PD Applications - MV, HV, EHV Cables & Cable Accessories

On- and off-line cable tests – overview

Instruments for onsite investigations on cables must be lightweight, with a sturdy design, and easy to operate. They should also provide all the necessary functions to handle noisy environments or accommodate the requirements of different power sources.

On- and Offline Tests on Cables

Field measurements under on-line (powered by the grid) or off-line (powered by an external high voltage source) conditions are common ways to check the integrity and quality of a cable insulation system. Besides the partial discharge (PD) measurement and PD fault location, a parallel tan delta or loss factor measurement will provide sufficient information to survey the cable.

Megger’s solutions are designed to fulfil the requirements of relevant field testing standards such as IEEE 400.1, IEEE 400.2, and IEEE 400.3. These solutions can be combined with any very low frequency (VLF) source, or even a resonant or hi-pot test system.

 ICMflex connected to a 110 kV HV cable under test

With temporarily installed clamp-on current transformers CTs, it is possible to check cross-link cable connections or terminations by picking up the high frequency signal from the screen of the interconnections in a joint group or from the earth/ground connection. In this case, the PD pattern provides the most information about the type of insulation fault, if present. This type of measurement focuses on the accessories of cables only, rather than the cable insulation itself.

 HFCTs connected to cross link boxes or terminations

Cable Testing According to IEEE 400.2

Cable testing according to IEEE 400.2

The IEEE guide for cable testing using VLF lists three different types of tests, each with its related test voltages:

  • Installation tests
  • Acceptance tests
  • Maintenance tests

The recommended VLF voltage testing levels for various sinusoidal and cosine-rectangular cable ratings are listed below. Voltage peak values are shown in parentheses for cosine-rectangular and square-wave waveforms.

Cable rating 
phase-to-phase (RMS)
Installation test 
phase-to-ground
Acceptance test
phase-to-ground
Maintenance test
phase-to-ground
kV RMS kV RMS (or peak) kV RMS (or peak) kV RMS (or peak)
5 9 (13) 10 (14) 7 (10)
8 11 (16) 13 (18) 10 (14)
15 18 (25) 20 (28) 16 (22)
25 27 (38) 31 (44) 23 (33)
35 39 (55) 44 (62) 33 (47)

Typical Packages:

1) Mobile PD fault location system:

  • 1 x Portable ICMcompact with built-in DSO board
  • 1 x Software ICMcompact with PD fault localization
  • 1 x Coupling capacitor CC25D/V or CC100D/V
  • 1 x Optional high voltage T-filter 
  • 1 x Impulse calibrator CAL1B
  • 1 x Preamplifier RPA1L
  • 1 x Preamplifier RPA1
  • 1 x Set of cables

2) Combined PD and TD measurement equipment:

  • 1 x ICMflex for 30, 50, 100, or 150 kVrms
  • 1 x ICMflex software
  • 1 x Reference and coupling capacitor RC30, RC50, RC100, or RC150
  • 1 x HV filter like T30/05, T50/05, T100/05, or T150/05
  • 1 x Battery pack plus charger
  • 1 x Transportation case
  • 1 x Impulse calibrator CAL1B
  • 1 x Set of cables
  • 1 x Laptop computer