Electric Motor Connections

[volxport]

Can Somebody tell me why this Works?

The Motor’s are a standard 230/460V-60hz 12 lead motor. They have this special connection that allows the motor to not be de-rated and run @ 380V-50hz with a 1.15 service factor. How’s does the Ground help this system? Any Ideas’s would be greatly appreciated.

Circuit Connection on 12 Lead motor
Leg 1 2-8
Leg 2 3-9
Leg 3 1-7

4-5-6-10-11-12 tied together and sent to Ground

With a Note
1.732 x low votlage
Operating at over 600V Neutral on 1.732 x l.v. must be solidly grounded

 

[volxport]

If we are Running this motor @ 380V-50hz then why the note about 600V?

 

[jraef]

1) There is no "special connection" for running at 380V, it is exactly the same as running at 460V. A motor creates torque based on the applied V/Hz ratio. 460V 60Hz is a ratio of 7.67:1 (460/60), 380V 50Hz is a ratio of 7.6:1, close enough not to worry about.

2) I personally believe that this chart was made by a nincompoop who really doesn't know much about motor connections and worldwide voltages. It's true that for running at 380V (400V nominal), the motor is connected internally in a Y (star) pattern. But I do not believe it is necessary to connect the WINDINGS to a solid ground as they seem to imply in that diagram. I'm no expert on IEC systems however, so maybe someone else will chime in.

I think they are confused with regards to power DISTRIBUTION systems and MOTOR internal connections. In a power distribution system, the 400V 3 phase system is a 4 wire system, so it is 400/230V where the voltages are 400V line to line and 230V line to neutral. But that is separate from motor internal connections, and somewhat irrelevant. If you want to use the motor at 400V nominal, connect the internal windings in a Y, the Y point is just an internal neutral reference. If you want to use it at 230V, IN THAT 400/230V Y SYSTEM, then you make up the motor connections in Delta. OUTSIDE of the motor connections, the 230V system will need to be derived from a neutral, but not inside the motor.

I'm not sure why they mention the 600V issue, I seriously doubt the motor is designed to run on 600V, it would likely saturate. this furthers my belief that the person who made those diagrams was a nincompoop.

<Word of the day: nincompoop>

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[volxport]

I half agree with you. There are some special Connections we have used with Toshbia product supplied by Toshiba Engineer's that allow some very goofy Voltages. In order to keep the 1.15 Service factor on this motor this particular Connection was needed. I agree that the 600V system shouldn't be on this Connection. Can someone help with the Math? I am assuming that the Ground isn't needed and that the Connections just need to be made in the box tying these leads together.

 

[ScottyUK]

jraef,

No star connected motor needs an earth connection to the star point over here in IEC-land. We don't connect the neutral to the star point, let alone the earth conductor. I agree - diagram was drawn by some pillock who doesn't know much about motors.


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If we learn from our mistakes I'm getting a great education!

 

[waross]

Grounding the star point is a good way to burn out the motor. Any unbalance in supply voltages or phase angles will cause heavy currents to flow. Easily over the motor current rating.
You will lose 1/6 of your power on 50 Hz. (50/60)
Same torque times fewer RPMs = less HP.

Bill
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"Why not the best?"
Jimmy Carter