摘要:

A method is described for detecting the loss of one or more turns in a concentric coil of the rotor field winding of a synchronous machine using two search coils in the airgap. This back-to-back method yields an EMF proportional to the rate of change of the ‘missing’ flux linking the search coils, and is sufficiently sensitive for the coils to be positioned close to the stator surface. A two-dimensional linear analysis of the airgap field is used to model the method with good accuracy, and includes an estimate of the resulting unbalanced magnetic pull. A simple one-dimensional analysis predicts the EMF harmonics that are introduced by static or dynamic rotor eccentricity. Results from a small four-pole experimental machine are presented, including the effect of a known amount of static eccentricity. Calculations for a larger two-pole machine are also included, and a possibly useful method of fault location detection using the ratio of the magnitudes of only two harmonics taken from the search coil output is discussed.

DOI:10.1049/ip-b.1988.0031

出版商:IEE    

年代:1988

数据来源: IET

摘要:

Over the past few years, a number of techniques have evolved for detecting discharges in the insulation systems of electrical machines by measuring the discharge currents flowing at the machine terminals. The propagation of these currents through the winding, from the discharge site to the terminals, is influenced by the capacitive and inductive coupling between the conductors of the winding. The paper is concerned solely with the inductive component of that coupling, through the laminated steel stator core of the machine. It describes how this coupling makes a significant contribution to the equivalent circuit for the propagation of discharge currents containing frequencies from 20 kHz to 20 MHz.

DOI:10.1049/ip-b.1988.0032

出版商:IEE    

年代:1988

数据来源: IET

摘要:

Using the simplified approach to the dynamic modelling of a variable reluctance step ping motor system developed in a companion paper [1], this paper develops dimensionless pull out torque curves and stability limits. These curves can be used to optimise system performance and allow the effects of variations in system parameters to be appreciated.

DOI:10.1049/ip-b.1988.0033

出版商:IEE    

年代:1988

数据来源: IET

摘要:

The concept of a split coil switched reluctance motor (SSWR) drive is introduced. This motor results from the separation of the phase coils of a conventional switched reluctance motor (SWR) into two halves. Excitation requirements for the SSWR motor are met by providing one half of the phase winding with a DC current, the other half being connected to a bipolar drive stage. Experimental results in the form of output power/speed characteristics are presented for the SSWR drive operating with a range of DC current and switching angle settings. A comparison between results obtained with a SSWR drive and SWR drive is given. These results indicate that an overall improvement in performance is achievable for the SSWR drive when compared to an SWR drive. Other features of the SSWR drive aimed at eliminating the position sensor and its capability for regenerative braking are also discussed in order to highlight the potential of the SSWR drive concept.

DOI:10.1049/ip-b.1988.0034

出版商:IEE    

年代:1988

数据来源: IET

摘要:

This paper describes new modulation techniques that remove all the major limitations of the noncirculating current cycloconvertor, including low maximum frequency, subharmonics, poor bank crossover timing, and distortion due to discontinuous current, when used to drive an induction motor. The new modulation techniques work by keeping the flux in the induction motor (sensed by voltage feedback) as close to sinusoidal as possible and give superior performance to the present current feedback techniques. An experimental 18-thyristor 3-pulse cycloconvertor showed that the new modulation techniques allow smooth speed control of an induction motor from 0 to 25 Hz (limited by software) with a peak output voltage of 95% of the input voltage. It is expected that the same techniques applied to a 36-thyristor 6-pulse cycloconvertor will allow smooth speed control up to 50 Hz. To obtain fast speed response, vector control can be easily added to the new modulation techniques. The new modulation techniques can also be used to advantage in other cycloconvertor and convertor applications. Patents have been applied for.

DOI:10.1049/ip-b.1988.0035

出版商:IEE    

年代:1988

数据来源: IET

摘要:

The recent accurate modelling of alternating-current machines sometimes requires, in addition to the known transient and sub-transient quantities, the use of sub-subtransient quantities. The sub-subtransient time constants are very small; they can, however, have a great influence on the machine performance. The physical meaning of these new sub-subtransient quantities for the stability and switch-on process of the synchronous machine is explained and illustrated with examples. It is shown that by introducing the sub-subtransient values, the effect of the solid turborotor and the behaviour of the salient-pole machine with solid poles can be treated with sufficient accuracy.

DOI:10.1049/ip-b.1988.0036

出版商:IEE    

年代:1988

数据来源: IET

摘要:

An analytical model for predicting the characteristics of variable airgap linear force motors is developed. The model takes into account magnetic losses, including the leakage and fringing effects, and the reluctance existing at the contacts between permanent magnets and polepieces. The model is validated by comparing its predicted characteristics with the results obtained from experiments and a finite element program. With the use of the modelled characteristics, computer programs based on the method of constrained steepest descent with state equations, is developed for automating and optimising the design of linear force motors. Numerical studies are made for both minimisation of weight and minimisation of power consumption.

DOI:10.1049/ip-b.1988.0037

出版商:IEE    

年代:1988

数据来源: IET

摘要:

New flat-top windows by which per forming the measurement of the parameters that characterise periodic signals are presented. It is shown how, by applying these windows in the frequency domain beyond the FFT, the negative effects of both the spectral leakage and the harmonic interference are reduced without employing interpolation algorithms. The high accuracy of the results is confirmed by an error analysis. These windows are very useful in the determination of the harmonic content of the inverter output PWM waveforms supplying electrical motors, in order to qualify the entire drive.

DOI:10.1049/ip-b.1988.0038

出版商:IEE    

年代:1988

数据来源: IET

摘要:

A voltage sourced reversible rectifier (VSRR) which achieves bidirectional power flow between a 3-phase AC supply and a DC bus voltage is described. The device features a pulse width modulated voltage control strategy that confines unwanted harmonics to known frequency bands where they can be easily filtered out while operating at near unity power factor, with sinusoidal currents, and maintaining a constant DC bus voltage. The paper considers both the steady state and transient response of such a device, and develops mathematical models to describe its performance under both analogue and digital control. Experimental results obtained with a micro processor controlled prototype VSRR are present ed and compared with theoretical predictions.

DOI:10.1049/ip-b.1988.0040

出版商:IEE    

年代:1988

数据来源: IET

摘要:

The paper proposes a simple model that enables the influence of rotor currents to be included in the calculation of the electromagnetic forces acting on the end windings of cage induction motors, using the Biot–Savart method. The inclusion of the rotor currents is shown to have greatest influence close to core, where the end-region fields are also highest. The validity of the model is established using experimental measurements of flux density made on a two pole machine. Calculated force distributions show the effect of the rotor currents to be significant enough to merit their inclusion in the model.

DOI:10.1049/ip-b.1988.0041

出版商:IEE    

年代:1988

数据来源: IET