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We have 800KW motor operating at 6600Volt,50 Hz
supply.During 1st startup it tripped on overcurrent
trip.It's FLA is 88 Amps.The K factor of Thermal overloaaad
was set on .94 initially.then we set at 0.97 and then it
started fine.i dont understand why it tripped first?What
are the protections which comes in picture during starting ?

Answers were Sorted based on User's Feedback



We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / prabhukumar

we all know that the starting current of motor is 5 times
more than of rated current.
for the starting current also some settings will be their
in that the starting current time may be less and the
starting time the heat will be their.

You just check it out and tell me.

prabhu.jsw@gmail.com

Is This Answer Correct ?    2 Yes 0 No

We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / ghani

It is right that starting current of this much big motor is
very high whihc varies as per data from 6 to 8 times, so if
the protection relay is of static or digital then there
must be a restraining setting for starting current with
time delay, so you can increas both values keeping the data
sheet of motor in view.

Is This Answer Correct ?    2 Yes 0 No

We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / kiran patil

You have increased thermal overload settings to .97 I think
because of load motor gets hot early and after incresing
the themal rating it will sustain.

Is This Answer Correct ?    5 Yes 5 No

We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / a.kossay

FIRST OF ALL THIS MOTOR MUST HAVE A SOFT STARTER BECAUSE
STARTING THIS MOTOR WILL DRAW A HUGE AMOUNT OF INRUSH
CURRENT + HUGE AMOUNT OF STARTING CURRENT, SO YOU HAVE TO
USE SOFT STARTER , AND YOU HAVE TO USE SMART RELAY BECAUSE
STARTING AND INRUSH CURRENT CONATINS A HUGE AMOUNT OF
HARMONIC CONTENTS SPECIALLY THIRD HARMONIC SO THIS SMART
RELAY WILL DETECT THE VALUE OF THE THIRD HARMONIC COMPONENT
AND IF IT EXCEEDS ITS VALUE IT WILL TRIP

Is This Answer Correct ?    2 Yes 2 No

We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / karthik_elec

u did'nt mention which type of starter you used,and which type of operation no load or full load, this type large motors always used soft starter only, auto transformer will not use, any way at the time of starting auto transformer only gradually increase the applied voltage , at that time the motor will take more amps to obtain the specific torque, due to that only, after obtain normal amps it will not take 88 amps also, because this is 100% efficiency current, below that only....

Is This Answer Correct ?    0 Yes 0 No

We have 800KW motor operating at 6600Volt,50 Hz supply.During 1st startup it tripped on overcurren..

Answer / parveen garg

I DO NOT KNOW ABOUT 6.6KV MOTORS & ALSO ABOUT K FACTOR.BUT
ACCORDING TO UR QUESTION IT LOOKS THAT MOTOR DRAW MORE
INSTANTANOUS CURRENT THAN ASSUMED BY THE CALCULATION & AT
THIS STARTING CURRENT OLR TRIPPED,WHEN U INCREASE THE
SETTING OF OLR.IT DO NOT TRIP.
FOR THE PROTECTION POINT OF VIEW ONE EXTRA CONTACTOR MAY BE
PROVIDE IN PARALLEL TO THE OPERATING CONACTOR WITH TIMER
WHICH WILL MADE OFF THE CONATCTOR(PROVIDED NEWLY)&ALSO THIS
CONTANCTOR WILL DRAW POWER FROM MAIN BUSBAR WITH EXTRA OLR .

Is This Answer Correct ?    0 Yes 5 No

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