GRID OPERATIONS
GRID OPERATIONS
(OP)
Many grid operators are requiring on load tap changers on generator step up transformers to provide voltage support outside normal generator voltage limits. Does anyone have any operating experience as to what the AVR settings are used? HV and EHV connections to a grid.






RE: GRID OPERATIONS
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: GRID OPERATIONS
AVR..are you menat AVR of generator or TC control?
Are it industrial generator, about 60-70MVA, or utilities generator?
Are it block generator-transfromer w/o GCB or with GCB and some load on the generator bus.
Best Regards.
Slava
RE: GRID OPERATIONS
RE: GRID OPERATIONS
Not sure how much that helps, still not exactly sure what you're looking for.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: GRID OPERATIONS
RE: GRID OPERATIONS
It's something new and used for the reactive power regulation.
Best Regards.
Slava
RE: GRID OPERATIONS
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: GRID OPERATIONS
Said another way, a generator has a limit on the quantity of VARs that it may produce depending on the capability curve.
With a tap changer, the plant may raise the voltage supplied to the grid with a lower excitation level on the generator.
Is it possible to generate more VARs and still stay within the capability curve with the help of a tap changer?
(Note: VARs is an acronym for Volt Amps reactive, not to be confused with the symbol var which must be used when writing a formula.)
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GRID OPERATIONS
The tapchanger allows the generator to export (or import) vars over a wider range of operating conditions than would otherwise be possible.
The generator ultimately supplies all the vars, but it is common for grid conditions to make it virtually impossible for the generator to deliver its full reactive capability without the assistance of the tapchanger. For example, a high grid voltage immediately makes it difficult to export vars because the flow of vars is dependent on the difference between the internal machine voltage, usually denoted 'E', and the terminal voltage denoted 'V'. 'E' is inherent in the machine design and is a function of excitation current; there are well-defined limits on 'E' because of thermal limits on the rotor winding and on stator end heating due to the flux distribution at low field strengths. The use of a tapchanger effectively changes the value of 'V' for a given level of reactive power flow. For example, when a high reactive export is required the tapchanger is adjusted to force the generator terminal voltage down below nominal, and the AVR then boosts the field to bring the terminal voltage back to setpoint. In doing so the machine export reactive power to the grid.
The use of the tapchanger doesn't notably increase the reactive capability of the machine, although there are some second-order effects which modify the capability diagram slightly, but the tapchanger makes it possible for the machine to operate over a wider envelope than would otherwise be possible. Without a tapchanger it is likely that a limiter such as over-fluxing or under-excitation would come in to operation before the machine delivered its full reactive capability as shown on the capability chart.
----------------------------------
If we learn from our mistakes I'm getting a great education!
RE: GRID OPERATIONS
RE: GRID OPERATIONS
xxjohnh:
In some cases transformer on-load tap changers can avoided by designing synchronous generators for plus/minus 10% voltage range. This would pose no problems. Increase of generator price may be minimal (about 1%).
Best regards
Wolf
WWW.HYDROPOWER-CONSULT.COM
RE: GRID OPERATIONS
Yours
Bill
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: GRID OPERATIONS
They're on manual control. Theoretically they're on ganged parallel manual control but in reality they are invididual control.
Bill,
No problem,
Wolf,
Have you actually managed to get this done? If so I am quite impressed in these days where the big three manufacturers make their standard product and stubbornly refuse to modify their 'tried and proven design'. I guess it is easier to get a semi-customised design in the non-CCGT market.
----------------------------------
If we learn from our mistakes I'm getting a great education!