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 location 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.
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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.
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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 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) |
