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The current-voltage curves of a composite bipolar membrane (CBM) were experimentally measured for the various mole fractions of methanol-water, ethanol-water and n-propanol-water mixed solution systems using 0.1 mol/L LiCl as electrolyte for each solution system. Results showed that a CBM has the characteristics of a bipolar membrane. The current-voltage curves showed that the maximum local effective value of a CBM resistance will increase with an increase in the mole fraction of alcohol. This is attributable to the weaker dissociative ability of alcohol as compared to water.

Krylov-subspace methods for complex-valued systems are still a present research topic in numerical mathematics. Due to the lack of theoretical results systematic numerical experiments are very important in order to find a sufficiently robust solution method. An important problem in high-voltage power plants are arc-overs on moist or contaminated insulators. A quantitative knowledge of the electric behaviour of layers of water droplets is necessary in order to understand the resulting ageing processes. Discretization of the electro-quasistatic problem leads to large sparse complex systems of linear equations. Comparisons between different Krylovsubspace methods, also in combination with residual smoothing techniques, and parameter studies are presented in this paper. Index terms - Electric fields, electro-quasistatics, linear algebra, algorithms, epoxy resin insulation

The unknown current distribution (UCD), self and mutual admittances (impedances), grounding impedances of coupled vertical mast antennas (CVMA) on a conducting half-space are presented in this paper. The UCD is determined by numerical solving of the system of integral equations of two potentials (SIE-TP). The simplified Sommerfeld's expressions for potentials (the Hertz vector potential and electric scalar potential) are used for establishing the SIE-TP. The influence of the earthing systems on the antenna characteristics are adequately treated. Index terms - Coupled vertical mast antennas, conducting half-space, current distribution, self and mutual admittances.

The use of spanning trees is discussed for a high-order hexahedral edge element method, for a source field computation method, and for the voltage forcing method. The first represents a generalization of the co-tree gauge, the second represents an efficient method for finding source fields, and for the voltage forcing method, it is demonstrated that a source field found using the right spanning tree results in a large reduction in CPU-time for solving the main (eddy current) equation system. Index terms - Trees, finite element methods, eddy currents, current, voltage, resistance, inductance.

Various methods for sampling of voltage and current signals in electrical drives are analyzed and compared. Two new methods for sampling the discontinuous voltage and current signals in a pulsewidth modulation drive are proposed. The methods are based on sampling the instantaneous values and locally averaged values (over one carrier period) of signals. Analytical expressions for adjustment of digital current regulators and achievable bandwidths with the various sampling methods are derived. The results are experimentally verified. Index Terms - Bandwidth, control, current, digital, discontinuous, drives, pulsewidth modulation, sampling.

Bearing currents and shaft voltages of an induction motor are measured under hard- and soft-switching inverter excitation. The objective is to investigate whether the soft-switching technologies can provide solutions for reducing the bearing currents and shaft voltages. Two of the prevailing soft-switching inverters, the resonant de-link inverter and the quasi-resonant de-link inverter, are tested. The results are compared with those obtained using the conventional hard-switching inverter. To ensure objective comparisons between the soft- and hard-switching inverters, all inverters were configured identically and drove the same induction motor under the same operating conditions when the test data were collected. An insightful explanation of the experimental results is also provided to help understand the mechanisms of bearing currents and shaft voltages produced in the inverter drives. Consistency between the bearing current theory and the experimental results has been demonstrated. Conclusions are then drawn regarding the effectiveness of the soft-switching technologies as a solution to the bearing current and shaft voltage problems. Index Terms - Bearing currents, common-mode currents, common-mode voltages, hard switching, induction machine, induction motor, power converter, pulsewidth modulation inverter, quasi-resonant de-link converter, resonant de-link converter, shaft voltages, soft switching.

The classical Hall effect presents a surprisingly unusual and challenging problem in electrostatics, with boundary conditions that are not of Dirichlet, Neumann, or of mixed Dirichlet and Neumann type. These unusual boundary conditions create several difficulties not normally encountered in standard problems, and ultimately lead to expansion of the electric potential in a nonorthogonal basis set. We derive the boundary conditions for the potential in a rectangular geometry, construct a solution for the potential, and discuss the relation between this problem and problems of the standard mixed type. We also address a commonly encountered misconception about the current distribution.

