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Electric Power Applications, IEE Proceedings B

Issue 2 • Date March 1982

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Displaying Results 1 - 7 of 7
  • Steep-fronted switching voltage transients and their distribution in motor windings. Part 1: System measurements of steep-fronted switching voltage transients

    Publication Year: 1982 , Page(s): 45 - 55
    Cited by:  Papers (31)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1353 KB)  

    Insulation failure in motor windings can be caused by interturn breakdown resulting from stresses generated by steep-fronted transient voltages. The production and severity of such transients and degree of voltage stress on the motor-winding insulation is governed by the characteristics of the overall system to which the motor is connected. The investigations described in this paper cover extensive tests carried out at two large offshore oil production/water injection installations on a number of high-voltage motor circuits where motor failures had occurred. In particular, the tests were made to determine not only the nature and severity of the switching transients but also to determine the system characteristics governing their steepness and amplitude. For this purpose, the test programme included circuit-breaker timing tests, recurrent surge tests and synthetic tests in addition to full energisation tests. The results obtained and presented indicate that although, in all the circuits studied, steep-fronted transients are produced ?? in certain circuits, the amplitude of the transient would be sufficient to cause severe interturn insulation stresses in the motor winding. The system parameters that define the steepness of the transients and the combination of parameters that give rise to high-amplitude transients are evaluated. Tests with capacitors connected to the motor-winding terminals, to extend the wavefront duration of the transient voltages reaching the motor winding, are also described and discussed. View full abstract»

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  • Steep-fronted switching voltage transients and their distribution in motor windings. Part 2: Distribution of steep-fronted switching voltage transients in motor windings

    Publication Year: 1982 , Page(s): 56 - 63
    Cited by:  Papers (11)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (1056 KB)  

    Severe interturn insulation stresses may be produced in motor windings by steep-fronted switching voltage transients. To evaluate the severity of such stresses, transient-voltage distribution tests must be carried out under conditions closely simulating those obtained in service. In a complementary paper, system tests were described which were carried out to determine the characteristics of the transients produced by circuit-breaker closure operations. The steepness and magnitude of the transients were determined and the system parameters defining them evaluated. Based on this information, a series of interturn voltage distribution tests were carried out on a motor winding under conditions closely simulating practical system conditions. From these tests, the magnitude of the interturn voltages in the winding, produced by normal switching operations, were estimated and shown to be severe. The effect that system parameters, external to the motor winding, and also the use of series inductors or shunt capacitors used as surge-protection devices, have on the voltage distribution are also studied. Impulse voltage tests to breakdown were undertaken on a number of the motor coils and the breakdown levels shown to be only marginally above the transient levels produced by normal switching operations. The impulse voltage wave used for these tests was closely correlated to that which might be produced by steep-fronted switching transients. View full abstract»

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  • Eddy-current distribution in cylindrical structures caused by rotating magnetic fields

    Publication Year: 1982 , Page(s): 64 - 74
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (713 KB)  

    Analytical solutions are given for the eddy currents (magnitude and phase) induced in a cylindrical shell of infinite length and thickness by a 3-phase winding of finite length placed coaxially inside the shell. The flux densities and associated loss are also determined. Solutions are obtained in integral form by solving Maxwell's equations and applying appropriate boundary conditions. Use is made of the magnetic vector potential. The loss is calculated by applying Poynting's theorem on the internal surface of the shell. Numerical results are obtained on a digital computer for different radii of the shell by using the Gauss- Laguerre method. The limitations of the method are discussed. The conducting material is nonmagnetic and the solutions are valid for all frequencies smaller than those of the optical spectrum. Tests were made on an aluminium shell and measurements of field values in the air were compared with the corresponding theoretical results. View full abstract»

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  • Inverter AC-drive efficiency

    Publication Year: 1982 , Page(s): 75 - 81
    Cited by:  Papers (7)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (942 KB)  

    Variable-speed drives comprising static inverters and squirrel-cage induction machines have attractive characteristics and are suitable for use in many industrial applications. A major attribute of some of these drives is their very high energy efficiency, and this paper is a presentation of the results of an experimental investigation into the factors affecting cage induction-machine efficiency on static inverter supplies. It is demonstrated that the conventional `constant V/Hz?? strategy must be modified if the best possible drive efficiency is to be realised. The sensitivity of the machine to the high-frequency distortion components present in some inverter waveforms is illustrated and the major loss mechanisms are discussed. The emphasis is on inverter drives using sinusoidal pulse-width modulation, and it is concluded that the properties of an `asynchronously?? generated pulse width modulated sequence can be used to improve the drive efficiency. Other inverter waveforms are also briefly considered. A control strategy, which requires a microcomputer for implementation in a practical drive but can run the drive at the maximum achievable efficiency under all operating conditions, is discussed. View full abstract»

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  • Comparison of 3-dimensional and 1-dimensional calculation of the thrust of a sector motor

    Publication Year: 1982 , Page(s): 82 - 86
    Cited by:  Papers (1)
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (457 KB)  

    The 1-dimensional analysis of a sector motor is described. Many assumptions, such as neglecting the magnetic field outside the edges of the airgap and supposing axial flow of induced eddy currents on the rotor surface, are made. The wide variation of the relative permeability of the rotor is approximated by a constant average value. The method shows how the rotating field theory can be modified to make it useful in the analysis of a motor with a pole pitch different from 180 electrical degrees. Results calculated, using this method, are compared with those obtained from a 3-dimensional analysis and the experimental values given by Bolte [2]. View full abstract»

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  • Dynamic response of a power-transformer winding under axial short-circuit conditions

    Publication Year: 1982
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (91 KB)  

    In a previous paper, a mathematical model was developed to consider the dynamic response of a power-transformer winding after it had been subjected to an axial short-circuit. In this paper, an analytic solution, which is valid for small times t, is produced which justifies the basic assumptions made in the original paper. View full abstract»

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  • Discussion on Experience with London Transport's traction motors

    Publication Year: 1982 , Page(s): 88 - 90
    Save to Project icon | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

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