Induction Motor

Just a question - Are you in wrong field or are you a student?

The current value looks to be too perfect to be true (except theoritically) and should not be in so lightly loaded motor.

The second option looks more likely.

If your mechanical load is only 5 hp, connecting in star will work, and will save a little (but not a lot) on energy usage.

1. In my experience, a 15hp motor, even on no-load, should draw ~ 10A (line current). Are you measuring line or phase current?

2. Energy = Power x time = kWH, not kW, pardon me for the editorial correction.

Since even at no load, it draws this kind of current, you can as well go for a smaller motor or switch off

What is the nameplate current of the motor?. The no load current should be between 30 to 50% of FLC depending on the design. There should be a relationship between no-load current,design code and FLC. I have suggested to print the no load current too in the nameplate of motors,who can do it. Also check the accuracy of the clamp-on-meter.

hey just dont get confused by the figures. i want to know the concept. Some doubts in my mind i want to clear them by discussion. my question, is there any saving by converting connection of induction motor from delta to star.pls. keep in mind mechanical output is same as before. thanks.

Delta, star, open delta, zigzag, you name it, the power will be exactly the same..... as long as the Current and Voltage change to suit.

For example, in Star and Delta, Power at the motor shaft = √3 x V x I x Cosφ x η.

So, if you can get the appropriate voltages, the currents will take care of themselves, and everything is hunky-dory

You really can't learn all electrical engineering here in a finite time Mr Goyal. You really need to study your textbooks.

The starting as well as running current will be less in star. Normally motors with 6 terminals should be connected in delta. The connection depends on the winding arrangements. In star line current flows through the winding and in delta 1/1.732 of line current flows through the winding,therefore the connection should be mentioned in nameplate or contact the manufacturer. To deliver the same horsepower or kW can the same winding carry higher current in star?.

Hi, what the matter have you described ,you are not going to save the energy.then obviously question will arise why the value of current is changing. when you will prefer delta connection or star connection theory ,you will find there is a 30 degree distortion in phase angle.that's why current value reduces by I/sqroot(3) means 1/1.732.

current value for delta connection was 6 amps then current value for star connection will be 6/1.732 = 3.46420amps and this value you are getting.for detail have a look the book of power system.

thanking you.

plz verify the answer and see that 3^0.5 *3.46 is actually 6

It depends on the motor. There are two conditions where the motor has leads brought out for connection in Star or Delta. It is either a Dual Voltage IEC motor, or it is a Start-Start / Delta-Run motor.

IF the motor is wound for dual voltage, i.e. 415 / 240V, then the Star connection would be for the 415V operation and Delta would be for 230V operation. Connecting for one voltage when you have the other will not result in a valid motor configuration. It will spin unloaded, but any load applied will immediately result in a problem of one sort or another. What you can observe when the motor is unloaded is completely meaningless.

If you have a 415V line and you use the Delta winding configuration, you are seriously over-exciting the windings (V = 1.732X) and they will saturate. It will create extremely high initial torque, but will quickly over heat because in saturation, you will consume energy while doing no additional work and the motor is not designed to dissipate that additional energy. The end result will be a damaged motor.

If you have 240V on the line and you use the Star windings, that motor will produce significantly less torque and as mentioned above, will become the equivalent of a 5HP motor, but with very little slip tolerance. So if your applied mechanical load requires 5HP or less it would technically work, but the instant the load needs more than 5HP, the motor will stall.

If on the other hand your motor is simply set up for Star-Delta starting, then running it in Star results in the second condition without the 240V line issue. In other words now you have a weak 5HP motor and if the load requires 5.5HP, it will stall.

Motors manufactured by GEC in UK to BS has 12 wires(each phase is split into two equal halves) and it could be started and run in DOL or star-delta at low voltage(220V,3ph)) by connecting the two halves in parallel or at high voltage(380V,3ph)by connecting in series.