under operating conditions. Below is a detailed breakdown of the main HV cable testing techniques.

1. Types of High Voltage Cable Tests

Tests can be categorized into factory tests (pre-commissioning), field tests (after installation), and maintenance tests (periodic checks).

A. Factory Acceptance Tests (FAT)

Conducted by manufacturers before delivery.

• Routine Tests (Mandatory for every cable):

• Insulation Resistance Test (Megger Test)

• Partial Discharge (PD) Test

• High Voltage DC/AC Withstand Test

• Type Tests (Sample-based, for design validation):

• Impulse Voltage Test

• Thermal Cycling Test

B. On-Site Field Tests (After Installation)

• Insulation Resistance Measurement

• DC Hi-Pot Test (For XLPE & PILC Cables)

• VLF (Very Low Frequency) AC Test

• Tan Delta (Dissipation Factor) Test

• Partial Discharge (PD) Measurement

• Sheath Integrity Test (For Metallic Sheathed Cables)

C. Condition Monitoring & Diagnostic Tests

• Tan Delta & Frequency Domain Spectroscopy (FDS)

• Time Domain Reflectometry (TDR) for Fault Location

• Infrared Thermography (Hotspot Detection)

• Oil/Polymer Analysis (For Fluid-Filled Cables)

2. Detailed High Voltage Cable Testing Methods

1. Insulation Resistance Test (Megger Test)

• Purpose: Measures insulation quality (megohmmeter applies 500V–10kV DC).

• Standard: IEC 60243, IEEE 400

• Procedure:

1. Disconnect cable from system.

2. Apply DC voltage (e.g., 5 kV for 1 min).

3. Measure leakage current → Calculate insulation resistance (IR = V/I).

• Acceptance Criteria:

• XLPE Cables: > 1000 MΩ/km

• PILC Cables: > 100 MΩ/km

2. DC High Potential (Hi-Pot) Test

• Purpose: Detects insulation weaknesses by applying high DC voltage.

• Standard: IEEE 400.1 (For XLPE Cables)

• Test Voltage:

• New Cables: 2–3 × U₀ (e.g., 22 kV for 11 kV rated cable).

• After Repair: 1.7 × U₀.

• Procedure:

1. Gradually ramp up voltage (1 kV/s).

2. Hold for 15 min.

3. Monitor leakage current (should stabilize).

• Failure Signs: Sudden current spike or breakdown.

3. VLF (Very Low Frequency) AC Test

• Purpose: Replaces DC Hi-Pot for aged XLPE cables (avoids space charge damage).

• Frequency: 0.1 Hz or 0.01 Hz (sinusoidal or cosine-rectangular wave).

• Test Voltage: 1.5–3 × U₀ (e.g., 27 kV for 11 kV cable).

• Standard: IEEE 400.2

• Advantages:

• Detects water trees in XLPE.

• Less damaging than DC for aged cables.

4. Tan Delta (Dissipation Factor) Test

• Purpose: Measures insulation dielectric losses (indicates aging/moisture ingress).

• Standard: IEC 60840

• Procedure:

1. Apply AC voltage (0.5–2 × U₀).

2. Measure tan δ (loss angle tangent).

• Interpretation:

• Good Insulation: tan δ < 0.5%

• Degraded Insulation: tan δ > 1%

5. Partial Discharge (PD) Test

• Purpose: Detects micro-discharges in insulation voids (early defect detection).

• Standard: IEC 60270

• Methods:

• Offline PD Test: Using HV source (AC/DC/VLF).

• Online PD Monitoring: Sensors detect PD pulses during operation.

• Acceptance Limit: < 10 pC (for new XLPE cables).

6. Time Domain Reflectometry (TDR)

• Purpose: Locates cable faults (open circuit, short circuit, impedance mismatch).

• How It Works:

• Sends a pulse → Measures reflected wave → Calculates fault distance.

• Accuracy: ±1% of cable length.

7. Sheath Integrity Test (For Metallic Sheaths)

• Purpose: Checks for cracks or corrosion in lead/copper sheaths.

• Method:

• DC Voltage Test (10 kV for 1 min).

• Spark Test (For PVC/PE outer sheaths).

3. Comparison of Key Testing Methods

4. Safety Precautions

• Discharge cables fully before & after testing.

• Use proper grounding (avoid floating voltages).

• Follow IEEE/IEC standards for test voltages.

• Wear PPE (gloves, insulated tools).

5. Industry Standards

• IEC 60502 (Power cables up to 30 kV).

• IEEE 400 (Field testing of shielded cables).

• IEC 60840 (Cables rated 30–150 kV).

Conclusion

Choosing the right HV cable test depends on cable type (XLPE, PILC, EPR), age, and application.

• For new cables: DC Hi-Pot + PD Test.

• For aged cables: VLF + Tan Delta.

• For fault location: TDR + IR Scan.

• The above content is published by demiks, please specify, demiks is a substation equipment manufacturer, specializing in the production of high-voltage tester, transformer tester, circuit breaker test equipment, relay tester, SF6 gas analyser, cable fault tester and other products, if you have power test testing needs, please feel free to contact demiks power science and technology limited company or send an email! Give us: contact@demikspower.com