Transformer is the heart of any electrical system. Whether it is a distribution sub- station or a receiving station, it is the most expensive and critical asset considered. To ensure reliable power supply, superior power quality, asset health and human safety, it is advisable to ensure optimum operation of a transformer. Reducing transformer losses can increase its efficiency.
Type of Transformer Losses
There are two components that make up transformer losses. The first is “core” loss (also called no-load loss), which is the result of the magnetising and de-magnetising of the core during normal operation. Core loss occurs whenever the transformer is energised; core loss does not vary with load.
The second component of loss is called copper or load loss (I2R loss), because these losses occur in the windings of the transformer. Copper loss is a function of the resistance of the winding materials and varies with the load on the transformer.
Variation of Transformer losses during operation The transformer losses vary during the operation due to loading, voltage changes, harmonics and operating temperature.
Variation of losses with loading level The basic D.C. resistance copper losses are assumed to be 90 percent of the load losses. Eddy current losses (in conductors) are assumed to be 10 percent of the load losses. Basic I2R losses increase with temperature, while eddy losses decreases with increase in temperature. Thus, 90 percent of the load losses vary directly with rise in temperature and 10 percent of the load losses vary inversely with temperature. Calculations are usually done for an assumed temperature rise, and the rise in temperature is dependent on the total losses to be dissipated. Operating temperature = Ambient temperature + Temperature rise.
Advertising
Variation in Constant losses The iron losses measured by no load test are constant for a given applied voltage. These losses vary as the square of the voltage.
Variation in iron losses due to system voltage harmonics The system input voltage may contain voltage harmonics due to aggregate system pollution in the grid. The current harmonics of the local harmonic load adds to this by causing additional harmonic voltage drop depending upon magnitude of a particular harmonic and the system short circuit impedance at the point of supply, and the transformer impedance for that specific harmonic frequency. The combined total harmonics affect the flux waveform and give added iron losses. The increase in constant loss is quite small, due to this voltage distortion.
Variation in Load Losses
About 90 percent of the load losses in a Transformer as measured by short circuit test are due to I2R losses in the windings. They vary with the square of the current and also with winding temperature.
Variation in load losses due to load power factor Any reduction in current for the same kW load by improvement in power factor reduces load losses.
Variation in losses due to current harmonics The system current harmonics increase the r.m.s current and thus increase the basic I2R losses. In addition, the major increase comes from the variation in eddy current losses in the windings (Usually 5 to 10 percent of the total load losses), which vary with the square of the frequen
-20240706113929.png)
