Connect the Test-Set to the Relay – Alternate AC Connections


Connect the Test-Set to the Relay – Alternate AC Connections

Topic Progress:

If you understand what the relay is looking for with a good understanding of phasors, you can create balanced three-phase systems with fewer test-set channels.  These skills come in handy when you have a situation where:

  • One or more of your output channels fail.
  • You need to test synchronizing systems, but you don’t have enough channels.
  • You need to test voltage balance relays and don’t have enough channels.
  • You need to create more three-phase balanced systems than you have channels for.
  • You need to simulate open-delta PT systems.
  • You need to test specialized equipment like two-element watt-meters that don’t don;t use all of the system channels.

Watch this video to see how you can solve any of these “problems” using alternate AC connections.


Click “Mark Complete” below after watching the video so you can keep track of your progress.

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Have you gotten around doing a video for the phasor math behind simulating 3 phase voltages and currents with only two leads?

Chris Werstiuk (Administrator) May 12, 2017 at 7:43 am

It’s not something that should commonly be done with our fancy new test sets unless a channel fails. We will cover voltages when we do a voltage/synchonizing seminar. In the meantime, here’s how to do it from The Relay Testing Handbook.

Two currents sources create three phase balanced currents Two voltage sources create three phase balanced voltages

I’m not understanding how those phase angles for the voltages are balancing out in this scenario. Is there somewhere to look that better explains how this works out?

Chris Werstiuk (Administrator) July 26, 2018 at 6:07 pm

Thanks for the comment.

You can try

Better yet, try it and see for yourself.

I have do use a neutral when testing open delta A-Phase 120-Volts @ 0 degrees Neutral from test set to B-Phase of relay and C-Phase 120-volt @ 60 degrees. The connections above looks like a wye connection and phase angles without the neutral from the test set. Kind of confused. Thanks for your help love your video.

Chris Werstiuk (Administrator) February 17, 2019 at 1:58 pm

This connection should only be used as a last desperate resort, or you need four voltages from a test-set that only has three voltage channels. See this topic for more information

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