ABB’s proven expertise in detecting and measuring partial discharge (PD) activity enables our service customers to gain a better understanding of the condition of their medium voltage (MV) assets – improving network reliability and safety
Partial discharge is simply an electrical discharge or spark that bridges a small portion of the insulation between two conducting electrodes. It can occur at any point in the insulation system where the electric field strength exceeds the breakdown strength of the local area of insulating material.
PD typically results from internal voids within solid insulation – such as bubbles created during the cast resin manufacturing process, as well as from the surface breakdown of insulating material due to contaminants or irregularities – usually resulting from ageing processes. PD activity is a clear indication that an asset’s insulation is deteriorating in a progressive manner that will eventually result in it being unable to withstand the electrical stress, leading to flashover.
ABB’s team of service engineers utilise hand-held PD monitoring systems that combine TEV (transient earth voltage) and ultrasonic technologies. This approach is not only non-invasive, it is vital for the equipment to remain energised to create the PD activity we are looking for. In the hands of our highly trained and experienced operators, our systems facilitate detailed identification and comparison of PD activity across multiple substation assets. This enables them to rapidly survey whole substations to detect faults before they lead to failure.
PD for MV switchgear
PD monitoring is most suited for use on MV assets from 3.3 kV to 33 kV – mainly metal clad switchboards, but also RMUs (ring main units) and transformer cable boxes.
A ‘go’ or ‘no-go’ indication
PD monitoring is a ‘go’ or ‘no-go’ indication. Thanks to ABB’s substantial experience – built up from PD surveys on hundreds of UK sites on many different types of equipment and across a variety of industries – if we detect PD above a certain threshold then we can say with a high level of confidence that there is a problem.
Raised PD levels could indicate that an asset is close to failure – and we have documented many cases where switchgear has literally fallen apart on investigation – or it could be an early indication of an incipient problem. Nevertheless, PD emissions invariably indicate that the asset needs some form of attention.
On the other hand, if equipment earns a clean bill of health from a PD survey than it could be a persuasive reason for extending maintenance intervals, which can of course save costs. We recommend that PD monitoring should be performed as an integral part of the commissioning of any new or refurbished switchboard or transformer cable box. This will then set a benchmark level for reference throughout the asset’s service life.
Location. Location, location
There are some installations where PD is detected but it is difficult to locate the precise panel generating it within a large bank of switchboards. In this case, we can call on TEV location technology to home in on the PD source. This technique is accurate to around 600 mm, which is usually sufficient to identify the panel that needs attention.
For more information about PD monitoring or ABB’s complete service portfolio for power networks please call Danny O’Toole on 01785 825050 or email [email protected]
