Motor delta vs. Y

rroze002

Member
Join Date
Jun 2013
Location
Florida
Posts
39
Hi all - I'll get straight to the point:

Problem: Customer has Chinese machines with all motors rated for 220 or 380, but the ware house distribution system is 208.

Background: With the motors setup as delta (220), the motors seem to be running just fine. Some of the motors that are still configured as Y (380) seem to be running well except for the 'soft start' effect from the lower voltage.

Question: Can we leave the Y (380) connected motors on the 208 distribution system?

Any help will be welcomed.
 
Question: Can we leave the Y (380) connected motors on the 208 distribution system?

220V DELTA/380V WYE 50Hz six lead 3PH dual voltage motors use the high voltage/WYE connection
to reduce the winding voltage without/instead of having ADDITIONAL series/parallel motor
windings, as in a typical dual voltage 3 PH motor. There are only 3 windings in these dual
voltage motors. The wye connection is what makes this dual voltage possible with only six leads.
This is also why the high voltage is not double the low voltage.

i.e. 220V is always "seen" by the motor phase windings, because of the direct low voltage
delta connection, where: V Line = V Phase (220V) or the high voltage wye connection,
where: V Phase = V Line(380)/ 1.73 = (220V).

If these are six lead 220/380V 3PH motors; for a supply voltage of 208V, only 120V, i.e.
(208/1.73=120V) is being "seen" by the 3 motor windings while WYE connected, instead
of 220V, i.e. (380/1.73 = 220V).

"The soft start effect", is the motor windings burning up from operating 100V low.
 
Cannot imagine why anyone would you leave the motors connected in Y @ 208V when the windings are for 220V.
Is it such a big job to change the motor connections ?

Another thing, the thermal relays are probably sized for the motors connected in D @ 380V. Connecting the same motors in Y @ 208 V will make the motor currents increase when the load is the same. So you will have to change all the thermo relays !
If you dont change the thermo relays, you will experience that they trip even if there is no overload.
 
Firstly, thank you for the comments and suggestions.

The actual problem lies in the fact that these machines came with motors setup in DELTA and therefore all of the motors only have 2 links. To be able to convert the motors to WEY we will need 3 links, which are not readily available for these types of motors.

The other part which bothers me personally is, all of the motors are between 2-5PH and the machine manufacturer only included individual 60A breakers (so each motor circuit sits on a 60A breaker) as the motor protection scheme. The next thing that I plant on doing is measuring the running current to get some idea on where we stand.

Also, all of the motors are rated at 50Hz so technically speaking I do realize that (at the same voltage) we are pumping more energy into the winding. Unfortunately, putting all of the motors on VFD's is completely out of the budget.
 
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To deliver with only 2 links is very bad style.
Are you sure that there are only 2 links, and not that one connection has 2 links on top of each other.
You can make your own links with a short wire with cable shoes on each end.

Also the 60A MCCB per motor is very odd.

The next thing that I plant on doing is measuring the running current to get some idea on where we stand.
No no no. You MUST check the name plates on the motors. Measuring the current can be interesting, but shouldnt be used for dimensioning the protection of the motor.
 
Regarding 50/60Hz. Check the nameplates. There is a good chance that there are values for 60 Hz operation.

Regarding the 208V, then use the current value from the nameplate for dimensioning the protection. The available power will be reduced by a factor (208/220)^2 = 0.89.
But you probably will just find out if everything runs without tripping, then you dont have to do anything.
edit: I assume that you change the motors to Delta connection !
 
"The actual problem lies in the fact that these machines came with motors setup in DELTA and therefore all of the motors only have 2 links. To be able to convert the motors to WEY we will need 3 links, which are not readily available for these types of motors".

DS.jpg
 
I also thought to look for the third link under one of the other links, but there are indeed only two links. These motors are some off-brand with terrible insulation and efficiency factors. For now most motors are running without a problem, but i do belive that they will fail sooner than later.

On a separate note; I also found motors which are rated for 208 Y, so what does this mean for the delta setup.... 120V 3P?

Also, one of the larger 19A motors was tripping the OV and checked out to be running at 35A. What could be the reason for this? I didnt have a megger with me, but the groung to winding resistance is OL, so it doesnt look like a short.

On a good note, I have managed to convince the ovners to invest in some motor protection, so I plan to set them at the nameplate rated FLA.
 
"On a separate note; I also found motors which are rated for 208 Y, so what does this mean for the delta setup.... 120V
3P?"

If these motors are 3 PH single voltage 208 Y connected, there is no delta connection.
Typically by design, 3 PH motors are permenently delta, or wye connected.
For example: 9 lead dual voltage motors are permenently Y or delta connected. There is no access to leads 10,11, and 12,
(which are internally connected), and thus; only 6 or 12 lead motors are capable of being connected in delta or wye.
Motors which can be connected in either delta or wye, are delta run connected motors that can utilise wye starting.
Except; dual voltage delta low V/wye high V motors, where the wye connection is used to provide a second operating voltage.

"Also, one of the larger 19A motors was tripping the OV and checked out to be running at 35A. What could be the reason for this?"

Winding insulation melting off if 380V/WYE connected at 208V? :)
Motor can't reach rated speed or HP?
Motor overloaded?

"On a good note, I have managed to convince the ovners to invest in some motor protection, so I plan to set them at the
nameplate rated FLA."

OL's should be set to 1.25% X FLA.
You will not be able to properly size OL's for Y/380V connected motors @ 208V.
Motor branch circuit short circuit, ground fault and overcurrent protection sizing for single or multiple motors is a whole other story.
 
rroze002 said:
On a separate note; I also found motors which are rated for 208 Y, so what does this mean for the delta setup.... 120V 3P?
How can you ask such a question ?
If you have a motor rated for 208V Y, and you have 208V line voltage, then connect the motor in Y.

rroze002 said:
lso, one of the larger 19A motors was tripping the OV and checked out to be running at 35A. What could be the reason for this? I didnt have a megger with me, but the groung to winding resistance is OL, so it doesnt look like a short.
If the overload (I guess it is an MCCB) trips instantanously without the sligtest delay, then it is a short circuit. If there is a bit of delay, 1 sec and up then it is an overload or locked rotor.
edit: The way you describe, it is not a short circuit. Is the motor connected properly for the rated voltage in Y or D ?

JRB said:
OL's should be set to 1.25% X FLA.
NO !
The overloads already have factored in some overload ability before they trip. Overloads must be set to the nameplate value. There are exceptions, for example using a standard overload for extreme heavy start conditions, but that is an exception.
 
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Question: Can we leave the Y (380) connected motors on the 208 distribution system?

Simple, NO you can't.

You have the correct voltage supply, use it.

How difficult can it be, to get a piece of copper to make a link, or indeed forget about the link. Use the two links you have to make two Delta connections, then undo the remaining two wires and put them on the one post and connect your third supply to it. Anything would be better than what you now have.
 
Remember...as briefly mentioned...These motors are probably 50 HZ which means they will run 20% faster on 60 HZ.
A VFD would solve all your problems..
 

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