The performance of the Clapham SVC after a control retrofit is described. The replacement of an analogue with digital control was completed in 1995. The retrofit was accomplished well within the ten days of allotted shut down time. With the original control system ac system voltage unbalance caused by untransposed lines had to be balanced by manual adjustment. The primary improvement provided with the new control is automatic and continuous voltage balancing. Key Words: control retrofit, untransposed lines, negative sequence motor currents.

The present work investigates the electromagnetic field and the eddy currents of a system consisting of a faulted power transmission line above parallel conductors buried in nonhomogeneous earth. The electromagnetic field diffusion equation has been numerically solved, using finite element method (FEM). Using FEM results, magnetic vector potential distribution in the cross-section of the parallel exposure, as well as eddy currents induced in all conductive parts, are calculated for various nonhomogeneous earth models. An analysis concerning the most important operational parameters in determining power transmission line influence is presented. Such parameters are the depth of the first earth layer, the resistivities of the different earth layers and the number of the mitigation wires. Keywords: power transmission lines, eddy currents, finite element methods, nonhomogeneous earth.

This paper presents a comparative analysis of the effects of expulsion and current-limiting fuse (CLF) operations in distribution systems on power quality and system protection. This analysis included field tests of both types of fuses on a distribution system in Florida. To further analyze fuse effects on the voltage dip duration and spread of the overvoltages created during the fuse operations throughout the system, computer simulations were also performed. Unique digital fuse models were developed for use with the EMTP/ATP program. This paper shows that CLFs improve power quality by supporting system voltage during faults, reducing the voltage dip duration, and do not affect load operation. Additionally, CLFs reduce the fault let-through [I.sup.2]t. Key words: Fuse, Current-Limiting Fuse, Modeling, EMTP, ATP, Distribution Systems, Power Quality

The equations given in IEC 287 and in the Neher-McGrath paper for the internal thermal resistance of 3-core cables were developed for paper insulated cables. For such cables, it was assumed that the insulation and filler materials have the same thermal resistivities. In reality, in 3-core cables a variety of materials are used as fillers. The majority of these will have a higher thermal resistivity than the insulation. In this paper, a new formula is developed to compute the value of this thermal resistance taking into account the thermal resistivity of the filler. The effect of filler resistivity on cable ampacity is also discussed.

In the overmodulation region, the operation of the electrical drive system with a current controller is characterized by a rapid deterioration of motor torque and speed. It is desirable to use the overmodulation strategy, which guarantees the fast response even in transient state and satisfies the overall closed-loop control performance. In this paper, in order to improve the dynamic characteristics of the electrical drive, a new overmodulation technique is proposed. Considering the current transition characteristics, an efficient overmodulation strategy is introduced to achieve better transient performance through an adequate voltage selection. With the help of a new overmodulation strategy, required electrical torque can be directly produced as quickly as possible, and stable drive characteristics can be achieved in the transient condition. The proposed method has been implemented on an actual inverter system and thoroughly tested on a 900W interior permanent magnet synchronous machine (IPMSM) to confirm its feasibility. Index Terms - Current regulation, IPMSM, overmodulation.

A new current-sharing technique for paralleled power converters, which is based on frequency encoding of the current-sharing information, is introduced. The approach has significant advantages over existing methods, including the ability to transformer isolate or eliminate current-sharing control connections. Operation of the current-sharing technique is analyzed, and the design and experimental evaluation of a three-cell prototype system are presented. Index Terms - Cellular, current sharing, load sharing, modular, parallel.

Irradiation of insulators with a pulse of high energy x-rays can induce photocurrents in the interconnections of integrated circuits. We present, here, a new method to measure and analyse this effect together with a simple model. We also demonstrate that these insulator photocurrents have to be taken into account to obtain high levels of dose-rate hardness with CMOS on SOI integrated circuits, especially flip-flops or memory blocks of ASICs. We show that it explains some of the upsets observed in a SRAM embedded in an ASIC.

A method combining charge pumping and current-voltage measurements is presented for determining the surface potential versus gate voltage relationship in irradiated MOS transistors. This technique uses parameter optimization and simple numerical equations. It can be applied even for a high interface state density and for a non-uniform distribution in the silicon bandgap. This makes the method attractive for all studies concerning interface trap characterization or accurate modeling of MOS transistors in subthreshold regime. In this study, this new approach is applied to n-channel transistors irradiated up to 10 Mrad (Si[O.sub.2]).

