• Transformer winding resistance measurement
• Transformer Ratio Test
• Vector Group Test of Transformer
• Dielectric Test of Transformer
• Temperature Rise Test of Transformer
• Transformer Impulse Test
• Sweep Frequency Response Analysis
• Tan Delta or Dissipation Factor Test
Over Fluxing in Transformer
Earthing or Grounding Transformer
External & Internal Faults in Transformer
Backup Protection of Transformer
Differential Protection of Transformer
Restricted Earth Fault Protection
Maintenance of Transformer
Air Core Transformer
High Voltage Transformer
Transformer Ratio Test
The performance of a transformer largely depends upon perfection of specific turns or voltage ratio of transformer. So transformer ration test is an essential type test of transformer. The voltage should be applied only in the high voltage winding in order to avoid unsafe voltage.
Ratio Test of Transformer and Check of Phase Displacement
Actually the no load voltage ratio of transformer is equal to the turn ratio. So ratio test of transformer.
Procedure of Transformer Ratio Test
- First, the tap changer of transformer is kept in the lowest position and LV terminals are kept open.
- Then apply 3-phase 415 V supply on HV terminals. Measure the voltages applied on each phase (Phase-phase) on HV and induced voltages at LV terminals simultaneously.
- After measuring the voltages at HV and LV terminals, the tap changer of transformer should be raised by one position and repeat test.
- Repeat the same for each of the tap position separately.
The above transformer ratio test can also be performed by portable transformer turns ratio (TTR) meter. They have an in built power supply, with the voltages commonly used being very low, such as 8-10 V and 50 Hz. The HV and LV windings of one phase of a transformer are connected to the instrument, and the internal bridge elements are varied to produce a null indication on the detector.
Let’s have a discussion on transformer turns ratio (TTR) meter method of turn ratio test of transformer.
This theoretical turn ratio is adjusted on the transformer turn ratio tested or TTR by the adjustable transformer as shown in the figure above and it should be changed until a balance occurs in the percentage error indicator. The reading on this indicator implies the deviaton of measured turn ratio from expected turn ratio in percentage.