Surge arrester standards must evolve continually in order to better reflect changes in the stresses and duty expected during service as well as in the current technology. Recently, an updated version of IEC 60099-4 was published with Rev 3.0 replacing Rev 2.2. Some of the changes made to type tests are relatively minor but others are substantive. This article from 2015, based on a contribution by Steve Brewer of Hubbell Power Systems at the 2015 INMR WORLD CONGRESS, explained the significant changes in the updated standard with the goal of promoting it rapid adoption by the power industry worldwide.
Table 1 compares the various type tests that used to be required as part of the prior version of the standard with those included in the new version.
Changes to Classification of Arresters
The first major change to the standard has involved replacing the four standard nominal discharge current ratings with six new classifications. These changed classifications, intended to more aptly reflect the diverse applications where an arrester is being used, are: Station High, Station Medium, Station Low, Distribution High, Distribution Medium and Distribution Low (see Table 2).
In the past, arresters were further classified by a long duration test, which required only 3 samples and was applicable irrespective of whether they were for use at a substation or were Class 1, as commonly used on distribution systems (see Fig. 1).
This has been replaced in the updated Standard by a Repetitive Charge Transfer Test – Qrs (see Fig. 2). This test requires 10 samples and has different energy input wave shape depending on the arrester’s intended application. Moreover, the long duration classifications are no longer used and thermal recovery is not a criteria for Qrs rating.
After establishing the arrester’s Qrs rating, the standards next require completing the appropriate operating duty test. Since most readers are already familiar with the requirements of the 2.2 Revision of IEC 60099-4, only the new requirements for Revision 3.0 are presented: The arrester sample is subjected first to a series of pre-conditioning discharges. Then, distribution arresters are subjected to two 8/20 current discharges of the appropriate energy, depending on class. After the energy injection, the arrester is energized at Ur for 10 seconds followed by a 30 minute recovery at Uc .
The test sequence is similar for station arresters except for the fact that the energy is input as a square wave simulating a switching event on a transmission line.
Power Frequency Voltage versus Time
The primary change to this section is that both ‘no prior duty’ and ‘with prior duty’ tests are now required. The prior duty energy injection wave shape is lightning in the case of distribution arresters and switching in the case of substation arresters (see Fig. 6).
Arrester Disconnector Tests
This new version of IEC 60099-4 recognizes that for some arrester designs the disconnector is a part of the sealing system. Testing of the disconnector is therefore performed to verify that Qrs and Wth or Qth duty do not cause the disconnector to operate. Additionally, the arrester with disconnector must demonstrate mechanical withstand and seal pumping capabilities to verify that the disconnector is not the weak link in the overall design.
Summary of Benefits from Recent Changes
The latest revision of IEC 60099-4 is seen as providing the following benefits to users:
1. Better aligning tests to classify the type of arrester more closely with its actual application. Line discharge classes have also been eliminated.
2. Providing a common basis for manufacturer test methods when it comes to publishing energy claims. This applies for both MOV durability and thermal recovery.
3. Modifying TOV tests to require ‘no-prior duty’ as well as ‘prior duty’ testing.
4. Requiring both mechanical and seal testing for disconnectors.