IEEE Std C62.55-2020 pdf download
IEEE Std C62.55-2020 pdf download.IEEE Guide for Surge Protection of DC Power Feeds to Remote Radio Heads.
Figure 12 and Figure 13 show temperature buildup in the MOV due to first and subsequent impulses together with continuing current pulses as shown in Figure 11, for component time constants of 1 s (MOV) and 3 ms (silicon).
To summarize, the important thing to consider is the amount of thermal energy deposited in a device by all components of the flash: first stroke, subsequent strokes, and continuing current. In particular, an SPD chosen without consideration of energy might be undersized due to temperature buildup, as the example just cited shows.
10. Guidance forselecting MOVSPDs
As Clause 9 suggests, MOVs should be selected on the basis of their ability to handle a defined multi-surge burst. However, a multi-surge burst test can be performed in only a very limited number of labs; therefore, MOVs are unlikely to be rated on this test. Thus, as a practical matter, alternatives to the multi-surge burst test based on standard test methods should be considered. The following paragraphs review proposed alternative test methods.
10.1 Repeated standard tests at elevated temperature
Clause 9 also suggests that the energy buildup in the MOV is the most important consideration. A multi-surge burst adds energy to the MOV, raising its temperature. As an alternative, energy from heating could be used to raise the MOV temperature. A method considered is to use a standard 6 kV, 3 kA 8/20 surge repeated at 60 s intervals, with the test run at elevated temperature. To evaluate this approach, a preliminary test on an MOV suggested that a standard surge test that was not destructive at room temperature was destructive at elevated temperature.
In another approach, calculations done to estimate the temperature rise in an MOV due to a burst of closely spaced 5.5/75 3 kA surges showed a stair-step increase in temperature with each new surge. Both these results suggest that the effects of a multi-stroke lightning flash on an MOV might be approximated by surging the MOV at elevated temperature with a standard surge. However, the research of Sargent et al. [B23j shows that the elevated temperature leading to failure occurs only in a tiny fraction of the device volume. Thus, it is not clear that raising the temperature of the entire volume of the MOV by putting it in a thermal chamber and then surging it is an appropriate substitute for a multi-surge burst test. Consequently, there are issues with repeated standard surge testing at elevated temperature as a substitute for multi-surge burst testing that would need to be resolved before this approach could be recommended.
10.2 Single high-energy surge
10.2.1 The rated impulse energy test
A possible alternative test is to deliver to the MOV one high-energy surge using a standard vaveforin having a charge equal to the sum of the charges of the individual surges in the burst. The rated impulse energy test as described in IEEE Std (‘62.33 is one way to do this, provided that the 2 ms test is used and not the alternative 8/20 or 10/1000 surge. An objection to this test is that the high voltage needed to drive the current for this test has been reported to cause failure by flashover. Additionally, the test using a single surge ignores the jackhammer effect alluded to in Clause 9. Therefore, damage caused by a single high-energy surge is not likely to approximate that done by a multi-surge burst. With all of that considered, the joule rating of an MOV based on the 2 ms test is the only energy-related value likely to be present on an MOV data sheet.
10.2.2 Single surge using an inductor source
During a lightning flash, the high thermal capacity of an MOV integrates the stroke and continuing current energies and this results in the stepped temperature rise shown in Figure 12.
