IEC 60099-8-2011 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.
6 RequIrements
6.1 Insulation withstand of the SVU and the complete EGLA
6.1.1 Insulation withstand of the housing of the SVU
The housing of the SVU shall withstand a lightning impulse voltage of
a) for Series X’: 1,4 times the residual voltage at the nominal discharge current
b) for Series Y: 1,13 times the residual voltage at high current impulse, but not less than 1 .3 times the residual voltage at nominal discharge current
NOTE The factor of 1.4 in case a) covers variations in atmospheric conditions and discharge currents up to three times the nominal discharge current.
6.1.2 Insulation withstand of EGLA with shorted (failed) SVU
The EGLA shall have the following insulation withstand performance:
a) the EGLA shall withstand the specified switching impulse withstand voltage level of the system even if the SVU has been shorted due to overloading (failure);
b) the EGLA shall be able to withstand the maximum temporary overvoltages phase to ground for their maximum durations even if the SVU has been shorted due to overloading (failure).
6.2 Residual vo’tages
The purpose of the measurement of residual voltages is to obtain the maximum residual voltages for a given design for all specified currents and wave shapes. These are derived from the type test data and from the maximum residual voltage at a lightning impulse current used for routine tests as specified and published by the manufacturer.
The maximum residual voltage of a given EGLA design for any current and wave shape is calculated from the residual voltage of SVU sections tested during type tests multiplied by a specific scale factor plus a calculated inductive voltage drop across the SVU, the gap and connection leads. The scale factor is equal to the ratio of the declared maximum residual voltage, as checked during the routine tests, to the measured residual voltage of the sections at the same current and wave shape.
The value of the residual voltage of the EGLA at nominal discharge current and at high current impulse, respectively, multiplied by a factor as given in 6.1.1, shall be lower than the minimum flashover voltage of the insulator assembly to be protected.
6.3 High current duty
The capability of the SVU for dischargin9 operations shall be demonstrated by injecting two high current impulses.
6.4 Lightning discharge capability
The capability of the metal-oxide resistors to withstand lightning discharges having current waveforms with durations of several tens of microseconds for arresters applied on shielded lines and several hundreds of microseconds for arresters on unshielded lines shall be demonstrated. The related test also covers effects of multiple lightning strikes.
6.5 Short-circuit performance of the SVU
The manufacturer shall claim a short-circuit rating of the SVU. The short-circuit currents according to this rating shall not cause violent shattering of the SVU, and any open flames shall self-extinguish in a given time.IEC 60099-8 pdf free download.