Surface Machinery and Methods for Oil-Well Pumping Page: 109
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POWER TRANSMITTING MACHINERY.
kv.a. capacity, which is protected on both the high and the low volt-
age sides by electrolytic lightning arresters and automatic switches.
A metering set checks the power consumption, and an ammeter
checks the load on the individual feeder from each of the four
11,000-volt feeders. Each 11,000-volt main distributing circuit is
stepped down through banks of transformers of 75 kv.a. capacity to
motor circuits of 440 volts. Each of these motor circuits carries six
wells and the transformer capacity permits five of them to be pumped
while the sixth is pulling rods and tubing.
As far as possible the motor circuits are carried on the same pole
line as the main distributing system, for which 35-foot poles are high
enough for clearance for two 3-phase circuits. Where motor lines
can not be carried on the poles of the main distributing lines, they
ire carried on 30-foot poles, and on 25-foot poles at the drops to the
pump houses. All of the poles are western cedar, butt treated.
For the 11,000-volt circuit the standard sizes of copper are No. 4
and No. 6 medium hard drawn. The standard sizes for the 440-volt
motor circuit are No. 1 and No. 4, solid weatherproof. As no motor
is more than 1,200 feet from a transformer, these sizes are sat-
If the wells are in two rows, the main distribution line is run
between the two. Under other conditions the lines are erected where
they will probably best meet future developments.
All insulators and switches for the main distribution lines are for
13,000 volts, allowing a reasonable factor of safety. Lightning
arresters and cut-outs are installed on each bank of transformers, and
provision is made for choke coils.
With the introduction of electric power, electric motors of various
types and of suitable speed and power rating have replaced steam
and gas engines in the oil fields for driving pumps, compressors, unit
powers, jack plants, and wells pumping on the beam, where many
pulling jobs are required. Pumping of the well requires that the
motor run continuously at high efficiency with low power demand,
and at comparatively low speed; pulling of rods and tubing requires
higher power demand, higher speed, and high torque. To meet both
conditions, several of the electrical manufacturing companies have
developed the two-speed, variable-speed induction motor in which
the lower horsepower rating is used for pumping and the higher rat-
ing for pulling rods and tubing.
Steam engines, like electric motors, give maximum torque at zero
speed and are therefore well suited for pulling rods and tubing.
However, the relatively high cost of running steam engines in small
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George, H. C. Surface Machinery and Methods for Oil-Well Pumping, report, 1925; Washington D.C.. (digital.library.unt.edu/ark:/67531/metadc12407/m1/138/: accessed April 24, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.