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On- and Offline Tests

Instruments for onsite investigations on cables must be leightweight in a sturdy design, easy to operate and they should provide all functions to handle bad noise situations or requirements of different power sources.

On- and Offline Tests on Cables

Field measurements under online (powered by the grid) or offline (powered by an external HV source) conditions are common ways to check the integrity and quality of a cable insulation system. Beside of the PD measurement and PD fault localization a parallel tan delta (TD) or loss factor (LF) measurement will provide sufficient information to survey the cable.

Power Diagnostix instruments are designed to fulfill the requirements of the relevant field testing standards like IEEE400.1, IEEE400.2, and IEEE400.3. They can be combined with any VLF source, resonant or hipot test system.

ICMflex connected to a 110kV HV cable under test

With temporarily installed clamp-on CTs it is possible to check cross link connections or terminations of cables by picking up the HF signal from the screen of the interconnections in a joint group or from the ground connection. Here, the PD pattern provides the most information of the type of insulation fault, if present. This type of measurement focus on the accessories of cables only.

 

HFCTs connected to cross link boxes or terminations

 

Cable Testing According to IEEE 400.2

The IEEE guide for cable testing using VLF lists three different types of tests:

  • Installation tests
  • Acceptance tests
  • Maintenance tests

each with its related test voltages.

The recommended VLF voltage testing levels for various cable ratings for sinusoidal, cosine-rectangular are listed below. Voltage peak values are shown in brackets for cosine-rectangular and squarewave.

Cable Rating
phase to phase
(RMS)
Installation Test
phase to ground
Acceptance Test
phase to ground
Maintenance Test
phase to ground
kV RMSkV RMS (or peak)kV RMS (or peak)kV RMS (or peak)
59 (13)10 (14)7 (10)
811 (16)13 (18)10 (14)
1518 (25)20 (28)16 (22)
2527 (38)31 (44)23 (33)
3539 (55)44 (62)33 (47)