Yes you are correct, the added cabling is figured into the equation figuring in about 100 meters or more which would be the closest transformer station and switchgear.
CL reactors are an option though they can be expensive. I had one priced recently 400A and 0.5 ohm with enclosure it was...
DVD I think that is a neat approach because the C channels would help make sure the skates stay on the rails that is one big downside to what I proposed is that you would really have to be careful when moving it to make sure you stay aligned and on the surface of the HSS.
On another note, I did...
I actually followed up with some engineers over there and got some additional information, for record:
They use transformers with impedances of around 33.5% impedance on 50MVA base, maximum short circuit level at the station bus is about 25kA. They do parallel all (3) 35/50MVA units together...
So here is a conceptual drawing of my last comment, with the HSS steel channels being used with the skates to move into place, for reference. Stacked solid plates could also be used to get the 4" elevation rather than the HSS but they would be heavier. Nylon rollers would be needed so it can...
Ok makes sense so it’s not necessarily the “column loading” compressive strength that is the issue it’s more of the deformation/deflection caused by the roller point loads moving on the timbers so adding a steel plate will redistribute the load on the joists so the rollers don’t indent the...
Hello,
So I am not a structural engineer but I know enough to be dangerous I suppose and I had to take some structural engineering courses in my undergrad.
Anyways, say that I have a load that weighs 35,000lbs and it is to be placed onto (4) machinery skates that have rollers. Those machinery...
And in thinking about this a bit more, with this configuration saying 25% impedance on 50MVA base with 11.5kV secondary, you would be able to run two transformers in parallel on a bus indefinitely and not exceed the peak ratings of the ring main switches and also not exceed the 25kA for 1 second...
I actually think they are running their transformers in a split bus configuration at the substation with the bus ties normally open. If you look in this article, I think they only parallel the 11kV breakers in switching operations for the low voltage AC supplies which they call LVAC to prevent...
Well I was looking at a utility that has paralleled 3 50MVA transformers on the 11kV bus so of supplying downstream ring main gear close to the station that is rated 25kA the issue is you need to be at 63kA peak or less for the load break switches. By my calcs with 150M of 240 mm 3C cu cable...
For a power transformer that is built to IEC standards say 132kV to 11kV and 40 or 50MVA top rating what is the maximum percent impedance? Is it possible to build a transformer that has roughly 30-35% impedance at the top rating? I know in US I’ve heard figures as high as 20% are possible at...
Actually I think I figured it out, the turns ratio is the same so it is still a single winding not (2) parallel. Thing is with the same conductor passing through twice even though the current is the same in both conductors (its seeing the 200A twice) now you have added a second turn to the...
Oh ok I think I see what you are saying so its really (2) parallel CT's each with the ratio of 80/1 internally. Since if you parallel (2) 80/1 CT's you will get a ratio of 40/1 which amounts to the 200:5A.
Hello,
I have attached an image of what I believe to be the case for a 3-wire current transformer. My thought is these are wired such that there are two half coils internally wound in series as shown, is this accurate? If they were full coils then the measured current would be double of what...
NEC 250.184 covers grounding of medium voltage systems. As a minimum, equipment grounding conductors, where present, need to be sized at least 20% of the area of the phase conductors (if considered a neutral) or based upon the short circuit withstand of the circuit. Shielded power cables often...
Hello,
FOR ANSI: It is my understanding that the ultimate interrupting capacity of a medium voltage expulsion power fuse is its asymmetrical RMS 1/2 cycle ampere rating, is this true? Therefore, for any X/R ratio, that fuse must be capable of interrupting the asymmetrical RMS current and the...
Hello,
In looking at the Neher McGrath calculations for ampacities of conductors routed in a conduit in air, I can't seem to find anything related to if you have multiple paralleled conduits with the same types of conductors in air, for example, if you had (3) 3" conduits spaced 2" apart in air...
True, I also believe there are some trade-offs for the utility practice, I know some utilities have equipment that would be overdutied by calculation. An example of that would be fuse cutouts, its often that the available short circuit current near a substation exceeds the asymmetrical duty of...
Hello,
Just was curious if anyone knows approximately what LADWP's RS substation transformer impedances are. I know their breakers at their substations were rated 25,000A for many years and the IEEE standard rates those at a test X/R of 17. Based on that the minimum impedance considering...
Hello,
If you have a transformer that is designed as a 55°C/65°C rise, what should the 12 x FLC at 0.1 seconds and 25 x FLC at 0.01 seconds multipliers be based upon? The 55°C rating, or the 65°C rating?
For example, if you have a 3000kVA transformer with 55°C rise, it is capable of being...
