Commissioning of high-voltage cable systems in wind farms

Before taking over a new wind farm, commissioning should be performed to verify that the system don`t have weaknesses that in the short or long term can lead to potentially dangerous and costly accidents. This should also apply to the HS cable system.

In a wind farm, the cable system is often an extensive part of the system, which often consists of kilometers of cable connected at hundreds of joints/terminations.

The cables come fully tested from the factory and with an approved sheath test, it is very rare that any faults are discovered with these. On the other hand, it is often seen that joints and terminations have weaknesses that will lead to a shortened service life.

To detect these weaknesses before putting the system into operation, it is recommended that a complete insulation test with PD diagnosis be performed in accordance with IEC 60502-2 or IEEE 400.

A pure Hipot test is a GO / NO GO test. Where the criterion is that the system holds the voltage for a given time. Alone, such a test can give some false positive results, especially at new systems. Minor and more typical installation errors such as; poorly prepared XLPE surface, air pockets, poor semiconductor removal, poor shrinkage and improper installation of field distributors will often "survive" the stresstest itself.

To detect this type of "normal" installation error, the Hipot test must be combined with Partial Discharge diagnosis. PD testing is considered as the best diagnostic tool for high voltage components. PD testing is usually a requirement when performing final inspection of components before they are delivered from the factory (FAT)

Commissioning with DAMPED AC & PD/diagnose (SAT)

Neka HV diagnostics perform commissioning on HV cable systems up to 132 kV:

• Damped AC Hipot test (2*U0)

• Damped AC PD diagnose (0,2-2*U0)

DAC technology have a test frequency between 20-300 Hz. This results in the cable being tested under almost the same conditions as during normal operation, 50 Hz.

During the PD diagnosis, the following information is obtained:

PD mapping (Location)

PDIV (Inseption voltage)

PDEV (Extinction Voltage)

PRPD (PD pattern)

PD level (Amplitude / intensity)

1. Verification that the cable installation can withstand 2 * Operation voltage (IEEE 400.4)

1. Verification that the installation is PD free. If PD is detected (IEC 60270)

1. Overview of the entire cable route with location of joints / terminations