Cat Vr3 to Vr6 Conversion. 3

[Offshoreboy]

Recently we had one of our Vr3 regulators break down. The regulators are fitted to 680kW 440V 60Hz SR4 gens driven by 3508 cat engines with 2301 Woodward speed control and EP governors.
On return to the quayside we rented a load bank and have adjusted the 2 Vr3 controlled units to run in parallel with the usual 5% droop. Load sharing excellent with only a max of 20A circulating currents. All governors and controllers are working well and have been verified individually versus the load bank. 650kW@0.8 pf.

When trying to set up the Vr6 unit for the 5% droop we are unable to get the voltage to get anywhere near the 5%. When we adjust to the 462V the generator only drops to 455V on full load. We have connected the CT to the correct terminals.

Do we have to purchase a special CT for the Vr6? Is there any gain adjustment on the Vr6? Do we have to wire the system in a specific manner to get it to work?

We received the new Vr6 offshore with no special literature and only now we find we have a problem. Please can anyone help.

Thanks in advance, any help/suggestions would be greatly appreciated.

 

[IBRCAN]

Two possibilities come to mind:

-Did you remove external droop pot connected across droop ct leads? VR6 has droop pot directly on regulator (first one from the top). Should be able to adjust droop up to 10%.

-Existing droop CT can be used. VR6 terminal 5 is for 1A CT, terminal 5A is for 5A CT. Terminal 6 is common. Check CT secondary current with full load applied (will be less than 5A or 1A nominal rating), and verify correct connections.

Also necessary to set knee frequency on VR6, utilizing second pot from bottom. Ensure that terminals 6A & 8 are jumpered to set underfrequency slope at 1 v/hz, which should match VR3s on other units. Run generator at 60hz and turn knee pot fully ccw. Observe output voltage. Then turn pot slowly cw until output voltage begins to decrease. Then turn pot back ccw until voltage just returns to initial observed.

 

[catserveng]

Not removing the old droop pot is a common mistake as pointed out above.

Here are a couple of references, the Basler AVC63-12 manual works quite well as the CAT VR6 is essetially the same as the AVC63-12B1.

I have had a number of retrofits where the use of the old droop CT was not successful, in many applications I found they never quite had the same droop as when used with the VR3. Depending what vintage wiring you have you may also have problems with the generator connection box mounted terminal blocks as well, so a good check of the wiring from the CT to the new AVR is required when retrofitting older units.

Hope that helps,

Mike L.

 

[catserveng]

Here's the other one,

 

[Offshoreboy]

Gents,

Thank you for the excellent replies. We had managed to figure out the inbuilt droop etc, the only things that are extra are the data sheets from Catserveng and the knee pot setting info from Ibrcan.

The generators are from the 1990's and we had several problems with them over the years regarding the wiring and chaffing. To overcome this we removed the control panels and installed them on the bulkhead, this reduced our faults until this one with the failure of the VR unit.

Will revert with results if successful.

Thanks once again