Star To Delta Parallel generators

[MarineElec]

Hello, I am new to these forums and noticed that they are very interesting. I am working on a vessel which has three generators. Two generators are winded star with earth neutral to steel hull and one winded as delta. What I was told is that last october the generator that is winded delta had to be rewinded because it melted the winding. I also had a confirmation from the winder that the generator was winded delta and they winded delta again. The voltage is 3 phase 220V. i.e. between phase 220V. The motors on board are winded as 3 phase 220 and for single phase systems they take between phases.

These generators are 160KVA and sometimes they are needed to run all in parallel. Gen 2 is the one winded in Delta. So G1 and G3 in parallel work perfectly. Synchronisation is done manually with a synchroscope. Load balance on generators when adjusting governor speed is done on KW meter. The strange thing is that when G2 comes into action between either G1 or G3 or on boat the current on the other genertors is twice as much as sometimes more and power is all equal.

When the system was checked with a power analyser I found that when Gen 2 goes on-line the Power factor drops to 0.2 form 0.9 even if load is very high 100Kw on two units.

Any suggestions would be welcome.

thanks in advance,

Ivan

 

[waross]

Trim your voltage controls. Check your cross compensation circuits.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[MarineElec]

Can you help further please. so trim voltage controls of the Delta generator on the AVR and what is the cross compensation circuits. Is it happeneing because there is Delta to Star paralleling?

 

[waross]

I have paralleled delta generators to star generators with no problems.
If the voltages of two generators are not equal, there will be a lot of reactive current circulating between the generators. This is corrected by adjusting the voltages before paralleling. Check your voltmeters. The voltmeter on the problem generator may be badly calibrated.
Different pitch windings in parallel may cause circulating currents but not of the magnitude that you are experiencing.
A cross compensation circuit or quadrature circuit is a circuit that helps balance reactive currents between generators. Google it.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[powerjunx]

waross is right. it's probably obvious that the cross current compensation circuit has a problem. Try to check the current transformer for this circuit; like loose connections, loss contact, etc from G2 to AVR2 - to - AVR 1 or AVR 3. Though, other OEM, this circuit is connected and embedded on AVR unit, plz refer to manual.

In ship's generator, voltage trimming is done usually thru remote rheostat located at generator switchboard. If not configured, others, trimmed directly on AVR assembly thru potentiometer.

Onboard ship;If available, try to replace with spare AVR otherwise try to utilize the AVR of either good working generator for further troubleshooting.


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