wye-delta

[chillerguru]

I encountered a wye- delta starter on a Trane aircooled srew chiller (RTAC). When starting up a replacement compressor, chiller has a starter integrity test, that engages start contactor and checks for no current, if that passes it kicks out start and engages shorting contactor and also checks for no current, if that passe it goes through regular start up. however on this compressor when start engages, amprobe pulls 700 amps and goes intop starter failure. windings all check out at .2 ohms, between 1-4, 2-5, 3-6. all terminals to ground also meg 1k mega ohm or greater. normally if any one of the 3 contactors are engage by them self , no current should be measured, unless in wye or delta configuration amperage should be noted. starter dry run also passed. anybody have ideas.

[CoolFox]

Is it failing during the contactor test or when it trys to run?
Check for incorrect wiring or welded in contactors. don't forget these starters use 4 contactors the 3 large ones and a small one for the resistors.

[jayguy]

how does the compressor sound when it tries to start?

you could easily have one of the windings wired backwards so that 2 phases go forward and 1 backwards (or visa versa)...this is essentially a locked up motor...

you could also have a locked up motor!

[cperk]

Is 700 the LRA for wye on this comp? Could comp. be trying to run backwards? Maybe from motor phase being wrong from the inside? If it's a reman. could be possible. 700 amps sounds like a lot on wye though.

[jayguy]

...700 amps sounds like a lot on wye though.

a 125 nominal ton compressor on 200/3/60 draws 821 amps on the YLRA.
on 230 it is 691 amps.

the 100 nominal ton compressor on 200/3/60 draws 701 on YLRA.

[ryjowy]

Had a friend run into this same issue. Compressor was wired wrong internally. Re manufacture company wouldn't cop to it.

[jayguy]

...windings all check out at .2 ohms...

if you have access to a milli-ohm meter...

a 230/3/60, 100 ton compressor would have an ohm rating of approximately 0.0591 ohms

a 230/3/60, 125 ton compressor would have an ohm rating of approximately 0.0485 ohms


sure would be nice to know for sure what we are dealing with so that we don't have to report on all sizes!

[chillerguru]

the compressor does not run at all and in wye configuration, shorting contactor and start contactor are engaged to measure wye amps. this compressor only engages the start contactor , that should not pull any current, however it is pulling 700 amps. Lra at wye is 396 amps, at delta Lra 1036 amps. compressor is rated at 460 volts/ 3 phase.

[RichardL]

That sucker gotta' be wired wrong....I would guess internally on the terminal board that some wiring got swapped...I mean putting power on term. 1-2 & 3 don't do squat' on a properly wired wye-Delta compressor. I am also assumint that the tripping out is also instantaneous and you never get a chance to even hear the compressor even grunt...
You gave the 1-4, 2-5, & 3-6 ohm readings along with the readings to Ground.....I am forced to ask did you read "Anything" between 1-2, or 2-3, or 1-3???? If so then the compressor id "Definately" wired wrong internallly..

[jayguy]

That sucker gotta' be wired wrong....I would guess internally on the terminal board that some wiring got swapped...I mean putting power on term. 1-2 & 3 don't do squat' on a properly wired wye-Delta compressor. I am also assumint that the tripping out is also instantaneous and you never get a chance to even hear the compressor even grunt...
You gave the 1-4, 2-5, & 3-6 ohm readings along with the readings to Ground.....I am forced to ask did you read "Anything" between 1-2, or 2-3, or 1-3???? If so then the compressor id "Definately" wired wrong internallly..

that is my thought too...continuity in the right place, but he probably has continuity in the wrong place too!

[Randy S.]

I'd be for calling the compressor supplier, after you do some more meter work.
It's either wired wrong internally or the terminals are not identified properly.

Pay attention to what Richard wrote.

[Nuclrchiller]

You may want to double-check for proper external connections to the compressor terminals also. I'm sure you've already done so, but it's hard to do this too many times. I would ignore any markings on wires or terminals. Mine, others, or even factory. I would ohm out the wires and be absolutely sure wires are correct from contactors to terminals.

[mryan1]

also, when the start contactor comes in the shorting contactor cannot being in at the same time or boom boom with happen maybe its sensing this. Sounds like a bad contactor to me.

[jsherhvac]

also, when the start contactor comes in the shorting contactor cannot being in at the same time or boom boom with happen maybe its sensing this. Sounds like a bad contactor to me.

Are you sure you said what you meant to say?? If so please explain to me what takes place as far as contactor sequencing in the wye configeration to start chiller.

[only1doug]

With Wye Delta startup (or what I call star delta) you are changing the motor terminal connections between 2 configurations so you need to have 2 contactors that MUST not both be energised at the same time (it is common to have a mechanical interlock to prevent them both from being on at once) and a third contactor to energise the entire arrangement.


You have six terminals on the motor (U1 V1 W1, U2 V2 W2)
each represents one end of one motor winding (winding U, V or W).

In Star the three windings are connected together and voltage applied to the other end of the winding. so U2, V2 and W2 are connected together in the shorting contactor and 3 phase power is connected to U1, V1 and W1.

In Delta the three windings are connected to each other (in a triangle arrangement) so in the delta contactor U1 is connected to V2, V1 is connected to W2 and W1 is connected to U2 and 3 phase power is connected to the corners of the triangle (again 3 phase power is connected to U1, V1 and W1).

If the Star contactor and Delta contactors are energised simultaneously you have a dead short between all 6 cables. BANG!

Start up
Power contactor and Star contactor Energise.
Motor starts spinning.
Time delay relay switches Star Contactor off and then Delta contactor on
Motor speed increases.

Now running in Delta.