3.3 KV MOTOR OVER CURRENT PROTECTION SETTING VALUES? 1

[afzumannu]

DEAR ALL,
WE HAVE 3.3 KV 160 KW MOTOR, 7SJ600 NUMERICAL PROTECTION RELAY USING FOR MOTOR PROTECTION
MY QUESTION IS WHAT SHOULD BE THE SETTING VALUES FOR OVER CURRENT PROTECTION I> LOW SET I >> HIGH SET I>>> INSTANTANEOUS SET AND IE> IE>> SETTING WITH DEFINITE TIME, MOTOR IS CONTINUOUS OPERATION, PLEASE GIVE ME IDEA WITH REFERENCE OF MOTOR RATED CURRENT, CT RATION IS 40/1 A,
I HOPE ALL WILL HELP ME

 

[afzumannu]

I m not confused there is 3 set values low set, high set and instantaneous with time setting..for instantaneous there should not be time delay as all we know....can someone tell me what is the normal starting time of Induction Motor.

 

[ScottyUK]

"As we all know..." - well, most of us know - that you don't enable the instantaneous element when you have a contactor starter. Contactors have very limited breaking capacity. Any fault big enough to trigger the instantaneous element will be greater than the contactor can safely interrupt; your protection settings must ensure that fault is cleared by the backup fuses, not the contactor.

 

[lvsenthil]

Dear afzumannu (Electrical)

Based on your input,

Considering the the Motor Rated current 28 A, Rated Voltage 3300V, 160KW, CT 40/1

You may set the following

I > 1.2x 28/40
0.84
Pick up time for
I> 10Sec

I >> 6x 28/40
4.2
Pick up time for
I>> 0.05 sec

Disable I>>> your back fuse will take care of it.

Thermal over load Setting

K-factor for thermal
overload protection 0.7

Time constant for thermal
overload protection 60 min

Multiplier of time
constant at standstill 4.0

Thermal warning stage 90%

Hope this will solve your purpose.

 

[afzumannu]

Thanx Ivsenthil

But only doubt what about starting time motor will take 6 times approx of Full load current it will trip immediately if time co-ordination not ok?

 

[Parchie]

@afzumannu,
@Ivsenthil specifically posted an example protection setting based on his experience with a motor load of 28A. He also said the "short-time delay" of 0.05 seconds for an expected starting current of 6X the FLA. If you find the setting too short, tweak the time delay a bit higher until the starter doesn't trip on starting.

 

[afzumannu]

What would be 3.3 kv 160 kw siemens centrifugal pump motor start up timing.I mean how long starting current will take place? I want to know the timing of starting current to become normal.

 

[zeusfaber]

Is this not something you can measure?

A.

 

[Parchie]

Is this not something you can measure?

It seems to me he doesn't want to read posts he doesn't like!

 

[RRaghunath]

To my knowledge 7SJ relay has starting supervision and stall protection which include definite time elements. These are set based on motor data.
Independent definite time and Instt O/C protection elements are for short circuit protection and are not set when the feeder is controlled by fuse backed contactor (Fuse provides the short circuit protection and is coordinated with the contactor interrupting rating.
Am I missing something here!

Rompicherla Raghunath