# What Will Happen if Delta Connected Motor in STAR

G

#### Gmahesh

we are using 3 hp motor in tray separator. motor is delta connected as per name plate but we ran the motor in STAR. now motor one coil has burnt. explain me the reason?

Motor run for 3 months. why it failed after 3 months?

<b>Moderator's Note:</b> By STAR, he may mean Wye connection.

J

#### JRaef2

It would depend on the configuration of your motor. But judging from your use of "Star" vs "Wye", I can assume you are in a place other than North America, and that your motor was a Dual Voltage version, as in 380/220V (or 400/230 or 415/240, basically the same thing). In that type of motor, the Delta connection would be for the LOWER voltage, the Star connection would be for the higher voltage. So if you HAD 230V available, but you used the Star connection instead of the Delta connection pattern, you were essentially starving your motor of voltage. The effective voltage across the coils would be reduced by the square root of 3 (1.732) the inverse of which is 58% of what the motor was expecting to get.

It would appear to the naked eye to run at the normal speed; AC induction motor base speed is only related to the number of poles and the applied frequency, neither of which would be different here. The torque capacity of the motor, however, would be severely curtailed; running torque would be no more than 58% of normal, but starting and re-acceleration (peak) torque would be reduced by the SQUARE of that reduction to just 33% of maximum peak torque capacity. So normally, the peak (Breakdown) torque of the motor. which is uses to re-accelerate after a step change in load, would be 200%, but in this case it would be reduced to just 66% of FLT. The motor would therefore run at a higher slip with any appreciable load, which would cause it to draw higher than normal current, yet perform less work.

B

#### barindra75

when you connect the delta connection motor into a star connection mode, the effective per phase voltage is reduced to (1/1.732) times hence to maintain the torque/speed it will draw 1.732 times higher current.

hence the motor will continue to run for some days/weeks or months depending upon your ambient and other cooling factors. but after a certain period, its winding will definitely burnt out which happened in your case also.

that's it.

re-wind the motor with higher size copper wire i.e. at least double of its existing size, then it will be stable.

G

#### Gaurav Katiyar

Sir,

>we are using 3 hp motor in tray separator. motor is delta
>connected as per name plate but we ran the motor in STAR.
>now motor one coil has burnt. explain me the reason?
>
>Motor run for 3 months. why it failed after 3 months?
>
><b>Moderator's Note:</b> By STAR, he may mean Wye connection.

pl. note that the motor full load current is specified for the connection type mentioned on the name plate. now considering your case you have delta motor with name plate full load of 3A (say) this is the line current and the actual current in the winding will be 3/1.732 = 1.732A. now if you connect this to star then line current equals winding current and since the winding is rated for only 1.732A you need to change the overload settings from 3A to 1.732A so that the motor winding don't get Overloaded.

As you have said that the motor got burnt, i am sure that this is due to running the winding at higher current than rated.

other things that happen due to changing delta to star is,

reduced starting torque, reduced speed.

it is generally recommended to convert delta motors running at less than 63% load from delta to star. this will conserve energy increasing the efficiency by increasing the loading on the motor.

#### Iglash

We have a motor 18.5 KW three phase and I found an instruction on the terminal box that " use only variable speed drive" but my team did not listen to me not to run in Wye- Delta. It ran for 5 days now the motor is getting tripped in starting itself. In nameplate voltage for Delta is 400V and for Wye is 630V but our power distribution system is 400V/230V system. When we start in Wye just 230V is applied i think for this case only It takes much current and CB trips... Am I right.?

#### joseph_e2

We had to replace an old DC motor and used a Reliance "RPM AC" motor that also said to only use it on a VFD. From what the vendor told me, the motor's insulation and windings are designed specifically for VFD service and it won't do well connected across the line (or wye-delta like yours). I wouldn't be surprised to find out that your has been damaged.

#### Iglash

We had to replace an old DC motor and used a Reliance "RPM AC" motor that also said to only use it on a VFD. From what the vendor told me, the motor's insulation and windings are designed specifically for VFD service and it won't do well connected across the line (or wye-delta like yours). I wouldn't be surprised to find out that your has been damaged.
Thank engineer Joseph

#### Zaheeb834m

What will happen if a star designed motor is connect with delta connection?

#### Guddu

Winding of your motor burnt because overload protection of its control circuit was not working properly. If overload protection was working properly, motor would have been tripped not burnt. If you ran motor in Star connection instead of Delta, and connected load is beyond it's capacity and motor control circuit is having proper protection arrangements, it will trip. Please get your motor rewound and get your motor's control circuit properly protected against overload.
we are using 3 hp motor in tray separator. motor is delta connected as per name plate but we ran the motor in STAR. now motor one coil has burnt. explain me the reason?

Motor run for 3 months. why it failed after 3 months?

<b>Moderator's Note:</b> By STAR, he may mean Wye connection.

#### Guddu

What will happen if a star designed motor is connect with delta connection?

If motor control system is having proper protection against overload then it will trip frequently and if there is no protection against overload or inadequate protection is there, winding of the motor shall burn.

#### PhilCorso

Zaheeb834m...
I suggest you address the topic "Delta vs Star" or "Star vs Delta" at the Magnifying Glass Symbol at the beginning of this thread? You will find many answers, dating back many years !
Regards, Phil Corso