IEC 60099-5:2000 pdf free download – Surge arresters
For range l systems containing overhead lines，the main risk to equipment arises frominduced and direct lightning strokes to the connected overhead lines. in cable systems notconnected to overhead lines，overvoltages due to faults or switching operations are mostlikely to occur. In rare cases, however, lightning induced overvoltages may also be generated.In systems of range ll, in addition to range l factors，switching overvoltages becomeimportant，increasing with higher system voltages.Overvoltages may cause flashovers andserious damage to the equipment and thereby jeopardize the supply of power to users. lt isessential to prevent this by the proper co-ordination of surge arresters with the insulation. ltis，therefore，recommended to use surge arresters if there are possibilities of lightningovervoltages or high switching overvoltages which may be dangerous to the equipment.
These surge arresters should constitute a reliable part of the system.They are designed towithstand the voltages and the resulting currents through them with a sufficiently highreliability taking into account pollution and other site matters. In each system such voltagestresses are (see lEC 60071-1):
– operating voltage;
– temporary overvoltages;
– slow-front overvoltages;
– fast-front overvoltages;
where the slow-front overvoltages due to switching are of particular importance for arrestersprotecting range ll equipment.
As a general principle，the best protection of equipment and high surge arrester ratedvoltages are contradicting requirements.Thus the selection of an adequate arrester consti-tutes an optimization process,which has to consider a great number of system and equipmentparameters.
Gapless metal-oxide surge arresters are of particular advantage for earthed neutral systems,because they offer better protection against slow-front overvoltages. This arrester type istoday widely installed in these systems and the application of arresters for such systemstends to concentrate on metal-oxide surge arresters. In some isolated or resonant earthedneutral systems,where earth fault temporary overvoltages may have long durations, gappedsurge arresters may offer advantages, if protective leveis are required to be low. While beingthe surge arrester’ traditionally used in all voltage ranges，the consideration of gappedarresters may be adequate for systems of range l, especially in the lower voltage range.
1.5 Polluted housing arrester withstand
Pollution on the arrester housing may cause sparkover or temperature increase of gradingcomponents in gapped arresters and high temperature increase of the varistors in metal-oxidearresters.To prevent arrester failures in polluted areas,arresters able to withstand the relevantpolluted conditions have to be chosen. Although not explicitly specified in lEC 60099-1 andiEc 60099-4，arresters used in normal operating conditions should withstand the mediumpollution stresses according to pollution level ll of IEC 60071-2.lf the arrester installationarea is subjected to a higher pollution,the surge arrester performance may be adverselyaffected. lf arresters of inadequate design are used in heavy (pollution level lli) or very heavy(pollution level lV) polluted areas, periodic cleaning or greasing may be effective in preventingthe events stated above.
When live washing of arresters is intended,arresters designed for such service conditions arerequired.