motor burn out 3

[colohara]

we have a three phase motor that arrived to us in star but we wanted to see what happened if we ran it in delta, the motor got really hot why would this happen the motor plate says that you can run in star or delta, the motor details are 3phase 415 volt 50hz 0.34 kw usually used on an small conveyor . also can you run a 3 phase motor off of a single phase supply if so how

 

[LionelHutz]

The delta connection would make the motor a 240V motor.

You can use a phase converter or a VFD to run a 3-phase motor on single phase.

 

[TommyOO7]

Colohara,

I think that motor is designed to run continuosly regardless of winding connection (Y or Delta ). Current and Torque are differenet for different connections, but max. temperature rise should be the same (check the insulation class).
Your statement that motor got "really hot", means almost nothing, you should check the motor current and compare with nominal current. (For example max. temp. for Class F motors is around 155C, with 40C ambient temp. This is really hot, but normal)

It is possible to run 3-phase motor as 1-phase. Only two windings are used (2 out of three phases). And a capacitor must be added in series with one winding.

I hope this helps!

 

[davidbeach]

LionelHutz is correct. The motor needs different voltages in wye and delta and feeding it at the wrong voltage can do serious damage.

 

[jraef]

Yes, LionelHutz has it.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[TommyOO7]

Tell me then how Y-Delta motor starting works! Two different voltages are used or the same voltage?

It is the same (line) voltage, but different phase voltage and each motor is designed to run permanently in either connection!

 

[davidbeach]

Wye-delta start is a reduce voltage starting method. A motor intended for wye-delta starting is a single voltage motor and runs in delta. When in wye, the winding sees only 58% the voltage it does when in delta, so while starting, the motor is seeing a voltage only 58% of the run voltage.

In the OP's situation, applying the wye voltage to a delta connected motor produced a 73% overvoltage, or course the motor was going to overheat.

 

[TommyOO7]

But, all motors are designed to run in Delta connection. So if it is connected in Y, everything is fine, just lower phase voltage and phase current.
Motor windings' insulation level is based on the line voltage, regardless of the connection.

Correct?

 

[stardelta]

The motor name plate may state Star and Delta but look closely and you will see that the star voltage will be stated as 415 (or thereabouts)and the delta voltage will be 240 (or thereabouts again). There will also be another set of current figures on the name plate, the delta current will be approx twice the figure quoted for star. I cant say I have ever seen a motor that will run reliably and perform the same in star or delta at the same voltage! As a rule of thumb most standard European spec` motors below 4kw are designed to run in star at 415v, higher than this its delta.
Converting a 3ph motor to 1ph (240v) operation requires the motor to be connected in star, a suitable capacitor needs to be connected across 2 legs and then fed on one side of the cap` and the remaining single leg. In my own experience this is a very hit and miss affair and despite theory I have never know it work reliably. Better to buy a properly designed 1ph motor of the same power/speed in the same frame size.
In addition to the comments made by DavidBeach a motor run in star thats designed to be run in delta will result in a loss of about 2/3rds its rated torque as a result of the reduced voltage.

 

[aolalde]

Wye-Delta motors are not intended to run permanently in either connection with the same voltage. Wye start ( a few seconds), Delta run (permanently) for the delta intended voltage.
On dual voltage motors, 173% of nominal voltage is applied if the delta connection is supplied with the voltage intended for wye connection. That will saturate the magnetic circuit reducing drastically the motor reactance, increasing the current even on no load condition. Regularly a motor is fried in matter of few minutes.

 

[Marke]

A three pahse motor can be run on single phase byu using a single phase input three phase output inverter (VSD)

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[LionelHutz]

Since it wasn't exactly spelled out, you could only use a Y-Delta starter with the origional motor in question if the supply is 240V.

You start in Y mode with the motor expecting 415V. This means the 240V souce is only 58% of the motor rated voltage. This effective reduction in supply voltage lowers the motor current and torque to provide a softer start.

Then, you switch the motor to a delta connection after some period of acceleration time. At this point, the motor is connected properly for the 240V supply and you will be able to get rated torque out of the motor.

You can not use a Y-Delta starter on a motor when your source is the higher of the two rated motor voltages. In this example, you can not use a Y-Delta starter on a motor that is 240V/415V rated if your source is 415V.

If you are using a 415V motor with a Y-Delta starter then the motor could theoretically be a 415V/720V rated motor. However, it would likely only be listed as a 415V motor on the rating plate with the 6 leads being supplied to allow the use of a Y-Delta starter, not to allow a dual voltage rating.

If you don't know, the conversion factor between Y and delta voltages is the square root of 3.

 

[jraef]

Tommy007,
You are obviously in N. America, where your experience would be correct in that we don't typically use Y connections for motors. But in the rest of the IEC world, they use the 2 connections to get the same output at 2 different voltages, because the lower of those voltages is the Y of the higher. I.e., 415V Delta is 240V Y (415 / 1.732 = 240). This reduces the number of motors needed in stock. We don't do that here in N. America so we have separate motors for each voltage, and each motor's internal connection becomes irrelevant.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[TommyOO7]

jraef,

I didn't know that, in the IEC world, there is a 3-ph, 240V power supply (distribution voltage)! I thought that min. 3-ph, voltage is 380V (or 400V, 415V). 220V (230V or 240V) is 1-phase (Line to neutral) voltage! So, my question is why would anybody make a motor for the voltage which is not widely used (3-ph, line to line 240V)?
I admit, I was wrong when I said that "all" motors are made for both connections. But it is logical to me that motors are designed for the worst case scenario (Delta connection in this case). If it is, by mistake, connected differently nothing bad would happen. But if motor is designed for Y-connection, it is very easy to change connection to Delta by mistake, which (we all agree) will destroy the motor. It should be "idiot proof" design.

Tommy.

PS. You are right, I am in North America

 

[Marke]

Hello Tommy007

There is no requirement for star/delta starters on motors less than 4KW in most regions, so there is no benefit in manufacturing motors that are designed for star/delta starting. There are some regions where 230volt 3 phase is used, but this is not normal in the 50Hz world. There is however, a big market for 3 phase motors on 230v for use on the output of VSDs that are fed from a single phase.

The norm curtainly is for small motors to be delta 230v and star 400V in the European market.

Best regards,

Mark Empson

http://www.lmphotonics.com

 

[waross]

North American three phase motors that are large enough to have more than three leads brought out usually have nine leads.
The standard voltages are usually 230/460 volts.
The exception is 550 volt motors which have three leads.
There are Star connected motors, and Delta connected motors. The choice is inherent in the motor internal connections and you have to check the connections on the name plate.
Both have 6 windings. The Star motors have an internal Star connection. Delta motors have three internal connections.
The connection diagrams are the same for the high voltage connection.
The connection diagrams are different for the low voltage connection.

Neither type of motor is suitable for star delta starting.
In North America, Star Delta starting requires a special motor with six leads as per European standards. It will then be a single voltage motor.
Star Delta starting is one of the cheaper ways of reducing starting current in Europe.
The North American equivalent is Part Winding Starting.

The motor is energised first on only one set of three coils. After a short acceleration delay, the second set of coils is energized. The equipment cost would be about the same as open transition Star Delta equipment.

Re VFDs installed to run three phase motors.
I did an installation where a factory rep recommended that a VFD be installed on an old machine for the soft start feature. We had to change the single phase motor to three phase in order to use the VFD.