IEC 60099-8 pdf download.Surge arresters – Part 8: Metal-oxide surge arresters with external series gap (EGLA) for overhead transmission and distribution lines of a.c. systems above 1 kV
1 Scope
This part of IEC 60099 covers metal-oxide surge arresters with external series gap (externally gapped line arresters (EGLA) that are applied on overhead transmission and distribution lines, only to protect insulator assemblies from lightning-caused flashovers. This standard defines surge arresters to protect the insulator assembly from lightning-caused overvoltages only. Therefore, and since the metal-oxide resistors are not permanently connected to the line, the following items are not considered for this standard: • switching impulse sparkover voltage; • residual voltage at steep current and switching current impulse; • thermal stability; • long-duration current impulse withstand duty; • power-frequency voltage versus time characteristics of an arrester; • disconnector test; • aging duties by power-frequency voltage. Considering the particular design concept and the special application on overhead transmission and distribution lines, some unique requirements and tests are introduced, such as the verification test for coordination between insulator withstand and EGLA protective level, the follow current interrupting test, mechanical load tests, etc. Designs with the EGLA’s external series gap installed in parallel to an insulator are not covered by this standard.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. 3.1 externally gapped line arrester EGLA arrester designed for installation on overhead lines to protect an insulator assembly from lightning-caused fast-front overvoltages only NOTE This is accomplished by rising the sparkover level of the external series gap to a level that isolates the arrester from power-frequency overvoltages and from the worst case slow-front overvoltages due to switching and fault events expected on the line to which it is applied. 3.2 series varistor unit SVU non-linear metal-oxide resistor part, contained in a housing, which must be connected with an external series gap to construct the complete arrester NOTE The series varistor unit may include several units. 3.3 section of an EGLA complete, suitably assembled part of a complete EGLA necessary to represent the behaviour of a complete EGLA with respect to a particular test 3.4 section of an SVU complete, suitably assembled part of an SVU unit necessary to represent the behaviour of an SVU with respect to a particular test 3.5 unit of an SVU completely housed part of an SVU which may be connected in series and/or in parallel with other units of an SVU to construct, in combination with the external series gap, an EGLA of higher voltage and/or current rating 3.6 rated voltage of an EGLA U r maximum permissible r.m.s. value of power-frequency voltage between the EGLA terminals, at which it is designed to operate correctly NOTE 1 The rated voltage is used as a reference parameter for the specification of operating and current interrupting characteristics. NOTE 2 Different to the rated voltage of gapless (line) arresters, the rated voltage of an EGLA is a voltage that may be applied continuously. 3.7 reference voltage of an SVU U ref peak value of power-frequency voltage divided by √2, which should be applied to the SVU to obtain the reference current NOTE The reference voltage of a multi-unit SVU is the sum of the reference voltages of the individual units. 3.8 reference current of an SVU I ref peak value (the higher peak value of the two polarities if the current is asymmetrical) of the resistive component of a power-frequency current used to determine the reference voltage of the SVU NOTE 1 The reference current should be high enough to make the effects of stray capacitances at the measured reference voltage of the SVU units negligible. It is to be specified by the manufacturer. NOTE 2 Depending on the nominal discharge current of the EGLA, the reference current will be typically in the range of 0,05 mA to 1 ,0 mA per square centimetre of metal-oxide resistor area for a single column SVU. 3.9 rated short-circuit current of an SVU I s r.m.s. value of the highest short-circuit current under which the SUV will not fail in a manner that causes violent shattering of the housing and under which self-extinguishing of open flames (if any) will occur within a defined period of time
IEC 60099-8 pdf download