A new biasing scheme for ac coupled strip detectors has been developed. Application of this scheme reduces the potential non-uniformity due to variations in the strip leakage currents. The circuit comprises an error amplifier that senses the strip current and compensates for the voltage drop across the biasing resistor. The error amplifier is powered by floating power supplies referenced to the bias voltage. A circuit was built that uses a low power amplifier with femtoamp inputs. The circuit regulates the strip potential to within few mV of the bias voltage for strip currents between 0 and 5 nA with a 1.2G[Omega] biasing resistor. The circuit has been tested with a CZT strip detector.

A new clock-feedthrough compensation scheme for switched-current circuits is proposed. The scheme is especially suited for the design of delay lines for high-frequency operation. The circuit operates by using an improved two-step technique, in which the input is sampled in a parallel combination of a coarse and a fine memory transistor. Since both transistors are of the same type, large switching transients compared to the conventional [S.sup.2] I scheme can be avoided. Using the proposed circuit, the coarse memory has considerably more time to settle. Compared to the simple cell, the circuit solution requires only one extra switch and one additional clock phase. Index Terms - Analog sampled-data circuits, charge injection, sample/hold, switched-current circuits.

A study was conducted to determine the current-induced resistance degradation of isotropically conductive adhesives. The isotropic conductive adhesives examined were a Bisphenol-A type and cycloaliphatic epoxy resin that have flake shapes and porous silver powder. The adhesives were subjected to different temperatures and current densities. Results showed that the current influences the increase or decrease of resistance with time in both adhesives.

This paper considers the sequence impedance and equivalent circuit of an HVDC converter and system. The results can be used in the steady state analysis of power systems containing HVDC terminals with systems operating under balanced or unbalanced conditions. The effects of commutation overlap are considered. The method described provides a simple model for steady state studies for power systems containing converters and HVDC links.

This paper describes an on-line PD (partial discharge) detection technique applicable to power cables. The method can be applied to both wire screen and solid shielded cables. In wire screen shielded cables, PD components with frequencies

EL (electroluminescence) in XLPE (crosslinked polyethylene) subjected to impulses of various amplitudes, shapes and repetition rates has been investigated. Defects that could occur in the polymeric insulation of underground HV cables were simulated by embedding semicon protrusions in XLPE to create highly divergent electric fields. Time resolved measurement of the EL pulses emitted during positive, negative or alternating polarity impulses has shown that the EL pulses are grouped into two distinct time periods between which there is no EL activity. The EL emission probability increased with fall time of the impulse voltage but was independent of the impulse rise time. A study of electroluminescence characteristics from unaged and aged XLPE, subjected to a pair of positive and negative impulses, indicated that the charge trapped in the polymeric insulation during aging plays an important role during impulse application and could affect insulation failure.

Surface PD (partial discharge) on an insulator from a TJ (triple junction) are reduced by recessing the TJ at the HV electrode. The insulators have an inner electrode connected to the ground potential. PD pulses whose magnitude is > 10 pC are measured. The applied HV (50 Hz) is 1 to 1.5x higher than that at the initiation of the PD. The thickness of the insulator is in a range from 2 to 7.5 mm. For insulator thickness of 7.5 mm, the integrated magnitude and number of the PV pulses from the recessed TJ are reduced to [approximately]20% and 50% of those from TJ without recess, respectively. The reduction in the PD by the recessed TJ is explained by the field conditions on the insulator near the TJ. It is considered that the reduction in the PD by the recessed TJ results mainly from the following three factors: high surface potential ([V.sub.s]) on the insulator, weak parallel component of electric field on the insulator surface, and strong normal component of the field on the surface. Propagation of the PD is restricted by these three factors. We have designed the improved configuration of recessed TJ in order to further emphasize these three factors. It is experimentally confirmed that the improved one reduces surface PD more efficiently than the recessed TJ before the improvement. At 7.5 mm insulator thickness, the integrated magnitude and number of PD pulses are reduced to [approximately]5% and 15% of those for TJ without recess, respectively.

The well number and length were varied to examine how they affect the temperature sensitivity of the threshold current in InGaAsP-InP multiquantum-well lasers. The 175 lasers analyzed contained five identical devices, seven different well numbers and five different lengths for each well number. Results showed a connection between the threshold and efficiency, and a relation between temperature sensitivity of the threshold current and the optical gain/loss and current loss mechanisms within the lasers.

