Overview

The Middle East based state owned utility company used the IRISS Sonus PD
instrument to test for partial discharge in their medium voltage switchgear and
accessories. In March 2014, high levels of discharge were detected on a ring main
unit using the Sonus PD, and in response to this, an offline investigation was
carried out. Significant PD damage was found on the fuse holder, indicating that the
asset was close to failure.

Details

Client engineers carried out routine tests on MV switchgear and accessories using
the IRISS Sonus PD instrument. High levels of partial discharge activity were
detected in the fuse chamber of a ring main unit by the inbuilt TEV (Transient
Earth Voltage) and ultrasonic transducers.

The Sonus PD is a dual transducer PD detector for switchgear. The instrument
detects TEV signals generated by internal discharge, as well as acoustic discharge
generated by surface tracking or corona. The Sonus PD is a quick and simple tool
for PD detection, enabling regular asset assessment by all substation staff.

Investigation

Following the detection of partial discharge activity, an offline investigation was
conducted on the asset to locate the discharging component. Clear evidence of
extensive burning and carbonization was seen on the fuse holder within the fuse
chamber, as shown in Figure 1 and Figure 2 below.

Figure 1 Extensive carbonization on the inside surface of the fuse chamber.

Figure 2 Evidence of water damage that led to the discharge activity.

Following the investigation, the defective components were replaced. Online PD tests
were carried out again, and the discharge ceased. It was clear from the extent of
damage that the unit would have failed if detected.