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This article describes some classic problems of interference in electric railway traction systems together with mitigation and modelling techniques. This article describes some practical noise problems in traction systems, with emissions spanning the complete frequency spectrum. The production of low-frequency (LF) noise from conductive and inductive coupling of currents and fields flowing in the traction system is described in terms of simple circuit and field models. Radio frequency (RF) noise is usually assessed by practical measurement, for which the current state of the art is reviewed. The article is concluded by a summary of the effect of European Community EMI limits.

The railway traction environment contains many noise sources and receivers, and is considered to be EMI unfriendly because of the mixing of power, information and communications signals in space, time and frequency. Railway EMC has received much attention for 30 years following the development of converter-fed traction drives and computerised signalling systems. This article covers systems issues including the fundamentals of electromagnetic coupling, disturbance noise sources and receiver susceptibility. The article discusses EM noise sources in traction systems including: rectifier and transformer substations; track and traction line; vehicles and drives; radiative emissions (RFI); and signalling equipment. The article then discusses track and equipment susceptibility to EMI including: track and traction line impedance; traction drive impedance; track signalling system impedance; and track circuit receivers.

This article describes systems in use for railway control and communications, and surveys current developments. This article describes the hardware necessary for detecting the position of trains and transmitting information between trains and track control systems. This equipment includes track circuits, transponders and beacons, track conductors, and freespace radio. The implementation of automatic train control systems as a hierarchical process is also covered and the article concludes with a summary of applications of computers and information technology in sophisticated integrated control centres with an overview of the development of the North American Advanced Train Control System (ATCS) and the European Train Control System (ETCS).

This article describes the theory and implementation of two basic railway control systems which are necessary to ensure safe and reliable operation of the complete network. The author discusses the theory of train dynamics, block signalling, and moving block signalling. The author then discusses the interlocking of points and signals including the theory, technology and implementation of interlocking.

Power is transmitted to electric railway locomotives and vehicles using DC or single-phase AC networks. The parallel development of traction technology in industrialised countries has led to a plethora of different electrification systems. This article covers the electrical engineering aspects of DC and single-phase AC traction power transmission systems.

For pt.I see ibid., Feb. 1994. This article describes DC-fed and AC-fed railway traction drives with three-phase induction motors, including the operation of the CSI, VSI and pulse converter. The dynamic performance of VSI-fed drives depends on the accompanying motor control scheme; two different arrangements are described: vector control with pulse-width modulation (PWM), and direct self-control.

This series of tutorial articles explains the electrical and control engineering background in electric railways. The articles cover traction drives with DC and AC traction motors, electrification systems, and railway signalling and control systems. This first article covers the nature of the traction load, the requirements of the traction duty cycle and power electronic controlled traction drives using DC machines.

A methodology for quantifying the safety and reliability performance of comma-free codes for railway track circuit data transmission under high levels of Gaussian noise is presented. Two decoding algorithms are described, based on the correct reception of one and two consecutive codewords, respectively. It is shown that use of the second algorithm in conjunction with a sub-dictionary with a minimum word distance constraint gives comparable safety and reliability performances to those obtained using longer-length synchronisable error-detecting codes. The paper also contains an outline of the properties of traction noise, knowledge of which is necessary for the design of digital railway data transmission systems.

Identification of the equivalent distributed transmission line parameters of rail track by electromagnetic field methodology requires the numerical values of the electrical material properties of the track components. The authors describe modelling to determine the electrical conductivity, permeability and permittivity of the rails, sleepers, ballast and ground as functions of frequency, current and the environmentally influenced moisture content. Appropriate verification procedures are described based on published reference data and practical measurements. The paper concludes by presenting reference track component material data for use in numerical models.

An electromagnetic field model for identification of rail track equivalent multiconductor transmission line distributed self and mutual series impedances is formulated, and used to illustrate the parametric behaviour of single track impedance with reference to current, frequency, track material properties and ground conductivity. Verification is demonstrated by theoretical analysis and comparison with published experimental data. The skin effect in both rails and earth is a critical phenomenon.

The authors present a detailed analysis of appropriate electrical impedance models for steel railway rails suitable for power supply circuit transient calculations. They extend existing models to fully describe the skin effect, so that power circuit transient behaviour can be taken into account with little error in prediction of response. Practical measurements of rail impedance are compared with calculated values of circuit impedance and demonstrate an accuracy of within 9% for resistance and 18% for inductance. An associated paper (see ibid., vol.139, no.4, p.289-94, 1992) shows how this model can be used to predict remote short-circuit-fault substation current profiles.< >

Theoretical models for rail internal self-inductance and resistance are proposed which include material saturation and hysteresis. Model data are obtained using experimentally derived ferromagnetic material B-H loops. Analytical methods for deriving the impedance variations with current and frequency for large-signal AC and incremental AC superimposed on DC excitation are in agreement with experimental measurements.

