need help and opinion

hello all....

i have a problem with electrical motor ..this may out of the box from plc but i guess all of you in here are genuis..here it goes..

1) 1 of branch plant bought a new pellet mill..which are using direct coupling to the mill..problem was when they start the breaker trip during start up..i had been ask by management to go there and have look ..after checking i feel the electrical motor supply by the supplier are under size but i have too proof them anyway..had check all the mechnical parts even it new installation..now i m confuse..is there any way i could proof them..1 easy way i know to change the breaker too bigger size which are not good at all for long term .

motor spec 160kw amp rated 238.5 volt 440~460
starter board..400amp using auto transformer 65% tapping.

the supplier ask us to change the breaker to bigger size ..but i told them it may solve for short term but long term it not good idea..

could you guys please give me hint how could i proof too them

Test the motor conductors and insulation with a megohmeter.

If it fails the meggar test, open the leads at the motor and use the megger to find out whether your ground fault is in the motor or the wiring. Repair/replace as necessary.

If it passes the megger test, put a clamp on meter on one of the lines set for peak hold and see how much current it draws before the breaker trips.

Repeat for the other legs, giving plenty of cooling time if it continues to trip the main after each attempted start.

Compare you findings with the motor data and expected inrush current.

okiepc..i had done insulation test all okay ..to ground it infinity ..which i know surely not ground fauly..
using clamp meter yes i did..and i do found it shoot up double on start up and trip the breaker..it hold for 3sec before trip..it overload loading during start up..i can change the main breaker but it might spoil the motor .motor rated amp 238.5. my current breaker are 400amp

some breakers have trip curve adj. does yours? is this a 480v 60hz motor and what is your incoming volts/hz?

yes it does ..i had adjust it from 0.9 to 1 that max..
this 440volt 50hz..incomer 440~442vac 50hz.

Is the motor wired wye or delta?
What is the motor full part number? Is it an unusual design? Is its load a difficult one to start (like a compressor)?

I agree based on what you have said that it seems the main breaker may be inadequate.

Is there an overload relay on the starter? If so, you should be able to set that correctly and then not have to worry about going too big on the main breaker as long as it doesn't exceed the rating of the conductors it feeds.

Okie is right. but also check rating of breaker some mfg. have diff. duty ratings is this breaker 100% rated? check with mfg. for your app. i usually see y- delta or soft starters in these apps. ,steve

it wired from auto transformer...which i blive should be delta .
/err how do i attach the name plate photo here
as for overload yes i had set it too 335amp

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Since the motor is protected by the OL relay, you should be okay to increase the breaker as long as you don't exceed the current rating of the conductors/devices downstream from it.

Having an autotransformer in the mix does make it "special", and I have no experience with them so all the wiring diagrams and parts specs you can supply will be helpful.

yes with this o/l setting you could dammage motor. lower it it works over time and the breaker protects from short circut. over load should be set as close to name plate as possible

here is the pic of name plate breaker and overload

looks lik typ y-delta start but you said 50hz incoming this motor is rated 60hz at your voltage is this correct?

yes it is 50 hz...coz in asia..the hz are 50 hz..i m using auto transformer as stater

That was happening with some of my motors too. But there s more than one thing to look at. I had solve this problem by setting the trip current just a lil more than rated name plate because of the rush current. And how far is that motor from from mcc. Especially when u r mentioning it happens on start up. Second thing to look at is insulation it could be just enough bad to not making a good contact all the time.

Have you measured the running average current?
Make sure it is balanced.
You should be able to set up the OL circuit to accomodate the normal running current, sometimes, I too have had to get 6 HP out of a 5HP motor by stretching the FLA settings when the motor is undersized for the job.

I don't know what rules you follow in Malaysia, but here, I would find the NEMA trip class of the load and measure the running amps and size accordingly. IF you can't get running amps or don't think it is normal, then contact the mfg of the driven machine and the motor and ask them.

Some loads my require up to 10 times FLA for up to 500ms to start, tohers my only be 300%

I am curious, having never worked on an auto-transformer starter, can you post an electrical schematic?

Thanks,
Paul