Selected feature of TTR application notes (power tranformer test)

APPLICATIONS
The TTR applies voltage to the high voltage winding of a transformer and accurately measures the resulting voltagefrom the low voltage winding. In addition to turns ratio,the unit measures excitation current, phase angle deviation between the high and low voltage windings and percentratio error.

Transformer Turns Ratio
Transformer turns ratio is the ratio of the number of turnsin the high-voltage winding to that in the low-voltagewinding. Complexity in the measured ratio versusnameplate ratio occurs with most three phase power transformers because multipliers such as √3 are required tomatch the measured ratio to the nameplate ratio. The three-phase TTR automatically applies the multiplier in a form which allows the operator a direct comparison to the nameplate (or expected) ratio. The TTR’s built-in calculator displays the % error versus nameplate for each tap and each winding, without the need of a computer or software.

Exciting Current
The TTR provides accurate measurement of exciting current (to 0.1 mA) which can help provide information about the condition of a transformer’s core. Unwanted circulating currents or unintentional grounds can increase the exciting current and indicate a problem.

Phase Angle Deviation and its Application
The phase angle deviation, displayed in either degrees(minutes) or radians, is the phase relationship between the voltage signal applied to the high voltage winding and the voltage signal extracted from the low voltage winding.The phase deviation together with ratio error can be used as a low cost method of verifying accuracy class of alltypes of PTs and CTs at “zero burden.”The phase deviation between the high and low side of atransformer is generally very small. If there is deteriorationor damage in the transformer core, however, the phase deviation can change significantly. The three-phase TTR can measure this phase relationship with the resolution of 0.1 minutes (equal to 1/600 of a degree), which is necessary to detect problems.

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