An electromagnetic speed sensor has been developed for use in automatic-train control on London Transport railways. The primary sensing element is a composite ferromagnetic-conductive rotor which introduces amplitude modulation, with frequency proportional to train speed, into a fixed audiofrequency carrier. A number of discrete rotational speeds are then defined by demodulation and low-pass filtering. An override system, operating by reducing the amplitude of a further AC signal with increasing train speed, provides integrity at low speeds, and a magnetic voltage reference unit maintains the power supply within predetermined safe limits. Fail-safe design principles are applied extensively on both component and system levels.

The safe operation of large power transistors in motor-drive applications often requires the use of snubber networks. The design of these networks depends upon the type of device being used and upon the circuit configuration. Some operating experience with a monolithic Darlington device is reported. The importance of controlling the switching losses in these devices by the use of snubber capacitors is indicated. It is shown that these capacitors produce side effects in a variable-voltage, variable-frequency inverter which can lead to overcurrent conditions in the transistors. These currents can be controlled by the use of snubber chokes. But the chokes, which are usually included primarily to limit reverse recovery currents in the free-wheel diodes, must be designed according to a different criterion to achieve this. It is suggested that `thermal feedback? should be provided for power transistors in order that they may operate at a safe and stable temperature.

Stepping motors, as digital machines, are commonly used in electromechanical systems since they can easily be interfaced to and controlled by computers. Electrical and mechanical interaction in multiple-motor systems, however, can lead to severe control problems, and in intelligent systems such as programmable XYtables, rotor position feedback from each machine is necessary to implement effective control algorithms.This paper describes new methods of detecting rotor position in stepping motors with chopper drives. By monitoring the motor phase current waveforms and detecting the chopping current rise-times, motor phase excitation angle may be varied continuously over a step cycle, and performance may be maximized.Two industrial applications are described: accurate trajectory control in an XY table, where close position coordination between two motors is necessary; and velocity control in a two-motor system where mechanical interaction creates a variable inertia load for one motor.

A closed-loop current controller using power MOSFETs has been constructed for two-quadrant chopper control of a DC disc armature motor intended for use in an electric cycle. Theoretical analysis shows that lower energy requirements and higher efficiency are obtained using constant current, rather than voltage, control, and that approximately 30% of the energy expended in accelerating to maximum speed would be available for regeneration. The practical difficulties of using MOSFETs for motor control are discussed, and experimental results are presented which agree well with the theory.

This paper describes the circuits and algorithms used in a microprocessor-controlled AC/DC thyristor convertor to implement a wide-bandwidth closed-loop current source. The convertor consists of two three-phase bridge circuits for four-quadrant operation, with direct digital control using a M6809 microprocessor. The timing pulse generator is linked to the supply frequency via a phase locked loop, making the system insensitive to supply frequency variation. The use of proportional-plus-integral (PI) control algorithms leads to fast responses to step changes in reference input. Results from constant-gain PI controllers are compared in the paper with theoretical responses based on approximate z-transform analysis to obtain optimum parameters for various modes of operation. In addition, results are presented from a simple variable-gain adaptive controller which adjusts the controller parameters depending on the reference change and operating point.

A general method is described for calculating the current drawn by an inverter from its DC source. It has special relevance to pulse-width modulated inverters and allows the ripple current rating of the filter capacitor to be specified with some precision. The method is for an inverter of any number of phases and uses switching functions derived from the harmonic coefficients of the inverter waveform. Experimental results from single- and 3-phase inverters demonstrate the validity of the method. Some generalised results are presented for a 3-phase inverter for the special case where the output current can be assumed to be the fundamental component only. Variation of the DC link current harmonics with power factor of the load and depth of modulation under these conditions is presented and discussed.

The paper describes the design of a fail-safe sensor used for the detection of the speed of a moving railway vehicle. The sensor is required for use in automatically controlled trains that run at one of a number of predetermined speeds, selected with reference to safety criteria, and governed by conditions ahead of the train. The device uses an axle-coupled permanent-magnet a.c. generator that, at the predetermined speed, saturates a transformer with low-frequency current, choking the passage of an audio-frequency signal from a constant-voltage source, and hence cutting off the output. Positive feedback is employed to sharpen the cut-off slope. A computer model based on a sinusoidal analytical method, superimposing the low and audio-frequency signals, predicts the possibility of in stability and hysteresis occuring in the output characteristic under certain conditions. Computed and test results are found to be in good agreement, and a series of circuit-design criteria are derived.