Ancillary Services & Essential Reliability Services

Transcription

1 Ancillary Services & Essential Reliability Services EGR 325 April 19, Basic Products & Ancillary Services Energy consumed by load Capacity to ensure reliability Power quality Other services? o (To enable the delivery of energy) 2 1

2 Voltage Drop Power, P = V*I If V i is constant? If V i fluctuates? 3 A/S FERC Definition Services necessary to support the transmission of electric power from seller to purchaser given the obligations of control areas to maintain reliable operations of the interconnected transmission system. Ancillary services supplied with generation include: o Energy imbalance services à Frequency regulation o Load following o Reactive power-voltage regulation o System protective services (disconnect devices to protect them) o Loss compensation service (transmission and distribution loss) o System control (ISO control centers and operators) Load dispatch services à Economic dispatch, etc. 4 2

3 A/S NERC Definition Ancillary services are those services that are necessary to support the transmission of capacity and energy from resources to loads while maintaining reliable operation of the transmission system in accordance with good utility practice. Because of the critical role ancillary services play in maintaining reliability, they are considered a subset of ERSs. 5 Ancillary Services Continuously used o Regulation (frequency; supply-demand balance) o Load following Contingency ( N-1 disturbance recovery) o Spinning & Non-Spinning Reserves o Replacement Reserves Other o Voltage Support o Black Start Evolution to: Essential Reliability Services 6 3

4 Contingencies Failure of power system equipment o There are N pieces of equipment in the power system, generators, transmission lines, substations... o If one fails, the system operates with N-1 pieces of equipment o The requirement is that the system must remain stable with N-1 devices... The N-1 Contingency Requirement Modeling and simulation performed for many what-if scenarios Different categories of reserves for recovery 7 Essential Reliability Services NERC identifies ERS as the essential building blocks necessary to maintain electricity system reliability. o Frequency Support: ensuring that the electricity supply system maintains the target frequency of 60 cycles per second or 60 Hertz (Hz) after system disturbances; o Load Following / Ramping: ensuring that there are sufficient flexible resources that can increase and decrease output to address swings in demand; and o Voltage Support: ensuring that there are sufficient resources to support system voltages

5 Operational Planning Time and Service Requirements 9 Service ERS Description Effects of Lack of ERS Availability Service Provided By Frequency Support Ensures the frequency of the bulk electricity system can be maintained and is stable for both normal and abnormal (loss of components) conditions. Resources are required to quickly engage to bring the grid back to its necessary level of 60 hertz. Controlling frequency can be broken into the following: Inertial Response; Primary Frequency Response; and Secondary Frequency Response. Large frequency deviations can result in equipment damage and power system collapse. Interconnection frequency deviation can result in: Loss of generation, Load shedding Islanding, where segments of the bulk power system are no longer operating synchronously. Inertial response typically provided by large synchronous generators (e.g., coal-fired, gas-fired, nuclear, hydroelectric) that have spinning momentum or large rotating masses to offset frequency disruptions. The momentum causes the generator to speed-up (with load loss) or slowdown (with generation or transmission loss) in response to a frequency disruption. Primary frequency response typically provided by generators governors (e.g., primarily hydroelectric and coalfired), which automatically respond to frequency deviations from the 60 Hz target Secondary frequency response typically provided by generators with Automatic Generation Control (e.g., coal and gas-fired and hydroelectric units), which allows the generator to respond to second-by-second dispatch signals from the system operator to increase or decrease output 10 5

6 Frequency Management, ERS Inertia: The ability of a machine with rotating mass inertia to arrest frequency decline and stabilize the system. Frequency Disturbance Performance: The ability of a system to ride through disturbances and restore frequency levels to pre-disturbance levels. 11 Frequency Management, ERS Operating Reserves: Spinning, non-spinning and supplemental reserves. o Load following is provided over a period of hours and a wider range of output versus: o Regulation that is provided within a time frame of minutes and over a smaller output range. o Contingency reserves ensure resources are available to replenish the amount of output used during the event, thus returning the system to the level of balance before the event. 12 6

7 Frequency Management, ERS Active Power Control (APC): control real power in order to maintain load and generation balance. APC attributes can include: o Frequency Control: resources automatically intervene with real-power output as a response to frequency deviation on the system. A generating plant s autonomous governor response. 13 Frequency Regulation 14 7

8 Actual Plant Capabilities 15 Frequency Support NERC Videos o

9 Load Following & Ramping Fast moving Fast generator Slow moving generator 17 Need for Ramping? Load following vs. (Frequency) Regulation o What is the difference? Effects of intermittent generation o Create the need for a ramping service? What technologies could provide a ramping service? o Combustion turbine (~jet airplane engine) o Demand response o Storage 18 9

