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IEE Proceedings A (Science, Measurement and Technology)

Volume 140, Issue 2, March 1993

Volumes & issues:

Volume 140, Issue 2

March 1993

Relationship between polarity of surface leader and contact angle on insulator with backing electrode under AC voltage application
  • Author(s): Y. Yamano
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 109 –112
  • DOI:  10.1049/ip-a-3.1993.0018
  • Type: Article
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  • p. 109 –112 (4)
    When AC high voltage is applied in air to a cylindrical insulator with a backing electrode the polarity of generated leaderlike surface discharges depends on the contact angle. The contact angle is the angle between the insulating surface and high voltage electrode on the insulator. In the range of the angle from 60° to 120° the negative surface leaders appear in the range from 120° to 180° the positive surface leaders appear. No negative surface leaders appear in the range of the angle from 120° to 180°. The onset voltage of the positive leader is higher than that of the negative one. AC flashover voltage along the surface in air also shows dependence on the contact angle, which results from the difference in the onset voltage between the positive and the negative leaders. Impulse flashover voltage, on the other hand, shows no precise contact angle dependence.
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First-generation SQUID-based nondestructive testing system
  • Author(s): A. Cochran ; G.B. Donaldson ; S. Evanson ; R.J.P. Bain
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 113 –120
  • DOI:  10.1049/ip-a-3.1993.0019
  • Type: Article
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  • p. 113 –120 (8)
    The paper is an overview of the results of an investigation of a first-generation SQUID NDT system working on the principle of the detection of magnetic inhomogeneities. The system incorporates a superconducting field generation coil—to apply a static magnetic field perpendicular to the test subject—and a differential two-coil planar pick-up coil connected to a SQUID, acting as the detector. These components are operated in a LHe cryostat in a normal (unscreened) laboratory environment. Test subjects are inspected by passing them beneath the cryostat during computer-controlled data acquisition. Typical experimental results are presented, and postprocessing techniques are outlined. Theoretical descriptions of the static field distortion technique have also been developed, based on the numerical solution of integral equations which model flaws as combinations of magnetic dipoles. The equations are presented, and results are compared with those obtained experimentally. Despite significant limitations it is concluded that potential applications for SQUID NDT exist and further investigation is worthwhile.
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Three-dimensional finite-element formulation for problems involving time-varying fields, relative motion, and magnetic saturation
Approach to partial discharge development in closely coupled cavities embedded in solid dielectrics by the lumped capacitance model
  • Author(s): D.P. Agoris  and  N.D. Hatziargyriou
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 131 –134
  • DOI:  10.1049/ip-a-3.1993.0021
  • Type: Article
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  • p. 131 –134 (4)
    The use of the typical ABC equivalent circuit for one cavity in solid dielectrics for internal partial discharge modelling has been common practice for many years. The introduction of an equivalent circuit for two closely coupled cavities permits the investigation of the interaction between discharges in such cavities in a solid dielectric when it is stressed by high AC voltages. In this model circuit, cavities and solid dielectric parts are represented as lumped capacitances, while the resistance and the inductance of the test voltage source are taken into consideration. By using a version of the Electromagnetic Transients Program (EMTP), the waveforms of the voltage across the two cavities, as well as those of the voltage across the neighbouring parts of the solid dielectric, have been traced, and the transient voltage stressing of these parts has been analysed for repetitive discharges in the two cavities.
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Induced current impedance imaging
Global geometry of electromagnetic systems
  • Author(s): D. Baldomir  and  P. Hammond
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 142 –150
  • DOI:  10.1049/ip-a-3.1993.0023
  • Type: Article
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  • p. 142 –150 (9)
    Engineering calculations of electromagnetic systems require information about both local fields and global system parameters. This information depends on the local geometry, the global topology and the relation between the two. Maxwell's differential equations describe the local geometry with its four-dimensional space-time metric. These equations are greatly simplified when they are expressed in terms of differential forms, in which physical and geometrical information is combined. The paper shows the geometrical significance of the conservation of electric charge and of the gauge invariance of the potentials. Global topology is explored in terms of the interaction of differential forms and the structure of the manifold containing the system. It is shown that this depends on integral relationships which cannot be inferred from the differential equations. It is also shown that the gauge invariance of the potentials is related to the phase properties of state functions in quantum mechanics, a relationship which provides a further link between geometry and physical interaction.
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Torque computation by mean and difference potentials
  • Author(s): E.S. Hamdi ; A.F. Licariao-Nogueira ; P.P. Silvester
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 151 –154
  • DOI:  10.1049/ip-a-3.1993.0024
  • Type: Article
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  • p. 151 –154 (4)
    A new technique for torque computation is proposed and applied to finding the cogging torques in a neodymium-iron-boron permanent-magnet motor. Results agree with measured values to within a few percent, within the limits of measurement accuracy and the approximations inherent in two-dimensional analysis. When applied to the same model, the virtual work method fails to predict torque adequately. The new computational method is shown experimentally to be robust under changes of mesh fineness. Details of the method are set out and the technique of torque measurement described briefly.
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Ion mobility scanning ion chamber
Comparison of open-field test sites used for radiated emission measurements
Geometrical approach to eddy-current systems
  • Author(s): D. Baldomir  and  P. Hammond
  • Source: IEE Proceedings A (Science, Measurement and Technology), Volume 140, Issue 2, p. 166 –172
  • DOI:  10.1049/ip-a-3.1993.0027
  • Type: Article
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  • p. 166 –172 (7)
    The discovery of the constant velocity of propagation of electromagnetic energy has led to the description of electromagnetic behaviour in terms of a 4-dimensional space having a metric defined by the distance ds, where ds2 = dx2 + dy2 + dz2 − c2dt2. This geometrical idea unified Maxwell's equations and highlighted the importance of the constitutive equations which enable energy to be associated with space. The object of the paper is to use a similar approach for eddy-current behaviour. A complex metric is defined which contains a complex velocity and propagation constant, both of which are dependent on frequency. By considering the interaction of a dissipative eddy-current system with an adjoint system in which energy is being generated, it is possible to produce an invariant 4-dimensional volume in terms of the separate electric and magnetic energies. By means of a variational method, upper and lower bounds can be found for both these energies. The propagation constant associates a characteristic length with the penetration of energy into a conductor. This penetration depth classifies conductors as being either thick or thin. In thick conductors the electric and magnetic energies are closely coupled, and the equivalent resistance and reactance are almost equal. In thin conductors the coupling is very slight, so that the resistance and inductance can be calculated from their DC values used as the first terms of a highly convergent series. Suggestions for efficient computation schemes are given.
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