what are the reasons for a pump motor to get trip? 2

[jithin john]

A abb squirrel cage 3 phase induction motor 415V ,585A ,1455 rpm coupled to a kirloskar multi stage pump with h=320m,q=216m3/hr power 215kw ,rpm 1487 is tripping while starting the pump.does this problem occurs due to water hammering .

 

[waross]

The problem may be electrical or mechanical;
Electrical:
Wrong settings on the protection relays.
Internal fault in the motor or the conductors to the motor.
Unbalanced supply voltages and/or phase angles.
Mechanical:
Not enough back pressure on the pump, (Too little differential pressure across the pump).
Design, pumped fluid has a different Specific Gravity from the value used for the sizing calculations.
Mechanical binding of the pump or motor.
Water hammer will not affect the over-load trips.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Compositepro]

"Not enough back pressure on the pump, (Too little differential pressure across the pump)."

To elaborate, the pump may operate at much greater than design flow rate when the discharge piping is empty when the pump starts.

 

[che12345]

Dear Mr jithin john

" ... squirrel cage 3 phase induction motor 415V ,585A ,1455 rpm coupled to a ... multi stage pump with h=320m,q=216m3/hr power 215kw ,rpm 1487 is tripping while starting the pump".
1. The motor 415V, 585A kW? is higher than the pump 215kW. Seems to be ok.
2. Please tell us a little more detail:
a) the power supply [measured] voltages [before starting] (i.e. L1-L2, L2-L3, L3-L1 and L1-N, L2-N, L3-N). If possible, also [during starting],
b) the starting method (i.e. Direct-on-line (DOL), Star-delta (S-D), auto-transformer (AT) etc. Note: unlikely DOL,
c) what is tripping (i.e. the breaker etc.. Note: if it is the [breaker], please show us the photo of the breaker (name-plate and settings). Does the breaker trips with lines to the motor removed (disconnected)? Does it trips [instantly] when starting; or after a some time say 3...10 seconds later? Or,
d) the [breaker] does not trip for some time say 10 seconds during (starting) but it trips [instantly] at the instant when changing over to (run),
e) if it is (S-D) starting, show us the control schematic diagram including the wiring from the starter to the connection on the motor terminals. Make sure that the [three links] on the motor terminals are [removed],
f) check and re-check that the wiring from the starter to the motor is per the schematic diagram,
As you are "mechanical", you may need some assistance from your "electrical" colleges to answer these questions. We standby to render our assistance at all times.

Che Kuan Yau (Singapore)

 

[jraef]

Assuming the pump is centrifugal (quadratic), load = flow. Too much flow = too much load, which is what the issue of a lack of back pressure brought up by waross and confirmed by Compositepro is all about. Your pump is going into an operating condition referred to as "open channel flow"; the same thing that might happen if the pipe breaks.

One way to fix this is to have a slow-opening check valve (often called a "pump control valve") in the piping, or to use a soft starter or VFD to slowly ramp the pump up to speed, filling the pipe before fully engaging the motor.




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

 

[quark]

At the given flowrate and head, the pump requires 225kW, even if the pump runs at 90% efficiency and motor runs at 93% efficiency unless you are pumping fluid with SG less than 0.95

 

[quark]

OK, I didn't see the 585A part. Waross summed it up.

 

[waross]

Water hammer may be related.
If the piping is empty there may be water hammer when the pipe fills.
Prior to the water hammer the pump may be overloaded as the empty piping fills, but water hammer indicates that the piping has been filled and the pump load should be normal.
There is a very small window of opportunity for water hammer to cause a trip.
It is unlikely that due to varying conditions one start may result in a trip and another start results in water hammer.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[Parchie]

Pumps that big needs to have an air chamber (installed near its discharge check valve) to absorb any pressure surges !
I took a quick calc and found out your pump to motor combo looks fine. I got a hydraulic power of about 300kW (assuming the worst efficiency)and your motor power above and over that 300kW value! Please investigate where in the pump's characteristic curve your motor's capability is at. Could have been a setup where you've chosen a Q-point at the end of the pump curve, any surge could throw you off the motor capacity there!