摘要:

The stator cores of large electrical machines are supported in a steel frame in which electrical currents are circulated by leakage flux from the core. These currents can cause serious overheating. The paper gives a qualitative review of the electromagnetic factors which affect the flowof these frame currents. The work shows that the effects of frame currents may be reduced if the frame members are connected electrically in a way which more effectively suppresses core-end leakage flux.

DOI:10.1049/ip-c.1983.0051

出版商:IEE    

年代:1983

数据来源: IET

摘要:

In the paper, sensitivity studies, described by the authors in an earlier paper (‘Sensitivity analysis of modal quantities for underground cables’,IEE Proc. C., Gen., Trans. & Distrib.,1981,128,(4), pp.229–234 for a homogeneous noncrossbonded cable system, have been extended to the case of the crossbonded cable. For the crossbonded case, the minor sections are represented by lumped parameter networks, and the equivalent series-impedance and shunt-admittance matrices are formed. Natural modes of propagation in one major section of the crossbonded cable have been identified. Finally, using the sensitivity expressions for the series-impedance and shunt-admittance matrices, sensitivities of modal attenuations and velocities of the crossbonded system having one major section have been obtained and tabulated.

DOI:10.1049/ip-c.1983.0052

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper presents a general computational method and the relevant computer program which can be easily used to perform availability/unavailability analysis on power-system configurations. The mathematical availability formulation of the program is based primarily on: the tie sets (or cut sets) of the system configuration, the component failure rates and repair and maintenance times, some aspects of a Markov model of two states and the functional block concept. A real prerequisite for the successful utilisation of the program is the availability of realistic statistical data for the system components. For purposes of illustration, the computer program has been applied to evaluate the availability of two practical high-voltage/medium-voltage (HV/MV) substation configurations, from the standpoint of design, practical functionality and repair and maintenance procedures. The program is suitable in performing system availability/unavailability sensitivity analysis, based on value variations of system-component failure rates and repair and maintenance times.

DOI:10.1049/ip-c.1983.0053

出版商:IEE    

年代:1983

数据来源: IET

摘要:

The paper presents a new approach to the minimisation of line losses in a given power-system network by means of certain sensitivity coefficients. These coefficients are used to see how sensitive is the line loss for small changes in the control variables, i.e. voltage magnitudes of the generators, reactive-power injections by VAR sources and transformer tap ratios. These sensitivity coefficients are derived using an eigenvector of the transposed Jacobian matrix. After establishing the objective function for minimising the system losses with the help of linearised sensitivity relationships of control variables, a dual linear programming (LP) technique is used to determine the optimum adjustments to the control variables, simultaneoulsy satisfying the constraints like reactive-power limits of the generators, limits on the load busbar voltages and the operating limits of the control variables.

DOI:10.1049/ip-c.1983.0054

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Owing to discontinuous current in a thyristor-controlled reactor (TCR) of a static VAR compensator, harmonic currents are generated in the supply system. The paper presents a new method for reducing these harmonics. In the method used, the TCR is fed through the sequentially controlled transformer taps. Two alternative approaches of sequence control of transformer taps are described. The feasibility of the proposed method has been verified experimentally.

DOI:10.1049/ip-c.1983.0055

出版商:IEE    

年代:1983

数据来源: IET

摘要:

A new method for high-resistance earth-fault distance protection, capable of calculating fault distance independent of fault resistance, is presented with an accuracy analysis which shows that calculation accuracy, which depends on various application parameters, may be uniquely established by a measurable index. Relay overreach is avoided by reference to the index. Conclusions aredrawn from results of laboratory tests of a microprocessor implementation of the algorithm. The resistive tolerance is found to depend on the actual application parameters, but may be as much as four times the forward relay setting at the exporting end of a typical line.

DOI:10.1049/ip-c.1983.0056

出版商:IEE    

年代:1983

数据来源: IET

摘要:

Fault resistances affect the accuracy of short-circuit location, when distance to the fault is determined by means of measuring reactance at one end of the transmission line. This is because the current which flows through the fault resistance is slightly shifted in phase with respect to the current measured at the end of the line in question, due to the effect of the prefault load current. As a result, the fault resistance is recognised as an apparent impedance with both resistive and reactive components. The latter produces an error in the fault location, as it affects the measured reactance. The paper presents a simple algorithm which compensates for the error, and makes it possible to locate short circuits accurately; even if fault resistances are comparatively high.

DOI:10.1049/ip-c.1983.0057

出版商:IEE    

年代:1983

数据来源: IET