MOV selection for 3phase energymeter

[Libin]

Dear friends,

I have small doubt regarding MOV.

I am using V480LS80B MOV from Littelfuse for 3 phase 4 wire energy meter application.

I have connected MOV in between each line and neutral.

Is there any standard says that, minimum how many number of pulse (surge voltage IEC61000 4-5. V- 1.2/50uSec- Current 8/20u sec ) has to be withstand for the product with 10year life.

I found my product can withstand only 1000 number of pulse with 20µ sec duration.

From attched graph of the pulse rating curve (Short circuit current with 400A can withstand only 1000 number of pulses).

Kindly let me know, for the product life of 10year, minimum how many number of pulse has to be withstand by Metal Oxide Varistor.

Best Regards
Libin

 

[FvM]

I don't see, why an energy meter would need to connect MOVs directly to the supply terminals?

 

[Libin]

Dear FvM,
As per IEC metering standard, energy meter should withstand 4KV surge voltage test (IEC61000 4-5, level 4). I am using MOVs across line to neutral in energy meter internal circuit.

Regards
Libin

I don't see, why an energy meter would need to connect MOVs directly to the supply terminals?

 

[betwixt]

I would have thought you were doing exactly the opposite of meeting the specs by adding the MOVs.

Being able to withstand 4KV is not the same as clamping it at 480V peak.

Brian.

 

[FvM]

Yes, that's also my consideration. As the energy meters internal power supply is basically low power, it would use a suitable current limiting device, e.g. a series resistor. A transformer should be able to handle the transients without additional protection means.

 

[Libin]

Dear FvM,

Internal powersupply is 10W and wide input voltage range . I am planning to remove series resistor as a part of cost reduction and for maintaining high accuracy in voltage sensing circuit.

Regards
Libin

Yes, that's also my consideration. As the energy meters internal power supply is basically low power, it would use a suitable current limiting device, e.g. a series resistor. A transformer should be able to handle the transients without additional protection means.

 

[FvM]

10 W is quite a lot. I can't answer your original question, but as a supplement, I can report from experience, that MOV connected directly to the mains terminals will be stressed sooner or later with surge events that exceeds the device capabilities and cause fatal damage.

The energy meter's voltage measurement should be connected independant of the power supply and protected by a respective rating of the voltage divider, I think.