Voltage (potential) transformer: help me find one - Page 1
Forum section: electronics / projects

author: balage
author_rank: Regular Contributor
timestamp: November 02, 2021, 02:36:34 pm
content: Hello,I am looking for PCB mounted voltage transformers to measure line voltage in an isolated way. On aliexpress I can find them like the ZMPT107, etc. but at Digikey or at Mouser I cannot find any. If I type voltage transformer then there are only power and pulse transformers.https://www.aliexpress.com/wholesale?catId=0&initiative_id=AS_20211102063316&SearchText=zmpt107Can you please help me find one?I wanna buy them from reliable source and not really from Alibay.Thanks!

author: BradC
author_rank: Super Contributor
timestamp: November 02, 2021, 02:54:22 pm
content: How small does it need to be? PCB mounted transformers are pretty common.

author: dtmouton
author_rank: Contributor
timestamp: November 02, 2021, 04:10:01 pm
content: Just search for "transformer" and not "voltage transformer".

author: balage
author_rank: Regular Contributor
timestamp: November 02, 2021, 07:36:45 pm
content: Quote from: BradC on November 02, 2021, 02:54:22 pmIt should be as small as possible.Quote from: dtmouton on November 02, 2021, 04:10:01 pmThere are no specific category. What I have found are the push-pull transformers, but they may have a bandwidth limit higher than 50Hz. However the windings could be okay:https://hu.mouser.com/datasheet/2/336/datasheet_p759_1608184853-2297978.pdfFor me it seems that these Aliexpress voltage sensing transformers are specific typesdesigned for measurement purposes. Do you think so?

author: dtmouton
author_rank: Contributor
timestamp: November 03, 2021, 07:06:36 am
content: How much bandwidth do you need?If you need to do very accurate measurements of the waveform then other options are probably better. How about a frequency-compensated voltage divider and an isolation amplifier?You can also look at the application notes of energy measurement ICs and see how they do it.

author: balage
author_rank: Regular Contributor
timestamp: November 03, 2021, 08:02:04 am
content: Quote from: dtmouton on November 03, 2021, 07:06:36 amLets say 1kHz is enough. I have found this method to replace voltage transformers:https://www.ti.com/lit/an/slaa552/slaa552.pdfIt is nice but the transformer method may be cheaper and needs less components.The IC datasheet says not much about it; it calls that a low phase-shift potential transformer.

author: dtmouton
author_rank: Contributor
timestamp: November 03, 2021, 09:12:03 am
content: Another option would be to ask a transformer manufacturer to wind a transformer with a ferrite core for you. It will have a large number of turns, but the wire can be very thin. You would probably have to design the transformer yourself, but there are many companies that can wind it for you.Just remember what the equivalent circuit of the transformer looks like. It is not an ideal voltage sensor.Anther option is a LEM voltage sensor.Do you really need electrical isolation? Do you now the earthing strategy in your country? Isn't neutral connected to ground, anyway?

author: balage
author_rank: Regular Contributor
timestamp: November 03, 2021, 03:20:20 pm
content: Quote from: dtmouton on November 03, 2021, 09:12:03 amI need the isolation because three sensors should be in the circuit so the line side of sensing must be isolated. And I want to sense the voltage between the phases.Just to make it more difficult.The ZMPT107 is fine actually but I try to avoid those sources.Here the earth and neutral can only be connected before the safety protection relay/switch.

author: dtmouton
author_rank: Contributor
timestamp: November 03, 2021, 03:59:40 pm
content: I suggest that you also take a look at :https://www.analog.com/en/technical-articles/trends-in-three-phase-energy-metering.html

author: balage
author_rank: Regular Contributor
timestamp: November 03, 2021, 08:26:53 pm
content: This isolated AD converter + energy metering IC combo is a nice one.Now I just wanna upgrade my existing 3 phase IoT current measuring device. This uses the CS5463.