remote switching between star and delta (both ways)

[Gmag]

Hi all,
I apologise for jumping straight in with a new thread asking questions. I did search and can't find any info on my problem.

Getting to the point...

I have fitted an ABB EXE2S star delta starter to run a 3phase 15kw motor on an extraction fan. The starter is working perfectly but the user wants to be able to remotely switch between star and delta and vice versa after the fan has been initially started.

The end idea is to be able to start the fan normally using the standard push button on the starter but then be able to remotely switch between star and delta via from a pc as and when needed.
My theory was to interrupt the wiring either going into or coming out of the timer for the starter and install and remotely activated relay. This way (in theory) The start button would be pushed as normal and the timer would count down as normal before allowing the delta switchover, although the switch to delta would not happen until the user activated the relay to complete the circuit from the timer coil to the timer contactor.
Also the user 'should' be able to de-activate the relay which would reverse the contacts again and return the motor to star configuration without having to stop the motor and restart it.

I had a quick look at this today and although I understand the star delta circuit wiring I am not 100% on the control circuit side of things.
From what I have researched, the timer should only be triggered when the start button is pushed. Then once the timer has counted down it will activate the timer coil which in turn switches the timer contactor.
When I tested with the multimeter today I found that all 4 wire terminal of the timer showed 230-240v all the time regardless of whether the motor was stopped, in star or in delta.
This seems strange to me so I am obviously missing something.

Is there a simple way I can achieve this using the like of simple relays and pc control? It would be an added bonus to also have the start/stop functions controlled in a similar manor but that isn't needed.

The fan runs in star or delta with no issues.

Thanks in advance.

Gav.

 

[Bobster]

Why did you not just install a VSD, would have made the motor a lot more controllable, it would have also saved putting the motor under stress everytime it changes over.

 

[snowhead]

What is the user trying to achieve by switching between Star and Delta?

Is it their idea?

Did you know of this before you fitted the S-D starter?

 

[Darkwood]

Why!!!!..... As already asked - Why would they want to do this its started in star/delta to limit inrush current on start-up then to swap to efficient running when up to speed...

If you had this info to start with then you could have fitted a drive (VSD) to give you a wide range of control options ..... again as mentioned ..

To consider - a motor under high torque swapped back to Star would lose alot of its available torque and could stall the motor but with regards to the fan i suppose the inertia may limit the negative effects of this as the spinning energy would allow it to slow down progressively until the reduced torque level of star is met but a very inefficient way to run it. IMHO

 

[Gmag]

I agree it sounds a little strange. A VSD wasn't installed initially due to cost as the starter was obtained relatively cheaply to get things up and running.
The reason for wanting to switch is that the fan does not need to run at full speed all the time. Say only around 20-30% of the time when needed. I suggested that something 'might' be able to be done to allow switching between star and delta. Most of the time it would run in star to save on running costs with the ability to use delta now and again for extra airflow when needed.
If it can't be done then of course it will run in delta as normal until something like a VSD is installed.

 

[Gmag]

Just to add.
The fan is flowing to open air so it happily runs in star configuration without stalling.

 

[Darkwood]

The star config for your fan wont see much in the way of speed reduction as Delta will pull in approx 75% - 85% of full speed if the sizing of the motor is such that the fan has all the available torque in star it will run happily in star but wont see alot of difference in running speed.... this is not a 2 speed motor the only issue here is if if the star torque is running near 100% then any slight issue like bearing wear etc could see a small under torque situation but with only small current rise, this may not be seen by the overload and overheating and failure of the motor could follow .... i would suggest you monitor current demand etc with knowledge of expected current flow for that config..... the nameplate will give the Delta config and not the running currents of star in this case - but its easy to calculate.

Star Delta Start Up Principles

 

[Knobhead]

There are no economical reasons for switching back to Y with light running loads. Power out = Power in + losses. The current inrush at the transition Y∆ can be higher than DOL starting, this can also cause mechanical damage. In Y the motor is trying to achieve its rated load speed but can’t quite make it. Power factor will be abysmal as will efficiency.
There is an Indian company peddling this idea as “energy saving”, it doesn’t do any such thing.

 

[Gmag]

In this case there is quite a difference in running speed between star and delta. I tested this by adjusting the timer to say 10-15secs. The fan starts and holds a steady (lower) speed in star after around 2-3secs. The speed stays steady until the timer switches to delta where it significantly increases in speed. I would guess star gives around 60% of full speed.

I will need to test the current draw as mentioned but by the sound of things, this can be done?
I am thinking a second lower rated trip switch wired in line somewhere with the star contactor would solve the overload protection issue with the original overload left to handle delta running?

 

[Knobhead]

The O/L in a Y∆ starter should be connected in to one leg of the delta anyway, you don’t need to change it.
Because the motor is running slower doesn’t mean it’s running more efficiently.

You seem determined to continue with this stupidity, carry on.

 

[Gmag]

Tony....
So running in star is less efficient of course but surely it will still use less energy overall compared to delta? Just that delta will give more flow for a given amount of energy input?
My thinking is simply that there may be no need to have the fan running full speed and using more energy all the time when star would be sufficient most of the time and although not as efficient it should still use less energy?

 

[Guest111]

There are no advantages to what you are trying to do,a VSD is the correct way to go,if you go down the road you are going I can see problems in the long term.Simple philosophy is if people want something then they pay for it to be done the correct way,by suggesting that you MAY be able to do something around star/delta the customer will have got it into his head that it can and will work this way.Important lesson here is to ensure brain is engaged before opening mouth.

 

[Gmag]

If the efficiency in star is so poor that it uses the same or more/less the same power consumption as in delta then of course there is no sense in running in star.
if that is the case then it makes my life easier and the user will simply run it as normal until a VSD is aquired.

Tony I would point out that I already stated this in my second post so stupidity is not the factor here! I simply thought I would try to adapt the circuits 'if possible' to best suit the users requirements. As I was unsure I thought it would be wise to seek advice from some more experienced people.

Thanks for the help guys.

 

[netblindpaul]

What is the point in doing this?

 

[bomjac]

Other than the VSD solution as already advised, you could install a 2 speed fan. Pretty common in HVAC systems.