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Hello, I'm wondering if anyone can point out any obvious drawbacks to having a normal source (utility) solidly grounded (3P 4W system), with an emergency system (separately derived) impedance grounded. All circuit breakers within the main and emergency distribution would be 4 pole. There would...

A great sketch on what engineers deal with on a daily basis. http://www.youtube.com/watch?v=BKorP55Aqvg#t=261&aid=P8SP8VtP0Sw

Hello, Has anyone ever seen or used an Arc Terminator or similar device (crowbar) in a switchgear lineup for arc flash/blast mitigation? I'm trying to see how prevalent the usage of these devices are, and if anyone think they will become more widely used. Where do people think the arc flash...

Hello, I am wondering if anyone has run across any whitepapers or IEEE articles relating to ultrafast tripping times. I am trying to find, given our current technology, what the fastest time a relay can initiate a correct trip signal is. As of right now I cannot find anything where the required...

Hello, I am wondering if anyone knows of any manufacturer (anywhere in the world) that can produce a high voltage, high frequency power supply of the following specifications: 20-35kV peak 2-5 kW output 40-60kHz ouptut single phase or three phase input it doesn't matter. Thank you

Hello, I have been reading many different IEEE articles that have been outlining designs for solid state circuit breakers using newer semiconductor technology (most are since 2008). I know the concept of the solid state circuit breaker has been around for at least 20 years (a Powell Electronics...

Hi there, I have a single phase system in which I require an arc flash analysis for. However, I do not have the single phase / unbalanced load package for SKM. I will thus attempt to model this as a three phase system to attain the single phase fault currents. I have looked through any threads...

Hello, I have a client who wishes to go to cogeneration as the price of electricity is now making it economically viable. I have planned on using three diesel generators in parallel that will come on-line and off-line in response to real time demand load. I have estimated the system demand...

Hello everyone, I have been doing coordination and arc flash studies for low voltage commercial and industrial distribution systems. So far, I have had no problems in acquiring the necessary information to do the studies (grid MVA, X/R, line voltage, R0/1/2, X0/1/2). However, I have come...

Hello, I have a question regarding synchronizing a small generator with the utility. I have a 15kW genset that a client wants to sync to the utility feeding his building. The synchronization can be done using a contactor and a synchronizing controller (like easygen or woodward EGCP-2). My...

Hello, I work in a consulting firm doing low voltage distribution design. A while back I had thought of an idea for a fault current limiting device using a saturable reactor. I immediately looked it up on the internet to see if it had been done already. Of course, it has, but only in high...

Hello, I have a question regarding a 300kVA 208Y/120V generator we are installing in one of our buildings. Do you think it is necessary to install either a NGR or ground fault protection into the genset? If so, which method is best at limiting ground fault damage? Based on cost it is probably...

Hello, I am doing an analysis on a system with an 800A 600V bus. The arc-fault current is calculated to be lower than my instantaneous setting on my circuit breaker, but I cannot lower the inst. setting as it will overlap the transformer inrush current. The arc flash energy is thus really high...

Hello, I have a question regarding transformer %Z. The things that are known are as follows: 1. %Z is acquired through testing the transformer via a short circuit test. 2. %Z is the percentage of rated primary voltage that when applied, produces the full load current through the secondary. 3...

Hello, I have a question regarding SMAW and MIG welds. People commonly use copper stock below, say, a but-weld to carry the pool along and create a better weld. I've tried to figure out physically why the copper does not melt or deform, with no luck. Does anyone have a chemical explanation...

Hello all, Can anyone explain mathematically how the voltage in the secondary of a current transformer is kept to a minimum? I understand that open circuiting a CT will cause some havoc, but I can't seem to derive why mathematically. Thanks, Daniel

Hi there, I have a couple of questions regarding available fault currents. I have a 208Y/120V 1200A distribution with an available fault current of ~30kA. I thus had planned to used current limiting fuses to knock down the available current so all my downstream equipment could be much...

Hi, I am starting to do some coordination work and I require some data. Does anyone know if you can get general oil-filled transformer data (%z, x/r, etc.) for units less than 5MVA without having to contact a specific manufacturer? This is for early design stage, which is why the exact...

I work in commercial and light industrial electrical design, so my experience with HV is limited. I have a question regarding bus synchronization. I have dealt with small scale generator synchronization of up to 1MVA, but nothing else. I am wondering, how is it substations synchronize the...

Hello, I have an installation at 600V that requires ground fault protection (RCD) on the main service disconnect. I have designed it with fuses, but obviously fuses have no RCD. As a GFI breaker at this size would be very expensive, has anyone heard of a stand-alone zero sequence transformer...