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Sadashiv Vaidya
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Join Date: Dec 2010
Posts: 13

Amine Motor Tripping After Replacement On Offshore Platform

07/21/2014 1:33 AM

· Old motor (Manufacturer-Weg) was replaced with new ABB make motor of 415V/50Hz/110kW/0.85pf. Old Weg motor has been replaced with ABB motor because of higher torque requirement. All motor parameters of Weg and ABB motors are same except motor torque value and shaft diameter. New motor torque value (1059Nm) is higher than old motor. Max. Starting time for new motor from cold is 29sec, and 16sec from hot, nominal speed is 992rpm, FLC is 196Amp, NLC is 81Amps, locked rotor torque ratio is 2.8, max. torque is 3.2, min. torque is 2.2, starting current 1571amps;

Upstream MCC motor feeder has: Cutler Hammer Series C motor circuit Protector-250Amp/3-pole

600Vac, Cat: HMCP250W5; Style: 1491D88G19

· Before taking no load trial motor winding and power cable IR value and Winding Resistance was checked and found normal. While taking no load trial motor protector tripped immediately after given start command. On further checking motor protector R-phase found open.

· Motor protector replaced with new one and started for trial. Motor started in second attempt and no load trial completed. Motor No load current was 80 amps.

· Motor coupled with pump and started on load but motor immediately tripped. Motor started on load successfully on 3rd attempt.

· Motor run for 7 days on load and stopped for routine pump changeover.

· Again during startup on load motor tripped immediately. Motor decoupled and tried to start on no load but motor protector is tripping frequently. Motor IR value and winding resistance is normal.

We are suspecting problem associated with current motor protector. It seems that currently used HMCP is of lower rating and giving nuisance tripping on Transient inrush trip while startup.

Q1. Is it ok to change the motor protector with higher rating, and with higher O/L setting?

Q2. Is it that the starting time for new ABB motor seems on higher side due to higher torque-hence nuisnace tripping on heavy inrush current.

>Request solution to rectify with permanent rebust solution. Thankx!
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SolarEagle
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#1

Re: Amine Motor Tripping after replacement on Offshore platform

07/21/2014 1:51 AM

It would seem that you need more of a delay during startup....I would contact them and see what they say....I would adjust the FLA all the way up....

http://www.galco.com/buy/Cutler-Hammer-Div-of-Eaton-Corp/HMCP250W5C

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Crabtree
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#2
In reply to #1

Re: Amine Motor Tripping after replacement on Offshore platform

07/21/2014 9:04 AM

I would set the trip amps to the FLC of the new motor, and see how it goes. I wonder if the original poster has a proper motor commissioning procedure?

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Sadashiv Vaidya
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#6
In reply to #1

Re: Amine Motor Tripping after replacement on Offshore platform

07/22/2014 1:16 AM

Thankx! yes... we did it but not much success.. still working on problem.
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JRaef
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#3

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/21/2014 11:20 AM

What you have likely done is replaced an older standard motor with a newer energy efficient motor, and discovered the "dirty little secret" about EE motors; the inrush current can be extremely high. This is a well known phenomenon, the result of lower winding resistance, different slot geometry and a smaller air gap, all things that make it more energy efficient, WHEN RUNNING. Unfortunately it often leads to the exact problem you are seeing, the breaker (or fuses) cannot hold in under the wrong conditions. The reason it seems random is because the exact moment in a sine wave when the contactor closes can make the difference between 800% current inrush and 2200% current inrush. Mind you, I am referring to the true definition of inrush current, the instantaneous MAGNETIZING current that flows for 1 to 1-1/2 cycles BEFORE induction takes place and creates impedance. So in that instant, it is only the wire resistance and some magnetic reluctance that is slowing the current flow, so it looks almost like a short circuit.

Here in the US you are allowed to increase the magnetic current trip settings up 1700% of motor FLA to attempt to allow an EE motor to start. Unfortunately that is often much higher than a breaker, previously sized for an older motor, will have in the adjustment range. This means it is often necessary to install a new breaker. But in a starter with an MCP, the starter is only designed to be used with a specific size, leaving you unable to increase it. The answer then usually involves changing to a higher rating of Thermal-Magnetic MCCB, because the sizing rules for those allow for larger sizes, and by using one with adjustable mag trips, you can end up with a high enough setting to allow the motor to start reliably.

Do NOT change the overload relay, it has NOTHING to do with this issue. Set the OL relay for the motor nameplate FLA as per the manufacturer's instructions.

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iqbalkhan
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#4
In reply to #3

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 12:52 AM

yes it is case of high starting current and it depends on point of wave where contact makes....
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Sadashiv Vaidya
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#5
In reply to #3

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 1:12 AM

Thank you for your valid comments. yes... we might have to revise the whole motor protection control circuit...especially MCCB as suggested. Anyways, still analysing the best solution considering all scenarios...! Thankx...
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raghun
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#10
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Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 2:52 PM

That's right, complete motor protection, including thermal and magnetic protection as well as starting protection.

The overload relays for LV motors are categorised in IEC based on the starting time of the motor. Considering that the new motor has higher starting time, the overload relay category also needs to be verified / confirmed for suitability.

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Rockyscience
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#8
In reply to #3

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 9:13 AM

Right again, as usual.. They might want to stay away from Weg motors as we found them to be poor quality in an independent test of several manufacturers motors.

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GW
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#9
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Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 12:00 PM

But they are lower cost initially!
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GW
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#7

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 1:25 AM

I find it difficult to understand how with two electrically identical motors, same NP amps, rpm, volts, can possibly have significantly higher toque in one of them - that would imply more HP if the RPM is the same.

However, if it is the starting torque that is higher in the new EE motor, then you may expect more inrush to support that.

A soft start drive or an AC VFD would solve the problem and control the current and torque, but more $$$.

If you use an ABB ACS800 or 880 drive with the ABB motor, you then have full attention from ABB.
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Rockyscience
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#11
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Re: Amine Motor Tripping After Replacement On Offshore Platform

07/22/2014 3:26 PM

How about delta vs. wye connection?

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James Stewart
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#12

Re: Amine Motor Tripping After Replacement On Offshore Platform

07/28/2014 9:26 AM

Why are you using a min o motor? Use a nice new motor instead.

In a similar vein, I bought a new transfer pump and motor a while back, and also found that the breaker tripped every time I tried to start this motor (while using the same extension cord I used for other older motor). Apparently, there is a higher inrush current at the beginning, but I certainly did not see a higher starting torque, since this pump would barely turn the rubber impeller pump it supposedly was designed to handle. Just another example of poor engineering in practice. The motor would start just fine with no extension cord in place, but then the hoses would not reach. Not only that, but the OEM changed the pump design to "fit" the outer bearing sleeve of the new motor, so the pump is also useless to put on an older motor that is still in 100% working condition. Change for the sake of change is never a good idea, unless thoughtfully and carefully planned out to actually advance the quality and reliability of the device. SC the new motor and put the old back in after having it serviced.

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Users who posted comments:

Crabtree (1); GW (2); iqbalkhan (1); James Stewart (1); JRaef (1); raghun (1); Rockyscience (2); Sadashiv Vaidya (2); SolarEagle (1)

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