STANDARD HANDBOOK OF PETROLEUM & NATURAL GAS ...

416 Auxiliary Equipment
time switch that can start and stop the motor according to a predetermined program,
a timing relay that delays the start of the motor following a power failure, and lightning
arresters. Pushbutton control is also provided.
Power-Factor Correction. The induction motors used for oil-well pumping have
high starting torques with relatively low power factors. Also, the average load on
these motors is fairly low. Therefore, it is advisable to consider the installation of
capacitors to avoid paying the penalty imposed by most power companies for lowpower
factor. They will be installed at the individual motors and switched with them,
if voltage drop in the distribution system is to be corrected as well as power factor.
Otherwise they may be installed in large banks at the distribution center, if it is more
economical to do so.
Oil Pipelines. The main pumps for an oil pipeline usually driven by 3,600 rpm
induction electric motors having NEMA Design B characteristics. Full-voltage starting
is used. Figure 3-13 shows a typical pumping station diagram. Such pumping stations
are located at the beginning of the pipeline and at intervals along the line. Intermediate
or booster stations must be capable of operating under varying conditions due to
differences in liquid gravity, withdrawals at intermediate points, and the shutting
down of other booster stations. Pumping stations often contain two or three pumps
connected in series, with bypass arrangements using check valves across each pump.
The pumps may all be of the same capacity, or one of them may be half size. By
operating the pumps singly or together, a range of pumping capacities can be achieved.
Throttling of pump discharge may also be used to provide finer control and to permit
operation when pump suction pressure may be inadequate for full flow operation.
Pumping stations are often unattended and may be remotely controlled by radio
or telephone circuits.
Motor enclosures for outdoor use are NEMA weather-protected Type 11, totally
enclosed, fan-cooled, or drip-proof with weather protection. Motors of the latter
type are widely used. Not only are they less expensive than the other types, but
they also have a service factor of 1.15. The above enclosure types are all suitable
for the Class I, Group D, Division 2 classifications usually encountered.
If the pumps are located indoors, a Division 1 classification is likely to apply. Motors
must be Class I, group D, explosion-proof, or they may be separately ventilated with
clean outside air brought to the motor by fans. Auxiliary devices such as alarm contacts
on the motor must be suitable for the area classification. The installed costs, overall
efficiencies, and service factors associated with the enclosures that are available will
influence the selection.
Throttling
Motoroperated
valve
8
I 1
I I
Pump No. 1 PumpNo. 2 PumpNo. 3
Figure 3-13. Typical oil pipeline pump station [lo].