Load control of Generators

[sakaran51]

Hi,
A process plant fed by the Utility is having their own captive Diesel Generator sets as a back up.Now the management has decided to set up a coal based Steam turbine Power plant for the process plant captive usage.The STG is a condensing turbine from which steam required for process will also be obtained.The STG will be running in parallel with grid. The process plant power requirement will be met both by STG and Utility.Load sharing is taking place automatically,between Utility and STG,depending on generation and demand.

But there is a talk about load sharing and control between STG and Utility,with WOODWARD DSLC and MSLC load controllers.

Questions are:
Whether it is,load control, really applicable for an STG running in parallel with Grid?
If not, where and when these controls are applicable?
How it is implemented?
My understanding is they are mainly used in Diesel Generators and Gas Engine Generators.Is it correct?
Pl.clarify.
Thanks.

 

[ScottyUK]

- Yes, it is entirely valid for an STG to operate in load control with the grid.
- This operating mode is available on pretty much every grid-connected steam turbine in commercial operation.
- The governor control loop is closed by power transducers, typically connected at the machine terminals.

- No, not correct.

 

[sakaran51]

Yes ScottyUK,the kind of load control when the STG is operating in parallel with grid,is valid.Probably, I have not expressed my doubts clearly with regard to load control.

Is it possible to implement the load control with WOODWARD MSLC,as Master,and DSLC,as slave in STG-Utility combination?

MSLC controls power flow from Grid and DSLC controls the power generation thro' governor?

 

[sakaran51]

To add to my previous post:
1.Depending upon the process steam requirement,i.e.,drawl of steam from turbine,the power generation also vary.
2.Eventhough,the process plant load requirement can be met by STG and Utility,both put together,there is a cut off limt to the power withdrawl(import)from the Utility,as per the contract agreement with Utility.Any excess import will attract penalty.
3.There is no intntion to export power to the Utility from the plant,eventhough it is tied to the Utility.
In this scenerio, is the the DSLC-MSLC control a must?
Sorry for the bits and piece information in instalments.

 

[squeeky]

Firstly check your agreement with your utility. Do you get paid for power sent to the grid? Sometimes they don't allow you to export power and will trip the breaker on a "Reverse Power" condition.

Next ensure that youhave all the correct protection. Ensure that they have disabled any auto-reclosers. Rapid diconnect and reconnect may close the breaker un-synchronised to your machine and damage it.

When you run with the utility your AVR shoud move to pfc mode or at worst Droop mode. If you run as an island, then the AVR must move to voltage regulation mode. This is done by monitoring the breaker status. Look at your AVR manual.

Your equipment should have no problem regulating the power sharing as long as you have followed the wiring diagrams correctly. How you supply the set point could be your biggest decission.

 

[ScottyUK]

Sakaran,

I'm sorry I don't know those specific controls, maybe another member will recognise them.

 

[FreddyNurk]

There is definitely a possibility that the Woodward DSLC and MSLC can carry out paralleling operations with a grid, I've seen such devices used for that exact application, though as you suspected, it was for a diesel station in parallel with the network.

That said, I'd gained the impression that the products mentioned from Woodward are an older product line and that there are likely other later units on the market that can do the job better. Woodward make some excellent products for this sort of application, as do Comap, Deif and Basler among others, though whether or not they're specifically suitable is beyond my experience.

Woodward has some excellent online documentation, it might be worth a quick glance at their webpage to see if the load control functions are suitable for steam turbines or not (in which case you might have a point, the governor functions might not be optimised for a steam turbine's behaviour). As for whether or not load control is required, ScottyUK is correct.

squeeky is correct too, though, your utility will have a say as to what is connected to their network and capable of export and how, even if the DSLC/MSLC application is accepted by them, any reverse power elements may not be, and you may find yourself requiring other protection devices as well.