ment quality, reporting and monitoring system, information and staff training are also essential for quality assurance of protection equipment serving in the power ...
protection relays where the operation of either relay will effect tripping on its own. Performance Assessment The performance of a protection system can be analyzed by the system performance index approach, the system-minute approach, the relay performance approach and the cause identification approach. Such means of monitoring and assessment are essential to pinpoint problem areas such that managerial actions can be directed to maintain or improve the level of performance. Control Measures Since any minor imperfection in a protection equipment may lead to mal-operation or non-operation, positive control must therefore be made on every piece of protection equipment during its life cycle so as to reduce the possible latent risks to an absolute minimum. These include the protection work activities of design, evaluation, installation, testing and
commissioning, maintenance, trouble shooting and improvement.
Apart from the above control measures adopted in protection work activities, other considerations of protection equipment quality, reporting and monitoring system, information and staff training are also essential for quality assurance of protection equipment serving in the power system network. Conclusion The performance assessment of a protection system using various statistical indices indicates that it is an effective tool to measure the protection system performance and problem areas can be visualized for further managerial actions. The control measures for various protection work activities, the selection of proven protection equipment, training of staff and the availability of protection information are necessary in order to achieve a reliable and economical supply of electricity to the customers. Discussers: J. E. Stephens, W. A. Elmore and B. Bozoki
Substations ters affecting the performance of the converter transformers
88 SM 712-2 April 1989
Effects of DC Ground Electrode Transformers
on
Converter
A. P. Sakis Meliopoulos and George Christoforidis School of Electrical Engineering Georgia Institute of Technology Atlanta, Georgia
Summary DC transmission systems are normally equipped with a DC ground electrode for emergency or normal operation with or without ground return. In all cases, the DC ground stabilizes the DC voltage. During operation with ground return, a DC ground potential rise occurs at the DC ground electrode and DC voltage is transferred to the station ground. The transferred DC voltage causes the flow of DC electric current through the converter transformers. The effects of this phenomenon are investigated in this paper. Specifically, a study of DC transfer voltage to the station ground and its effects on the converter transformers is presented. The primary tool for this investigation is a time domain simulation program which comprises a set of generic power system models. Any number of power system elements can be interconnected in appropriate ways to form specific converter station configurations to simulate monopolar, homopolar, or bipolar operation. The converter is modeled with a linear system which has variable topology depending on the state of the valves. A number of innovations have been introduced in the model of the converter. The developed algorithm minimizes computations at each time step as well as computer storage requirements. The model also provides an accurate representation of turn-off and turn-on times. The transformer model takes into account the nonlinearity in the magnetizing inductance. The ground electrodes are modeled with equivalent circuits. The parameters of the equivalent circuits are computed based on the grounding system geometry and soil data. A parametric study has been performed using a typical system and assuming monopolar operation with ground return. The investigation has revealed that the major parame5858
are: (a) the separation distance between station ground and DC ground electrode, and (b) source voltage. Representative results of the parametric study are illustrated in Figs. 10 and 13 of the paper which are also illustrated here. Figure 10 illustrates the transferred DC voltage to the station ground parametrically in terms of the separation distance between DC and station ground and source voltage. For separation distances greater than 10,000 feet (less than 2 miles), the effect of DC ground electrode to station ground is negligible. Figure 13 illustrates the parametric variation of the peak value of the magnetizing current, phase A, of the converter transformer. Note that the source voltage has a pronounced effect on the magnetizing current as it is very well known. On the other hand, the separation distance between the two grounds has a very small effect on this current. The conclusion of this investigation is that, for usual system designs, the transferred DC component of electric current to the converter transformer will not have a major effect on the performance of the system.
IEEE Power Engineering Engineering Review, IEEE Power Review, April April 1989
88 SM 710-6 April 1989
Addendum I to Bibliography of Gas-Insulated Substations Working Group K9 of the Gas-Insulated Substations Subcommittee of the IEEE/PES Substations Committee
so
CL
*,
CD
This Addendum I to the Bibliography of Gas-insulated Substations, which was published in the IEEE Transactions on Power Apparatus and Systems, Vol. PAS-101, No. 1 1, November 1982, was prepared by Working Group K9 of the Gas-insulated Substations Subcommittee of the IEEE/PES Substations Committee. The new entries included will update the Bibliography to mid-1 987. The Working Group was chaired by J. F. Quinata with R. Matulic, W. P. Y. Chang, G. E. Heidenrich, L. M. Laskowski, P. R. Nannery, and F. Y. Chu contributing.
~0 4O0
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Separation Distance between Station Ground and DC Ground Electrode (feet) (a)
a.30.
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2.0-
88 SM 709-8 April 1989
10
Short-Circuit Effects in HV Substations with Strained Conductors Systematic Full Scale Tests and a Simple Calculation Method
Ca 100
1
1000
40000
Separation Distance between Station Ground DC Ground Electrode (feet) (b)
and
Fig. 10. Parametric analysis of DC transfer voltage to station ground. a) Station ground potential rise in volts. b) Station GPR as a percentage of the DC GPR.
B. Herrmann, N. Stein FGH Forschungsgemeinschaft fur Hochspannungs- und Hochstromtechnik e.V. Mannheim, Federal Republic of Germany G. KieB3ling Lehrstuhl fur Elektrische Energieversorgung Friedrich Alexander University Erlangen-Nurnberg, Federal Republic of Germany
Until some ten years ago experience indicated no general need to consider "long spans" of conductors-i.e. suspensions between steel structures of roughly 25 m and morez for short-circuit strength. The usual static load assumptions covered the short-circuit case. However, increasing shorto circuit levels changed the situation. The German national 400%. committee of IEC TC 73 together with FGH laboratories have * therefore carried out an extensive programme of tests on a c -w >cL variety of typical long-span arrangements to help the committees concerned to make progress in long-span calculation. ON le The general test arrangement consisted of two-phase conductor span between portals representing strained conSeparation Distance between Station Ground and ductors of typical 123 kV and 420 kV substations. Span DC Ground Electrode (feet) length and crossarm height for the tests described here are Fig. 13. Parametric analysis of peak value of converter shown in Fig. 1. In seven main test series the following influences on short-circuit stresses were studied: transformer magnetizing current. the type of suspension, i.e. single string and V-string insulation, the type of insulation, long-rod and cap-and-pin type, the insulating length of 123 kV and 420 kV insulation, the conductor weight, mass, cross-section and number of subconductors Each of the seven main test series was divided into two series of different short-circuit currents according to the possible values in high voltage instailations. IEEE Power Engineering Review, April 1989 59 59 IEEE Power Engineering Review, April 1989 .-
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