My day gig– New Updated 2/16/04 (updates in blue)
When I am not messing around with modular synths or shipping parts for synth builders
around the world, I have a regular job. Like most musicians, I call it my day gig. I have
worked for an electric utility company in the Midwest, USA for over 27 years. I am what
is called a "high-voltage specialist." So, while my synth circuit abilities are somewhat
limited, I am well versed in the operation of high voltage AC circuits.
The photo to the left will link you to an amazing video (~1.5 Mb) of a ½ million volt switch failing to interrupt the arc when operating. Special thanks to Old Crow for hosting this popular video. If you are interested in some light technical analysis of what you are looking at, see the text below this photo.
I was not given the details of this clip when it was sent to me.However, a couple of
Based on what I do know about the equipment in the video, what I see,and now what
The video was taken at Eldorado Substation in Boulder City, NV. The file is called
Lugo because this switch and shunt reactor are on the line that goes to Lugo.
In this case, the switch is being used to connect a special kind of transformer. The 3
single-phase transformers can be seen behind the truck. I say transformer, but as you
can see, they have leads going in, but not coming out. These are actually single winding
inductors connected from phase to ground and are commonly called "shunt reactors."
These inductors are installed to offset the capacitive effects of un-loaded transmission
lines, When a long 500 KV or 765 KV line is energized from one end, its inherent
capacitance causes an unacceptable voltage rise on the open end of the line. The
"shunt reactor" is installed to control that open-circuit voltage. Where current into the
capacitor component of the line impedance leads voltage by 90 degrees, current into
the shunt reactor lags voltage by 90 degrees. I have since learned that these shunt
reactors are rated at 33.3 MVAR each to make up a 100 MVAR bank.
The switch being opened is called a "circuit switcher." It consists of two series SF6
gas puffer interrupters (similar to a circuit breaker) and an integrated center-break
disconnect. The interrupters are to the right of the switch blades. They just look like
gray porcelain insulators. At 345 and 500 KV these types of switches typically have
two interrupters per phase in series in order to withstand the open circuit voltage
encountered when de-energizing a line or transformer. They rely on synchronized
opening of the two interrupters and voltage even distributed across the two interrupters
by "grading" devices (typically lots of series capacitors or resistors).
The way they are supposed to work is the interrupters both trip, grading capacitors or
resistors cause the open circuit voltage to split evenly across the two interrupters, the
switch blades open with no current flow, and the interrupters close as the switch
reaches the full open position. I originally titled this very BIG capacitor because that
is what unloaded transmission line looks like. The parallel wires have a huge capacitive
effect between ground and each other. On a 500KV line like this the current (leading the
voltage by 90 degrees) required to energize this capacitor is approximately
Since I have seen many people speculate as to the amount of current in the arc, I will
offer the actual calculations that are based on the assumption that the switch is only
interrupting the current into the shunt reactor and the second hand report I received
that this is a 100 MVAR reactor bank. Let’s look at only one phase:
33,300 KVAR divided by 289 K Volt = 115.2 amps.I was told by the person who took
I hope you enjoyed the show.
back to main menu