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Harmonics in Normal Transformers

DUE TO PRESENCE OF NONLINEAR LOADS THE TRANSFORMERS WHICH ARE NORMALLY DESIGNED AND BUILT FOR RATED FREQUENCY AND NORMAL RATED CURRENT CAUSES REACTIVE POWER LOSSES WHICH CAUSES HEATING IN TRANSFORMER WHICH LEADS TO HIGHER LOSSES, EARLY BREAKDOWN IN INSULATION AND REDUCTION OF USEFUL LIFETIME OF TRANSFORMERS. TRANSFORMERS ARE ONE OF THE COMPONENT WHICH ACTS AS AN INTERFACE BETWEEN SUPPLY AND MOST NONLINEAR LOAD.

HARMONIC VOLTAGE INCREASES INCREASE LOSSES IN MAGNETIC CORE WHILE HARMONICS CURRENT INCREASES LOSSES IN ITS WINDING AND ITS STRUCTURES. IN GENERAL HARMONIC LOSSES OCCUR FROM INCREASED HEAT DISSIPATION FROM IN THE WINDING AND SKIN EFFECT WHERE BOTH ARE FUNCTIONS OF SQUARE OF IRMSCURRENT AS WELL AS EDDY CURRENT AND CORE LOSSES.

TRANSFORMER LOSSES IN HARMONICS LOAD 

  • TRANSFORMERS ARE DESIGNED GENERALLY IN A WAY THAT THEIR MINIMUM LOSSES OCCUR AT THE RATED VOLTAGE AND RATED FREQUENCY AND SINUSOIDAL CURRENT. HOWEVER BY INCREASING THE NONLINEAR LOAD THE CURRENT IS NO LONGER SINUSOIDAL. THIS NON SINUSOIDAL CURRENT CAUSES EXTRA LOSSES AND TEMPERATURE IN TRANSFORMER. TRANSFORMER LOSSES ARE DIVIDED INTO TWO CATEGORIES VIZ., NO LOAD LOSSES AND LOAD LOSSES.
  • PT=P NL+P LL (PNL: NO LOAD LOSS; PLL: LOAD LOSS; PT: TOTAL LOSS).
  • NO LOAD LOSS: NO LOAD LOSSES ARE PROPORTIONAL TO FREQUENCY AND MAXIMUM FLUX DENSITY OF THE CORE AND ARE SEPARATED FROM LOAD CURRENTS.
  • LOAD LOSS: LOAD LOSS INCLUDE WINDING RESISTANCE LOSS, EDDY LOSS IN WINDING AND OTHER STRAY LOSS.
  • PLL=PDC+PEC+PSL(PDC: WINDING RESISTANCE ;PEC :EDDY CURRENT LOSS ;PSL :STRAY LOSS)
  • INCREASE IN EDDY CURRENT LOSS AND STRAY LOSS
  • INCREASE IN DIELECTRIC STRESS IN INSULATION
  • RESONANCE BETWEEN WINDING REACTANCE AND FEEDER CAPACITANCE
  • ELECTROSTATIC INTERFERENCE WITH COMMUNICATION CIRCUITS
  • LOWER EFFICINECY
  • REDUCED CAPACITY
  • REDUCED POWER FACTOR AND DECREASE IN PRODUCTIVITY