Megger 550005B Calibration Instruments
  • Megger 550005B Calibration Instruments

Megger 550005B


Single-Phase, Hand-Cranked TTR Transformer Turns Ratio Test Set



The Megger 550005B Single-Phase, Hand-Cranked TTR Transformer Turns Ratio Test Set measures the turns ratio and exciting current of windings in power, potential and current transformers. Deviations in turns ratio readings indicate problems in one or both windings or the magnetic core circuit.

The TTR test set aids in identifying:

  • Shorted coils
  • Open circuits
  • Incorrect connections
  • Internal faults or tap-changer defects in step regulators as well as in transformers.

The single-phase, hand-cranked model measures highly sensitive turns ratios of up to 129.99:1 with accuracy of +/- 0.1%.

The TTR set operates on the principle that the voltage ratio of the transformer at no load is practically equal to the true turns ratio. The major source of error in a transformer is a primary impedance drop due to magnetizing current, which is kept to a minimum by excitation at a fraction of rated voltage. By employing a design that meets both of these conditions along with the use of a null balance system, the turns ratio of a transformer can be determined accurately.

When measuring the turns ratio of distribution and power transformers, the accuracy is well within 0.1%.


The single phase model is primarily used for testing single-phase power and distribution transformers, for low-ratio readings up to 129.99:1, or up to 329.99:1 with an optional auxiliary transformer. It can be used to test three-phase transformers by connecting and testing each phase separately.

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