Partial discharge detection testing for HV systems

Wyko's Condition Monitoring unit has developed a new highly accurate method of partial discharge detection testing for high-voltage (HV) systems, including motors, switchgear and transformers.

Wyko's Condition Monitoring unit has developed a new highly accurate method of partial discharge detection testing for high-voltage (HV) systems, including motors, switchgear and transformers.

The test takes only a matter of minutes to complete and can be carried out while HV systems are in normal operation, as opposed to traditional test procedures such as dielectric loss analysis that can take up to 12 hours per machine and require the system to be shut down and then stressed.

The result is a complete HV systems health check that can be carried out using a set of small coils and a suitcase sized detector rather than a large vehicle full of support equipment as it has done in the past.

Any industrial, processing, power generation installation on land or sea can now have a complete HV systems health check carried out by Wyko without disrupting normal operations.

As the test can be carried out quickly and easily, more regular checks are practical and the risk of poor system performance or failure and the resulting loses through unplanned downtime can be greatly reduced.

It is estimated that many companies only test their HV equipment as infrequently as every five years; this can prove a serious issue as problems can develop over a much shorter time period.

The new partial discharge detector has been a joint development between M and B Systems (Power Instrumentation), HV Solutions and Wyko.

It has been designed primarily for use with Rogowski coils; the main advantage of the coils is that they provide detailed feedback in a completely noninvasive way.

The more traditional, dielectric loss analysis method requires the system to be shut down and then all the windings to be stressed up to operational voltage, this not only takes time, but can be destructive if carried out too often.

Once fitted, Rogowski coils remain on the HV equipment and are simply plugged into Wyko's unique partial discharge detector unit to provide monitoring feedback.

This is the most technically advanced and quickest way for companies to carry out preventive maintenance and eliminate costly unplanned downtime.

The detector units are also compatible with all previous methods of predicting faults in high voltage systems and machinery, the suitcase sized detector can analyse information from multiple sources to provide a more accurate and comprehensive picture of system status and predict future behaviour.

Wyko technicians have worked closely with Professor David Edwards to develop this system.

Prof Edwards is largely responsible for first realising that Rogowski coils could be used to monitor partial discharges in HV circuits (they were originally used to detect high frequency radio waves).

Thanks to the partnership, Wyko has been able to develop equipment to meet every new application of the technique from monitoring HV motors and generators across industry, to producing the new generation of detectors for testing all high voltage equipment, supply and control systems.

"What puts this new condition monitoring equipment at the forefront of the technology", explains Ian Smith, Wyko's Technical Development Manager, "is the fact that it has been uniquely designed to accept inputs from various sources eg Rogowski coils, capacitive couplers, radio frequency current transformers (RFCTs), transient earth voltage probes (TEVs) and various acoustic devices.

Wyko engineers can therefore utilise any existing monitoring points to gain information, locate potential faults in a system and accurately predict how long it will remain in service before remedial work needs to be taken".

He continues: "By using the equipment to test HV rotating shaft equipment Wyko engineers can now detect surface contamination, internal discharge, inter-phase discharge, surface tracking, end winding movement and slot section movement using a piece of equipment the size of a suitcase.

By using one piece of test gear as opposed to the mini container load of heavy cumbersome equipment traditionally required for the host of available testing methods, Wyko engineers can assess larger plants and installations in a fraction of the time".

Where cables and switchboards are concerned, the equipment takes up to 16 channels of information from split current transformers and TEV probes to accurately pinpoint fault areas.

This allows Wyko engineers to identify failing HV cable joints and components before dangerous "blow outs" occur, preventing injury to personnel and damage to other equipment within the system.

The equipment is the most recent string in the bow of Wyko engineers, who routinely carry out vibration analysis, thermographic surveys, laser alignment and on-site balancing in locations throughout the UK.

Oil sampling, particle discharge, current injection and relay testing are also elements of the service provided, all ensuring that the most accurate overview of a system is achieved.

The service also enables a customer to reduce running costs through system efficiency, energy saving and labour requirements.

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