Motor connection

grousedogtom

Hi
I fitted a vsd on a water pump motor today and noticed the motor was connected in star, it was originally connected DOL via contactor and overload, looking at the name plate on the motor should it actually be connected in delta for 3 phase 400 volt supply?

Luckysasha

Certainly looks that way according to the plate.

2011

If I were doing this I would connect it in delta. This will mean that the motor will be able to provide up to 7.5kW output (at 50Hz) with a full load current of 14.9A

As I am sure you know high starting currents are no longer a concern and the output can be varied as required. Remember the cable between the VSD and the motor should be a 3 core with the earth cable run separately.

Out of interest what type of VSD are you using?

Is it connected to a PLC / control system?
How is the VSD being controlled?

grousedogtom

Invertek vsd,

grousedogtom

0 to 10 bar pressure transducer wired back to vsd set up on drive at 50 percent to maintain 5 bar pressure in the line

2011

grousedogtom wrote: »

0 to 10 bar pressure transducer wired back to vsd set up on drive at 50 percent to maintain 5 bar pressure in the line

Very good.

So 0BarG corresponds to 4mA and 10BarG corresponds to 20mA with the 5BarG set point at 12mA ?

Not familiar with that make of VSD.

frankmul

Might here be an issue with excessive power been developed, if the motor completed the task wired in star, will it be too powerful in delta, the inverter may be running at min speed to maintain 5 bar pressure?

Bruthal

frankmul wrote: »

Might here be an issue with excessive power been developed, if the motor completed the task wired in star, will it be too powerful in delta, the inverter may be running at min speed to maintain 5 bar pressure?

Interesting question. My opinion on it.....


If its a pump it shouldn't matter. Pumps are based on rpm, which should be the same in star and delta apart from slightly less magnetic slip in delta, slip depending on mechanical loading. As in the synchronous speed is the same.

Put a 100kw motor on a pump that needs 10kw, and there will be little difference I'd say.

But if a pump only needs 5kw, a 15kw motor in star will do fine, but should be fine in delta too.

An underpowered motor would be a problem.

2011

frankmul wrote: »

Might here be an issue with excessive power been developed, if the motor completed the task wired in star, will it be too powerful in delta, the inverter may be running at min speed to maintain 5 bar pressure?

Remember the pump will be controlled by a VSD so the power output will vary as required.
If concerned it is possible to "clamp" the VSD output.

Bruthal

2011 wrote: »

Remember the pump will be controlled by a VSD so the power output will vary as required.
If concerned it is possible to "clamp" the VSD output.

Won't matter anyway. If the motor is connected at 50hz in star or delta, it can't give anymore power to the pump no matter how big the motor is, once the pump is spinning at 3000rpm (minus slip)

2011

My point is that according to the name plate the motor can deliver 7.5kW when connected in delta to a 3 phase 400V supply, however a VSD is used the output power can be restricted to a value below that if required. In addition the output from the motor can modulate (using a control algorithm such as PID) to suit load requirements.

Bruthal

My point is to reply to a poster with my own view, asking if the motor powers the pump adequately in star, will delta then be overpowering the pump.

So if the motor is rated 7.5kw in delta, but is connected to a pump requiring 2kw for example, connecting in star will be using 80 percent of the star output, but if connected in delta, it would use only 27 percent of the delta rating.

So my view is, for a given mechanical pump, making an induction motor to power it bigger than required, won't really make the pump output any more. Assuming the motor rpm is the same.

frankmul

I was just wondering, if the load required to maintain 5 bar is only 2kw (star connect 7.5Kw is 2.5 KW)and the motor is been ramped down to maintain the 5 bar. Will the pump running at a minimum speed to allow for self cooling cause the pressure to be in excess of 5 bar if the motor is connected in delta.

Bruthal, I understand your point regarding the delta connected motor only developing the required power but as a result running closer to synchronous speed. I'm just wondering about putting in an inverter to control a pressure with motor speed, will there be any issues if the motor is too powerful and needs to be slowed down too much to achieve a set point

2011

A few things to think about:
1) The synchronous speed variable because it is a function of the frequency.
2) The cooling required by the pump will reduce as the motor ramps down.
3) The VSD makes it possible to vary the voltage, frequency and power output of the motor. Ultimately it can solve a lot of problems.
4) Motors are de-rated when connected to a VSD, so oversizing the motor is inline with best practice.
5) The VSD will correct the power factor of the load (as seen from the upstream supply) to unity.