Regenerative braking

[chief]

i am in the process of specifying equipment for a drilling rig on an artificial island. Because of tidal conditions the only available cooling source will be air cooled radiators. To limit the number of radiators and reduce the consequent noise emissions i wish to regenerate the braking power from the hoist equipment drawworks back to the National Grid. The hoist equipment will be driven by 2 x 1100 hp VFD MOTORS WITH 4-QUADRANT DRIVE. i must state here that the island has 2 power supplies, one from the production gas turbine and from the grid both at 6KV - 50hz.
The regenerative power must not feed back to the plant system as this will reduce power from the production gas turbine and interfere with production.
I realise i must have some type of THYRISTOR which will allow the regenerative power to feed to the GRID but not to the plant.
is this feasible and are the controls sophisticated, as i wish to keep the system simple and reliable. Appreciate any input from persons with previous experiece of this set-up.
Regards
Chief

 

[jbartos]

Suggestion: If the VFD is powered from the grid the regenerative feature will be enabled. If it is powered from the plant, the regenerative feature will be disabled. The dynamic braking may be used. This is a matter of VFD controls/programming.

 

[Baldor]

You will definitely need an active (SCR) front end. Keep in mind that drawworks braking is crucial. I have only seen a chopper/resistor used for DW braking with an AC drive.

I'll willing to bet that your drive manufacturer already has a regen brake designed. You should ask about the time differential between a brake chopper and regen braking. Protecting the drive caps, rig floor, and especially personnel must be considered.

 

[chief]

I should also have mentioned that the excess power generated by the production gas turbine is fed to the grid. So we could have a situation where the regen power and the excess power are feeding to the grid simultaneously. What sort of control complications can i expect. There obviously will be times when production is shut down and power is taken exclusively from the grid and the regen in this case is simplified, i am mainly concerned about when both power supplies are available and i want the regen power to go in one direction , namely to the grid.
Regards
Chief

 

[chief]

Thanks Baldor, I also have experience of brake resistor cooling systems, but because of the lack of a water cooling medium and the wish to avoid large noisy fan cooled radiator banks i wish to regenerate all of the brake regen power to the grid. I am in an environmentally sensitive area and noise emissions are to be kept to a minimum.
Regards
Chief

 

[DanDel]

chief, are the production gas turbine and the grid used to power the hoist equipment separately at different times, or are they all connected together at the same time?
If you want the regenerative power to only go out to the utility grid when your gas turbine is also supplying power there, then the output voltage from the regenerative power must be limited to a value below the gas turbine generator but above the grid voltage.