IEC 60700-1:2021 pdf free download – Thy4.1.1Evidence in lieu
4.11 Each design of valve shall be subjected to the type tests specified in this standard. If thevalve is demonstrably similar to one previously tested, the supplier may, in lieu of performinga type test,submit a test report of a previous type test for consideration by the purchaser.This should be accompanied by a separate report detailing the differences in the design anddemonstrating how the referenced type test satisfies the test objectives for the proposeddesign.
4.1.2 Test object
Test object should meet the following requirements:
a) Certain type tests may be performed either on a complete valve or on valve sections,as indicated in Table 2.For those type tests on valve sections，the total number of valvesections tested shall be at least as many as the number in a complete valve.
b) The same valve sections shall be used for all type tests unless otherwise stated.
c)Prior to commencement of type tests, the valve,valve sections and/or the components of them should be demonstrated to have withstood the production tests to ensure propermanufacture.ristor valves for high voltage direct current (HVDC) power transmission
4.4.1General
Experience in industry shows that，even with the most careful design of valves, it is notpossible to avoid occasional random failures of thyristor level components during serviceoperation.Even though these failures may be stress-related,they are considered random tothe extent that the cause of failure or the relationship between failure rate and stress cannotbe predicted or is not amenable to precise quantitative definition.Type tests subject valves orvalve sections，within a short time, to multiple stresses that generally correspond to the worststresses that can be experienced by the equipment not more than a few times during the lifeof the valve. Considering the above，the criteria for successful type testing set out belowtherefore permit a small number of thyristor levels to fail during type testing, providing that thefailures are rare and do not show any pattern that is indicative of inadequate design.
4.4.2Criteria applicable to thyristor levels
The following criteria are applicable to thyristor levels:
a) lf, following a type test as listed in Clause 5, more than one thyristor level (alternatively more than 1 % of the series-connected thyristor levels in a complete valve, if greater) hasbecome short circuited, then the valve shall be deemed to have failed the type tests.
b) lf, following a type test, one thyristor level (or more if still within the 1 % limit) has become short circuited, then the failed level(s) shall be restored and this type test repeated.
c) lf the cumulative number of short-circuited thyristor levels during all type tests is more than 3 % of the series-connected thyristor levels in a complete valve，then the valve shallbe deemed to have failed the type test programme.
d) When type tests are performed on valve sections， the criteria for acceptance above also apply since the number of valve sections tested shall be not less than the number ofsections in a complete valve (see 4.1.2 a)).
e) The valve or valve sections shall be checked after each type test to determine whether or not any thyristor levels have become short-circuited. Failed thyristors or auxiliarycomponents found during or at the end of a type test may be replaced before furthertesting.