Experimental Testing and Model Validation of a Small-scale Generator ...
Paper accepted for presentation at 2003 IEEE Bologna Power Tech Conference, June 23th-26th, Bologna, Italy
Experimental Testing and Model Validation of a Small-scale Generator Set for Stability Analysis. G. Quiñonez-Varela and A. Cruden
Abstract — The integration of numerous small-scale
generators into existing power systems is anticipated to impact the operation, control and protection of such systems. In particular, maintaining voltage and frequency stability within defined limits is more onerous and requires investigation. The effect of protective limiters and characteristics such as the genuine inertia of the generation set must be taken into consideration in planning studies in order to accurately represent the overall dynamic characteristics of distributed generators. This paper focuses on the investigation of these issues by studying a small-scale reciprocating engine/generator set. The experimental procedures used to determine the genuine inertia of the test rig are described, and the influence and importance of considering the action of protective limiters such as voltage-per-hertz (V/Hz) in stability studies is demonstrated. This work is directly relevant to the review of current UK stability limits, and to the generation planning framework supported by the Scottish Executive. Index Terms — AC generator excitation, dispersed storage and generation, frequency control, power system dynamic stability, power system simulation, synchronous generator excitation, synchronous generator stability, voltage control.
T
I. INTRODUCTION
HE integration of numerous small-scale generators such as reciprocating engine sets into existing power systems is anticipated to impact the operation, control and protection of such systems. In particular, maintaining voltage and frequency stability within defined limits is more onerous and requires investigation. Consideration is now being given to the revision of system stability limits and the examination of novel coordinating procedures system [1]. Consequently, an accurate representation of the overall dynamic characteristics of generators is crucial in order to properly investigate the interaction among distributed generators, local loads and the utility.
G. Quiñonez-Varela and A. Cruden are with the Centre for Economic Renewable Power Delivery, University of Strathclyde, Glasgow G1 1XW, UK. (e-mail: [email protected]; [email protected]).
0-7803-7967-5/03/$17.00 ©2003 IEEE
In addition to the typical automatic voltage regulator (AVR), modern excitation systems incorporate a number of control, limiting and protective functions to ensure that both the exciter and the synchronous generator are properly protected against overfluxing, overloading, overheating, etc. Relevant functions are the overexcitation (OEL), underexcitation (UEL) and voltage to frequency ratio (V/Hz) limiters [2], [3]. Although their action is active under normal operating conditions during some relevant system disturbances, such as substantial loss of load, uncontrolled load shedding and short-circuits, their effect can be particularly significant to the ultimate behaviour of the system under these conditions [4], [5]. However, the effect of these devices is usually not taken into consideration in planning studies and, according to available literature [3]-[6], there is little examination of the dynamic performance of these limiters and small-scale distributed generators. Failure to consider the action of such protective limiters may lead to inaccurate assumptions of the generator responses during planning studies [6], [7]. Along with voltage stability, frequency stability is now a crucial consideration in power system analysis, particularly as a consequence of the relatively recent proliferation of distributed generation. One of the parameters that significantly influence the ‘firmness’ of generators and overall system stability is the inertia values of the generator sets. Distributed generators are in general small-scale (
Experimental Testing and Model Validation of a Small-scale Generator Set for Stability Analysis. G. Quiñonez-Varela and A. Cruden
Abstract — The integration of numerous small-scale
generators into existing power systems is anticipated to impact the operation, control and protection of such systems. In particular, maintaining voltage and frequency stability within defined limits is more onerous and requires investigation. The effect of protective limiters and characteristics such as the genuine inertia of the generation set must be taken into consideration in planning studies in order to accurately represent the overall dynamic characteristics of distributed generators. This paper focuses on the investigation of these issues by studying a small-scale reciprocating engine/generator set. The experimental procedures used to determine the genuine inertia of the test rig are described, and the influence and importance of considering the action of protective limiters such as voltage-per-hertz (V/Hz) in stability studies is demonstrated. This work is directly relevant to the review of current UK stability limits, and to the generation planning framework supported by the Scottish Executive. Index Terms — AC generator excitation, dispersed storage and generation, frequency control, power system dynamic stability, power system simulation, synchronous generator excitation, synchronous generator stability, voltage control.
T
I. INTRODUCTION
HE integration of numerous small-scale generators such as reciprocating engine sets into existing power systems is anticipated to impact the operation, control and protection of such systems. In particular, maintaining voltage and frequency stability within defined limits is more onerous and requires investigation. Consideration is now being given to the revision of system stability limits and the examination of novel coordinating procedures system [1]. Consequently, an accurate representation of the overall dynamic characteristics of generators is crucial in order to properly investigate the interaction among distributed generators, local loads and the utility.
G. Quiñonez-Varela and A. Cruden are with the Centre for Economic Renewable Power Delivery, University of Strathclyde, Glasgow G1 1XW, UK. (e-mail: [email protected]; [email protected]).
0-7803-7967-5/03/$17.00 ©2003 IEEE
In addition to the typical automatic voltage regulator (AVR), modern excitation systems incorporate a number of control, limiting and protective functions to ensure that both the exciter and the synchronous generator are properly protected against overfluxing, overloading, overheating, etc. Relevant functions are the overexcitation (OEL), underexcitation (UEL) and voltage to frequency ratio (V/Hz) limiters [2], [3]. Although their action is active under normal operating conditions during some relevant system disturbances, such as substantial loss of load, uncontrolled load shedding and short-circuits, their effect can be particularly significant to the ultimate behaviour of the system under these conditions [4], [5]. However, the effect of these devices is usually not taken into consideration in planning studies and, according to available literature [3]-[6], there is little examination of the dynamic performance of these limiters and small-scale distributed generators. Failure to consider the action of such protective limiters may lead to inaccurate assumptions of the generator responses during planning studies [6], [7]. Along with voltage stability, frequency stability is now a crucial consideration in power system analysis, particularly as a consequence of the relatively recent proliferation of distributed generation. One of the parameters that significantly influence the ‘firmness’ of generators and overall system stability is the inertia values of the generator sets. Distributed generators are in general small-scale (
