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What you need is load current, first. Size the CT based off that, first. That will put you into the 0-1A range, secondary. If you're dealing with IEC or European standards, they use 0-1A CT's, secondary. USA uses 0-5A CT's, secondary. As for saturation, that's a different issue. If you want the...

Hey, everyone, thanks for contributing. I believe I got the problem solved by using ETAP v. 12.5. Neplan is Swiss-made software that has many capabilities...probably overkill in many cases I've seen...however, I got the job done with ETAP. Thanks!

Hi, what's the best power quality software for analyzing voltage variations from a resistive arc welder that cause light flicker on a radial system. So far, I've found Neplan flicker analysis software. Does anyone know of something better; has anyone used the Neplan flicker module, and is it...

It was use the blue boxes or slew after slew of auxiliary relays that have a reputation for failure and complexity in this type of control scheme. We are using primary 487B, with a backup 487B. Yes, they're both 487B relays and not different manufacturers/models like GE B90 for a backup, but the...

I'm using the 487B on a single breaker, double bus substation. This will use six zones of protection, one per phase for each bus. There's significant local generation present that can be switched onto either bus. So, dynamic zone switching is necessary, with some sort of check zone or a...

I get it, fault once then done until inspection time. Sure, but many bus faults are temporary and they're very, very rare compared to other power system apparatus faults. Also, it seems to me that the SEL-487B response is slowed by using a LOR, especially if high speed outputs are used. Unless...

I think you need to run a transients study and get the isokeraunic data for your area. You can do a transients study via the ATP-EMTP free program (http://www.emtp.org/), set up a little model of your system and estimate what the voltage would reach; odds are good that lightning isn't going to...

I'm trying to get an answer as to why use a lockout relay (LOR) on a 487B low-impedance bus differential relay that uses dynamic zone protection. In my opinion, this isn't necessary unless the utility wants someone to be forced to go to the substation and inspect the bus before resetting the...

I have used SEL, and they're fine, probably one of the best. I think GE's Multilin family of UR "Universal Relays", which are designed on a modular platform, are interesting...especially with the hard-fiber process bus "brick". The brick is a remote I/O device that would mount in substation...