Harmonic amplification with Turbogenerator supply 1

[deeveeyes]

In one of the cement plant where we conducted harmonic audit we found that on the HT 6.6. KV BUS, the Voltage as well as current distortion drastically increased when the supply was switched from Utility supply to their own Captive Turbogenerator supply. It increased from nearly 2% to almost 10% both for current and Voltage. The cement plant also faces a problem of heavy vibrations in HT motors when the supply is switched to Captive generation. Why the distortion has gone up so much ?? Is the vibration due to this distortion ? Will installing a passive filter on Captive Generation bus, help solve the problem ?

 

[dpc]

Without a one-line of your system it is difficult to say, but if the generator capacity is significantly less than the capacity of the utility service then this could cause an increase in measured harmonic distortion, depending on where you are measuring. This assumes you have adjustable frequency drives or other non-linear loads on the system.

It is unlikely that the generator is the source of the harmonics you are seeing.

This is a fairly common problem when standby generators are used for pump stations where 99% of the load is non-linear.

Filters may help, but it would be best to locate the filters near the source of the harmonics, if possible.

 

[jwerthman]

I agree with dpc that the turbogenerator is probably not the source of the higher harmonic loading. The higher harmonics are likely the result of the higher impedance of the generator compared to the utility source. When the harmonic current flows through a higher impedance, the result is increased voltage harmonics. You may also be experiencing some resonant conditions that are only manifested when the plant is on the generator source, particularly if you have some shunt capacitor banks in the system. The resonant frequency is lowered as the system impedance is increased so with a weaker source from the generator, the system resonant frequency may be shifting close to a dominant harmonic, usually 5th, 7th, 11th, or 13th. As you approach a resonant point, the harmonic distortion can be quite severe, to the point of tripping or damaging equipment.

 

[avishai]

The two answers are wright . You have to take in account also that the utility is much stronger than your generator and as a result much less successible to let harmonics develop in the network. You have to be very careful about resonnance problems that my trouble your generation system .
As said before for a more detail answer a single line diagram would help . A.Rash BScEE & PE
a_rash@bigfoot.com