10 Ramping Capability, ERS Ramping Capability: uses real-power control to raise or lower generation to maintain load generation balance. o Ramping capability is most needed at times of major load shifts, such as morning ramp-up, afternoon ramp-down, and evening ramp-up. o California sees ramping needs from integrated solar PV. o As typical load curve change due to integration of off-peak electrical loads (e.g., electric vehicles, smart appliances), ramping needs may also change from morning and evening ramps to off-peak ramps. 19 Load Following & Ramping Service ERS Description Effects of Lack of ERS Availability Service Provided By Load Following Ramping Daily operation of the bulk electricity system requires a continuous balancing of generation and load. Operational flexibility is needed to manage real-time changes in load and generation. Changes to the generation mix or the system operator s ability to adjust resource output can impact the ability of the operator to keep the system in balance. System stability and reliability are at risk. Imbalance in generation and load can overload transmission facilities (surplus of generation relative to load) or cause voltage to drop (deficit of generation). Protection equipment can malfunction or be damaged. Typically provided by peaking (e.g., simple cycle gas turbines) and intermediate generators (e.g., combined cycle gas turbines) that can ramp up and down (i.e., have available output capability or head room to increase or decrease output) and turn on rapidly to meet immediate system requirements 20 10

11 Contingencies Failure of power system equipment o There are N pieces of equipment in the power system, generators, transmission lines, substations... o If one fails, the system operates with N-1 pieces of equipment o The requirement is that the system must remain stable with N-1 devices... The N-1 Contingency Requirement Modeling and simulation performed for many what-if scenarios Different categories of reserves for recovery 21 Contingency Event 11

12 Reserves For contingencies (unexpected, large disturbances; equipment failure ) Spinning reserve & non-spinning reserve o Able to be at full output within 10 minutes Replacement reserves o Full output in 30 to 60 minutes o Used to allow spin and non-spin reserves to return to pre-contingency set-point 23 Spinning Reserves & Economic Dispatch For power systems we have: min C T = ΣC i (P Gi ) s.t. Σ(P Gi ) = P L P Gi min <= P Gi <= P Gi max Identify the o Objective function o Constraints o Decision variables 24 12

13 NERC Videos Load Ramping o 25 Voltage Drop à Voltage Rise Voltage support is a basic system service As power flows down a distribution feeder, the voltage level drops. Voltage drop: V drop = I ( Rcosθ + X sinθ) What happens when distributed generation is added into the distribution system? 13

14 Voltage Drop Power, P = V*I If Vi is constant? If Vi fluctuates? 27 Inflating Fire Hoses with Reactive Power 28 14

15 Power = V * I Voltage Support o If voltage is constant, a changing need in power triggers a change in current delivered o If voltage fluctuates, then current will fluctuate, and may damage wires NERC Videos o 29 Service ERS Description Effects of Lack of ERS Availability Voltage Support The primary objective of voltage support is to maintain transmission system voltages within a secure, stable range. Voltage support is locationspecific and requires reactive power control from resources distributed throughout the power system. Localized voltage issues can manifest to a wide area causing loss of load. Exceeding design voltage parameters can destroy equipment by breaking down insulation. Undervoltage conditions can lead to motor stalls and equipment overheating. Voltage collapse can lead to a cascading drop in voltage and system outages. Service Provided By Controllable sources for voltage support include generators that are able to vary their reactive power output, inductive and capacitive compensators, and transformers, which are utilized to inject and absorb reactive power and keep voltage between the necessary minimum and maximum levels. These sources work in tandem with each other to provide voltage control

16 Voltage Support, ERS Reactive Power/Power Factor Control controls leading and lagging reactive power to maintain system voltage levels and provide for operational flexibility under normal and abnormal conditions. Voltage Control: maintain adequate local and regional voltage to support system loads and maintain transfers and devices connected to the system. Voltage Disturbance Performance: maintain voltage support during and after a disturbance in order to avoid voltage collapse. 31 Voltage Rise A concern with distributed generation During times of low load (low local load), what might distributed generators do? And what effect might this have on the surrounding distribution system? 16

17 Voltage Drop Voltage Drop H Lee Willis, page 285 (bus #s shown), with V regulator at bus

18 Blackstart Final Ancillary Service o Ability to supply real and reactive power to self, to restart, and to other generators, as they start up after a blackout. 35 Essential Reliability Services Identified to better support emerging distributed and intermittent technologies Frequency Support Ramping Voltage support NERC Videos o

19 Summary Ancillary services are system services o A form of collective, or public, good Increased use of intermittent generation is creating the need for new A/S à ERS Storage technologies often seen as excellent for providing fast response à Expensive Demand response providing system services o Smart Grid needed 37 19