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Anonymous Poster #1

Setting of Motor Protection

01/13/2012 5:48 AM

we have a motor which always tripped during start up .we check in name plate in motor FLA is 40A. but the setting in protection relay is :

Set Is1 40A

unbalance protection 40%

and stalled rotor 40% of Is.

in this new installation we have got similar 5 motors with similar type of setting, please help me to set protection of this motor as i didnt receive any data sheet from the manufacturer. and the vendor himself very poor knowledge in electrical.

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Guru
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#1

Re: setting of motor protection

01/13/2012 5:50 AM

OK. On what basis is the trip operating - FLA, unbalance or stalled rotor?

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Anonymous Poster #1
#2
In reply to #1

Re: setting of motor protection

01/13/2012 5:55 AM

Stalled rotor, and we doubt between Is and FLA why it's same value?

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Anonymous Poster #1
#5
In reply to #1

Re: setting of motor protection

01/14/2012 11:43 AM

Mr PWslack,

do you have an idea what's different between Is and FLA because i think this only mistake for setting protection relay. because they put Is and FLA same value.maybe Is is starting current? thanks for your help

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Guru
United Kingdom - Member - Indeterminate Engineering Fields - Control Engineering - New Member

Join Date: Jan 2007
Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on.
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#6
In reply to #5

Re: setting of motor protection

01/16/2012 3:33 AM

If the trip is set to the FLA of the motor and the motor is tripping on FLA then either:

  • The motor is too small for the job or
  • The job is too big for the motor.

It's as simple as that.

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#3

Re: Setting of Motor Protection

01/13/2012 1:55 PM

Prepare time current coordination of your equipment and you will see that starting curve is hitting the protection curve. Maybe starting time is very long then you have to adjust the time dial of your protection.

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#4

Re: Setting of Motor Protection

01/13/2012 4:51 PM

It looks that motor trip on overload settings.

If such is the case then check the in rush current and measure the time for which the in rush current persist.

Match the suitable overload relay possibly with a time delay setting.

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Users who posted comments:

Anonymous Poster (2); jonald (1); PWSlack (2); zaheer khan (1)

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