Modes of operation of STGs located apart.

[sakaran51]

Hi,Everybody,
Here is an interesting situation,but real!
There are two steam turbine generators in two steel plants located two kilometers apart.Plant-A is existing. Plant-B under erection.
Plant-A -STG capacity 15MW 11KV- Type of boiler AFBC and WHRB-Connected to 132KV grid through a Generator Transformer.
Plant-B -STG capacity 8MW 11KV- Type of boiler only WHRB- No Grid.

The 11KV Switchboards of both the plants are tied together by means of overhead lines, with circuit breakers at both ends.The balance of power,if any,after steel plants consumption,will be exported to the grid through 132kV switchyard,which is available only in Plant-A.

There are four important likely scenarios out of many when the new plant becomes operational.
1.Both the generators operating in parallel with the grid.
2.Both the generators operating in parallel but in islanding.
3.Both the generators operating independently.
4.Either 15MW STG or 8MW STG only operating in parallel with the grid.

In order to meet the requirements of above conditions the following mode of operations are envisaged.
It is pertinent to note that the steam generation from WHRB boiler is very much variable unlike AFBC boiler and Plant B is having only WHRB.

1.Both the generators operating in parallel with the grid.
15MW STG-Set KW(Governor)/PF(AVR)
8MW STG-Set KW(Governor)/PF(AVR)

2.Both the generators operating in parallel but in islanding.
15MW STG-Set Frequency(Governor)/Voltage(AVR)-like swing machine.
8MW STG-Set KW(Governor)/PF(AVR)

3.Both the generators operating independently.
15MW STG-Set Frequency(Governor)/Voltage(AVR)
8MW STG-Set Frequency(Governor)/Voltage(AVR)

4.Either 15MW STG or 8MW STG only operating in parallel with the grid.
15MW/8MW STG-Set KW(Governor)/PF(AVR)-as applicable.

Hope the above settings are in order.Your views on this will be valuable.

 

[crshears]

Hi sakaran51,

Interesting scenario!

So...

What exactly is/are your quesdtion?

CR

 

[sakaran51]

Hi,CRSHEARS,
1 The two plants are in different locations.
2.The power generation from new 8 MW STG is solely depends on Waste Heat Recovery Boiler(WHRB)steam and by its very nature, is not constant.
3.The load sharing controllers for both the generators are not feasible because of location constraints and for want of simple cost effective solution.
4.Hence the above mentioned settings are proposed in the respective Governors and AVRs for different operating conditions.

The questions are WILL THIS APPROACH WORK? ARE THERE ANY OTHER IMPORTANT ISSUES TO ADDRESSED?

 

[waross]

Due to the variable nature of the WHRB that unit will probably not meet expectations when islanded.
You may not have the switchgear capability to connect the second HRSG unit to the grid if the first unit is not already connected to the grid.

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

 

[sakaran51]

Hi,Bill,
Of course.The generation from the 8MW STG will not be consistent as it is run on WHRB only.That's why it is proposed to run it at lower KW setting(may be 5-6 MW) either during parallel operation with Grid or with the 15MW STG.
When both the generators are running in parallel WITHOUT Grid tie up,the total plant load should not be allowed to go below the load set in 8MW STG.
When the 8MW STG is completely isolated both from the Grid and 15MW STG,it will go on frequency/voltage mode,catering to the loads present of its own plant.

But I am not able to understand the statement you have made as below:

"You may not have the switchgear capability to connect the second HRSG unit to the grid if the first unit is not already connected to the grid."

 

[waross]

Look at your single line. If the existing plant is islanded will you be able to connect the second plant to the grid? It depends on your switchgear line-up.

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

 

[sakaran51]

Yes,Bill..That is the peculiarity of this set up.When the first plant looses the Grid, both the plants will be islanded, since the second plant is connected to the Grid only through the first plant.During islanding either both the generators will be operating in parallel or operate independently.