Motor Starters and overload protection

[leestaf]

Hi Guys
I have had little contact with industrial motors and switchgear but would like to broaden my knowledge and would like some help.When choosing a motor starter what must be considered? obviously the loading and the voltage (230v or 400v), with or without isolator also overload protection of motor circuit and how to work this out. I was asked if i could recommend a motor starter for a small single phase motor on a small conveyor but with little experience in this field i couldnt.
College went into basic motors and the various types but nothing specific, does any one know of any courses on this?
Im not totally green just thought id ask my peers! 80)

 

[Knobhead]

Unless you’ve got a specific question I don’t know where to start other than point you towards Electrical calculations and induction motor control
It’s mainly motor theory but it will give you a good grasp of the questions you need to be asking.

 

[topquark]

Unless you’ve got a specific question I don’t know where to start other than point you towards Electrical calculations and induction motor control
It’s mainly motor theory but it will give you a good grasp of the questions you need to be asking.

Interesting site Tony, lots of useful info on there

 

[Knobhead]

It’s got my ares out of the fire lots of times.

 

[Marvo]

You could also try this for the basics.

Nice site by the way Tony

 

[alarm man]

this might help

Buy Training Books Fundamentals of Industrial Control Schneider Electric TRF10001 online from RS for next day delivery.

 

[bomjac]

The regulations state that an overload protective device must be fitted for any drive of 0.37kW and above. The important thing to remember is that the device should be set at the rated flc of the motor.

 

[Knobhead]

The important thing to remember is that the device should be set at the rated flc of the motor.

As a general rule of thumb. But some motors have different duty cycles as do overloads. I’m afraid that “regulations" are sadly lacking in the field.

Modern thermal overloads you would set to 100%, where as dashpots to 115%.

Foundry crane motors using dashpot O/L’s would be set at 150%. OK they are a breed apart. Built like tanks and nearly indestructible, I think I’ve changed about 5 in 35 years. Only one was a winding failure.

 

[johnboy6083]

i was taught to set thermal magnetic overloads to 110% of the FLA, and ive been taught to set VSD's to 105%. i beleive its to stop nusiance tripping during voltage fluctuations, which may cause increased current to be pulled, but im not 100%. can anybody enlighten me please?

 

[Knobhead]

John, you have to look at the motor and O/L’s as a combination.

The sauce for the goose isn’t always right for the gander!

I’ve had to upgrade a MCCB from 4000A inrush to 7000A just because we had a policy of all replacement motors had to be “high efficiency”. The original motor started fine, the new one……

 

[TailSpin]

Another question :

if Inverters are put in circuit and the old Allen West over loads are left in would this cause nuisance tripping ?

 

[netblindpaul]

TailSpin,
It could blow the inverters if the overloads open up depending on the inverter design!

 

[Marvo]

I would recommend setting up the inverter as the overload protection and removing any older type thermal overloads.

 

[johnboy6083]

The mitsubishi f700 vsd's we fit have integral overloads, but there are bs88 for short circuit protection and as backup.

 

[netblindpaul]

johnny,
On the input side surely?

 

[johnboy6083]

Yes mate. Nothing at all in-between the drive and the motor.