SUBTRANSIENT REACTANCE - VERSION II

[basiliou]

Only one thing i have to add here , the specific customer is a telecomunication company , and they pay huge attention to the harmonic levels of the generator.
By the way the winding pitch of the generatos is 3/4 .

Is actually X"d affecting directly the harmonics level produced by my generator ?

I'm trying to figure out a reasonable answer for why they need lower X"d values , taking as a fact that only telecomunication companies have this low x" requirement (their loads are inverters , converters , and other similar telecomunication equipment)

Regards


George

 

[rbulsara]

I dont think its X"d that affects harmonics level but the winding pitch do. Different winding pitch will affect X"d to some extent.

If in the USA, contact Caterpillar and ask for their EDS 70.4 which is bulletin discussing winding pitches and harmonics. What you want to specify is the correct pitch. In fact you should monitor for what kind of harmonics they have.

For example, 2/3 pitch eliminates triplen harmonics, 4/5 pitch elminates 5th and 6/7 pitch the 7th.

 

[rbulsara]

Also I might add, that if you are paralleling the gens with the utility supply, which are rich in 3rd harmonic voltages which creates significant 3rd harmonic circulating currents with generators other than 2/3 pitch.

You have to evaluate your set up. There are other mean to mitigate the circulating current issues, if you need 3/4 pitch for load harmonics.

 

[alehman]

X"d doesn't affect harmonic voltages produced by the generator, but lower X will tend to reduce the harmonic voltages resulting from harmonic producing loads (if this is critical to your application, a detailed analysis would be recommended).

If paralleling multiple generators, the winding pitch should match to mimize circulating harominc current. The Caterpillar article is an excellent reference.