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View Full Version : 'Nother one for you guys: Three phase power, Delta or Y?



Fasttrack
04-11-2008, 05:00 PM
Is there a difference between Delta and Y motors? Can you just rewire them like changing voltages or ...?

What happens if you put a Y motor on a Delta source or vice-versa? Don't jack about three phase, so ... enlighten me! :D

NickH
04-11-2008, 07:18 PM
You wire it appropriately for your voltage, check the motor plate,
Regards,
Nick

Mosside
04-11-2008, 07:21 PM
This would be a good question to pose on the Electrical Form over on the PM site. There are some really smart guys over there that would give you some of the backgound info.
When you mean a Y source are you refering to 208 3 phase that has a reference to nuetral?
Most of us mere mortals just wire it like it tells us to on the diagram and don't dig any deeper.

Doug

NickH
04-11-2008, 07:28 PM
Star can have center connected to neutral return although with a balanced load that ought not to be necessary and when using an inverter neutral is almost always not used.
If you read up a little on how and why 3 phase works it all makes sense, if you listen to bar room electricians none of it makes sense,
Nick

bytewise
04-11-2008, 07:32 PM
There is a difference in the internal winding of a motor for Y or delta but it is not important when using the motor. Many 3 ph motor are dual voltage,(e.g. 220/440 volt). If so they should have a diagram about which wires to connect together for the voltage you have available.
Note that you can change the direction of rotation of a 3 ph motor by swapping two of the input power connections.
Most 3 ph power commercial sources consist of 5 wires: 3 power wires, Neutral, and Ground. In the case of 220 volt service this provides 115 volts between each power leg and the neutral. A 3 ph motor does not need the neutral regardless of its internal style. It only needs the power and ground for safety.

darryl
04-11-2008, 07:32 PM
There is a difference, but either configuration would be wound properly to use common 3 ph power. I don't recall which, but one requires less turns per winding for the same voltage. I wonder if the design rpm of the motor has anything to do with the choice of how the motor is wound- maybe the delta wind is for slower speeds and the Y wind for higher speeds, or vice versa- . At any rate the motor would be spec'd for the voltage it runs on and you wouldn't need to know what type of wind it has. Like Doug said, just wire it according to the diagram and it will run. Reverse any two of the wires to reverse direction.

Dawai
04-11-2008, 07:58 PM
For common American 9 lead motors

Wye is the center tapped version..
tie 4,5,6 together lines on 1&7, 2&8, 3&9
This is normally used for 220 run connections also.

Delta?
4&7, 5&8, 6&9 lines go on 1, 2, 3
This is normally used for 440 run connections.

Used to be big motors started WYE, ran till up to speed, then you pulled a big handle that looked like a truck gear lever to shift it off, then into Delta run position..

If it blowed up as you switched it in? you'd have a blackened face and a handle in your hand.
The later versions had multiple contactors and a vacuum relay that switched the start relays in, and out when it timed out, then the run relays in.. All 9 leads had to come out to the starter. The starter box for a 200 hp was about the size of a sheet of plywood and two feet thick.

The nameplate rules.. read it.. hook a 12 lead motor up like a 9 and have problems.. ok? Oriental motors, learn Chinglish, european motors find them lil brass links to make the connections.. store them on the motor or you will surely need them later.

Fasttrack
04-11-2008, 09:36 PM
Maybe I should have explained better - the issue here is that I'm buying a lathe from a guy currently running a 10 hp 3ph motor off of a rotary phase converter. I've asked for any pertinent information from the motor plate because I intend to wire this directly to 3 phase power. (no converter needed) however the 3-phase power that this shop has is delta. I was just wondering if that was a potential problem that I should be looking out for.

Thanks guys, and thank you David for your information! - I'm no electrician but you spelled it out pretty well for me.

J Tiers
04-11-2008, 09:50 PM
Wye applies less voltage per winding, by a factor of 1.73.

So for instance, if your factory is wired with 480V (measured delta) then you can run 277 V (which is 480/1.73) lights from the phase wires to neutral (i.e. wye).

A motor if wired delta would operate on a lower voltage 3 phase line than the exact same motor wired Y.

Or, conversely, a motor that was operated delta would be operating on a lower voltage if started Y. That is why the "wye start" is used, it is a form of reduced voltage starting.

It's generally possible to re-wire one, but the factor of 1.73 isn't that common; 120 : 208 (common, but not overly useful), 208 : 360, 220 : 380, 240 : 415, 265 : 460, 277 : 480.

A wye motor can be hooked to delta 3 phase, no problem. The neutral is not brought out from wye motors. A typical treatment is to common-up the three windings through a 3 contact thermal protector.

clutch
04-11-2008, 10:50 PM
Used to be big motors started WYE, ran till up to speed, then you pulled a big handle that looked like a truck gear lever to shift it off, then into Delta run position..



Most of the cnc's I repair have wye/delta motors with a winding changer that the spindle amp controls to change the number of poles and synchronous speed as various rpms are developed.

Beats shifting a gear box.

