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Home > Archive > Electrical Engineering > February 2007 > What are root causes for higher starting current in HT motor (500 kW, 3.3 kV)
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What are root causes for higher starting current in HT motor (500 kW, 3.3 kV)
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| sunilkeluskar@gmail.com 2007-02-26, 1:25 pm |
| I have replaced all stator coils of the 500 kW 3.3 kV motor. The
winding phase resistances are exactely equal to the designed one, also
the insulation is tested (HV Test & Tan Delta- Capacitance test) and
is OK. But during No Load trial of the motor, the no load current has
exceeds the limits and hence, the breaker got tripped off. Other motor
works satisfactorily with the same breaker. Let me know about the
reasons/ root causes for such high starting current in HT motor,
Please.
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| Fred Lotte 2007-02-26, 1:25 pm |
| In article <1172510140.973500.7610@k78g2000cwa.googlegroups.com>, sunilkeluskar@gmail.com
wrote:
> I have replaced all stator coils of the 500 kW 3.3 kV motor. The
> winding phase resistances are exactely equal to the designed one, also
> the insulation is tested (HV Test & Tan Delta- Capacitance test) and
> is OK. But during No Load trial of the motor, the no load current has
> exceeds the limits and hence, the breaker got tripped off. Other motor
> works satisfactorily with the same breaker. Let me know about the
> reasons/ root causes for such high starting current in HT motor,
> Please.
The winding is not the same as the original. It sounds like some coils are connected backwards
or otherwise out of the proper sequence.
--
Fred Lotte
flotte@nospam.stratos.net
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| SparkyGuy 2007-02-26, 1:25 pm |
| Thus spake sunilkeluskar@gmail.com:
> I have replaced all stator coils of the 500 kW 3.3 kV motor. The
> winding phase resistances are exactely equal to the designed one, also
> the insulation is tested (HV Test & Tan Delta- Capacitance test) and
> is OK. But during No Load trial of the motor, the no load current has
> exceeds the limits and hence, the breaker got tripped off. Other motor
> works satisfactorily with the same breaker. Let me know about the
> reasons/ root causes for such high starting current in HT motor,
> Please.
Sunil,
I know nothing about 3.3 kV equipment, but if my math is right, that motor
should draw about 150 A.
What size is the breaker?
Is this a 3 phase motor?
Are windings connected correctly?
What does the manufacturer's support rep have to say? (If replacement
windings are available, I presume support is also available...)
Sparky
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| AL BENSER 2007-02-27, 1:25 pm |
| The resistance of the windings is of very little importance!!!
The most important issue is the number of turns in each coil!!
because it is the number of turns that create most of the "impedance",
which determines the current the motor draw with or without load!!!
<sunilkeluskar@gmail.com> wrote in message
news:1172510140.973500.7610@k78g2000cwa.googlegroups.com...
>I have replaced all stator coils of the 500 kW 3.3 kV motor. The
> winding phase resistances are exactely equal to the designed one, also
> the insulation is tested (HV Test & Tan Delta- Capacitance test) and
> is OK. But during No Load trial of the motor, the no load current has
> exceeds the limits and hence, the breaker got tripped off. Other motor
> works satisfactorily with the same breaker. Let me know about the
> reasons/ root causes for such high starting current in HT motor,
> Please.
>
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| daestrom 2007-02-28, 8:25 pm |
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<sunilkeluskar@gmail.com> wrote in message
news:1172510140.973500.7610@k78g2000cwa.googlegroups.com...
>I have replaced all stator coils of the 500 kW 3.3 kV motor. The
> winding phase resistances are exactely equal to the designed one, also
> the insulation is tested (HV Test & Tan Delta- Capacitance test) and
> is OK. But during No Load trial of the motor, the no load current has
> exceeds the limits and hence, the breaker got tripped off. Other motor
> works satisfactorily with the same breaker. Let me know about the
> reasons/ root causes for such high starting current in HT motor,
> Please.
>
As the others have mentioned, it is the number of turns and proper
connections that come to mind (especially since it was just rewound??).
Another item is check the air gap for the rotor. If the rotor is off-set in
the stator iron (unlikely, but possible), then the wider air gap can cause
higher current surge.
But my money's on the coils are not connected correctly. (worked in a
rewind shop for a few years, seen it before, it happens).
daestrom
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