CEI IEC 60099-5:2000 pdf download

CEI IEC 60099-5-2000 pdf download.Surge arresters -Part 5:Selection and application recommendations.
NOTE If high current impulse values different from the standardized values are necessary (see IEC 60099-4, table 6, note), these values should be selected according to the lightning discharge current,
— select the pressure relief class of the arrester with respect to the expected fault current,
— select a surge arrester that fulfils the above requirement;
— determine the lightning and switching impulse protection characteristics of the arrester:
— locate the arrester as close as possible to the apparatus to be protected;
— determine the co-ordination switching impulse withstand voltage of the protected equipment taking into account the representative slow-front overvoltages and system layout:
— determine the co-ordination lightning impulse withstand voltage considering:
• the representative impinging lightning overvoltage surge as determined by the lightning performance of the overhead line connected to the arrester and the acceptable failure rate of the protected equipment:
• the substation layout:
• the distance between surge arrester and protected equipment:
— determine the rated insulation level of the equipment from IEC 60071-1;
— if a lower rated insulation level of the equipment is desired, then a lower continuous operating voltage, a lower rated voltage, a higher nominal discharge current, a higher line discharge class, a different arrester design or a reduced distance between arrester and protected object should be investigated.
NOTE A lower continuous operating voltage or a lower rated voltage may reduce the service reliability ot the arresters.
Details of this iterative procedure are given in sections 2. 3 and 4 of this document.
1.5 Polluted housing arrester withstand
Pollution on the arrester housing may cause sparkover or temperature increase of grading components in gapped arresters and high temperature increase of the varistors in metal-oxide arresters. To prevent arrester failures in polluted areas, arresters able to withstand the relevant polluted conditions have to be chosen. Although not explicitly specified in IEC 60099-1 and lEO 60099-4, arresters used in normal operating conditions should withstand the medium pollution stresses according to pollution level II of IEC 6007 1-2. If the arrester installation area is subjected to a higher pollution, the surge arrester performance may be adversely affected. If arresters of inadequate design are used in heavy (pollution level Ill) or very heavy (pollution level IV) polluted areas, periodic cleaning or greasing may be effective in preventing the events stated above.
When live washing of arresters is intended, arresters designed for such service conditions are required.
2.1 Characteristic data of gapped surge arresters
2.1.1 General
Basic characteristics of surge arresters with series spark gaps are their rated voltage, their sparkover voltages, their nominal discharge currents and their residual voltages at these currents.
The protective performance is characterized by the sparkover voltages for front-of-wave, lightning impulse and, when applicable, switching impulses; and is also characterized by the residual voltages at nominal discharge current and, when applicable, at switching impulse currents. For a given rated voltage, different types of arresters and, therefore, different protection levels exist.
Additional characteristics of an arrester to be considered are continuous operating voltage, long duration discharge class, pressure relief class, pollution withstand capability, live washing capability and special mechanical properties.
2.1.2 Rated voltage
The maximum permissible r.m.s. value of the power frequency voltage between the arrester terminals, at which it is designed to operate correctly as established in the operating duty test. The rated voltage is used as a reference parameter for the specification of operating c ha ía c te r i st i c s.
NOTE Some types of arresters to be used in range II are designed to reseal at power frequency voltages higher than the rated voltage. This voltage is generally called the “temporary overvoltage reseal voltage”, Since IEC 60099-1 does not specify tests to assure the correct operation of such arresters, test details and application should be agreed between user and manufacturer.
In some cases, e.g. for the pollution test according to lEO 60099-3, the maximum r.m.s. value of power frequency voltage which can be applied continuously between the arrester terminals should be known. For arresters to be used in range I according to IEC 60071-1. this voltage may be equal to the rated voltage of the arrester. For arresters to be used in range II it is usually lower. As IEC 60099-1 does not specify tests to assure this voltage, the applicable value should be obtained from the manufacturer.