315 kw star delta motor 2

[Lasg]

Afternoon. I have connected two 315 kw delta star motors for split casing pumps the 1 pump is running just fine, star vacuum contactor closes and opens after the set 10 seconds than the delta closes, but pump no 2 trips on over current and tried changing the phasing now when it transitions to delta the motor rumbles as if it's single phasing and the line voltage drops from 525v to 420v.please help

 

[LittleInch]

What is your load doing?

Is pump 2 in parallel or what?

Could be the load is too high for the starter. You normally need to start no load or closed pump.

Needs some diagnostics to show voltage and current over time to see what's happening as we can't tell a lot fomr two lines of text and no drawings or time traces.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[waross]

tried changing the phasing now when it transitions to delta the motor rumbles as if it's single phasing and the line voltage drops from 525v to 420v.please help

Change the phasing back to the original connections.

but pump no 2 trips on over current

What is the motor current?
What is the O/L setting?

--------------------
Ohm's law
Not just a good idea;
It's the LAW!

 

[Lasg]

I had the same motor on this pump the motor went for maintenance now this

 

[Lasg]

Will get the full load motor amps ND all other ratings tomorrow

 

[che12345]

I have the following questions, please advise.
1. Why you state
a) ...315 kw delta star motors. It should be 315kW star delta?
b) ... star vacuum contactor closes... Check whether the three contactors are vacuum contactors on 525V system?.
2. ... line voltage drops from 525v to 420v. ...trips on over-current. Do you mean the Breaker (not the thermal overload relay) tripped after a short duration while it is on Star running up stage i.e. before the Delta stage? What is the motor rated current and the breaker Ir current setting?
3. Attention: for SD starting, there are 6 wires from the starter to the motor. Check carefully for correct connection.
4. This is not applicable to your case.
Info: If the Breaker trips on Instantaneous (Imag) [during the instant of transfer from S to D], revisit the "revised" SD circuitry. The old circuitry which had been in used for the past 70+ years had been proven with flaw.
Che Kuan Yau (Singapore)

 

[RRaghunath]

Apparently, the transition to Delta is taking place when the motor has not yet reached 90+% speed.
The reasons could be two:
1) the transition timer is set lower
2) the motor is taking longer to pick up speed, which means the discharge valve of the pump is open or closed but leaking.
It could also be that there is problem with the bearings of the pump / motor.
Hope you checked the contact making at the contactors and ruled out any loose contact.

R Raghunath

 

[jraef]

And along the lines of what R Raghunath has said, I’d be concerned about the fact that this was done with vacuum contactors. There can be massive transition spikes in an open transition star-delta starting scheme which can cause damage to contacts. In vacuum contactors the gap between contacts is ver small, so their tolerance for errors is very small as well. One mistake and you could have a welded vacuum bottle. The rough sound might be the telltale sign of that.


" We are all here on earth to help others; what on earth the others are here for I don't know." -- W. H. Auden

 

[panter]

Is there a time delay between the release of star contactor and activation of delta contactor. Often, a small time delay is solution to solve problem if large currents occur at that moment .
Since the motor was replaced, winding connection should definitely be checked .
Good luck .

 

[Kiribanda]

Are you using one set of STAR to DELTA contactor arrangement for both motors or otherwise?