2 Transformer Ratio - Rev 2 detailed Explanation

Transformer Turn Ratio

1. Transformer Turns Ratio Workshop on Power Transformer Testing 2015

2. Transformer Turns Ratio The  turns ratio   is defined  as the ratio of the number of turns of wire in the primary winding (N P ) to the number of turns of wire in the secondary winding (N S ) Turns Ratio : N P / N S Workshop on Power Transformer Testing 2015

3. Also the turn ratio (N) can be defined as The no-load voltage ratio between two windings of a transformer. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio V P V S N = V P / V S

4. Purpose of Turns Ratio Test: Identify if there is : - any shorted Turns , - any Open turns in HV winding . Provides Information on insulation failure between turns . Helps in Identifying the Vector Group of the Transformer. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio

5. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Instruments Required to Test : AC voltage Source and Voltage Measurement input, like STS 5000.

6. Before Test: Need to know : Type of Transformer Number of winding Phases Voltage Applied : must not exceed the Rated Voltage of Transformer always to the HV side of the Transformer Voltage Measured : must not exceed the measurement input of the Voltmeter. Turns Ratio must be measured on all Taps. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio V P V S

7. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Testing on a single Phase Transformer

8. Ratio Measurement on a Single Phase Transformer Workshop on Power Transformer Testing 2015 Transformer Turns Ratio 2kV Output Measurement Input

9. Ratio Measurement on a Single phase Auto Transformer . Workshop on Power Transformer Testing 2015 Transformer Turns Ratio

10. Transformer Turns Ratio Plot wrt Tap Workshop on Power Transformer Testing 2015 Transformer Turns Ratio

11. Ratio of Three Phase Transformer. Three phase transformer consists of three sets of primary windings, one for each phase, Three sets of secondary windings wound on the same iron core. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio

12. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio 220kV Three Phase Transformer

13. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Connection on 3 Phase Transformer Vector Group The vector group of transformer is an essential property for successful parallel operation of transformers. Eg : Dyn11 “D” indicates delta 1ry winding. “ yn ” indicates Star with Neutral 2ry winding “11” indicate the difference in phase angle between the windings, with HV winding is taken as a reference. The number is in units of 30 degrees. Selection of Phase in case of phase by phase measurement is very critical.

14. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Vector Groups of Transformer Phase Shift ( Deg ) Connection Yy0 Dd0 Dz0 30 lag Yd1 Dy1 Yz1 60 lag   Dd2 Dz2 120 lag   Dd4 Dz4 150 lag Yd5 Dy5 Yz5 180 lag Yy6 Dd6 Dz6 150 lead Yd7 Dy7 Yz7 120 lead   Dd8 Dz8 60 lead   Dd10 Dz10 30 lead Yd11 Dy11 Yz11

15. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Transformer Ratio test on a YNyn0 Vector Group

16. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio r b y R B Y Transformer Ratio test on a YNd11 Vector Group

17. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Transformer Ratio Test with Switch Box One time connection Automatic control of OLTC Perform the test as per the Vector Group mentioned

18. Workshop on Power Transformer Testing 2015 Transformer Turns Ratio Test Result of Ratio Test on 400kV Transformer