摘要:

The Maxwell stress equations are used to determine the distribution of electromagnetic forces at the surface of the stator bore for the dual purpose of investigating the cause of the observed variation of double frequency stator core vibration with load and power factor, and of providing the basis for supplying information about the current status of this vibration to an online bearing monitoring program. The main cause of the change in vibration with load is the way in which the radial and circumferential stress distributions combine in space and time. However, magnetic saturation of the iron is also highly significant, and so a scheme to incorporate this non-linear effect into an intrinsically linear model is developed. Calculation of the actual vibration level of a given machine depends on two structural finite-element analyses, the first yielding the transfer coefficient linking radial force to radial vibration, and the second the coefficient linking circumferential force to radial vibration.

DOI:10.1049/ip-c.1991.0049

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The paper deals with the optimum selection of a governor speed regulation parameterRin the design of an appropriate governor for automatic generation control of an interconnected power system in discrete mode taking into consideration the generation rate constraint (GRC). Investigations reveal that there is no necessity for a very low value ofRas is usually the practice because under realistic operation of an AGC, a larger value ofRcan be acceptable and can even provide better dynamic responses. A governor designed with a larger value ofRwill be simpler and cheaper. A sensitivity analysis for an AGC system with a higher value ofRreveals that the optimum integral gain setting obtained for nominal system parameters is quite robust for a ±25% change in system parameters.

DOI:10.1049/ip-c.1991.0050

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A new approach using artificial neural networks (ANNs) is proposed for short-term load forecasting. To forecast the hourly loads of a day, the hourly load pattern and the peak and valley loads of the day must be determined. In paper I a neural network based on self-organising feature maps to identify those days with similar hourly load patterns is developed. These days with similar load patterns are said to be of the same day type. The load pattern of the day under study is obtained by averaging the load patterns of several days in the past which are of the same day type as the given day. In Part II of the paper a feedforward multilayer neural network is designed to predict daily peak load and valley load. Once the peak load and valley load and the hourly load pattern are available, the desired hourly loads can be readily computed. The effectiveness of the proposed neural network is demonstrated by the short-term load forecasting of the Taiwan Power Company.

DOI:10.1049/ip-c.1991.0051

出版商:IEE    

年代:1991

数据来源: IET

摘要:

In Part I of the paper, a neural network with unsupervised learning has been proposed to identify the day types and compute the hourly load pattern by averaging the load patterns of the same day type. In this part of the paper a neural network, commonly referred to as the multilayer feedforward network, is developed to forecast daily peak load and valley load. Unlike the self-organising feature maps in Part I, the multilayer feedforward network is a neural net with supervised learning. The neural net is first trained using historical weather and load data. Then the trained neural net is applied to predict daily peak load and valley load. These peak and valley loads, when combined with the hourly load pattern, can yield the desired hourly loads. Results from short-term load forecasting of the Taiwan power system are given to demonstrate the effectiveness of the proposed neural networks.

DOI:10.1049/ip-c.1991.0052

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A systematic approach is used to design a controller for a superconducting magnetic energy storage (SMES) unit to improve the torsional modes damping of a turbogenerator. To suppress the unstable torsional oscillation, a proportional-integral-derivative (PID) controller is employed to modulate the power input/output of the SMES unit according to generator speed deviation. The gains of the proposed PID controller are determined by the pole assignment method based on modal control theory. Eigenvalue analysis of the studied system shows that the PID controller is quite effective over a wide range of operating conditions. Computer simulations using the nonlinear system model are also performed to demonstrate the damping effort of the proposed controller under disturbance conditions.

DOI:10.1049/ip-c.1991.0053

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A static reactive power (VAr) compensator (SVC), constructed by fixed capacitors (FC) snd thyristor controlled reactors (TCRs), is designed and implemented to improve the damping of the synchronous generator. A digital propotional-integral (PI) controller is synthesised by the Motorola M68HC11 single chip microprocessor board to modify the reactive power compensation of the SVC from adjusting the conduction angle of the thyristors. The SVC is placed at the generator bus terminal with the speed deviation (Δω) as the feedback signal for the PI controller. The pole assignment method is used to determine the gains of the PI controller. Results from digital simulation and the implementation test show that the SVC with the PI controller can greatly enhance the damping of the system oscillation caused by disturbances. Although the PI controller is designed at a special operation point, it can also provide a good damping effect at other operation conditions. The voltage profile of the generator is also improved by the SVC.

DOI:10.1049/ip-c.1991.0054

出版商:IEE    

年代:1991

数据来源: IET

摘要:

A new decomposition-aggregation approach is developed to perform transient stability analysis of anN-machine power system with a speed governor. The system decomposition is performed so that every subsystem includes four machines, instead of only two or three machines as considered in other work. The system model is derived and decomposed into (N− 1)/3 11th-order interconnected subsystems considering transfer conductances, nonuniform mechanical damping, electromagnetic damping and speed governor action. Each of these subsystems is decomposed into a free subsystem containing 12 nonlinearities and interconnections. A square aggregation matrix of order (N− 1)/3 is obtained instead of ordersNand (N+ 1)/2 for the pair-wise and triple-wise decompositions, respectively. The approach is applied to a 10-machine power system and an estimate for the system asymptotic stability domain is determined. System transient stability computations are carried out considering a three-phase short circuit fault, with successful reclosure, near a system bus or a sudden loss of one of the system loads. The approach is used to determine a reclosure time for the faulted line and a reconnection time for the lost load required for the system to regain its prefault (normal) conditions. The approach developed is suitable and can be easily used for stability analysis of power systems (the number of machines may be more than 10). The developed approach can also reduce the conservativeness of the decomposition-aggregation method.

DOI:10.1049/ip-c.1991.0055

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The paper discusses the use of a ferromagnetic coating applied to the busbars of an SF6busduct as a means of controlling disconnect transients. A software travelling wave model is described. The model is based on a frequency-domain characterisation of the busbars in the system. The model accounts for the skin effect in coated materials, and incorporates the effect of discontinuities in the system. The influence of the various coating attributes are noted. The model is shown to perform accurately as a travelling-wave analysis tool. Consideration is also given to the transient skin effect, which is shown to increase the attenuation of transients. Results recorded in a laboratory system with and without ferromagnetic busbars are presented. Ferromagnetics are shown to introduce marked risetime lengthening, as well as an envelope attentuation to disconnect transients.

DOI:10.1049/ip-c.1991.0056

出版商:IEE    

年代:1991

数据来源: IET

摘要:

Diakoptics, superposition, and the mismatch theorem are used to study theoretically the effect of neglecting line resistances when forming the variousBmatrices on the mismatches of theXBand theBXversions of the decoupled load-flow algorithms. The fixed Jacobian method (FJM) is used as a yardstick to compare the effectiveness of theXBand theBXversions. It is shown that theBXversion is a better approximation to the FJM than theXBversion for highr/xratios. Results are reported using simulated networks.

DOI:10.1049/ip-c.1991.0057

出版商:IEE    

年代:1991

数据来源: IET

摘要:

The paper presents detailed results on the performance comparisons of the investigated AC load flow techniques, i.e. fast decoupled, second-order Newton Raphson and the super-decoupled load flows. The results are compared on the basis of the convergence rates, iteration counts, memory requirements and the CPU times. Comparative performance evaluations of these three methods with respect to ill-conditioning networks and line-outage simulations are also investigated. Extensive performance tests have been carried out on the standard IEEE 5, 14, 24 and 57 bus test systems.

DOI:10.1049/ip-c.1991.0058

出版商:IEE    

年代:1991

数据来源: IET