Transformer Testing & Maintenance - Dry & Oil Filled
The Successful Operation Of Transformers Is Dependent On Proper Installation, Loading, & Maintenance, As Well As Proper Design & Manufacturing.
Transformer testing has evolved over the years to determine electrical, thermal and mechanical suitability for the systems on which they will be applied. Both primary and secondary transformers are continuously subjected to thermal cycling, voltage, and current stresses. The environment in which a transformer is placed has a direct impact on its maintenance requirements.
Below is a list of the electrical testing and maintenance PowerCom provides for transformers.
VISUAL & MECHANICAL INSPECTIONS - DRY & OIL FILLED TYPE TRANSFORMERS
The transformer will be cleaned and inspected for any component damage. A visual inspection will be made for signs of overheating and for voltage creeping over insulation surfaces. Operational checks on transformer auxiliary devices will also be performed.
PowerCom will examine and test for oil and /or nitrogen leaks. Gauges will also be tested for proper operation.
In addition to inspecting dry type transformers, PowerCom is able to visually examine and inspect the inside of many oil filled transformers. We have a specialized video scope that allows us to inspect the inside of many oil filled transformers without having to completely drain the transformer of oil. With this video scope, we are able to take pictures and videos of any damage we find during our internal inspections.
TRANSFORMER TURNS RATIO TESTING - TTR
This particular test determines the turns ratio of a transformer. This is done by measuring the number of turns of the primary winding with respect to the number of turns in the secondary winding. This test can detect shorted turns in the windings or a defective tap changer. It can also be used for transformer acceptance testing to ensure nameplate voltage ratios.
INSULATION RESISTANCE TESTING - MEGGER TESTING
The insulation resistance test is a DC evaluation test of the insulation and gives a reliable indication of the presence of moisture, contamination or breakdown in the insulation.
This test also establishes a benchmark for future comparative tests.
LOW VOLTAGE EXCITATION TESTING
This test is one of the means used to verify that the transformer’s core design and performance are satisfactory. To realize the full potential of these tests, “Signature” tests should be performed before putting the transformer in service.
These signature values, along with a detailed description of the instruments used, the connections, test leads, temperatures and applied voltages should be recorded and maintained for use in the future analyses.
POLARIZATION INDEX TESTING
The polarization index test is to determine if equipment is suitable for operation even for an overvoltage test. The polarization index is a ratio of the resistance at the end of a 10 minute test to that at the end of a 1 minute test at a constant voltage.
LOAD TAP CHANGER TESTING
These operational and electrical checks performed during a TTR help determine the condition of the load tap changer. The oil in the load tap changer is drained and changed.
Moving and stationary contacts are inspected and checked. Contact adjustments or replacements are made as necessary.
INSULATING POWER FACTOR TESTING
The insulating power factor test, better known as the Doble Test, is a complete and overall test of the insulating properties of the transformer. Elements such as carbonization, ionization, moisture and heat can breakdown the insulation’s strength. The Doble test measures the power losses due to leakage of current through the insulation.
INSULATING LIQUID TESTING AND OIL FILTRATION
Insulating liquid testing is used to determine if the liquid’s dielectric strength has been lowered due to the accumulation of contaminants. Results from these tests can determine treatment of the oil or if replacement is required.
Oil filtration provides a means of removing carbon, water and sludge when suspended in the oil. The filtering treatment of the oil increases its insulating properties and prolongs the life of the transformer or tap changer.