# Making Transformer Turns Ratio Tester using Null Detector Bridge

#### Ifrah Sabeena

Joined Oct 16, 2017
3
Hello guys,
please give me ideas of how to make transformer turns ratio tester using null detector bridge.
the theme would be that i have to apply ac voltage to HV side of transformer suppose 11000V, and then maybe 415V will be induced on secondary side of transformer. So, turns ratio at this stage would 11000/415*1.732=45.908 .... so having 6 tapping transformer, turns ratio would be different for all taps... i want to feed these turns ratio values to my null detector bridge and as i energize the transformer, whatever value will be induced on secondary side should be shown on my bridge circuit, or null detection indication.... please guide me how to do that...

#### GopherT

Joined Nov 23, 2012
8,012
Hello guys,
please give me ideas of how to make transformer turns ratio tester using null detector bridge.
the theme would be that i have to apply ac voltage to HV side of transformer suppose 11000V, and then maybe 415V will be induced on secondary side of transformer. So, turns ratio at this stage would 11000/415*1.732=45.908 .... so having 6 tapping transformer, turns ratio would be different for all taps... i want to feed these turns ratio values to my null detector bridge and as i energize the transformer, whatever value will be induced on secondary side should be shown on my bridge circuit, or null detection indication.... please guide me how to do that...

I would get a micrometer, measure the thickness of the wire, then measure the resistance of the coil and determine the length of the wire and work from there.

#### Alec_t

Joined Sep 17, 2013
12,815
Welcome to AAC!
Where will you source a 11000VAC supply?
Is it current-limited for safety?
Why do you need such a high test voltage?
Where does the 1.732 factor come from?

#### Ifrah Sabeena

Joined Oct 16, 2017
3
Welcome to AAC!
Where will you source a 11000VAC supply?
Is it current-limited for safety?
Why do you need such a high test voltage?
Where does the 1.732 factor come from?
11000V AC is just the rated voltage of the transformer winding. i mean to say if the rated voltage of HV side of transformer winding is 11000 and LV side rated voltage is 415 volts. then turns ratio would be calculated as i did in the above post. 1.732 is just root 3 which is understood when you are working with three phase AC circuits and Three Phase Transformers. there is a big derivation to prove this root 3 factor.