7.5 kw motor

When does the mcb trip?? is it on start up, or when then motor is running??

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Thank you and good night

at starting..........the breaking capacity of mcb was 10KA.the contactor for delta and star connection also was damaging.the contactor used was 32A.

is there any problem for connecting this motor in star only

looking into the motor name plate, the motor operating voltage is 400/690 v that means running in star at 400v & in delta at 690v and since your system voltage is 400v, then it is impossible to run this motor in delta otherwise your mcb will trip.

if that is not the case, then you need to check the star-delta starter connections to the motor to confirm that the change-over to delta is correct.

thks

Adam

As others have pointed out, that's the wrong way round. It's 400v delta, 690v star. With a 400v supply ther's no reason in principle why he can't connect it in delta and start it DOL.

Also, to prasobh83 - what load are you driving? If it's constant torque (conveyor, winch, PD pump or blower et)c, there may be insufficient torque in star on star-delta starter to get it away.

Codey

Dear, Codey

you are right, connecting the motor in delta with DOL starter should never make any trouble if the system voltage is 400v, but it seems there is a problem with the star-delta starter which can be rectified by removing the motor leads from the motor terminal box and reconnecting them to the starter as U1 V1 W1- W2 U2 V2.

hi friends,

i changed the motor to delta connection and it is running smoothly in DOL starting.the application is not constant torque....its pump application..its used for a fountain nozzle.

but what shall be the reason for not working in star -delta.we cant connect this motor in star only.?

i know three phase motors work efficiaently in delta but why we cant connect them in star.

when we connect in star by my experiance i have seen that the motor is gettting too much hot and the bearing getting damaged.

Hello prasobh83 - it depends how a motor is wound. Yours is 400v delta, 690v star, so as you have a 400v supply, you must run it in delta (you can have star-delta starting). If you had a 690v supply (uncommon but possible in principle) you could run it in star, but star-delta starting not possible.

Some motors are wound 230v delta, 400v star. In this case, on 400v supply you would run it star (star-delta starting not possible). If you had a 230v supply (phase-phase of course) you would run it in delta, with star-delta starting possible.

Codey

Adam is correct - what you have here is a three phase motor which can be configured in Star at 400v or Delta at 690v. Attempting a Delta connection at 400 v will result in a load current of 24A and your breaker will not permit the starting current of that load.

If the motor has been connected for only one voltage then the shorting links require to be changed at the motor terminal box to change the configuration. If connecting to Star/Delta - which you cannot - given your voltage then there should be no shorting links at the motor and all 6 ends taken to the starter unit with the winding ends correctly identified for three pairs of windings.

Either way the motor configuration has no effect on the bearings, this is a motor to pump coupling issue.

The 7.5 KW motor would be 400V Delta 690V Star. This should be displayed on the motor plate. (lower voltage range generally Delta to give the required power especially in pump applications). The MCB should be a C type to take the initial inrush current typically 4-6 times the rated in star delta. It is important that the 6 ends of the windings are identified and connected in the correct sequence usually U1 V1 W1, W2,U2,V2. If this is correct un couple the motor from the pump and prove the motor.

The motor will be 400Volt Delta and 690V Star.This should be identifiable on the name plate. The MCB should be a 32A C type so it can handle the initial inrush currents. The six ends need to be correctly identified and connected in the right sequence i.e. U1,V1,W1. W2,U2,V2. If the motor still trips disconect it from the pump and prove the motor works.

The motor will be 400V Delta 690V Star and this should be indicated on the name plate. The MCB wil need to be a 32A C type to handle the initial starting current. The six ends will need to be identified correctly and usually connected U1,V1,W1. W2,U2,V2. If the MCB still trips un couple the motor from the pump and prove the motor

Dont that the "Start-up" current for this motor is probably 2 to 3 times what

the full load amps are, so use either a higher rated circuit breaker, or a "Slo-Blo"

Breaker

this 7.5 KW motor taking a current of 13.6 A when connected in delta at 400V ...whether its overloaded.?

No. Full-load current is about 16 A.

Codey

The art of motor starting is documented in standards such as British Standard 7671. Nothing has been mentioned about the cabling, which is what the circuit protective device is there to protect. Motor overload devices are there to protect the motor.

It sounds as though this task is best delegated to a qualified local electrician, who will design/calculate, install, test and certify the installation on completion. Any other course of action is nonsensical, based on the content of the original posting.