Kraft paper is used extensively in the electricity supply industry for the insulation of HV apparatus, such as transformers, capacitors and cables. Because of the fibrous nature of the paper, many layers are stacked or rolled to obtain the required electric strength. The insulation is thus a combination of cellulose and an impregnating fluid, which may be a liquid, a gas or vacuum. The dielectric properties of such a system depend on the dryness, temperature, frequency and the degree of mechanical compression. Although the effects of moisture, temperature and frequency on the dielectric properties of kraft paper have been studied, very little work has been done on the effect of compressive stress, particularly long-term effects. Results are presented of measurements, in the frequency range 50 Hz to 20 kHz, of the effects of compressive stress and temperature on the real and imaginary parts of the complex relative permittivity of a multilayer stack of dry kraft paper under vacuum. The variations of the dc resistance with compressive stress and temperature also are reported. Results are given of the variation of the dielectric properties of a stack of paper following a step change in either the temperature or the air pressure. The long-term variations are attributed to the slow diffusion of ions through the stack, particularly those held at the interfaces between layers.

The coordination scheme of water in myoglobin and haemoglobin, the two oxygen carrier proteins in vertebrates, is still far from being fully understood. The TSDC (thermally stimulated depolarization currents) technique is a sensitive tool to study water molecules bound to biological macromolecules and characterized by mobility and order degree, quite different from those of bulk water. TSDC spectra for both proteins were recorded in the temperature range 100 to 300 K, at very low hydration levels (h = 0.01 to 0.62) obtained with different procedures. Different classes of water molecules were found: the preferred hydration sites and the water dipole activation energies are discussed. In particular, the existence of a critical hydration level which induces a partially irreversible structural transition was monitored in myoglobin. The technique allowed estimation of the average number of hydrogen bonds established by the water molecules in the inner cages of haemoglobin at different hydration levels.

The control problem for a series dc motor is considered. based on a nonlinear mathematical model of a series-connected dc motor, it is shown that the combination of a nonlinear transformation and state feedback (feedback linearization) reduces the nonlinear control design to a linear control design. To demonstrate its effectiveness, an experimental study of this controller is presented. These experimental results are also compared with a simulation of the closed-loop system. Finally, it is shown that a nonlinear observer (with linear error dynamics) for speed and load torque can be constructed based only on measurements of the motor current. Experimental results of this speed and load-torque estimator are also presented. Index Terms - Feedback linearization, nonlinear control, series dc motor.

Energetic neutrons with an atmospheric neutron spectrum, which were demonstrated to induce single event burnout in power MOSFETs, have been shown to induce burnout in high voltage (>3000V) electronics when operated at voltages as low as 50% of rated voltage. The laboratory failure rates correlate well with field failure rates measured in Europe.

The paper presents the results of a theoretical analysis of the influence of electric fields, temperature gradients and the effects of mutual electron-phonon drag on the thermal field-emission properties of metals. The processes of energy release and dissipation in the bulk of a metallic thermal field-emission cathode have been investigated in the approximation of two-fluid hydrodynamics for electrons and phonons.

The aim of this project was to find a correlation between contact gap length and switching behavior of a vacuum circuit breaker. A large number of interruption experiments was executed in a vacuum chamber with butt type contacts made of Cu, CuCr 50/50 and AgWC. The currents to be interrupted varied from 2.5 to 32 kA. The rate of change of current and recovery voltage were kept at a fixed value at current zero. Many re-ignitions of the dielectric type, scattered over a wide range of re-ignition voltages, were observed and only a few of the thermal type. The total amount of energy dissipated in the vacuum chamber appears to be determinative for the type of re-ignition. On Cu severe anode spot melting was found, whereas CuCr and AgWC suffered little anode melting. The wide range of re-ignition voltage values found shows that a straight correlation with the contact gap length can not be defined. At 5 to 10 [[micro]seconds] after current zero a 'second' post arc current did appear.

In this paper, we developed an optimization algorithm of a HV electrode contour to improve insulation performance of gas insulated power apparatus. Under the consideration of insulation performance of gaseous dielectrics, we could obtain an optimum electrode contour with the highest breakdown voltage. Moreover, we investigated the calculation efficiency and applicability of the optimization algorithm by means of a Borda electrode profile facing a grounded square corner as the optimization example.

