needed to solve. While the trans- former was my de- sign, the remainder of the power equip- ment was taken from actual plans. Another Internet search found that ABB had designs that were visually
Disconnect 35 KV Medium Voltage Disconnect Switch con- sists of three insulators; two fixed and one on a pivot. The pivoting (center) insulator moves the contact arm up and away from the output electrode, carrying the arc away until it extin- guishes. Operating at 35 KV results in a much smaller arc than the high voltage side. I made these using plastic insu- lators and brass shapes. Again, I attempted to make it somewhat func- tional with not much suc- cess. It does look good!
interesting accompanied by ex- cellent information including three-view construction draw- ings. I printed these and took measurements directly from them using digital calipers. I con- tinuously used Northwest Short- line’s Chopper II, Duplicutter, and Precision Sander to facilitate construction.
Corona Rings Making the lightning suppressor stacks was straightforward. Making the corona rings, on the other hand, was not. It wouldn’t have been too bad if the ring was in the same plane as the cap, but the design has the ring hanging below the cap supported by three rod hangers. A soldering fixture was called for to support everything in the proper orientation. I turned the fixture out of wood and used the RSU to provide the heat and control needed for this delicate operation.
HV Current Transformers Current is measured by a transformer that lies at the insu- lator’s bottom. They step down the line voltage to a very low sig- nal voltage that is then used to control many functions, includ- ing transformer temperature control and circuit breaker trip- ping. The coils are housed in alu- minum donuts, which I made out of turned aluminum with a sty- rene junction box glued to the outside. I’ve modeled these on both the transformer primary side and the six insulators on the HV Hybrid Breaker.
High Voltage Gantries
One thing that immediately identifies my model as contempo- rary is the structural steel gantry towers, which carry the conduc- tors from one piece of equipment to the other. The conductors are 1/16-inch aluminum tubing rep- resenting the aluminum bus bars, replicating prototype prac- tice. With the operating voltages these substations employ, you must separate the conductors from any possible opportunity to seek earthing, and to protect personnel from ever getting close enough for an arc-over to contact them. It explains why everything is so high above ground. It also explains why, in addition to con- crete foundations and footings, substations (mine included) are paved with gravel. The styrene HV gantries presented no diffi- culty since it was a straight sty- rene assembly task. Older sub- stations use latticework towers. You can purchase lattice girders from Plastruct, but they would have exceeded my budget. These are Evergreen styrene ¼-inch H- beams with hanging insulators attached with brass wire. The base plates are also styrene epox- ied to Masonite foundations with some Tichy NBW castings.
Medium Voltage Side
I chose to stretch my skills a bit and build it entirely in brass. I purchased a resistance solder- ing unit (RSU) several years ago; I’ve been looking for opportuni- ties to use it. It really facilitates construction of brass assem- blies. For the uninitiated, this de- vice works by sending low voltage (3 to 4 volts), high amperage (50 amps) electric current through a pair of conductive tweezers. You clamp the pieces to be sol- dered in the tweezers, press the foot pedal, which quickly heats the metal between the tweezers’ points. Apply the solder while continuing to hold the tweezers
64 RAILROAD MODEL CRAFTSMAN
closed. When the solder flows correctly, release the foot switch, but keep the tweezers closed. Done! It does it so fast that other pieces don’t desolder. Parts can be as little as an 1/8-inch away but stay put if you’re fast. The medium voltage gantry carries the conductors from the transformer through the MV dis- connect switch to the breaker and out to the distribution net- work. It is all soldered brass us- ing Special Shapes brass chan- nel. My cabling is all black iron wire.
Corona Rings The corona ring hub is brass, and the ring is 14 AWG copper ground wire that received a coat of Tamiya chrome silver, so they matched the other real alumi- num parts. To make the rings, I machined a coil winding mandrel out of aluminum with the outer diameter the same as the inner diameter of the desired coil. I drilled a starting hole in the man- drel where I inserted the copper wire. I led the wire through the tool holder and turned the chuck by hand. In a few moments, I had a coil of the right size. After cut- ting the rings off, I filed the cut ends so they would close tightly. Other details include a scratchbuilt ladder, three gauges that register some critical operat- ing parameters, and lots of con- duit fashioned out of 0.032-inch brass wire. I machined the gauge bodies and used photos taken from Google Images for the gauge faces.
All that remained was put- ting on all the insulators and the lightning suppressors. Getting the lightning suppressor prop- erly positioned called for a jig. Because of the corona rings, I couldn’t pull the jig off the tops of the suppressors once glued; I simply used scissors to cut the jig away.
Next up was the hybrid break-
er. This is a three-phase breaker with all phases supported on one
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