motor
I have a motor with specifications:
and motor is of course 3 phase.
Now the question is, how can I connect the motor to delta connection if I have only 400V line to line voltage? Where can I get 230V line to line? Will I damage the motor in delta connection? Is delta configuration only meant to be using with VFD in that case?
If the rated voltage for the delta connection is applied to a star-connected motor, the resulting torque and current are about one third of the characteristic torque and current for the delta connection. As a result, at the transition from star to delta, the change in current and torque is about a three times increase. Therefore, an increase from 40 to 130 amps is within the normal range.
If the current doesn't drop to a normal running current in six to ten seconds after the transition, the motor is not adequate for the load, there is a problem - possibly an unconnected phase in the delta connection, there is a mechanical problem with the load or some other problem.
Star-Delta Starting Characteristic Curves and Explanation
The torque and current vs. speed curves shown below are for a typical IEC Design N or NEMA Design B motor with star-delta starting. The load torque requirement shown increases as the speed increases as it would for a fan or centrifugal pump load. The substantial torque requirement at zero speed would be a requirement of a pump with a substantial static head. Note that the torque available to accelerate the motor and load is the difference between the steady-state load torque requirement and the available motor torque shown by the motor cur torque vs. speed curves.
In this case, there is very little star-connection acceleration torque available between 40% and 70% of full speed. If the load torque was a little more, or the motor torque a little less, the motor capability torque curve would cross the load torque requirement torque curve and the motor would not accelerate the load to a higher speed until the star-delta transition. The load and motor curves are shown as crossing at a little above 90% of rated speed, a little below the star-delta transition speed.
At the star-delta transition, the torque and current increase to the points at which the vertical transition line crosses the delta torque and current curves.
As Marko Buršič pointed out, the motor is rated 3.7 kW (5 Hp) not 15 Hp. Either the motor's power rating is not high enough for the load, or the transition from star to delta is being done too quickly. If the load is a fan or centrifugal pump, the load will be very low at first and then it will increase very quickly as the motor speed increases. The very low current in star seems to indicate that the motor can supply the initial starting torque, but, in delta, the motor very quickly accelerates the load to a speed where the motor can no longer supply enough torque for further acceleration. The motor draws a high current attempting to accelerate the motor to full speed, but it does not have enough torque.
With a weak (high impedance) power distribution system, the higher current may cause the voltage to drop if the transition is done too quickly. In that case also, the motor may not have enough torque due to lack of sufficient voltage.
There is also the possibility of a mechanical problem with the load, some problem with the motor or a wiring error.
Best Answer
If you have 400 V, use the star connection. There is no reason to use the delta connection and the motor will draw too much current and overheat if you apply 400 volts to a connection designed for 230 V.
There places in the world where 230 V, 3-phase is available and not terribly uncommon, but if you don't have it and have 400 V, there is no reason to find it.
The delta configuration is for people that have 230 V 3-phase. However you could use it with a VFD if you want to operate above the rated frequency. You could probably go 25% above rated frequency and voltage, but the motor bearings and rotor balance are probably not adequate for any speed higher than that.