CEl IEC 60099-5:2000 pdf download

CEl IEC 60099-5-2000 pdf download.Surge arresters -Part 5:Selection and application recommendations.
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 characteristics.
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 IEC 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.
2.1.3 Protective levels
The lightning impulse protective level of the surge arrester is the maximum of the following values:
— 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 withstand strength of the oil-immersed insulation in the transformers is at least 15 % above its full lightning impulse withstand strength for voltage durations shorter than 3 .ts. 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 (GIS) may have different 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. It is the maximum of the switching impulse sparkover voltage and the switching impulse residual voltage.
NOTE When the switching impulse sparkover characteristic of an arrester type is not known, only approximate information 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 an arrester. It is also the discharge current which is used to initiate the follow current in the operating duty test and to establish the protective level of the arrester for lightning overvoltages.
2.1.5 Long duration discharge class
A number related to the energy absorption capability of an arrester to discharge long lines. Increasing class numbers (see IEC 60099-1, table 5) indicate increasing system voltages and line length and decreasing surge impedance and overvoltage factors.
2.1.6 Pressure relief class
A number related to the capability of an arrester to withstand internal fault currents after a failure without violent shattering of the housing. Reference is made to clause 8.7 of
IEC 60099-1.
2.1.7 Pollution withstand characteristics
For arresters to be used in polluted areas according to IEC 60071-2, pollution levels Ill and IV, a pollution test according to IEC 60099-3 is necessary. From this test, information about the sparkover performance is obtained. The flashover performance of the housing can be checked in accordance with IEC 60507.