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Volume 129
Issue 1
IEE Proceedings C (Generation, Transmission and Distribution)
Volume 129, Issue 1, January 1982
Volumes & issues:
Volume 129, Issue 1
January 1982
Fatigue damage of turbine-generator shafts due to fast reclosing
- Author(s): N. Aspragathos and A.D. Dimarogonas
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 1 –9
- DOI: 10.1049/ip-c.1982.0001
- Type: Article
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Breaking in a large electric power system causes torsional vibrations on the turbogenerator shafts. Damping of such vibrations is very low compared with the damping of the electrical system. Therefore, during a strong electric transient, the shafts connecting the turbine and the generator rotors may undergo heavy loading and considerable deformations, both elastic and plastic, for prolonged periods of time. As a result, the fatigue life of the shafts may be substantially reduced. The paper introduces an improved mechanical dynamic model of the system for torsional response, which can account for the plastic material model, to yield the cumulative damage during the transients due to high and low cycle fatigue. Moreover, a procedure for the calculation of fatigue life expenditure is developed based on the ‘equivalent strain range’ derived from a known twist angle history of the shaft. A detailed discrete model for both the mechanical and the electrical system was used in conjunction with modelling of the fast reclosing mechanism. In this manner, fatigue life reduction due to a certain fast reclosing strategy was evaluated. The system thus developed can lead to a better understanding of the mechanism of fatigue life reduction due to the electrical transients.
Optimisation of load-frequency control parameters for power systems with reheat steam turbines and governor deadband nonlinearity
- Author(s): S.C. Tripathy ; G.S. Hope ; O.P. Malik
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 10 –16
- DOI: 10.1049/ip-c.1982.0002
- Type: Article
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In the paper a systemic method of choosing the frequency bias parameter and the integrator gain of the supplementary control is presented by using the Lyapunov technique. The reheat effect of the steam turbines is considered in the state space model. The effect of governor deadband nonlinearity is considered by using the describing function approach and including the linearised equations in the state space model. It is shown that the governor deadband (backlash) nonlinearity tends to produce a continuous oscillation in the area frequency and tie-line power transient response. When proportional feedback of area frequency error is used to stabilise the response it it found that only overshoot is reduced, but settling time remains the same.
Design of decentralised load-frequency regulators for interconnected power systems
- Author(s): T. Hiyama
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 17 –23
- DOI: 10.1049/ip-c.1982.0003
- Type: Article
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The paper presents a new method of designing decentralised load-frequency regulators for interconnected power systems. Within the framework of this method, the interconnected mutliarea power system is decomposed into several subsystems, each of which is controlled separately by a decentralised regulator. Each subsystem consists of one area and its external equivalent in a simplified form. A decentralised control law for the study area is introduced by using a quadratic performance index. Feedback gains of the decentralised regulator, which minimise the index, are determined by a Newton-Raphson iterative algorithm. The proposed method is applied to an interconnected longitudinal 4-area system, and the effects of the proposed regulator are examined by digital simulations and associated sensitivity analysis of the system. Furthermore, a suitable means for preventing excessive control action is also considered involving a significant system nonlinearity, i.e. some generation rate constraint.
Voltampere reactive compensation using chance-constrained programming
- Author(s): T.A.M. Sharaf and G.J. Berg
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 24 –29
- DOI: 10.1049/ip-c.1982.0004
- Type: Article
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A new technique is developed for solving the voltampere reactive (VAR) compensation problem under uncertain operating conditions. The technique employs chance-constrained programming (CCP), and transforms the problem into a standard linear programming problem. In providing optimal allocation of VAR support, busbars with unacceptably high probability of violating voltage limits are identified and assigned appropriate chance-constraints. Two cases are considered using the new technique. In the first case, capacitive compensation is evaluated for peak load conditions. Inductive compensation is considered in the second case, assuming light load conditions. The method in its general form can be applied in cases where there is uncertainty with respect to equipment cost and/or the coefficients of the voltage-magnitude/reactive power relationships. Normal distributions are not necessary conditions and, if desired, dependent variates can be assumed. The method has been applied to the AEP 30-busbar test system for both heavy and light load conditions, and sample results are presented in the paper.
Calculation of transient current in transformers
- Author(s): S. Akpinar ; M. Coulson ; R.R.S. Simpson ; R.D. Slater
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 30 –34
- DOI: 10.1049/ip-c.1982.0005
- Type: Article
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The paper describes two general methods of calculating inrush currents in single-phase transformers, allowing for the effects of magnetic hysteresis. One method is to use a normalised representation of the magnetic characteristic. A numerical solution to the circuit equations is carried out, but, because the equations are dimensionless, the number of independent parameters is reduced from seven to three. This makes it possible to carry out a general study, with the results presented in the form of charts. The charts can then be scaled to obtain inrush current values for particular cases. The other method is based on a simple, yet accurate, modelling of magnetisation curves using a hyperbolic expression. In this case an algebraic solution of the circuit equations is obtained. Comparisons are included between experimental and calculated results.
Novel fail-safe earth-fault protection schemes for underground coalmines using restricted-neutral system of power supply
- Author(s): D.K. Mittra ; S.K. Basu ; R.K. Mondal
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 35 –40
- DOI: 10.1049/ip-c.1982.0006
- Type: Article
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The paper reports the development of two novel fail-safe sensitive earth-fault protection schemes for coal mines using restricted-neutral system of power supply. Minimisation of earth leakage current for an underground coal mine's power-supply system is of great advantage in reducing hazards like electrical shock from exposed metal works, fire and methane explosion. Restricted-neutral system of power supply can effectively limit earth-fault currents to a very low limit (100–200 mA) as compared to that of 500–1000 A in solidly earthed neutral system. With such drastic reduction of earth-fault current, the earth-fault relay design becomes quite complex and requires application of electronic circuits, because the weak output voltage of the core balance transformer can no longer operate a conventional relay directly during an earth fault. Most of the existing earth-fault protective devices used for this purpose are either nonfail-safe or partially fail-safe, and to the author's knowledge no attempt has been made, so far, to study their fail-safe characteristics in a systematic manner. This leaves a scope of doubt about their degree of fail-safety feature. The new protection schemes developed by the authors use two novel circuits with fail-safe features, such that in case of failure of most of the circuit components the circuit breaker is tripped off thereby offering additional safety for underground application. The fail-safe feature of the protective devices developed have been critically ascertained by typical laboratory simulation of component faults. The protection schemes developed offer good reliability for earth-fault setting of 100mA and above.
Conference report. Cired
- Author(s): D.F. Crawley and I.R. Homer
- Source: IEE Proceedings C (Generation, Transmission and Distribution), Volume 129, Issue 1, p. 41 –43
- DOI: 10.1049/ip-c.1982.0007
- Type: Article
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