Wye-Delta with finesse.
Wye-Delta with finesse.
(OP)
I have three single phase loads that I need to reconfigure between delta and wye depending on available power sources. Not voltage, just kW abilities - meaning the supply voltage is constant.
I'm thinking the same scheme as a wye-delta starter should work fine. I'm just replacing the coils in the picture with my heaters.

Ignoring 1,2,3.
WYE: 4,5,6 CLOSED 7,8,9 OPEN
DELTA: Reversed.
It looks like I can do this with one contactor since there are common points between the two groups of contacts.
See any problems?
I'm thinking the same scheme as a wye-delta starter should work fine. I'm just replacing the coils in the picture with my heaters.
Ignoring 1,2,3.
WYE: 4,5,6 CLOSED 7,8,9 OPEN
DELTA: Reversed.
It looks like I can do this with one contactor since there are common points between the two groups of contacts.
See any problems?
Keith Cress
kcress - http://www.flaminsystems.com






RE: Wye-Delta with finesse.
If you are below about 12 amps you may get away with using a tripple pole double throw relay. Use the normally closed contacts for your wye connection and if the kWs are available, energise the relay to go to delta. If you buy an off the shelf star delta starter it may come with a two pole contactor for the shorting contactor. If you are building from scratch, I doubt that you will find a two pole contactor at a reasonable price. Just use a three pole contactor for shorting.
Bill
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"Why not the best?"
Jimmy Carter
RE: Wye-Delta with finesse.
Do you need it for starting or for extending speed range in VFD situations?
For the latter application, it would probably work very well for small motors. But, for the usual Wye/Delta applications, I doubt if you can find contactors where the auxilary contacts can do any useful work.
A problem with standard VFDs is that they don't like switching in the load circuit while running. You will need to disable the IGBTs, then switch and then use the "catch" function (flying start), which needs to be available in the VFD.
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Wye-Delta with finesse.
Okay I will just use two definite purpose contactors and for the unfun of it I will add aux contacts to prevent them both from ever being closed at the same time.
Gunnar...
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wye-Delta with finesse.
Consider a reversing starter or the contactors from same. This will give you the added safety of a mechanical interlock.
Also, some of the IEC lines have available mechanical interlocks that may be added to two basic contactors. Try GE's line of IEC control gear.
When I was doing a lot of motor and motor control work I had a number of exciting events. All of them could have been prevented by at least two safety interlocks. Your mechanical interlock is very good protection but still add the cross connected electrical interlocks. When I was teaching motor controls (hands on with actual industrial control components) I had a set of contactors that was able to "Kiss" two phases if both operating coils were energized at the same time. Once one contactor seated, it would hold out the other contactor but a control circuit failure that allowed both coils to be energized simultaneously could make a bang. I used light bulbs to demonstrate the possibility to the classes. 120 volt lamps on a 208 volt circuit made a "flashy" demonstration.
I always use at least two interlocks on reversing and similar contactors.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Wye-Delta with finesse.
But!! Turns out that we have a set of contractors on the shelf that has a mechanical interlock between them that prevents them both from ever being closed simultaneously. Probably a three phase reversing contactor as you describe. So we should be good to go.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wye-Delta with finesse.
Or is it an automated thingy ?
RE: Wye-Delta with finesse.
Gunnar Englund
www.gke.org
--------------------------------------
100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: Wye-Delta with finesse.
RE: Wye-Delta with finesse.
This is back to that damned water heater. It's three single phase 10kW 240V heater elements that get staged on from one to all three depending on hot water demand.
Supply 1) On HEP we have three dry type 480V to 240V transformers hooked up delta delta. They are 20kVA each.
Supply 2) The generator is only 52kW 240 3ph delta
This *&($^#!! heater is single phase 10kW + 10kW + 10kW fully cranked or 41A + 41A + 41A = 123A
Simultaneous loads can be 30A 3ph refrigeration + 50A 1ph range/oven + psycho water heater(WH).
We have been told by the factory that the WH can be run three phase. So this means we can break the heaters up into each element across a different phase.
We will do this but this means it could be a 1ph load, then a 2phases load, then a balanced 3ph load(rarely).
My initial intent was to reduce the load when constrained by the generator by switching the WH to a wye configuration. (Less water heating but them's the breaks.)
Then it dawned on me that the wye-delta scheme for motors was based on three even phase loads. If the WH is set up without a neutral(there is none) and all the heaters in wye and only one is commanded on, I'll get nada.
I think we need to hook this beast up delta and running on the generator, and see what happens. If it ends up being too much for the generator dealing with these horrible unbalanced loads then I'll have to come up with some other scheme - hair brained probably.
Present consideration is that we have 120V 3ph with a neutral. Perhaps using this. It causes wiring conniptions because I'd have to ditch the neutral altogether during 240 operation. Hopefully I won't need it.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wye-Delta with finesse.
Ah, that WH case.
The wye-delta, 6-lead motor is meant for two different voltages. In your case, you are stuck with one voltage.
How about using a 240/120 V step-down transformer from the generator and then connect the heaters to the 120 V ?
RE: Wye-Delta with finesse.