Clutch

Paul Alciatore
04-11-2008, 11:56 PM
OK, here goes.

Three phase is three phase. It has three different hot wires and possibly a neutral (neutral is optional with three phase). The Voltage between any two of the phases is the same. V12 = V23 = V31. A given hookup may or may not have a neutral. The Voltage between any phase and neutral will be the same, but not the same as the Voltage between the phases. Vn1 = Vn2 = Vn3 but not = V12, etc. The most common three phase is 208 Volts and in this form, there is 208 Volts between phases (V12 = V23 = V31 = 208 Volts) and 115 Volts between any phase and neutral (Vn1 = Vn2 = Vn3 = 115 Volts).

Motors can be connected in either a delta or a Y configuration. In the delta connection there is no neutral and the three coils are connected between the three possible pairs of lines 1-2, 2-3, and 3-1. The coils see the Voltage that exists between these pairs.

In the Y connection, there is a neutral connection and each of the three coils is connected between the neutral and one of the three hot wires. N-1, N-2, and N-3.

Some motors may be wired for only one connection and others can be wired differently for different situations. If a three phase motor has only three or four wires in the connection box, then it probably has only one possible connection and you have no choice. If it has 6, 7, or more wires, then it very likely can be connected in different ways.

Many motors have all of the connections to the windings brought out to the connection box (more than four wires) and they can be connected to the power source either way, Y or delta. They WILL run either way as long as the correct Voltage is present on the coils. This is important if you want it to run at the proper speed and if you want to avoid burnouts. If the motor coils are connected to a Voltage that is too high, they will draw too much current and overheat. Smoke and possible burn out. If they are connected to a Voltage that is too low, the motor will run slow and also may overheat for more complicated reasons. Again, possible burn out.

So the Voltage on the coils is more important than the actual type of connection. As mentioned above, the delta connection provides a higher Voltage to the coils than the Y connection will with the exact same three phase power. This is due to the nature of the thing.

So, if you have a motor with coils that are rated for 208 Volts and a power feed of 208, three phase, then you are going to need a delta connection to put the full 208 Volts on each coil. If you use a Y connection you will get only 115 Volts on each and it will run slow. The opposite can also be true.

You need to look at the connection diagram for your motor to find out exactly how it should be connected to the power you have. It may not specify Y or delta, but just the colors of wires to connect together and to the three phases and possibly to neutral. Just follow it and you will be OK.

Note: I spoke of three coils in the motor and that may be the case. But many motors are built for many different configurations for different Voltage hookups as well as Y and delta. An actual motor may have split windings and there may be six or more actual coil connections in the box. Six coils would have 12 wires, two for each coil. Again, you must follow the wiring diagram for your actual motor to connect it for the Voltage you actually have.

Just remember that Y and delta refer to the way the load (motor) is connected, not to the incoming power.

Peter.
04-12-2008, 01:19 AM
Over here in the UK most of the 3-phase motors I have ever used have had a Star-Delta starter. The motor starts running on star (Wye) then once it gets up to speed it switches (or you switch it) over to delta. Newer systems use what we call a "Euro-start" which makes the motor sound like it's 'pulsing' at start-up but there's no switchover.

J Tiers
04-12-2008, 08:50 AM
Motors can be connected in either a delta or a Y configuration. In the delta connection there is no neutral and the three coils are connected between the three possible pairs of lines 1-2, 2-3, and 3-1. The coils see the Voltage that exists between these pairs.

In the Y connection, there is a neutral connection and each of the three coils is connected between the neutral and one of the three hot wires. N-1, N-2, and N-3.



A motor which is wired wye (star), is generally NOT referenced to a real neutral wire........

Usually the neutral, or common connection, is just the connection point of three wires, and has NO external connection at all. Motor function does not require such a connection, and it may actually be a problem, depending on the type of 3 phase.

Obviously the supplied neutral of the common "stinger" three-phase 240/120 service is NOT equivalent to the 3phase neutral, and any motor which needed a neutral would not function on that type service.

Dawai
04-12-2008, 10:43 AM
YOU MEAN TRANSFORMER? input Delta?? OKAY..

DELTA INPUT NORMALLY DOES NOT HAVE A NEUTRAL.. it works just like wye 3 phase.. except you can't pull a light off the phases since it floats about, you must use a transformer to transform the delta no neutral to a voltage with a bonded neutral there.. OK.. that will refrence the voltage to ground and allow stable voltages..

WYE the center tap is the neutral, common refrenced to ground and all three phases are stable voltages..

Sometimes they use two transformer coils to make 3 phase, also tied in WYE, but one leg is a stinger leg that floats from 70 volts to 180 to the neutral leg.. will burn up all 120 devices tied to it.. CHECK with a meter.. ok.. If you don't know how to read a meter, back off the project and let someone else come in.. ok?

You could however use 220 volt lights and use two phases.. Okie dokie? In between phases it is stable.

If you require more knowledge that that? I suggest the "electricians handbook" for all to read.. available through the local JATC or college library.. it is about 3 inches thick so be prepared.. a used one is about $50..