# Transformers in series for AC phase measurement

#### ToonooT

Joined Aug 8, 2013
11
Hi all,

I want to measure AC line voltage and frequency from a 3 phases ~400V generator (wind turbine application) and no neutral.
In order to measure this I need to get this signal to let's say 0-3.3V and isolated from high voltage.

The best solution for me is to measure between two phases with a transformer.
So, I was looking for a transformer which can directly handle such voltage but it seems hard to find. By doing research on compenents I found this one :
It can provide two 5V outputs output from 230V.
My questions are :
- Can I put 2 of this one in series to handle up to 460V ?
- Do I need to equilibrate load between this 2 transformers ? (link all outputs in parallel so 4 outputs because of 2 outputs per transformer)
- Do I need to install this solution between each phase to equilibrate the load ? For me, assuming the load will be very light, it's not necessary.

Hope someone can help me
Thanks and Happy new year !

#### RRITESH KAKKAR

Joined Jun 29, 2010
2,829
I want to measure AC line voltage and frequency from a 3 phases ~400V generator (wind turbine application) and no neutral.
For this i think, you should use less VA transformer or Current transformer
by this convert to voltage divider 3.3V max.
by this it can work.

#### ToonooT

Joined Aug 8, 2013
11
Thanks for your answer but how can I measure Voltage with a Current transformer ?
Is it not only to measure current ?

#### RRITESH KAKKAR

Joined Jun 29, 2010
2,829
No current transformer are used to measure current only.
potential transformer are used to measure voltage/emf

Current transformer

#### ToonooT

Joined Aug 8, 2013
11
I want to measure AC line voltage and frequency from a 3 phases ~400V generator
By the way, I do not need to measure current...
Can someone answer my 3 questions ?

#### Kermit2

Joined Feb 5, 2010
4,162
A 100:1 voltage divider would not load down your generator, and would provide a 0 to 5 volt scaled reading of your generator voltage.
A 2 Meg resistor in series with 20k resistor would be my suggestion

#### ToonooT

Joined Aug 8, 2013
11
Of course it will not load the generator but this solution is not isolated from power lines which can be dangerous.
Also, I don't have a common voltage reference between generator and my device so for me, it's not a good approach.

#### Kermit2

Joined Feb 5, 2010
4,162
ANYTHING which generates 400 to 500 volts is dangerous, so having a current of 200 or so microamps flowing through a 2 Meg resistor to ground is not an increased risk in this respect.

Ground is a common electrical condition with both your generator and your meter. Use it.

#### ErnieM

Joined Apr 24, 2011
8,090
Yes the series combo should work. Loading them the same is also a good idea to keep it all in balance.

I would not worry about the load on the 3phase power, it should not notice the slight imbalance.

Isolating the monitor from the HV as you are doing recommended.

#### BR-549

Joined Sep 22, 2013
4,938
They make "control transformers" that go directly across two 480 legs. They usually output 120 or 24 vac. I use to find them at 12 v, but that's been awhile.

The output is proportional the the leg(line) voltage. Yours will be a little lower.

You can measure the frequency and voltage across the <24 vac. Or knock that down to where you need it.

One transformer per phase.