New mobile testing services from Kinectrics enable practical testing of very long High Voltage (HV) Cables

In January 2007 Kinectrics carried out highly-successful HV cable commissioning testing for the Keyspan Energy Engineering / Design group of New York on a project for the Long Island Power Authority. The equipment used to complete the work was Kinectrics’ Mobile HV Resonant Test System (RTS), the only commercially available unit of its kind in North America.

This project is notable as the subject cable was the longest 345 kV High Voltage underground XLPE cable that has ever been commissioned in the U.S. using an AC Hi-Pot / Partial Discharge Test.  Two cables were tested, both provided by LS cables, of Korea. Circuit 1 is approximately 4 miles long and required the use of 1 RTS unit.  Circuit 2 is approximately 9 miles long and required 2 RTS units operating in parallel.

The purpose of commissioning field testing of transmission class cable is primarily to check the integrity of the individual system components (terminations, cable sections and joints) as well as the installation workmanship.  Field commissioning consists of two tests:  A Go/No-Go test (AC Hi-Pot) as well as a diagnostic test (Partial Discharge).  As prescribed by international standards, an over voltage of up to 1.7 U₀ (rated phase-to-ground voltage) having a frequency of 20 Hz to 300 Hz is applied continuously for 60 minutes. After the initial over-voltage, the cable is held at rated voltage while Partial Discharge (PD) measurements are performed. 

The goal is to detect any latent defects before the cable is placed in commercial service. This is done by raising the voltage to a sufficiently high level, and for sufficient duration to initialize any latent potential for electrical treeing. If such potential exists, it will occur during the over-voltage and cause a line fault. The moment a fault is detected; computer control within the test equipment will automatically curtail the test and significantly reduce the impact of the fault. Even so, the possibility of a defect being present but not manifesting itself as a cable fault is real. For this reason, a PD test is also performed as the presence of partial discharge typically indicates an incipient problem.  

The challenge in this testing is twofold: to access a power supply of sufficient rating to energize the cable at voltages up to 1.7U₀ within a frequency range as prescribed by the standards and secondly, to ensure sufficient coupling of partial discharge signals originating from terminations and joints as well as the cable sections.

Kinectrics’ mobile RTS can energize long lengths of transmission class cable at resonance frequencies up to 260 kV. Because of the impedance properties of these cables, high frequency partial discharge signals are subjected to significant attenuation and dispersion. To ensure proper signal detection, Kinectrics performs a partial discharge measurement at every cable joint and termination. 

The AC Hi-Pot test for Keyspan and LIPA was performed in accordance with IEC 62067, which states a cable of this type and rating can be subjected to an over-voltage of 260 kV for 1 hour. This translates into 1.25 times the rated line-to-ground voltage. The mobility and advanced set-up features of Kinectrics’ RTS System also contributed significantly to the efficient 2-1/2 week schedule for completion of this project.

AC Hi-Pot testing by Kinectrics can provide assurances of the integrity of the cable and insulation. In most cases, these compromised areas would not be detected by a traditional 24 hour soak test.

For further information, contact Russell Pennington, 704.948.4118, russell.pennington@kinectrics.com