Paralleling generators of different winding pitches

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ron

ron

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Even with the best paralleling controls, load sharing Woodward equipment, etc, I understand that it is very difficult to parallel generators with different winding pitches (2/3, 4/5 etc.) due to the characteristics of the output sin wave and how different numbered harmonics are handled differently by the different types of generator windings (2/3rds with 3rd harmonic etc). We've heard of poor load sharing and circulating currents.

Has anyone had a different experience?
 
ron said:
Even with the best paralleling controls, load sharing Woodward equipment, etc, I understand that it is very difficult to parallel generators with different winding pitches (2/3, 4/5 etc.) due to the characteristics of the output sin wave and how different numbered harmonics are handled differently by the different types of generator windings (2/3rds with 3rd harmonic etc). We've heard of poor load sharing and circulating currents.

Has anyone had a different experience?
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Why would one want to install this type of installation?
 
All generators regardless of pitch can be paralleled. Yes, you could have circulating current issues depending on how they are installed. The best thing to do is run them in an ungrounded wye. If the Owner is intent on grounding them, then use a resistor. This can be a single resistor where all neutrals are brought to one device, or a resistor in each neutral (my preference). Stay away from line reactors as they are difficult to size for multiple units, and as system parameters change the reactor rating will need to also change.

The circulating currents that are produced could cause you to lower the output rating of the generator, if it is excessive. Some generators can tolerate 10% of the line current rating at full KW loading.

For parallel operation, a current sensing system must be included with each voltage regulator. Make sure the current sensing transformers are all in the same phase or line lead.

Also, circulating currents will be more noticeable when the generator has not reached rated operating temperature. As it heats up, some of the circulating current will subside.
 
Nick,
Yes that's me.

Pierre,
There is an existing installation of 4/5ths pitch gens, and the new generators from the same manufacturer (Cat) now are only available as 2/3. They will all be paralleled together eventually.

Kingpb,
Good suggestions, thanks.
 
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