Protection in AC Drives

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technology Associate Join Date: Nov 2008 Posts: 31	Protection in AC Drives 10/20/2011 7:03 AM
	In an AC Drive (VFD / Inverter ) short circuit protection is for the vfd input side or for vfd out put side ??
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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	#1 Re: Protection in AC Drives 10/20/2011 9:32 AM
	Input. Otherwise, if the thing goes BANG then so will the upstream wiring. __________________ "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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JRaef Guru Join Date: Sep 2006 Location: California, USA, where the Godless live next door to God. Posts: 4665 Good Answers: 804	#2 Re: Protection in AC Drives 10/20/2011 9:32 AM
	The output side. Think of the VFD as a new "source" of motor power. If the motor or leads short or go to ground, the line side protection may not see it in time because the VFD is limiting the power that can flow into the circuit. So the VFD must protect the downstream systems from its own capacity. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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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	#3 Re: Protection in AC Drives 10/20/2011 2:22 PM
	Wait, now that I read PW Slack's response it dawns on me: there is a semantics issue here. Are you referring to the motor Short Circuit protection FEATURE of the VFD, or are you referring to the Short Circuit protection that YOU MUST SUPPLY for the VFD installation? My answer would relate to the FEATURE in the VFD, PW Slack's answer would relate to what YOU MUST SUPPLY for the VFD installation. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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technology Associate Join Date: Nov 2008 Posts: 31	#4 In reply to #3 Re: Protection in AC Drives 10/21/2011 7:01 AM
	Dear Jeraf I am referring to the FEATURE IN VFD.
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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	#5 In reply to #4 Re: Protection in AC Drives 10/21/2011 11:02 AM
	OK, but please realize, both statements are still true. The feature in the VFD is for the motor, it does not preclude your need for upstream short circuit protection FOR the VFD. __________________ All I every really wanted to be, was... A LUMBERJACK!.
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JRaef (3); PWSlack (1); technology (1)

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