Chilled Water Pump Starter
Chilled Water Pump Starter
(OP)
I have 45 KW Chilled water constant flow pump.It was earlier proposed to start it by DOL.But now due to limitation in incomer breaker size and transformer capacity we have to go for another method of starting.Which method can I use so that I can keep starting current to the least possible value.Is it possible to have full load current as starting current by any means of starting..say like VFD?





RE: Chilled Water Pump Starter
A soft starter will be less expensive, but starting current will be higher than an AFD.
RE: Chilled Water Pump Starter
RE: Chilled Water Pump Starter
The upstream transformer will drop voltage during the motor start. The extent of the voltage drop can be calculated with the transformer impedance, X/R, and motor starting current.
A voltage drop of 20 or 25% should not be an issue for most loads on the same bus, and the motor should start just fine if it is a centrifugal pump. If the voltage drop is expected to be much higher than this and you have sensitive loads on the bus, consider a soft starter. In a centrifugal pump application, it should reduce your startup current by half. A VFD is much more expensive and would normally be overkill for this type of application.
What is your transfomer size?
RE: Chilled Water Pump Starter
I have the following loads connected to Panel:
1.Two chillers of max load current 1003 A.Their starting current is 969 as the 4 compressors in it have inbuilt star/delta starters and are started in sequence.
2.Three pumps of FLA 81 and Locked Rotor Amps of 555,out of which only two will be working.
3.One lighting DB
4.One 5.5 KW AHU
5.One 20 KW heater
RE: Chilled Water Pump Starter
CR
RE: Chilled Water Pump Starter
Also, I highly doubt the motor will take 10 seconds to start full-voltage. That is the motor limit, not what it will actually take. It would probably take more like 1 to 2 seconds to start a centrifugal pump full-voltage.
RE: Chilled Water Pump Starter
Soft starting will not reduce the average load / heating of your transformer. It will reduce starting current, but starting time will be increased accordingly, and total heating will be approximately the same. The only benefit to soft starting would be to reduce voltage dip on your bus during starting. With such a large transformer, this is not an issue.
Also, Lionel is correct regarding the starting time.
RE: Chilled Water Pump Starter
When I have both Chillers,one pump n minor load running Total FLA is 2145..at this time if the pump starts ,the total current will be 2145+555=2700A..Im just wondering if this could be a problem for the transformer..Also can the 2500 A Breaker withstand this without tripping?
Motor Data sheet of Pump attached..you can check that too
RE: Chilled Water Pump Starter
I'm reading this with increasing concern that you're out of your depth here. It's commendable that you're trying to learn and trying to move this job forward, but you need some guidance from a more senior engineer at your employer. You need more help than we can realistically offer over the internet.
The transformer won't be bothered about a light overload for a few seconds. There's enough thermal mass there to ensure that the temperature barely moves in the timeframe of a motor start.
The 2500A breaker will have a thermal or perhaps thermal-magnetic characteristic, so it will tolerate increasingly severe overcurrent conditions for progressively shorter periods of time. If the protection is set properly there should be no problem with tripping at 2700A during a motor start.
RE: Chilled Water Pump Starter
RE: Chilled Water Pump Starter
I have done my bit of searching & researching..I have checked the time current characteristic of the breaker..from that it should hold even higher currents..i also send a technical query to schneider regarding this..But the consultant has advised us to use starters of the pump hence absolving them of any responsibility in future..Hence it is my responsibilty to make sure..hence posted a query here too..Its all a learning experience..
RE: Chilled Water Pump Starter
RE: Chilled Water Pump Starter
RE: Chilled Water Pump Starter