Handling mains transient failures with smart power meters?

[treez]

In smart power meters, when the MOV in the meter’s smps blows up due to age, then as you know, the fuse blows by croebar action…is it true that they then have another fuse and mov get switched in by a relay so it can have an extended life?
The relay is switched by a micro running off a small 1W flyback which has a massive RC filter ahead of it so that it never gets taken out by transients, and so is always there to switch the relay in the said way.
Is this the way they extend the life of power meter power supplies in the face of mains transients?

 

[smijesh]

Well MOVs are protective devise but it is very slow it can’t protect from surge voltage (less than 2ns pulse). TVS diodes are often used for surge protection( high-speed but low-power ) . TVS can’t protect from lightning strike it required lightning arresters . I am recommending parallel combination of TVS and MOV for protection of power meters.
MOV
• Protection time: 10 - 20ns
• Protection Voltage: > 300V
• PowerDissipation: Nil
• Reliable Performance: No
• Expected Life: Degrades
• Other: Fusing required. Degrades

TVS
• Protection time: 50ps
• Protection Voltage: 3-400V
• PowerDissipation: low
• Reliable Performance: yes
• Expected Life: long
• Other: Low power dissipation. Bidirectional requires dual
https://www.littelfuse.com/products/tvs-diodes.aspx

 

[treez]

thanks, but sorry the 10-20ns response time of a mov is easily quick enough to catch any mains transient, since the impedance of the mains cable and its filtration effect with the smps's capacitors will make any pulse stretch out to be longer than 20ns...

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What i am saying is that mov's die...and so why do people not just switch in a new mov and fuse when the old mov and fuse is dead...this could extend the life of mains connected equipment.