A new laboratory test for evaluating the tracking and erosion performance of HV outdoor polymeric insulating materials is described. The materials evaluated include various formulations of HTV (high temperature vulcanized) silicone rubber and polyolefin polymers. The test is based on combining some features of the ASTM D2132 DF (dust and fog) test and the ASTM D2303 IP (inclined plane) test. The new test employs IP test geometry, IP test equipment, and IP specimen plaques. The plaque is coated with a mixture of clay and salt similar to the contaminant of the DF test and identical to the contaminant used in the IEC clean fog test to rate ceramic insulators for use in contaminated environments. A liquid contaminant with a conductivity similar to that of the DF test is applied to the test specimen in the same way as in the IP test. Data collected from the field on the maximum concentration of insoluble and soluble ionic materials on surfaces of contaminated insulators which have been for 21 years in contaminated regions, provide a basis for choosing the minimum concentration of the solid contaminant to apply to the specimens. This choice also serves to define, at least tentatively, the geographical area where the results of this test have significance. It is expected that this test could be used also for screening materials and obtaining a relative ranking of the tracking and erosion resistance of various materials. Measurements of the leakage current via a computerized data acquisition system, and the discharge activity with a high speed camera were performed, and have resulted in a better understanding of the onset of material degradation.

A new synthetic test circuit is presented to test the 765kV - 63kA - 50Hz circuit-breakers. The new synthetic test circuit consists of a combination of a current injection circuit and a voltage injection circuit. This configuration is especially appropriate for the interrupting test of Ultra-High-Voltage circuit breakers. After the description of the new circuit and its operation, the test circuit parameter combination and the calculated results are studied in this paper. The new synthetic test circuit can be used for voltage ratings up to 1100kV. Keywords: Ultra-high-voltage, circuit breaker, synthetic test circuit, switchgear

CFD (computational fluid dynamics) calculations for high- and low-current arcs in an interrupter of the self-blast type have been performed. The high-current simulation provides information about the mixing process of the hot PTFE cloud with the cold [SF.sub.6] which is difficult to access for measurement. In addition, it yields the gas state inside the pressure chamber when the fault current approaches its current zero. Depending on the arcing time, fault current and interrupter geometry blow temperatures of up to 2000 K with a PTFE mass fraction of up to 10% have been found. The low-current simulation performed for this blow temperature gives detailed information about the arc behavior in the time immediately before current zero. Special attention has been paid to the flow phenomena in the expanding nozzle region. Due to the interaction of the supersonic flow with the obtuse arcing contact and the nozzle geometry, a complex flow structure with a shock is established. This has been simulated for low-current arcs in an extinguishing flow with boundary conditions as obtained from the high-current simulation. Index Terms - Ablation-controlled arc, arc modeling, CFD, gas flow phenomena, high-voltage circuit breaker, self-blast circuit breaker, switching arc.

Several new submarine HVDC connections between the hydro dominated Norwegian power system and the thermal dominated UCPTE system of Western Europe are being planned, giving a total transfer capacity of approximately 3000 MW. Both existing and new HVDC exchange agreements are based mainly on the pumped storage principle, where Norwegian hydro power is exported during peak load, while surplus energy can be imported during off-peak periods. This paper focuses on an additional benefit of these HVDC connections: the possibility to supply frequency control in the thermal system of northern UCPTE. Typical costs related to frequency control in thermal units are estimated, giving a strong economic motivation for this possibility. Furthermore, it is shown that the substitution of thermal frequency control reserves with a long submarine HVDC connection is possible without additional equipment-or extensive control strategies, and without causing large disturbances in neither the thermal nor the hydro system. Key Words: Frequency control, Primary control, HVDC, Reserve costs

This paper proposes unique dc control strategies to prevent dynamic commutation failures during and following faults, and to obtain better recovery from the faults. The strategy is based on an idea of sine-cosine components detector in which ac voltages are detected fast in terms of two components on the rotational reference frame synchronized with an ac system frequency. The controller quickly predicts a necessary control angle according to the magnitude, the phase angle, and involved harmonics that are calculated from these two components. The validity and effectiveness of the controller are confirmed through the EMTP simulations. The dc simulator results using the fabricated controller confirm the EMTP simulations.

Explicit formulas for determining system loss, current flows and voltages in terms of system and network data are developed for large-scale unbalanced distribution systems. The three-phase formulas consider multi-phase grounded or ungrounded loads and lines, cogenerators, multi-phase shunt elements and transformers of different connections all of which exist in large-scale unbalanced distribution systems. Test results on a number of distribution systems, including an actual 394-bus distribution network, are included to illustrate the accuracy and speed of the proposed formula for real-time analysis and control of distribution systems. It is shown numerically that the results given by these closed-form formulas are very close to those obtained by rigorous three-phase power flow methods. Applications of the explicit expressions to real-time control of distribution systems are also identified. Also, some features of the explicit formulas which are not possible with traditional power flow studies are discussed.

