IEC 60099-5 pdf download – Parafoudres – Partie 5: Recommandations pour le choix et l’utilisation
2.1 Characteristic data of gapped surge arresters2.1.1General
Basic characteristics of surge arresters with series spark gaps are their rated voltage,theirsparkover voltages，their nominal discharge currents and their residual voltages at thesecurrents.
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 theresidual voltages at nominal discharge current and,when applicable, at switching impulsecurrents. For a given rated voltage，different types of arresters and，therefore,differentprotection levels exist.
Additional characteristics of an arrester to be considered are continuous operating voltage,long duration discharge class,pressure relief class，pollution withstand capability，livewashing capability and special mechanical properties.
2.1.2 Rated voltage
The maximum permissible r.m.s. value of the power frequency voltage between the arresterterminals, 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 operatingcharacteristics.
NOTE Some types of arresters to be used in range ll are designed to reseal at power frequency voltages higherthan the rated voltage. This voltage is generally called the”temporary overvoltlage reseal voltage”. SinceIEC 60099-1 does not specify tests to assure the correct operation of such arresters, test details and applicationshould be agreed between user and manufacturer.
Iln some cases,e.g. for the pollution test according to lEC 60099-3, the maximum r.m.s. valueof power frequency voltage which can be applied continuously between the arrester terminalsshould be known. For arresters to be used in range l according to IEC 60071-1, this voltagemay be equal to the rated voltage of the arrester. For arresters to be used in range ll it isusually lower.As lEC 60099-1 does not specify tests to assure this voltage,the applicablevalue should be obtained from the manufacturer.
2.1.3 Protective levels
The lightning impulse protective level of the surge arrester is the maximum of the followingvalues:
– the standard lightning impulse sparkover voltage;- the residual voltage at nominal discharge current.
NOTE When considering the protection of equipment from fast front overvoltages it is assumed that the withstandstrength of the oil-immersed insulation in the transformers is at least 15 % above its full lightning impulse withstandstrength for voltage durations shorter than 3 us.Therefore,the maximum voltages specified in IEC 60099-1,table 8, for the front-of-wave sparkover are 15 % higher than those for the standard lightning impulse.
other types of insulation as in instrument transformers，cables or gas insulated substations(GlS) may havedifferent withstand characteristics and the front-of-wave sparkover voltage may need special consideration.
The switching impulse protective level is applicable to the protection of equipment from slow-front overvoltages. lt is the maximum of the switching impulse sparkover voltage and theswitching impulse residual voltage.
NOTE When the switching impulse sparkover characteristic of an arrester type is not known, only approximateinformation about this is obtained from the power frequency sparkover voltage.
2.1.4 Nominal discharge current
The peak value of a discharge current having a 8/20 shape，which is used to classify anarrester. It is also the discharge current which is used to initiate the follow current in theoperating duty test and to establish the protective level of the arrester for lightningovervoltages.
2.1.5Long duration discharge class
A number related to the energy absorption capability of an arrester to discharge long lines.Increasing class numbers (see lEC 60099-1, table 5) indicate increasing system voltages andline length and decreasing surge impedance and overvoltage factors.
2.1.6Pressure relief class
A number related to the capability of an arrester to withstand internal fault currents after afailure without violent shattering of the housing. Reference is made to clause 8.7 ofIEC 6o099-1.
2.1.7Pollution withstand characteristics
For arresters to be used in polluted areas according to IEC 60071-2，pollution levels ll andlV, a pollution test according to lEC 60099-3 is necessary.From this test,information aboutthe sparkover performance is obtained. The flashover performance of the housing can bechecked in accordance with IEC 60507.
2.1.8 Live washing characteristics
Application of live washing may require a special arrester design and suitable tests have to bedefined.
ln the design of the washing equipment, care should be taken on the following points:- water with an adequate resistivity must be used;
the pressure and the nozzle configuration should be arranged so that the arrester in itswhole length and circumference is wetted as uniformly and simultaneously as possible.For this it is necessary to consider the maximum permissible wind speed.
IEC 60099-5 pdf download – Parafoudres – Partie 5: Recommandations pour le choix et l’utilisation
