VFD leakage current too high for non-fixed installation - Page 1
Forum section: electronics / projects

author: Oaklander
author_rank: Regular Contributor
timestamp: January 15, 2024, 09:57:50 pm
content: I've been trying to find a VFD for a machine to be connected to grid by regular mains plug. The machine must comply to European standards.There's however a significant problem. If the earth leakage current on the drive is more than 3.5 mA a fixed installation is required to quarantee uninterrupted protective earth.But I haven't been able to find a single VFD whose leakage current would be less than 3.5 mA. I've looked at ABB, Schneider Electric, Omron, Eaton and other common manufacturers and on all of them the leakage current is more than 3.5 mA.How can that be? There are plenty of machines using VFDs without a fixed installation. Is there some kind of special type of VFD for these applications I'm not aware of?

author: duak
author_rank: Super Contributor
timestamp: January 16, 2024, 02:02:12 am
content: I believe it's inherent in an off the line power device where the line inputs and the load outputs can have significant capacitance to earth.Here's a link to an article:https://acim.nidec.com/drives/control-techniques/news-and-media/blog/technical/earth-leakage-in-variable-speed-drivesI can think of only one sure fire way around this: an isolating transformer on the line input. This would contain any VFD specific leakage currents to earth from the VFD and motor and not pass them back to the line circuit.The link above talks about removing the line to earth capacitor connection on the VFD and minimizing the motor cable length to reduce the parasitic capacitance. This could work but the first fix would cause the conducted emissions level to go up.All the VFDs I've worked with are for industrial applications where EMI isn't as much of a consideration. I have a VFD on my home drill press and I avoid the leakage problem by not having an RCD on the line. I also shielded the motor drive cable.Cheers

author: themadhippy
author_rank: Super Contributor
timestamp: January 16, 2024, 02:14:44 am
content: QuoteIn the uks regs if the current is below 10ma your allowed to use an EN 60309 plug and socket,not that helps with plugging into a standard socket,but if the customer decides to use an adapter

author: inse
author_rank: Super Contributor
timestamp: January 16, 2024, 06:04:09 am
content: I assume (and the article states the same), the earth leakage is caused by generous Y capacitors.If you try to work around with an isolation transformer, you might compromise the EMI performanceA kW isolation transformer is no fun either.

author: Oaklander
author_rank: Regular Contributor
timestamp: January 16, 2024, 11:08:06 am
content: The machine would be "pluggable equipment type A" which is connected to mains with non industrial plug as described in IEC 61800-5-1. The leakage current limit for such equipment is 3.5 mA.Now I've found some VFDs with low enough leakage current (like this one:https://www.nidec-netherlands.nl/media/5204-frequentieregelaars-commander-s100-user-guide-en-iss5-0478-0650-05.pdf).However the manual still states that the plug must conform to IEC 60309. I'm not sure what that is based on as that VFD has the option to disconnect the capacitors to decrease the leakage current well below 3.5 mA. Maybe it's just because as standard the VFD has higher leakage.