Demonstrations of high voltage phenomena are among the most spectacular and visually beautiful illustrations of physics. Here, we describe a high potential generator (several hundred thousand volts) which is based on a resonant transformer, derived from a standard Tesla coil arrangement with high Q secondary coil. Control electronics have been implemented that allow the user to command single shot discharges, should they be required for a particular demonstration. We review the behavior of a coupled resonant system with relevance to the spark-gap excited Tesla circuit implemented in our generator. The importance of the Q factor in the secondary coil design is emphasized, but only with due regard to other design factors including the coupling coefficient and primary spark-gap, which in certain configurations can outweigh the benefits of achieving very high Q.

A magnetic field parallel to the current flow in the arc column can improve the breaking capacity of vacuum switches by affecting the arc mode. To calculate the field distribution in the interelectrode space of axial field contacts, a model has been generated by using a finite element program. A segmented coil behind the contact plates creates the magnetic self field. The three-dimensional analysis takes into account all parts of the current path within the contact structure. The generation of eddy currents by the 50 Hz excitation is also considered, as well as means to reduce them. Examples of calculated results with respect to current density distribution, axial magnetic field and phase shift between current and field are given. The simulations are completed by switching experiments with axial field contacts at currents to 45 kA.

This paper presents a survey of voltage and current harmonic distortion levels at 40 power transformers and 10 capacitor units in Northern Taiwan. Through one year measurement, about 12,000 sets of harmonic voltage and current data are recorded and analyzed. The types and levels of harmonics are showed in each power transformer which supplies different residential, commercial, and industrial customers with various loads. At the same time, a suggestion is given to the representative value of background level of harmonic voltages with 95% cumulative probability which is adopted by Taipower. At last, effects of harmonics on capacitors and power transformers are discussed. Keywords: harmonics, distribution substation, survey, electric power quality.

This paper describes a new technique for sampling synchronisation in a numerical differential feeder protection relay. The protection uses a Global Positioning System satellite receiver for sampling synchronization at each end of the protected feeder. The EMTP/ATP power system simulator was used to simulate a typical distribution feeder with faults at various locations. The current signals generated at both ends of feeder were used to evaluate the performance of the protection. These tests were carried out using a protection simulator. The results illustrate the effect of current transformer saturation on the sensitivity and stability of the protection. Finally it is shown that a precisely synchronized differential protection is fast, selective and accurate. On an internal fault it provides a high operating sensitivity, whilst it remains stable on all external faults. Keywords: - Synchronized sampling, Current differential feeder protection, Global Positioning System.

The current distribution of each of the 12 strands of a Nb3Sn cable-in-conduit conductor was measured during current/external magnetic field ramping. The strand currents exhibited severe non-uniformity before quenching. A simple model was developed to represent the ramp rate phenomenon causing the peculiarities in the current characteristics of the conductor strands.

The current distribution properties of parallel strands and Rutherford cables were compared. Results show that Rutherford cables's characteristics are very similar to those of insulated parallel strands. Results also indicate that the side-by-side contact resistances were higher than those of edges in Rutherford cable strands. The steady state current distribution also seems unaffected by the transport current.

A study was conducted on the influence of current redistribution on the stability of Nb3Sn compacted-strand cables with chrome coating and without any coating. Minimum quench energy (MQE) measurements were derived under different external magnetic fields and transport currents. Results show that the cable with the chrome coating has a slightly higher MQE than the cable without any coating.

An iron core circuit was proposed for addressing current imbalances in superconducting cables' insulated strands. The approach provides current balance through the electrical resistance in the current leads. Current strands carrying high frequency direct current and alternating current may be balanced by passing two insulated strands through an iron core for transporting currents in opposite directions.

Peltier thermoelectric elements were used as the high-temperature components of current leads for reducing heat leaks into cryostats. The thermoelements were found to provide efficient cryostat heat pumping without employing other electricity sources. Experimental and numerical calculations also reveal that Peltier current leads care capable of minimizing heat leaks by 20%-30% at 77 K.

A pair of 1.5 kA high temperature superconducting current leads was developed and tested for microSMES system applications. The leads feature a lower BSCCO stage, copper upper stage and twin-cold-finger GM cryocooler intermediate cooling. Tests show the consumed cryocooler power, helium boil-off rate and joint resistances. The cold bus thermal inertia was found to be the most important element in identifying the allowable operation time subsequent to cooling loss.