Stability of synchronous machines with 2-axis excitation systems

Abstract

The paper describes analogue-and digital-computer studies of a synchronous machine with various 2-axisexcitation control systems. The steady-state and transient performances of the same machine are analysed, assuming different control schemes, such as rotor-angle control and asynchronised operation, and are compared with a conventional machine. The effects of damper windings, regulator time constants and stabilising circuits on the steady-state performance are shown by regulation curves. It is confirmed that the voltage-regulator loop gain has virtually no effect on steady-state stability, provided the winding with a.v.r. control is aligned with the flux axis by an angle regulator. The improved transient-stability limits obtained with high gains are shown. The fundamentally different transient behaviour of unregulated doubly excited and conventional synchronous machines is explained, and confirmed using accurate mathematical models of the machines. The method of 'small oscillations' is applied to determine the speed stability of an asynchronised synchronous machine, and the transient performances of three different control schemes are compared in terms of swing curves and switching-time curves.List of symbols 8 = angle between quadrature axis and voltage vector of power system (called rotor angle) 6 -angle between stator e.m.f. and ordinate axis 8 e = angle between voltage vector of power system and resultant excitation vector (called load angle) COQ = system frequency, rad/s a) = rotor angular velocity, rad/s s = p8loj 0 , slip p = d\dt, differential operator t c = clearing time, s H = inertia constant, kWs/kVA K d = mechanical damping coefficient P = active power R -resistance (of armature, unless subscript is used) Q = reactive power T{ -input torque from prime mover T e = electrical output torque V = system voltage v = voltage / = current ifj = flux linkage X = reactance fx = regulator gain T = time constant of regulator loop, s E f -(Ef d + Ej q ) i/2 , resultant field excitation A = prefix used to denote a small change in a quantity A = reference signal in angle-regulator loop Subscripts:0 initial value of quantity r reference d direct-axis armature fd direct-axis field kd direct-axis damper ad direct-axis mutual q quadrature-axis armature fq quadrature-axis field kq quadrature-axis damper aq quadrature-axis mutual m machine terminals b busbar v voltage regulator \v voltage regulator, first derivative 2v voltage regulator, second derivative a angle regulator Paper 6257 P, first received 3rd February and in revised form 9th June 1970 The authors are with the

Transient performance of doubly excited synchronous machine

“…The phenomena described in this paper have been established using a rigorous mathematical model, 6 but, to facilitate explanation, it is convenient to revert to approximate theory. Therefore the rotor (electrical) damping and stator transients are neglected.…”

“…This has been confirmed by the present authors. 6 Robinson 7 has shown that the divided-winding-rotor (d.w.r.) machine has virtually no transient saliency and can be represented by a voltage behind transient reactance.…”

Optimal design of q ‐axis field winding structure of dual‐excited synchronous condenser

“…The authors in ref. [9] investigated the effects of damper windings on the steady-state performance of the dual-excited synchronous machine. The authors in ref.…”

Dynamic-stability analysis of d.w.r. synchronous generator with feedback-stabilised voltage and angle regulators

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