RE: Wye-Delta with finesse.
Maximum heat demand, all three heaters on. 120 volts instead of 240 volts = 1/4 output. No problem.
Reduce heat demand, two heaters on. two heaters in series across 208 volts. Each heater gets 104 volts instead of 120 volts. Not enough unbalanced load to bother a small gen set particularly a delta connected set. Capacity is now 2/3 of (240/104)^2 = 12.5% of rated output. This is probably enough to keep the tank hot when there is no flow. Any water usage will promptly kick you back to 3 elements.
One heater connected, no current flow, no heat. No problem, any temperature drop will soon kick in two or three elements.
Bill
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"Why not the best?"
Jimmy Carter
RE: Wye-Delta with finesse.
wayne440; Welcome to Eng-Tips.
That's a good idea. Lockout one and run the other two against the range. I like that a lot. And since we are already presuming to reduce heating that is a good way to do it. It would take only one set of contacts. Nice.
Bill; No tank. That's the entire problem. We had this problem solved for about $2k. We had a tank heater with upscale heating elements for fast recovery all speced out, and the perfect place to put it. Then the customer dropped this on demand heater on us. We tried every way we could to abort this. No luck. So we've just exceeded $20k so far on this lamoid heater. I am wary of a low voltage scheme because I don't know what the built in controller will think of the lower voltages. I am sure the actually controller has to have 240V to operate. I am concerned that if I power the controller on 240 and then feed its power control elements 120/208 it might not like that. I think I'll propose the wayne440 solution as then we just interrupt one heater element during generator operation. Easy to do.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wye-Delta with finesse.
I have suffered with on demand heaters from Canada to Chile. I have yet to see one that does not need more power input than it actually has. There may be one somewhere but I haven't seen it. Yes there are a few niches where they work well and yes, there may be one somewhere that does actually have enough power input to achieve rated temperature at rated flow, but I haven't found one yet.
Can you share with us the overall picture? What is the duty cycle? For 100% duty cycle, on demand becomes viable. I have seen on demand used to preheat water ahead of a conventional tank or heater. They will work well to greatly improve recovery time. I have seen a couple of implementations where a large tank was heated by a loop that circulated the water through a demand heater.
I'm guessing that one of your rail cars is getting a new kitchen.
Do you have any wiggle room on the generator? If your proposed gen set is naturally aspirated, upgrading to a larger alternator and the turbo charged version of the same engine may give you the capacity you need with very little increase in space requirements.
when I am getting that close, I start to juggle power factor, KVA and kW. It usually isn't enough but sometimes you get lucky.
Another trick if you get close is drop the voltage to 230V or 235V. 230V gives you about 8% extra.
The oven is more forgiving than an on demand heater. You can use a small dry type transformer configured as an auto-transformer to shed some load. The initial warm-up will take longer but it should maintain the temperature well when cooking.
Keep us posted.
I always find that the toughest challenges are man made rather than natural!!! LOL
Bill
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"Why not the best?"
Jimmy Carter
RE: Wye-Delta with finesse.
Now days no steam, propane is strictly verboten, and wheel driven 32VDC generators and their truly massive battery banks are frowned upon, or not allowed. The middle of the road 52kW 62kW(intermittent) turbo Cummins powered generator was installed. The 15kVA transformer bank was put in. Heat was converted to electric.
Car changes hands. To be improved while maintaining historical look for museum service.(absolute requirement)
Lighting remains 32VDC, large power supplies installed. Stove converted to electric. Blowers from 32VDC to 3ph 240V.
Then in from left field this on-demand water heater lands in our laps. It completely misses the entire spirit of the situation. This is a passenger rail car.. It only carries enough water to get by for 2 days if people conserve. It isn't an endless supply, to be endlessly heated, and supplied to the Roman Baths. The system has 3 baths, 3 showers, and the kitchen which will occasionally be called on to serve up to 400.
The hot water circuit is looped to circulate because water is so precious we can't have it running into holding tanks while someone waits for it to heat up. Unfortunately I'm not even sure it will trigger on the ciculation alone.
The other concern is that someone will show up at the car, in a yard, with near freezing temperatures, fire up the generator the car heat and the heater will simultaneously hammer it with the full 60kW until the loop warms up.
To accommodate the heater the 15kVA bank of transformers were scrapped. The thousands of pounds of new 20kVA ones, and their increased size, required the building of a huge underslung welded subframe by certified welders.
Then they call me! So you see this isn't an engineered system with a plan and execution. It is sort of a rolling hairball you try to do the best you can with, as events unfold.
I have told them to set it up with the WH third phase (used by range) locked out on generator and we'll try it with cautious testing. This way the yard doesn't have to argue further with the ee who is the historical refurbisher who provides incorrect water heaters. If testing shows a problem then the problem "does the explaining", and you find the author of the problem to be much more receptive, than otherwise, to needed changes.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Wye-Delta with finesse.
(Why delta on the generator? And why the transformers? Is this a three lead or six lead generator? Fairly rare if it is!)
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Wye-Delta with finesse.
The generator.. not sure actually. I'll ask.
Keith Cress
kcress - http://www.flaminsystems.com