On-site, off-line power cable diagnostics.
Power cable diagnostics is an important tool for the asset managers to answer questions like: "What to do now, what in the short term and what on the long term?". Power cable diagnostics are pro-active and future-oriented.
Power cable diagnostics is an effective tool for the maintenance of an underground power cable system. The diagnostic services we offer comprise:
- determination of the present condition of various system components
- guidance on identifying required actions in order to insure continued reliable performance
- developing strategies focused on resources and actions to maximize the impact on company profitability.
Off-line PD testing for MV cable circuits
Yes, you can locate weak spots in your cable circuit before breakdown. You will be able to make repairs before breakdown and save money on network components that otherwise might be damaged as a result of breakdown. How? Energize your cable with a Very Low Frequency (VLF) voltage and then measure and locate partial discharges. Convert measurement results into clear recommendations for actions using established expert lines. Plot the partial discharge levels on a discharge map showing the position in the circuit. This technique has been successfully applied to more than 10,000 km of circuit length in Europe, Asia, the Caribbean and the USA.
Withstand testing for MV and HV cable circuits
Many electric network owners request tests on MV and HV polymeric cable systems as part of the commissioning of new systems or on existing systems after repair or modification. Since it has been determined that DC testing of polymeric cable insulation is not effective and may be harmful, present International and IEC standards require DC testing of the outer sheath and AC testing of the cable insulation.
The KEMA test set can test a cable having a capacitance of up to 2.5 µF (about 13 km). The maximum voltage is 254 kV and the maximum current is 80 A. The frequency range is between 20 Hz and 300 Hz. For longer lengths or higher voltages, KEMA applies a second set to realize double the above test parameters. We perform the following field tests:
- outer sheath testing
- main insulation testing of HV underground cable systems with AC voltage.
Dielectric Spectroscopy (DS) method for MV cable circuits
DS is being used to find water treeing in extruded MV power cables. The DS method is based on measuring the losses (tan δ) and the capacitance values of the cable at different voltage levels (0.25 Uo, 0.5 Uo, 0.75 Uo, Uo, and 2.5 Uo) as a function of the frequency of the ac voltage applied. The frequency is varied from 1 Hz to 0.01 Hz.
Cable length and joint position determination
Cable length and joint position may be determined by using the "echo-method”. A low voltage impulse signal is injected into the cable conductor and its reflection is measured over time. Joints produce weak reflections, whereas the cable end produces a strong reflection. By making use of the pulse propagation velocity of the specific underground cables and the composition of the cable circuit, the cable length and joint positions may be determined with an accuracy better than 0.5% up to 1,500 m.