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High Voltage Insulation Tester — Field Use Beyond 5 kV

2026年05月12日

HV insulation testing is as much about procedure as instrument — here is the EK field protocol.

The Field Procedure Matters as Much as the Tester

A high voltage insulation tester is only as accurate as the technician's setup. EK service teams have audited hundreds of substation tests and find the same procedural mistakes year after year. Follow the protocol below before you trust any reading above 1 kV.

1. Pre-Test Safety Lockout

  • De-energise the circuit; lock and tag at the upstream breaker.
  • Verify zero potential with a separate voltage detector — never trust a single instrument.
  • Discharge cable capacitance via a 1 MΩ bleeder for at least 5 × test-voltage seconds.
  • Establish a 3 m exclusion zone around the test set.

2. Equipment Setup

Connect the guard terminal to break the surface-leakage path on porcelain bushings. Without a guard terminal the apparent insulation can read 30 % low because surface dirt provides a parallel leakage path.

3. Voltage Step-Up Sequence

  1. Apply 25 % of test voltage for 1 min — observe steady current.
  2. Step to 50 %, then 75 %, then 100 % at 1 min intervals.
  3. If current rises non-linearly between steps, abort — the insulation is breaking down.

4. Reading Interpretation

For new MV cable, expect > 10 GΩ at 5 kV. For 20-year-old service cable, > 1 GΩ is acceptable if PI > 2.0. A reading that rises during the 10-minute test indicates good polarisation; a reading that falls indicates moisture or contamination.

5. Post-Test Discharge

Capacitive cable energy must be discharged through the meter's internal resistor. The EK-C350 forces a minimum 5-second discharge before the test leads can be removed; the front-panel LED stays red until voltage is < 50 V.

6. Documentation Requirements

  • Ambient temperature and humidity (insulation is temperature-dependent).
  • Test voltage applied and duration.
  • 1-minute and 10-minute readings.
  • Calculated PI and DAR.
  • Technician initials and calibration cert number.

The EK-C350 HV insulation tester ships with a printed field log enforcing all six items. Request a demo through EK service teams.