Scotty,
A common way to filter out the most egregious harmonics (5th harmonic) while at the same time improve the power factor is to install a filter at the 4.7th harmonic. You size the capacitor to provide the desired PF correction and then install a reactor in series with it to resonate at...
These two equations give dramatically different results.
For example:
TD=2, and various pickup multiples, I get:
P/U 1st curve 2nd curve
2.48 1.52 sec. 2.27 sec.
5.24 0.43 sec. 0.63 sec.
9.05 0.25 sec. 0.37 sec.
I haven't compared this to the published curves...
I'm trying to set up relay coordination curves on a spredsheet to assist me in establishing some relay settings. I know it sounds like a lot of work, but it's the best I have right now without spending $15K on the right software.
I've got the calculations for Schweitzer relays, which we have a...
All within the same utility I've seen:
1, 2, 3
A, B, C
Red, White, Blue
Add onto this the transformer indications of H1/X1, etc. 123 or ABC are the two most common.
Mark in Utah
A UPS is not a battery friendly environment. 5 years is a good life in most UPS applications. You can pick and choose which battery to replace, but my experience is that you'll be back in there replacing a battery soon. The failed batteries put an additional strain on the remaning batteries...
I'm not atl all surprised that a 25 kVA transformer would have problems starting a central air unit. That's one reason why many utilities have stopped stocking 25 kVA transformers and started stocking 37.5 kVA transformers as their minimum size. I know of one utility that has almost...
Bus protection circuits are generally installed where there is a desire to minimize the damage from a bus fault. Don't assume that relaibility will be increased from having differential protection, reliability will actually decrease on that particular bus or that section of the system due to...
You have two factors at work.
1. The NESC dictates how close the electrical system can be built to other facilities.
2. Other governmental laws stating how close other facilities can be built to the electrical system.
3. Clearance requiremence for maintenance people to be away from...
I've had very poor experience with 15 kV class bus duct. Generally in an outdoor application bus duct doesn't like getting dirty, but you can't get it out of service to clean it. We had several throat-connected 22 MVA transformers that we had to convert over to air-insulated bus, not a pretty...
Peterb follows much of what I have found. A lot of the cost is tied up in the wiring itself, and not so much on the hardware. By using multi-function relays you can eliminate a lot of hardware AND potential for misoperations. This will also dramatically reduce the hardware costs and wiring...
The main thing you're trying to do is limit the overvoltage between the transformer windings, don't be fixated about keeping the absolute magnitude of the voltage down won't happen if you're hit by lightning....
The best performance is obtained by placing the arrestor under oil inside the...
The closer you place the capacitors to the load, the more overall loss reduction you can accomplish. Be careful in placing capacitors on the same contactor as a motor, you can create oscillation problems and actually create an overvoltage spike when the motor is turned off that can puncture the...
Any method of heating a transformer will take energy, and you might be better off keeping them energized. Insulating them will allow you to reduce the energy required, and thus using some other method besideskeeping them energized.
I have seen substation transformers de-energized during the...
Maybe I can add some. As the altitude increases, there is less air, which acts as an insulator. Dry and clean air is actually quite a good insulator. Dirt and moisture degrade the insulation (air). There is a curve that shows the insulating qualities of air vs. pressure. As the air presure...
The only times I've seen a circuit switcher used has been for transformer protection, and in all cases they've been rated for at least the fault-duty on that bus. For example: on a 138 kV bus capable of 10 kA of fault duty, a circuit switcher is used to feed a 138/12 kV transformer. The...
