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Custom Transformers for Industrial Applications

ANSI Test Codes for Dry Type Transformers

C57.125.91 Test and Term Definitions

  • No Load Losses (excitation losses) = Xfmr excited @ Rated V and Freq. (Not supplying load)—includes Core loss, dielectric loss and windings loss due to exciting Current)  NL typically is IRON loss in xfmr core
  • Full Load Loss  = Result of current flowing to the load—Includes ALL losses incurred above/beyond NL losses
  • Polarity and Phase rotation Determines the angular displacement (phase difference between 2 sinusoidal functions expressed as an angle).  and relative phase sequence
  • IZ  (Impedance) @ Reference Temperature= a voltage or load loss test (I2R) loss due to load current..  It's the voltage req’d to circulate rated current under short circuit conditions on the rated V tap—the watt loss measured is the load loss
  • Efficiency @ 25%  75%  100%   and 80% PF (Power Factor) = Ratio of the useful power output to the total  power input.
  • Audible Sound Levels= sound generated internally by the xfmr measured by instrumentation
  • Insulation class= What use to be Class A B F & H are obsolete. Now classified numerically by temp rating of the insulation system..  Now 55Dec C Rise 80Deg C Rise  115Deg C Rise and 150Deg C Rise—Our Class H is now a 150Deg C Rise xfmr utilizing a Class 220 insulation system
  • Temperature Rise = Test under load as near as possible to name plate rating. Normally on the tap giving the highest winding temp rise. Ultimate Temp Rise is when temp does not vary more than 2 deg C during consecutive (3) hour periods.. Surface temp’s are measured by thermocouples.  Average and winding temp rise are measured by hot-resistance method—Ambient temp is also taken in the surrounding air and should not less than 10 Deg C or more that 40 deg C
  • Applied potential = a voltage test
  • Induced potential = a standard dielectric test which verifies the integrity of insulating materials and clearances between turns and layers of the xfmr winding
  • Excitation Current = The input current under NL expressed in % of rated current
  • IR IX IZ % (Percentages) = Percent Resistance Reactance Impedance – Voltage drop at rated current in % of rated voltage.
  • Reference and Ambient Temperatures = average temp of the air in the immediate neighborhood of the xfmr

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