The whole old substation in Abbeville, SC.

Dave explained how this substation works. I had to add this! Thank You Dave!!!

First you have the 69kV line coming into the sub and which passes through the main disconnect switch up on top then swings around and back down below to the set of fuses.

From the fuses it swings up into the bus wires that pass above the three transformers.

The three transformers are connected delta-style on the primary side (each one connects to a different pair of wires). The cylinder tanks are expansion tanks to hold excess cooling fluid - just like in a car where there's a reservoir to hold excess coolant as the engine warms up - when the engine cools down, it's drawn back in. Same concept at work with these transformers (to help avoid heat-related leaks of the coolant which is usually mineral oil).

It looks like the fourth, slightly smaller transformer is an emergency spare kept on hand (which is in line with good practice - but ideally that spare should be the same size as the three normal ones)

On the secondary side, the three transformers are connected wye-style (one side from each transformer goes to the neutral wire along the front and which is grounded to the substation frame).

The are two possible reasons for there being four different bushings on the secondary side: One is to use one standard transformer style for different distribution system voltages (for example 4160/2400V, 6600V, 12.5kV/7200V, etc.) or where the actual voltage on the primary is consistently higher or lower than nominal.

With the two disks on the low-side bus wires, I'm going to guess the transformers put out somewhere between 7200V and 8400V (12 to 14kV 3-phase).

Anyhow, from the bus wires it continues into a set of three disconnects - the normally open one up on top and two sets of normally-closed manually operated vertical switches just below.

On its way through the disconnects and down into the bank of voltage regulators, there are three modern polymer-cased lightning arresters.

The three voltage regulators have 2 sets of coils - one connected in parallel with the line (incoming wire to the third, grounded bushing) and one in series (the two bushings with the small lightning arrester between them). The voltage regulator is actually an autotransformer where the series coil has a number of taps wired to a rotary switch, which in turn is controlled by a sensor in the unit. As the load on the output fluctuates or the voltage available on the input fluctuates, the circuitry automatically advances the rotary switch to an appropriate tap on the series coil to keep the output voltage in the desired range.

You'll often see a downward-angled round box on the regulator (they're evident here but almost out of view) with a window and a pointer to indicate which tap is being used. Coming back to those disconnects for a moment, if the regulators have to be taken out for work, they would close the normally-open bypass switch, pull those vertical links open, then the regulators can be exchanged or serviced. Before that can be done, the manual controls on the regulators would be accessed and the rotary switch in the regulator advanced to put it into the 'neutral' (bypass) position or else the act of closing the external bypass switch will short out the series winding in the regulator (and which helps explains the presence of that lightning arrester across the 2 main terminals).

After all that, the regulated voltage now enters the two breakers by way of that buswork - the large older gang-type unit (which I assume is oil-filled) and the smaller vacuum-type breaker just behind. It seems that at least one of the bays on the older unit has failed and which was replaced by the vacuum unit just behind. It also looks like one of the distribution circuits landing into the sub is no longer used (no leads from the circuit down to the breaker terminals).