Bin-Kwie Chen

Scheduling of direct load control to minimize load reduction for a utility suffering from generation shortage

This paper adopts the method of dynamic programming to optimally determine the schedule of the direct load control, but its objective function is to minimize the amount of load reduction with appropriate constraints. This approach is intended to solve the chronic problem of severe power shortage in the summer for the Taiwan Power Company (Taipower or TPC). This scheduling scheme is to reduce the resulting inconvenience to customers as well as the effects to the total income from electricity sales to the minimum under the particular management conditions the TPC finds itself in. >

Allocating the costs of reactive power purchased in an ancillary service market by modified Y-bus matrix method

In an open accessed transmission system, the costs of each ancillary service will be unbundled. This paper proposes a straightforward method of allocating the costs of reactive power purchased by contract or from a bidding market. This method uses basic circuit theory and partitions the Y-bus matrix to decompose the voltage of the load buses with a view to calculating the reactive power sharing. This method is derived from the system equations without such assumptions as the proportional flow or lossless transmission line.

Effects of various unbalanced voltages on the operation performance of an induction motor under the same voltage unbalance factor condition

Abstract This paper investigates the effects of different unbalanced voltages with the same voltage unbalance factor (VUF) on the performance of a three-phase induction motor and its feedback influence on the power system. Under eight different voltage unbalance conditions, the performance of a three-phase induction motor was measured through a real load test. The loss, efficiency, power factor and temperature rise of the motor under different unbalanced voltages are investigated. According to the test results and analysis, the importance of the positive-sequence voltage on the motor’s apparent performance and the negative-sequence voltage in the hidden damage were pointed out. Finally, it is strongly suggested that (1) the derating and temperature rise curves and related regulations should consider the VUF percent and the magnitude of positive-sequence voltage, and (2) the effects of unbalanced voltage on induction motors should also be modeled in power system voltage stability studies.

Three phase models of specially connected transformers

To reduce power system imbalance, various types of specially-connected power transformers have been adopted in Taiwan and abroad. Because three-phase transformer models are necessary for three-phase load flow simulation, specially-connected transformers which have been adopted so far are selected to derive three-phase models in this paper. These transformers include the single-phase connection, the V-V connection, the wye-delta connection, the Scott connection, the Le Blanc connection and the modified-Woodbridge connection. The three-phase models with the specially-connected transformers offered in this paper distinctly represent the HSR feeding system by means of the physical three-phase circuit and the symmetrical-component equivalent circuit. The three-phase model could be joined to the three-phase load flow program to exactly analyze the system imbalance in the future. The symmetrical-component equivalent circuit may also be used to derive the approximate unbalance-estimating formula.

Optimum operation for a back-pressure cogeneration system under time-of-use rates

This paper proposes a Newton based algorithm which will decide the optimum load allocations of boilers and generators under the time-of-use rates subject to satisfying all the operation constraints. This scheme is capable of handling the nonlinear cost function and correlated constraints between the electric power and steam generation for the cogeneration system. The proposed scheme has been successfully applied to a real cogeneration plant, and results indicate that: (1) at least 2% energy saving can be achieved; (2) TOU rates play an important role in the operation strategy; and (3) it might be of help in choosing the cogeneration system.

A Novel Power System Defense Plan to Cope With 30% Wind Power Penetration in the Isolated Penghu System

In the plentiful wind resource on Penghu Island, the capacity factor of the wind park is up to 47%. It is expected that, in a near future, more wind generating units will soon be integrated into this power system. However, many blackouts occurred at the Penghu Island in the past, and the present power protection scheme has not taken the influence of the wind generating units into consideration; therefore, it is necessary to revise the defense plan for Penghus power system. In this paper, different generation/load patterns in different seasons are considered, and then, system steady-state and transient responses in some specific buses and important feeders are analyzed. The accurate modeling on wind turbines and relay settings are performed by using the power system simulation program PSS/E. The original power defense scheme using only under-frequency load shedding is examined, and a new protection scheme is proposed based on numerous contingency simulations, including islanding operation protection for some specific cases. It is expected that the reliability improvement of the Penghu system can be achieved by using the new defense scheme.

The Economic Dispatch with Consideration of Transmission Service Charge for a Generation Company

This paper presents a novel economic dispatch strategy for a generation company that owns several units with different fuel costs, efficiency, and locations, and has a bilateral contract with several large customers. The proposed strategy not only considers the generation cost, but also takes into account the wheeling charge for the use of the transmission system. A modified megawatt-mile method is proposed to calculate the wheeling cost in this paper. Finally, the calculation results of economic dispatch for a generation company with two units and their loads in a real power system will be demonstrated.

Optimal operation strategy for cogeneration power plants

The electrical power system has been increased both in the size and complexity at a rapid rate in the last few decades. With the trend of deregulation, power systems are operated in a more stressed state. Since the establishment of the cogeneration promotion law in 1988, over one hundred cogeneration power plants with the total installation capacity about 16% of total Taiwan Power Company (TPC) system in Taiwan. Also, after TPC adopting the time-of-use (TOU) tariff rate schedule, electricity price of peak and semipeak period is higher than off-peak period. These factors promote greater incentives for more effective utilization of the current facilities. This paper uses genetic algorithms to develop an optimal operation strategy for the cogeneration power plant (CPP) to improve its competitiveness in the power market. A real cogeneration power plant is used to verify the feasibility of the proposed algorithm.

Underfrequency load-shedding scheme for co-generators connected to an unreliable utility system

The authors describe a load shedding scheme for an existing cogeneration system interconnected to an unreliable utility. The various considerations involved in the design are presented. A full-scale transient stability program was used as a design tool. Extensive studies were carried out to select three-stage load shedding scheme that optimized overall performance. Many factors related to the load shedding scheme, including frequency settings, underfrequency limits, tripping of neighboring utility generation, directional power flow, and antimotoring, were examined. Since the overload could exceed 100%, an exceptionally fast load shedding scheme was developed.<<ETX>>

Lessons Learned From the Generator Loss of Field at a Cogeneration Thermal Power Plant in Taiwan

The contribution of this paper is that we present experiences from dealing with practical issues related to synchronous machine stability events. We describe and analyze the scenarios of generator loss-of-field occurring two times at a cogeneration thermal power plant in Taiwan in the years 2003 and 2005. Since the total production loss from both events was quite large, some improvements have been implemented to prevent the recurrence of similar events in the future. They consist of installing the sequence of events recorder at the generator output terminal, regulating the generator lagging power factor operation from 0.95-0.99 to 0.91, adjusting the tap position to decrease the secondary voltage of the 161 kV/161 kV interconnecting transformer, operating the phase-leading capacitors attached with a multi-stage chain cut-off control unit, and running two or three generators in automatic voltage regulation mode instead of automatic power factor regulation mode. Although similar events occurred twice at the same power plant in 2006, the generating units were capable of continuous stable operation which had effectively verified the improvements of operational changes. In conclusion, we suggest that the operating modes of generators in a cogeneration plant should reexamine constantly as well as monitor power quality of different end-user sectors continuously in order to ensure the security of power-system operation.