A.K. David

Transmission congestion management in an electricity market

Managing transmission congestion in an unbundled electric power system poses a challenge to an independent system operator (ISO). This paper considers an open transmission dispatch environment in which pool and bilateral/multilateral dispatches coexist and proceeds to develop a congestion management strategy for this scenario. Prioritization of electricity transactions and related curtailment strategies are explored and a mechanism for coordination between market participants to achieve additional economic advantages is described.

Optimal dispatch under transmission contracts

Open transmission access is now the most topical issue in power system deregulation. Power system operation poses the greatest challenge to a competitive environment incorporating open transmission access and there are some fundamental operational problems that are still unresolved. This paper seeks to provide an approach to the power dispatch problem in a structure dominated by bilateral and multilateral transmission contracts. A framework for price-based operation under these conditions is developed and a methodology for optimal transmission dispatch is proposed. The case study results illustrate that the proposed market arrangement and operating mechanisms are compatible with this new business environment.

Pricing transmission services in the context of industry deregulation

The changing structure of the electricity supply industry and the emergence of independent power producers and independent customers is bringing transmission pricing into a new focus. The costs of operating, maintaining and expanding the transmission system, that is pricing transmission services, needs to be addressed. This has to be done on an economically rational and technically meaningful basis and this paper suggests an approach which distinguishes between operating and embedded costs and develops separate methods in respect of each of these components. Capacity use as well as reliability benefits derived by different users are taken into account in the disbursement of charges for investment recovery. New insights into the marginal pricing approach to the recovery of operating costs are also briefly mentioned.

Strategic bidding for electricity supply in a day-ahead energy market

Abstract The problem of building optimal bidding strategies for competitive suppliers in a day-ahead energy market is addressed in this paper. It is assumed that each supplier bids 24 linear energy supply functions, one for each hour, into the day-ahead energy market, and the market is cleared separately and simultaneously for all the delivery hours. Each supplier makes decisions on unit commitment and chooses the coefficients in the linear energy supply functions to maximize total benefits in the schedule day, subject to expectations about how rival suppliers will bid. Two different bidding schemes, namely ‘maximum hourly-benefit bidding strategies’ and ‘minimum stable output bidding strategies’, have been suggested for each hour, and based on these two schemes an overall bidding strategy in the day-ahead market can then be developed. Stochastic optimization models are first developed to describe these two different bidding schemes and a genetic algorithm based method is then presented to develop an overall bidding strategy for the day-ahead market. A numerical example is utilized to illustrate the essential features of the method.

Optimal bidding strategies for competitive generators and large consumers

Abstract There exists the potential for gaming such as strategic bidding by participants (power suppliers and large consumers) in a deregulated power market, which is more an oligopoly than a laissez-faire market. Each participant can increase his or her own profit through strategic bidding but this has a negative effect on maximising social welfare. A method to build bidding strategies for both power suppliers and large consumers in a poolco-type electricity market is presented in this paper. It is assumed that each supplier/large consumer bids a linear supply/demand function, and the system is dispatched to maximise social welfare. Each supplier/large consumer chooses the coefficients in the linear supply/demand function to maximise benefits, subject to expectations about how rival participants will bid. The problem is formulated as a stochastic optimisation problem, and solved by a Monte Carlo approach. A numerical example with six suppliers and two large consumers serves to illustrate the essential features of the method.

Coordination of bidding strategies in day-ahead energy and spinning reserve markets

In this paper, the problem of building optimally coordinated bidding strategies for competitive suppliers in day-ahead energy and spinning reserve markets is addressed. It is assumed that each supplier bids 24 linear energy supply functions and 24 linear spinning reserve supply functions, one for each hour, into the energy and spinning reserve markets, respectively, and each market is cleared separately and simultaneously for all the 24 delivery hours. Each supplier makes decisions on unit commitment and chooses the coefficients in the linear energy and spinning reserve supply functions to maximise total benefits, subject to expectations about how rival suppliers will bid in both markets. Two different bidding schemes have been suggested for each hour, and based on them an overall coordinated bidding strategy in the day-ahead energy and spinning reserve market is then developed. Stochastic optimisation models are first developed to describe these two different bidding schemes and a genetic algorithm (GA) is then used to build the optimally coordinated bidding strategies for each scheme and to develop an overall bidding strategy for the day-ahead energy and spinning reserve markets. A numerical example is utilised to illustrate the essential features of the method.

Fast transient stability estimation using a novel dynamic equivalent reduction technique

A new dynamic equivalent power system (DEPS) model for fast first swing transient stability assessment is proposed in this paper. The DEPS model makes use of the phenomenon that during a fault on a large power system, there are many generators that are only lightly disturbed when compared with severely disturbed machines. The method substitutes these less disturbed machines by one equivalent generator but allows some model parameters to become time dependent. The crucial feature is that a novel method of classification of the less disturbed machines based on a Taylor series expansion which achieves a very rapid assessment of first swing critical clearing time (CCT) has been developed. This method is fundamentally different from other published dynamic equivalent techniques, such as the extended equal area criterion method and the identification of coherent generators, and both reliability and efficiency are better. With this DEPS model the efficiency of the traditional first swing transient stability analysis could be fundamentally improved. Extensive tests performed on several IEEE test systems show that the proposed model is suitable for fast transient stability assessment in large systems. >

Capacity-use and reliability based transmission embedded cost allocation with temporal considerations

Abstract Transmission services have to be provided as a separate item in a de-regulated or vertically restructured electricity supply industry. Though the primary function of a transmission line is to transmit power from source point(s) to loading point(s), major lines also play an important role in security. Sometimes a particular transaction cannot take place if a particular line is unavailable and, moreover, a specific line may be more important for the security of a particular transaction than it is for others. Clearly reliability is a relevant consideration in equitable cost allocation. A method for transmission line embedded cost allocation among transmission transactions accounting for both line capacity-use and reliability benefit is presented. Line capacity-use is determined by the amount of power transmitted, while the reliability benefit is calculated as the increment of the total probability of system failure, with the line out of service, compared to when the line is in service. Capacity-use is determined using a full AC power flow and hence the effects of reactive power can also be investigated. The cost allocation to each transaction according to the capacity-use and reliability benefit patterns throughout an accounting period during which system loading and line failure probability are varying are studied.

Evaluation of transient stability limit using a transient time margin sensitivity approach

Abstract This paper addresses the issue of how to evaluate transient stability limit using a transient time margin (TTM) approach and the sensitivity of this margin to key system variables such as generation and load. This allows fast control decisions to be assessed for a power system on-line control purpose. The difference between fault clearing time and critical fault clearing time, called the TTM, is proposed as a transient stability index. The single machine equivalent system (SMES) is employed to represent the TTM as a function of system parameters such as plant generation and load, and the sensitivity of the TTM to these parameters is found. The generation or load changes that can be made while preserving stability, or the changes that are needed to restore stability in dynamically insecure systems, are next derived from this sensitivity. Test results for several real size test power systems show that the proposed approach is feasible and promising for on-line control application.

Inter-area mode transient stability estimation

Inter-area mode transient stability evaluation of large interconnected power systems has proved to be difficult because of the complexity of the phenomena and the long time duration over which instability manifests itself. Very few studies have been published and this paper describes a new method which is reliable for this complex problem, fast and accurate in its evaluation of critical clearing time, provides an estimate of transient energy margin and has some potential for control evaluation. The technique is a hybrid between the detailed multimachine representation, the single-machine equivalent and energy methods. It has been tested on three standard test systems including the IEEE 50-generator system.