Operation for GDBC-901 Transformer Turns Ratio TTR Tester GDBC-901 Transformer Turns Ratio Tester is used to measure turns ratio,vector group and so on of transformer, it can also measure turns ratio and polarity of CT PT. The test standards are IEC76-1 and IEC60044.10kV/400V DYN11 Power Transformer There are five terminals in primary:1)10500V ( Range in t