IEC 62501-2017 pdf download.Voltage sourced converter (VSC) valves for high-voltage direct current (HVDC) power transmission – Electrical testing.
4.4 Criteria for successful type testing
4.4.1 General
Experience in semiconductor application shows that, even with the most careful design of valves, it is not possible to avoid occasional random failures of valve level components during service operation. Even though these failures may be stress-related, they are considered random to the extent that the cause of failure or the relationship between failure rate and stress cannot be predicted or is not amenable to precise quantitative definition. Type tests subject valves or valve sections, within a short time, to multiple stresses that generally correspond to the worst stresses that can be experienced by the equipment not more than a few times during the life of the valve. Considering the above, the criteria for successful type testing set out below therefore permit a small number of valve levels to fail during type testing, providing that the failures are rare and do not show any pattern that is indicative of inadequate design and providing that the failed valve level permits the rest of the valve or valve section to continue operating without degraded performance.
4.4.2 Criteria applicable to valve levels
Criteria applicable to valve levels are as follows.
a) If, following a type test as listed in Clause 5, more than one valve level (alternatively more than 1 % of the tested valve levels, if greater) has become short or open -circuited, then the valve shall be deemed to have failed the type tests.
b) If, following a type test, one valve level (or more if still within the 1 % limit) has become short or open -circuited, then the failed level(s) shall be restored and this type test repeated.
c) If the cumulative number of short or open -circuited valve levels during all type tests is more than 3 % of the tested valve levels, then the valve shall be deemed to have failed the type test.
d) The valve or valve sections shall be checked after each type test to determine whether or not any valve levels have become short or open -circuited. Failed IGBT/diode or auxiliary components found during or at the end of a type test may be replaced before further testing.
e) At the completion of the test programme, the valve or valve sections shall undergo a series of check tests, which shall include as a minimum:
— check for voltage withstand of valve levels;
— check of the gating circuits;
— check of the monitoring circuits;
— check of any protection circuits forming an integral part of the valve;
— check of the voltage grading circuits.
f) Valve levels short circuits occurring during the check tests shall be counted as part of the criteria for acceptance defined above. In addition to short or open -circuited levels, the total number of valve levels exhibiting faults which do not result in valve level short circuit, which are discovered during the type test programme and the subsequent check test, shall not exceed 3 % of the number of tested valve levels in dielectric and operational type tests, whichever is lower. If the 4o4a1 number of such levels exceeds 3 %, then the nature of the faults and their cause shall be reviewed and additional action, if any, agreed between purchaser and supplier.
g) When applying the percentage criteria to determine the permitted maximum number of short or open -circuited valve levels and the permitted maximum number of levels with faults which have not resulted in a valve level becoming short or open -circuited, it is usual practice to round off all fractions to the next highest integer, as illustrated in Table 2.IEC 62501 pdf free download.