Description

Megger TTR310 Three Phase Transformer Turn Ratio

Applications
The TTR300 Series applies voltage to the high-voltage winding of a transformer and accurately measures the resulting voltage from the low voltage winding. In addition to turns ratio, the units measure excitation current, phase angle deviation between the high- and low-voltage windings and percent ratio error.

Transformer Turns Ratio
Transformer turns ratio is the ratio of the number of turns in the high-voltage winding to that in the lowvoltage winding. Complexity in the measured ratio versus nameplate ratio occurs with most three-phase power transformers because multipliers such as √3 are required to match the measured ratio to the nameplate ratio. The TTR300 Series automatically applies the multiplier in a form which allows the operator a direct comparison to the nameplate (or expected) ratio. The built-in calculator displays the % error versus nameplate for each tap and each winding, without the need for a computer.

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 core 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 all types of PTs and CTs at “zero burden.”

The phase deviation between the high and low side of a transformer is generally very small. If there is deterioration or 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.

Specifications: