This geocache will take on a short tour of a typical electricity substation. Every wondered what all that stuff inside the fence is for ? You no doubt know about transformers, but what about all that other stuff ?
Please note: it is quite safe to wander around outside this substation, nothing will zap you.
At the initial waypoint, you are standing under one of the two sets of feeder lines. When you hear the term the "electricity grid" this is what they mean. This is bulk power from a power generation plant at 132,000 V in 3-phases hence the 3 lines. On the middle pole there is a 5-digit number: 95A58
At the second waypoint you will find youself at a fence where the feeder lines enter the substation. Each line is fed down to a device on a tall insulator. This is a "potential transformer" and it is used to monitor in voltage, but to do this, the voltage needs to be lowered to something more easily measurable, usually in the range 0-500V. You can see a a cable heading into the ground at the base of the pole. This line heads to the control building down lower. There is often, but not here, a second set of devices to monitor the current. There are some "current transformers" further down, see the annotated image below if you're interested.
Next in line is an air-switch. This is a manually operated switch designed the isolate a portion of the substation from the feeder lines. Air switches are almost never opened when under load. View this video to what happens if you do: https://www.youtube.com/watch?v=3WU6xtPWyrc Such arcs burn the switch contacts meaning the switch might need to be replaced. Even worse, arcs can cross phases creating massive short circuits. There is a sign visible from here that says: "Earth Switch BGE".
At the 3rd waypoint is probably the most interesting piece of equiptment. This is a circuit breaker designed to open/close while under a power load. The switch itself is enclosed in a sealed container containing a gas: sulfur hexafluoride (SF6) which is an inert, fantastically insulating gas meaning the switch can be opened and closed, manually or automatically, without generating any arcs. So this is the main circuit breaker. There is one of these for each of the phases. From this viewpoint, to your right, you can see the nearest 3 phases. Just before the enter the circuit breaker there is a vertical insulator for each line. C is the number of brown insultators [hint: between 1 and 3].
At the 4th waypoint, you are standing in front the the 'bus' which is a series of connectors that allow power to be routed between the feeder lines and the transformers. This provides flexibility and redundancy when maintenance is required. About a 1 metre off the ground here are small coloured stickers on each pillar. These indicate the phases. Reading left to right: if they are Yellow-Red-Blue, then D=1. If you see Red-Yellow-Blue then D=2. If you see Blue-Red-Yellow then D=3 otherwise D=4.
At the 5th waypoint you are standing in front of one of the 3 transformers. These lower the feeder potential from 132,000 V to 11,000 V. The output (secondary) lines travel underground to the smaller transformers you would see on streets or on poles. There is a metal loop under the nearest transformer in the cement slab. If it is painted blue: E=1, red: E=2, green: E=3, yellow: E=4.
The last tour-stop is a sump at the lowest point and is a tank place to collect any spilled fluids. The transformers are filled with a large quantity of oil used for both cooling and insulation. The whole site drains though this point and any oil is captured here. F is the number of round manhole covers on the tank.
The cache can be found at : S 35 1(D+A).(E-F)(F-C)(F+C) E 149 0(A+D+E).(B-F)(A+C+E)(D+E-F)
Checksums: S: 20 E: 34
