Motivation Power balance-frequency basics

Motivation

• Motivation

• Power balance-frequency basics

• Frequency Performance Analysis

In many parts of the country, wind and/or solar is increasing.

• In many parts of the country, wind and/or solar is increasing.

• Fossil-based generation is being retired because

• There is significant resistance to coal-based plants due to their high CO2 emission rates.
• There are other environmental concerns, e.g., once-through cooling (OTC) units in California and the effects of EPA’s Cross-state air pollutions rules (CSAPR) and Mercury and Air Toxic Standards (MATS) (also known as Maximum Achievable Control Technology, MACT). For CSAPR effects, see, e.g., www.powermag.com/POWERnews/4011.html (Texas shut downs) and for CSAPR/MATS effects, see the next slide. For OTC effects, see www.world-nuclear-news.org/RS-California_moves_to_ban_once_through_cooling-0605105.html, http://www.caiso.com/1c58/1c58e7a3257a0.html, and next-next slide.

• Fossil-based generation contributes inertia. Wind and solar do not contribute inertia, unless they are using inertial emulation.

• Inertia helps to limit frequency excursions when power imbalance occurs.

•  Decreased fossil w/ increased wind/solar creates trans freq risk.

Inertia

• Inertia

• The greater the inertia, the less acceleration will be observed and the less will be the frequency deviation. Inertia is proportional to the total rotating mass.

• Primary Control

• Senses shaft speed, proportional to frequency, and modifies the mechanical power applied to the turbine to respond to the sensed frequency deviations.

Reduced inertia, assuming renewables do not have inertial emulation

• Reduced inertia, assuming renewables do not have inertial emulation

• Decreased primary control (governors), assuming renewables do not have primary controllers

• Decreased secondary control (AGC), assuming renewables are not dispatchable.

• Increased net load variability, a regulation issue

• Increased net load uncertainty, a unit commitment issue

Aggregation

• Aggregation

• Network frequency is close to uniform throughout the inter-connection during the 0-20 second time period of interest for transient frequency performance.
• For analysis of average frequency, the inertial and primary governing dynamics may be aggregated into a single machine.
• This means the interconnection’s (and not the balancing area’s) inertia is the inertia of consequence when gen trips happen.

A squirrel-cage machine or a wound-rotor machine (types 1 and 2) do contribute inertia.

• A squirrel-cage machine or a wound-rotor machine (types 1 and 2) do contribute inertia.

• DFIG and PMSG wind turbines (types 3 and 4) and Solar PV units cannot see or react to system frequency change directly unless there is an “inertial emulation” function deployed, because power electronic converters isolate wind turbine/solar PV from grid frequency.

• No inertial response from normal control methods of wind & solar

• Neither wind nor solar PV use primary control capabilities today.

• There is potential for establishing both inertial emulation and primary control for wind and solar in the future, but so far, in North America, only Hydro Quebec is requiring it.

Category C disturbance

• Category C disturbance

• Loss of large amounts of generation via two units at a single power plant

• Category D disturbance

• Loss of large amounts of generation via three units at a single power plant
• Loss of the California-Oregon Interface (COI) followed by activation of the NE/SE islanding scheme
• Loss of large amounts of generation simultaneous with a reduction in solar or wind power output

• The category (C or D) is indicated in a small box below lower left-hand corner of each plot. Remember:

• Category B minimum freq dip is 59.6 Hz.
• Category C minimum freq dip is 59.0 Hz.
• Category D does not have a minimum
• Category “D-” indicates it is a particularly unlikely, but severe event

Spinning reserve levels affect on-line inertia and therefore results of transient freq performance

• Spinning reserve levels affect on-line inertia and therefore results of transient freq performance

• Solar-PV is “inertial-less.” Solar-thermal is not.

• Underfrequency load shedding can activate for “worse” initial freq performance and make it look better at 10 secs.

• Severe voltage decline can reduce power consumption and improve freq performance.

• The contingency selected has much effect.

Nadir is around 59.82 / 59.74 Hz for reduced inertia in SCE area when Loss of two Palo Verde units (2800MW in total)

• Nadir is around 59.82 / 59.74 Hz for reduced inertia in SCE area when Loss of two Palo Verde units (2800MW in total)

Less Inertia causes steeper drop of frequency

• Less Inertia causes steeper drop of frequency

• Loss of 3 PV units, nadir is about 59.72/ 59.68 Hz for Peak/Off-Peak case

Less Reserve causes slower restoration of frequency, lower post-contingency frequency

• Less Reserve causes slower restoration of frequency, lower post-contingency frequency

• Loss of 3 PV units, nadir is about 59.71/ 59.68 Hz for Peak/Off-Peak case

Less Inertia and Less Reserve causes faster drop and slower restoration of frequency, lower post-contingency frequency

• Less Inertia and Less Reserve causes faster drop and slower restoration of frequency, lower post-contingency frequency

• Loss of 3 PV units, nadir is about 59.67 Hz for Off-Peak case

Lower Inertia case has better frequency performance for loss of 2 Songs units in load center area

• Lower Inertia case has better frequency performance for loss of 2 Songs units in load center area

• Voltage sensitive load influences frequency response positively (“less” load for lower inertia case)

Less Inertia and primary control in each island

• Less Inertia and primary control in each island

• For peak case, there is 4719 MW of power flow on those lines which are part of the separation scheme.

• For off-peak case, there are only 1405 MW.

• Only Peak Case is studied

Lower Inertia or less reserve causes bigger ROCOF, which leads to more load shedding (2000MW more) and higher post-Frequency

• Lower Inertia or less reserve causes bigger ROCOF, which leads to more load shedding (2000MW more) and higher post-Frequency

Lower Inertia and less reserve causes bigger ROCOF, which leads to more load shedding and higher post-Frequency

• Lower Inertia and less reserve causes bigger ROCOF, which leads to more load shedding and higher post-Frequency

Simulation Conditions:

• Simulation Conditions:

• Max-solar case (Peak)
• Disable all automatic load shedding in dynamic data
• In 0.1 s, turn off 3300 MW renewable( 1500 wind + 1800 Solar)
• At 0.1s, shut down 1 Palo Verde unit
• Lower Inertia and Lower governor ( only for one case)

Lower nadir is about 59.63Hz at 500KV bus

• Lower nadir is about 59.63Hz at 500KV bus

Change all solar thermal units to solar PV in dynamic models

• Change all solar thermal units to solar PV in dynamic models

• Reduce reserve level to 5% from 18% for solar PV case by decreasing Pmax at SCE/WECC

• Or

• Shutdown conventional units to reduce reserve level to 10%

Max-solar case under NE/SE islanding contingency, all Solar PV case is with less Inertia and less governor

• Max-solar case under NE/SE islanding contingency, all Solar PV case is with less Inertia and less governor

NE/SE islanding contingency.

• NE/SE islanding contingency.

• Circle Red—with all solar PV model and reserve is reduced to 5% in area SCE.

• Star green— with all solar PV model and reserve is reduced to 5% in WECC for max-solar case.

Circle Red—with all solar PV model and 5% reserve in area SCE,

• Circle Red—with all solar PV model and 5% reserve in area SCE,

• Star green— with all solar PV model and 5% reserve in WECC,

• Square Brown-- with all solar PV model and 10% reserve in SCE by shutting off units for max-solar case under NE/SE islanding contingency.