HT Cable Hi-Pot Test Procedure Using HT Testing Van

For 11 kV / 22 kV / 33 kV Cables (Step-by-Step Procedure)

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1. Purpose of Test

High Voltage (Hi-Pot) testing is carried out to verify the dielectric strength and insulation integrity of High Tension (HT) power cables before commissioning.

The objectives of the test are:

• To confirm the insulation strength of the cable
• To detect damage during transportation, laying, or jointing
• To identify manufacturing defects or insulation weakness
• To ensure the cable is safe for energization

This test is normally conducted after cable laying, jointing, and termination work is completed but before the cable is energized.

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2. Equipment Available in HT Testing Van

A standard HT testing van used for cable high voltage testing generally contains the following equipment:

• High Voltage Step-Up Transformer
• Voltage Regulator / Variac
• Control Panel with Protection System
• Rectifier Unit (for DC Hi-Pot Testing)
• kV Meter (Voltage Measurement)
• Leakage Current Meter (µA / mA)
• Digital Timer
• Earthing System
• HV Test Leads and Connectors
• Discharge Rod with Earthing Cable
• Safety Interlock System

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3. Pre-Testing Safety Checks

Before commencing the Hi-Pot test, the following safety checks must be completed.

✔ Confirm that the cable is completely isolated from the power supply.
✔ Ensure all circuit breakers and isolators are open and tagged.
✔ Disconnect the cable from switchgear, transformers, and panels if required.
✔ Ensure both cable ends are accessible and properly identified.
✔ Visually inspect cable terminations and joints for any damage.
✔ Ensure proper earthing of the HT testing van.
✔ Place warning barricades and danger signage around the test area.
✔ Ensure all personnel maintain a safe distance during testing.

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4. Preliminary Electrical Tests (Before Hi-Pot Test)

Before performing the high voltage test, the following preliminary tests must be conducted.

4.1 Continuity Test

The continuity test verifies that the conductor is electrically continuous from one end of the cable to the other.

Procedure:

• Use a multimeter or continuity tester
• Check continuity for each phase conductor

Expected Result:

✔ Proper continuity without open circuit.

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4.2 Insulation Resistance Test (IR Test)

The IR test is conducted to measure insulation resistance between phases and earth.

Equipment Used:

• 5 kV Insulation Resistance Tester (Megger)

Measurements Required:

• Phase to Phase (R-Y, Y-B, B-R)
• Phase to Earth (R-E, Y-E, B-E)

Typical Acceptable Values:

• Above 100 MΩ for new HT cables
• Normally several Giga Ohms for new installations

Record readings before proceeding to Hi-Pot testing.

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5. Earthing Arrangement of HT Testing Van

Proper earthing is essential to ensure operator safety and accurate testing results.

The following earthing connections shall be made:

• HT testing van body → Dedicated earth pit
• Cable armour → Earth pit
• Test equipment → Earth
• Discharge rod → Earth

Minimum requirement:

✔ Two independent earthing connections

Earth resistance should preferably be less than 1 Ohm.

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6. Cable Connection with HT Testing Van

For a 3-core HT cable, each phase must be tested individually.

Example: Testing R Phase

Connection arrangement:

HT Van HV Output → R Phase conductor
Y Phase → Earth
B Phase → Earth
Cable Armour → Earth

After completing the R phase test, the same procedure is repeated for Y phase and B phase.

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7. Hi-Pot Testing Procedure (Step-by-Step)

Follow the sequence below carefully during testing.

1️⃣ Start the HT testing van generator.

2️⃣ Switch ON the control panel and measuring instruments.

3️⃣ Ensure the voltage regulator (Variac) is set to ZERO.

4️⃣ Connect the HV test lead from HT van to the cable core under test.

5️⃣ Connect remaining cores and cable armour to earth.

6️⃣ Confirm all personnel are at a safe distance from the test area.

7️⃣ Slowly rotate the voltage control knob.

8️⃣ Increase the voltage gradually and smoothly until the required test voltage is reached.

9️⃣ Maintain the test voltage for 10 to 15 minutes.

During testing continuously observe:

• Leakage current value
• Any abnormal sound
• Flashover or sparking
• Sudden current fluctuation

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8. Standard DC Test Voltage

Typical DC Hi-Pot test voltages are as follows:

Cable Rated Voltage	DC Test Voltage	Duration
11 kV Cable	25 – 30 kV	10 – 15 minutes
22 kV Cable	40 – 45 kV	10 – 15 minutes
33 kV Cable	60 – 65 kV	10 – 15 minutes

Note:
Exact values may vary depending on cable manufacturer specifications and project standards.

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9. Leakage Current Observation

Leakage current should be monitored throughout the test.

Typical behavior:

• Current may initially rise as voltage increases
• It should then stabilize after a few minutes

Example observation:

Time	Leakage Current
1 minute	120 µA
5 minutes	95 µA
10 minutes	90 µA

Stable or decreasing leakage current generally indicates healthy insulation condition.

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10. Test Completion Procedure

After completing the test duration:

1. Slowly reduce voltage to zero using the voltage regulator.

2. Switch OFF the HT test equipment.

3. Discharge the cable using a discharge rod connected to earth.

4. Keep the cable earthed for 2 to 5 minutes to remove trapped charges.

5. Remove all test connections.

6. Repeat the same procedure for remaining phases.

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11. Acceptance Criteria (Test Results)

Cable PASS Condition

✔ No insulation breakdown
✔ Leakage current remains stable
✔ No flashover or sparking observed
✔ No abnormal sound or discharge

Cable FAIL Condition

❌ Sudden increase in leakage current
❌ Insulation breakdown during testing
❌ Flashover or sparking observed
❌ Unstable leakage current trend

In case of failure, the cable must be investigated for damage, faulty joint, or insulation defect before re-testing.

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If you want, I can also create a fully professional EPC SOP version with:

• HT cable testing training diagrams
• HT van connection schematic
• site safety layout
• inspection checklist & test report format

— which will make this perfect for commissioning engineers and site training.

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