Diagnostic Systems
The dielectric condition of power equipment like power transformers, cable terminations, HV, and switchgear can be satisfactorily diagnosed by means of PD measurements.
Partial Discharge (PD) measurement technique
Smart measurements are able to classify the type of defect and the more sensitive the measurements are, the earlier the corresponding defects can be diagnosed. PD levels exceeding a certain threshold, can be regarded as an alarm after which the exact location and risk of a failure should be assessed in order to determine adequate action.
UHF PD Measurement technique
Conventional PD measurements use a coupling-capacitor and a test-transformer, making this technique laborious and expensive. Besides, the equipment has to be taken off-line and the sensitivity of a conventional PD detector is limited by surrounding noise levels. Therefore, KEMA developed a new method, offering higher sensitivity and on-line use. The method is based on the application of UHF antennas as sensors for UHF signals coming from the PD’s. These sensors can be installed inside the enclosure by the manufacturer or special made antennas mounted outside existing installations. Outside installation can be carried out with the equipment on-line. KEMA possesses a UHF-receiver andtransmitters enabling long-term monitoring of suspected equipment. Both measurement and interpretation system are integrated into one single and powerful diagnostic tool, helping you to make the right decision.
Dynamic contact resistance measurement for tap changers
Approximately half the number of defects in a power transformer is caused by the tap changer. Contact erosion is the most important cause of malfunction in tap changers. KEMA’s dynamic contact resistance measurements provide a quick and accurate information about the condition of the contacts, as the high self-inductance and relatively high resistance of
the windings is by-passed. The diagnosis provides also information about possible faults in the fine selector, coarse selector, and diverter switch. From the switching time, eventual mechanical defects can be detected. The results are stored as fingerprints, which can be used for trend analysis in the course of time.
Power of the driving motor
Apart from switching times, mechanical malfunctions in the tap changer can be diagnosed more precisely by measuring the power of the driving motor. KEMA knowledge rules and experience can recognize the various stages of the switching action, and wear can quantitatively be determined by comparing two or more measurement-fingerprints.