Nuclear CSAs + HOTS

The table below summarises which stations provide which special actions.

• Instructed via Special Actions classified under each site's CSA
• Used to prevent thermal overload of the transmission system.
• NG will agree availability in advace with EDF's Energy's nuclear power stations as they require a reasonable period of time before they can safely drop load - through the TOPAM process
• STT responsibilities - when a nucelar unit has an active special actions, the unites are expected to have their bid prices to £-500MW/h instead of £-10,000MWh. This is carried out in the overnight nuclear metering review. Liase with the station and NG where appropriate.
• Station responsibilities - Advise NG and STT of availability, update SEL inline with de-load capability, ensure compliance with NG instructions dispatched via EDL, keep STT informed.
• Payments - deloads are settled as per the bid price. If a unit trips while providing a load drop then de-syncronisation payments and tripping payments.

• An intertrip will automatically disconnect the generator from the Transmission System. Two types: Commerical intertrips and System to Generator Operaional Intertrips
• Heysham falles under the commerical intertrip type as the station has a CSA in place.
• EDFE is required to inform NG of the availability. The required availability depends on the combined outout across the 2 heysham stations. >2100MW output and 4 units generating = 2 unites to be declared available for intertripping. >1500Mw and atleast 3 units generatring = 1 unit to be declared available.
• STT responsibilities - redelare availability if it changes following discussion with the station, arming/disarming instructions recieved by fax to be emailed to barnwood settlements, maintain filing of faxes, treat the trip the same as any other, provide report to NG following any failire undee the scheme within 2 days - falls under OC210.
• Station responsibilities - CPs to identify which units to offer to trip and provide 2 weeks of availability to NG at the week ahead stage, redelare availability if it changes, ensure all equipment is maintained, on trip - confirm trip to NG and STT, redeclare MEL to zero.
• Payments - will recieve arming payments and tripping payments. Tripping payments are either the circuit breaker trip or the turbine stop valve trip.

• Due to the high volatage system around Hinkley B, there are times when NG might need to arm System to Generator tripping. Automatic trip of one or two units.
• STT responsibilities - liase between the station and NG, confirm all information with NG via fax, treat the trip as you normally would.
• Station responsibilities - ensure all equipment is maintained and armed, ensure STT is aware of their availability, on trip - confirm trip with NG and STT, redeclare MEL to zero
• Payments - capability payments and intertrip payments

• Defined as a drop of atleast 80% of thermal power for up to 8 instances per calendar year.
• NG can de-sync a unit if the level on NRAPM is too high to avoid it or if the station has failed to offer flexibility within its limits.
• STT responsibilites - liase with station and NG, ahead of time a reforecast would likely be carried out under a Schedule 7a trade, discuss the price with NG however the £-10,000MW/h should be used, if the unit is tripped then treat as any other trip.
• Station responsibilities - ensure STT are aware of the availability and any communication they have with NG, update SEL with de-load capabiloty, ensure compliance with NG instructions, return the station to full power asap.
• Payments - in advance agreements- as per the Schedule 7a trade or out of hour agreements the price is the bid price.

• Automatic Frequency Response Operation
• Only sizewell B
• Three types of frequency response: primary, secondary and high
• STT responsibility - liase with station and NG, redeclare BO data to £-2000 for gate open periods requiring a de-load in order to delivery AFRO.
• Station responsibility- compliance with NG
• Prices are set with the type of frequency response.