EXPANSION OF TRANSMISSION SYSTEMS IN A DEREGULATED ENVIRONMENT Yong Zheng Saskatchewan Power Corporation N.A.Chowdhury University of Saskatchewan

Regulation: Regulated Monopoly Deregulation: Re-structuring of the Market Re-regulation

Unbundling of Services Competition Privatization Open access

Electrical Industry Regulation and Deregulation Generation Transmission Distribution Retail Sale Traditional regulated System Model Deregulated System Model Generation Company Transmission Company Distribution Company Retailers Customers Monopoly Franchise Limited Benefit Return Generation & Retailing - Deregulated Transmission & Distribution - Regulated

GOALS OF DEREGULATION n Lower utility rates n Choice of electricity providers n Efficient, cost based pricing n Encouraging renewable energy sources n Customer specific services

Transmission System Congestion Transmission system congestion means that one or several transmission lines in the system are overloaded. G1 G2 Load1 Load2 Line1 Limit: 80MW Power Flow: 90MW 150MW 60MW 0MW 90MW $20/MW $40/MW

Transmission System Congestion The introduction of competition in electric power market has made power flow control issues more complex and difficult than ever before. The scarcity of transmission capacity and a continued demand for power from less expensive sources lead to transmission system congestion.

Causes of Congestion n Market participants are blind to system operating conditions n Generation schedule is determined by competitive market n System operator has no right to interfere with market-based generation schedule unless congestion occurs

Consequences of Congestion n Unsolved congestion will threaten system security n Congestion relief will increase system operating cost n Congestion will bring extra cost to electrical users n Congestion will hinder fair competition between generators

Ways to Relieve Congestion n Generation reschedule n Interruptible load curtailment n Transmission system expansion

Congestion Relief G1 G2 Load1 Load2 Line1 Limit: 80MW Power Flow: 80MW 110MW 60MW 40MW 90MW $20/MW $40/MW New Added Line

Research Objectives n To develop methods to optimize generation re-schedule when congestion happens n To include the effect of short-term power market on transmission network expansion n To assess several alternatives to find the optimal transmission expansion in case of congestion

Optimization of Generation Reschedule n Mathematical Model of Optimum Generation Reschedule n AC Optimal Method

Mathematical Model for Re-dispatch Objective Function: Subject to re-dispatch price submitted by Generator i C i = re-dispatch price submitted by Generator i active power variation of Generator i  P Gi = active power variation of Generator i change in transmission loss  P L = change in transmission loss number of generators n = number of generators

AC Optimal Method n Based on AC power flow method n Linearized relationship between power flow variation and generation variation n Linearized relationship between transmission loss variation and generation variation n Takes transmission loss into account

A System with Three Transactions

Reloading Bids

Active power flows before and after re-dispatch Line No. FromTo Initial Flow (MW) Flow After Re- dispatch (MW) The increased cost due to the re-dispatch is $ /hr.

Load function can be expressed as: P(t) = Q 0 + Q(t) + Q(r); t = 1, 2, 3, ……, 24 andare non-price responsive parts Q 0 and Q(t) are non-price responsive parts is the price responsive part Q(r) is the price responsive part Load Model

Benefit Function can be expressed as: B(P Gi ) = F(P Gi ) + M(P Gi ) Bidding Model Cost function: Cost function: F(P Gi ) =  P Gi 2 +  P Gi +  Profit function: Profit function: M(P Gi ) = k* P Gi Bidding price function: H(P Gi ) =  B(P Gi )/  P Gi = 2  P Gi +  + k

Total generating cost as seen by the ISO Market Clearing Price, r can be found by solving

Bidding Price Curve

Transmission System Expansion n Expanding transmission system is more economic if congestion fee is higher than the investment cost of building new transmission line. n Future short-term power market should be considered when planning transmission system expansion. n Different expansion options should be assessed when selecting the most acceptable expansion scheme.

Steps involved in transmission system expansion planning n Forecast short-term market generation schedule on the basis of typical load curves and bidding price functions. n Combine the predicted short-term generation schedule with long-term generation schedule to evaluate system power flow distribution and congestion fee. n Select new lines that can relieve congestion with investment cost less than congestion fee.

Summary and Conclusions n Deregulation makes power flow control more complicated n Market-driven generation schedule results in transmission system congestion n Congestion will threaten system security and must be relieved n Generation reschedule will increase system operating cost n Expansion of transmission becomes economic if the investment cost of building new transmission facilities is less than the congestion fee.

Question?