Assessment of Spinning Reserve Requirements in a

Deregulated System by

Ifedi K. Odinakaeze

April 9th, 2009Department of Electrical and

Computer Engineering

Introduction

A deregulated power system is a horizontally integrated system.

Power generation, transmission, and distribution are unbundled, and consumers are allowed to choose their suppliers.

Independent system operator (ISO) is responsible for real-time load balancing, congestion management and provision of ancillary services.

Ancillary services are additional services required to provide stable and reliable electricity supply to meet the real-time electricity market’s need.

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Definitions

Spinning reserve (SR) is the on-line reserve capacity that is synchronized to the grid system and ready to meet load demand within 10 minutes of a dispatch instruction by the ISO.

Spot Market (SM) is a real-time energy market for procuring emergency power when demand exceeds scheduled generation capacity plus reserve.

Day-Ahead Market is a market conducted prior to the commencement of each day and location-based hourly prices are set based on generation and energy transaction bids that were offered in advance to the ISO.

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Test System and Assumptions

The test system is a 3-Generating Zone system and all zones must supply energy the next day based on unit commitment.

The load forecast uncertainty is a discrete 49-step normal probability distribution with the forecast load as the mean and with a known standard deviation.

There are no spot market power limits and the spinning reserve market is independent of the energy market.

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Load Forecast Uncertainty Model

7-step Normal distribution of the load forecast uncertainty with known % standard deviation, σ. 5

Cost ModelThe cost model is divided into three scenarios.

Scenario A is the surplus part of the load model where the actual load is less than the total scheduled generation capacity that is for s =1...24.

Scenario B is the part of the load model where the actual load is equal to the total scheduled generation capacity that is for s =25.

Scenario C is the deficit part of the load model where the actual load is less than the total scheduled generation capacity given for s = 26...49.

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The cost model is a non-linear formula that is developed based on these three scenarios for each hour.

The goal is to minimize the hourly total cost of the energy based on certain constraints.

The amount of Spinning Reserve required during each hour depends on the constraints and the cost of providing it.

For every step in the 49-step model, energy settlement decisions are made based on energy prices and incremental loss for each MW change (either up or down) in the generating capacity schedule.

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Development of the Cost Model

For each value of s, the Actual load is given by the equation:

For (s =1,…, 24) such that Forecast load > Actual load, the corresponding cost, sTA is given by:

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• Similarly for s = 25, that is when Forecast load is unchanged on the Actual consumption day, the cost with its corresponding probability is given by:

• There is no reloading down or up process required in this decision making since the total scheduled generating capacity is equal to the Actual load.

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The last part is for when the Forecast load is less than the Actual day load and it is for (s = 26,…, 49).

The corresponding cost is given as:

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The optimization problem is formulated for every hour by the combination of the three cost scenarios with constraints to give:

subject to the following constraints

  

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The hourly Ploss equation is given as:

The effects of the change in the Spot Market and Spinning Reserve Prices and Zone Reloading Limits on the SR Requirements are analyzed for different % Load Forecast Uncertainty given by σ.

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Results

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Conclusions The amount of SR is affected by the % of the

load forecast Uncertainty The Spot Market Price (SMP) affects the

amount of SR required in the system The amount of SR is affected by the Spinning

Reserve Price (SRP) A change in the reloading limits of the

sources also affects the quantity of SR required

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Future Work

Incorporation of generator failure rate data in the cost model.

Assessment of the SR requirement based on cost-benefit analysis (EENS and VOLL) considering Load Forecast Uncertainty.

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Thank you! Any Questions??? 19

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