ELR Tripping Sometimes While Starting the Motor Through VFD

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Jeeson Peter Participant Join Date: Apr 2018 Posts: 1	ELR Tripping Sometimes While Starting the Motor Through VFD 04/08/2018 7:31 AM
	Hello, I have recently changed a VFD in my company and after installing the new one (15KW), while switching ON the motor , the earth leakage relay trips ( sometimes). Is it due to leakage current from vfd? I changed the default carrier frequency of vfd from 8Khz to 6 Khz, and then afterwards ,the same ELR started tripping while turning on other motors with other VFDs.
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	Pathfinder Tags: "AC Drives" "Earth Leakage" "Leakage Current"

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RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#1 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/08/2018 12:07 PM
	Why was the new VFD installed? If the problems occurred after the new VFD was installed, then contact the VFD manufacturer. If there were problems that led to the replacement of the VFD, then make sure that the problems were resolved properly. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#2 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/08/2018 4:52 PM
	Newer VFDs use transistors that turn on faster than old ones, upward of 10x as fast. So that then increases the common mode noise that is created by the drive and that often shows up as causing nuisance trips of ground / earth fault protective devices. Add a shielded isolation transformer ahead of the drive, add common mode chokes (ferrite cores) to the output conductors, make sure everything is properly grounded, turn your carrier frequency down to 2kHZ. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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SolarEagle Guru Join Date: Mar 2007 Location: by the beach in Florida Posts: 33392 Good Answers: 1817	#3 In reply to #2 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/08/2018 5:05 PM
	This hardly sounds like a step forward if you have to do all that just to make it work properly.....even if it is cheaper... __________________ All living things seek to control their own destiny....this is the purpose of life
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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#6 In reply to #3 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/09/2018 3:15 PM
	Very few drives need to be installed behind Earth Leakage / Ground Fault protective devices that would be sensitive enough to trip on the CM noise involved here. it's a rare enough situation that it's dealt with on a case by case basis. I only brought it up by way of an explanation because the OP had CHANGED from an older drive to a newer one and had not previously experienced it. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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RAMConsult Guru Join Date: May 2007 Location: NYC metropolitan area. Posts: 3230 Good Answers: 444	#4 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/08/2018 6:02 PM
	Another thing to check is if all the motors are rated for "Inverter Duty". Many older motors are not, and the fast rise times from VFDs have a nasty habit of slowly puncturing the end-turn insulation in them. Many times this incipient failure mode exhibits itself as higher and higher earth leakage current. __________________ “Tell me and I forget. Teach me and I remember. Involve me and I learn.” Ben Franklin.
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daveoliver Active Contributor Join Date: Feb 2015 Location: Greater Memphis, Tn. Metro Posts: 20	#5 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/09/2018 11:02 AM
	I would highly recommend installing a Line Reactor ahead of the VFD. __________________ Dave Oliver
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PWSlack Guru Join Date: Jan 2007 Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Kettle's on. Posts: 32175 Good Answers: 839	#7 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 04/09/2018 5:06 PM
	Question the need for the earth leakage relay. Question its setting. Question the quality of the VFD. If it is new and CE-marked, for example, then this sort of thing shouldn't happen. Question what happens when the VFD is removed from circuit and the motor is started by other means. Evaluate what to do after the above has been completed. __________________ "Did you get my e-mail?" - "The biggest problem in communication is the illusion that it has taken place" - George Bernard Shaw, 1856
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Fardan Commentator Join Date: May 2011 Posts: 76	#8 Re: ELR Tripping Sometimes While Starting the Motor Through VFD 05/08/2018 2:59 AM
	Some VFDs equipped with EMC/RFI filters to protect them from the radio frequency which causes capacitive current discharge to ground during power up where using ELR or ELCB is not sufficient, so check with manifacturer.
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