Calculation of capacitor value for conversion from star to delta

[The Ghost]

Hi does anyone have a notion of how to calculate the capacitance value for the above?

 

[Lucien Nunes]

There is no one ideal value as the third leg current depends on the mechanical load, and if this is highly variable a compromise value is needed. The motor will always be running under abnormal conditions and its performance and power will be reduced.What is the application?

 

[The Ghost]

It's a 2Hp 9a 2Kw motor for irrigation on a farm. It may be it is single phase so nice and simple I am not sure if they send them all out as three phase or what at the moment awaiting more information.

 

[The Ghost]

So this pump will pump clean water to the field and has a Domino UP controller which is really just a fancy switch(ing) system to control and alarm running dry, or managing other switches such as float switch or pressure switch (Danfoss KPI35) for the expansion tank. I realise the float switch may be redundant. The Domino checks dry running through setting the Cos/Phi level at the motor.

 

[Andy-1960]

A single phase to three phase inverter may be a better option

 

[The Ghost]

single phase to three phase inverter

Mhmm that seems a lot less of a head ache.

 

[The Ghost]

capacitor come in to

Sorry meant to put your quote in on post #10

 

[westward10]

Rotary inverter.

 

[The Ghost]

Rotary inverter

Rotary Inverter, mhmm yeh, errr what is that?

 

[Lucien Nunes]

OK I don't think you want to be messing about with mismatched capacitors in that application. If the pump is supplied with a correctly sized 3-phase motor, it may be inadequate and/or overheat running on a single-phase supply; irrigation pumps run long hours at full load. A proper inverter drive is the solution, that will give it an accurate 3-phase supply, however the monitoring in the controller may not understand what is going on and might have to be disabled or modified. I would seek advice from the controller manufacturer.

 

[The Ghost]

Yes indeed overheating is very possible. The water, head lift and supply bar in (none of my concern) also better be right for the same reason as the bar in must equal the bar out and so on. Fortunately that is being all taken care of by experts the client are consulting. I am just waiting for more info. But ultimately was just curious regards calc. for cap. on conversion of three to single phase as a more general head banger for a quiet Saturday night.

 

[Andy-1960]

VFNC3 Nano Inverter up to 2.2Kw - https://www.pes-group.co.uk/shop/variable-speed-drives/toshiba/single-phase/vfnc3-nano-inverter-up-to-22kw

The prices shown are list, may be eligible for discount to trade

 

[westward10]

It is possible to run a polyphase motor from a single phase supply using the Steinmetz method which employs a capacitor to shift one of the windings but power and efficiency are reduced as the shift and balance will never be correct. Whilst this can be achieved practically in reality it will never be a solution this is why you are not likely to see it outside of a classroom.

 

[davesparks]

Exactly, converting from three phase to single phase.

Right, that’s not what it says in the thread title, hence my confusion. Star and delta are both three phase configurations.

 

[westward10]

I think an approximate rating is 70uf for every 1kw of motor power.

 

[The Ghost]

not what it says in the thread title

Agreed, I could have been clearer and stated three phase to single phase, it would have helped!