• • • TEST AND MEASUREMENT • • •
Top five tips for maintaining
legacy excitation systems Addressing common causes of excitation system failure and how to prevent them
W
hether it’s electronic component failure, loose connections, calibration drift or mechanical component failure,
excitation systems require periodic maintenance to continue running reliably. With full system replacements often prohibitively expensive, it is crucial that maintenance programmes are effective and keep systems operating at peak reliability. Here Douglas Cope, director at excitation control system specialist Excitation Engineering Services, discusses common causes of excitation system failure and how to mitigate for them and keep systems up and running for the long term. Age, contamination and mechanical and electrical stress all cause ongoing wear and tear in excitation systems which, if ignored, can eventually lead to machine failure and costly downtime. A significantly less expensive option than replacing whole systems is to adopt a preventative maintenance approach. This allows engineers to identify potential faults and fix them before they
impact system performance. An effective preventative maintenance programme should include routine inspections of all components, particularly mechanical ones such as contactors and motorised potentiometers. It should also include inspection of all connections, whether they are small control cables or high current busbar. Testing should also be performed on any power supplies and transducers, along with injection testing to verify calibration and correct setting of limiters. Further testing should be performed with a running machine to assess the dynamic performance of the system. This will normally consist of open circuit step response tests, followed by tests on load, including step tests into the under and over excitation limiters.
Mechanical Component Failure Contactors can fail to open or close due to misalignment, oxidisation or contamination. High ambient temperatures over a long period can
32 ELECTRICAL ENGINEERING • JULY/AUGUST 2024
cause contactor coils to fail, as can voltages that are outside the manufacturer’s recommendation. Static exciters typically have a field switch capable of controlling hundreds or thousands of amps which require regular maintenance to prevent failure. Older analogue excitation systems often have motorised potentiometers to provide setpoints for field voltage or field current control. These can wear down the track on the potentiometer around the nominal operating voltage of the machine, leading to transient spikes in voltage and reactive power.
Electronic component failure Electronic components in excitation systems can fail due to a variety of causes. Overheating is one of the primary reasons for failure, as excessive temperatures can cause materials to degrade or circuitry to malfunction. Voltage spikes or electrical surges can also lead to component failure, potentially causing
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