Standstill micromachine for turbogenerator parameter studies

Abstract

A micromachine is described for use in studies of standstill (particularly frequencyresponse) test methods for obtaining the transient impedance parameters of a tubogenerator. The severe design compromises associated with dynamic micromachines are completely avoided, rotor induced-current field and magnetic nonlinearity being correctly scaled. Advantages for the micromachine are listed and a detailed specification provided. First tests, in open-circuit field configuration, have shown the effect of surface contact resistance of aluminium wedges to be very pronounced, as is coming to be recognised in turbogenerator studies. Tests with wedges removed are compared with field computations, and with new data (obtained from installed probes) on the measured effectiveness of inducedcurrent paths in wedges and teeth. Standstill frequency-response measurements are possible in the micromachine up to 20% current, contrasting with 0.5% in a turbogenerator. Measurements of operational inductance and transfer function, over a full frequency range, thus show for the first time the changes that occur as excitation increases above the low-B range of magnetic nonlinearity. It becomes clear that the standard procedure for adjusting only the mutual branches of the d-and g-axis equivalent circuits, to allow for this nonlinearity, is inadequate. = scale factor of length = pitch factor of stator winding = scale factor of magnetic saturation density = scale factor of time List (for B E f H Us) if of symbols definition of per-unit system, see Sections 3.2 and 4.) = magnetic flux density = electric field strength = frequency 0 = operational transfer function (see eqn. 9) = magnetic field strength = Laplace transform of d-axis stator current = field current = base stator phase current (peak rated value) = base field current = current density = distribution factor of stator winding Paper 5137C (PI), first received on 6th May and in revised form 22nd October 1986 Prof. Harris and Dr. Jack are with the = d-axis mutual inductance L aq = <?-axis mutual inductance L dd (s) = operational d-axis self inductance (see eqn. 10) L qq (s) = operational g-axis self inductance M df (s) = operational mutual inductance (see eqn. 11) N f = field-coil turns N p = stator phase-coil turns R a = resistance per phase s = Laplace operator (=jco in sinusoidal excitation) t = time v^s) = Laplace transform of d-axis stator voltage Vj{s) = Laplace transform of field voltage v ao = base stator phase voltage (peak rated value) v fo = base field voltage H = permeability v =\/n a = conductivity co = 2nf 1 Introduction Determination of turbogenerator parametersAccurate prediction of the transient behaviour of a turbogenerator, and also by implication, of the steadystate operating point from which the transient is initiated, are important requirements for power-systems studies. This subject has been known for some time to pose difficulties [1], and although there is an extensive recent literature which has resulted in much improved transient modelling of performance and und...

Review and application of micromachines for wind energy integration

“…Transient performance is one of the key interests of machine performance and time constant regulators (TCRs) for these micromachines have been created to extend the usefulness of micromachines to accurately simulate transient and dynamic behaviour of practical machines [22]- [24]. They have been used to simulate turbine generators [25], create generator models [26], determine generator parameters [27]- [29] and validate digital models of electric power systems [30]. They have been used to study generator stability and for the digital control of generators [31]- [34].…”