Page 220 - Shale Shakers Drilling Fluid Systems

202 SHALE SHAKERS AND DRILLING FLUID SYSTEMS

Figure 12-1 provides general guidelines for age vary, the combined total variance is not to
the effects on induction motors of voltage varia- exceed 10%.
tion and the effects of voltage unbalance on
motor performance. 50 Hz versus 60 Hz operation. A 50-Hz motor
should not be operated at 60 Hz unless it is spe-
cifically designed and marked for 60 Hz operation.
TEMPERATURE CONSIDERATIONS A 60-Hz, three-phase induction motor may be
operated at 50 Hz if the voltage and horsepower
The National Electric Manufacturer's Association is reduced by 80%. It should be noted that the
(NEMA) full-load motor ratings are based on an speed and the slip will also be reduced by 80%.
ambient temperature of 40°C (104°F), at a maxi- The shaft torque will remain the same.
mum altitude of 1,000 meters (3,300 feet) above
sea level. Variations above 1,000 meters may require
"derating," or using a larger motor (Table 12-1). MOTOR INSTALLATION
Machines intended for use at altitudes above AND TROUBLESHOOTING
1,000 meters (3,300 feet), at an ambient tempera-
ture of 40°C (104°F), should have temperature rises When replacing a motor, its exact dimensions,
at sea level not exceeding the values calculated as well as speed, horsepower, and torque charac-
from the following: teristics should be determined and duplicated if
the same performance is desired. When replacing
When altitude is expressed in meters: a motor, the entire system should be inspected for
internal and external degradation. Neither the
T T Alt
RSL = R A[! - ( -1,000)710,000]
motor mounting nor mechanical coupling should
exhibit signs of wear. The power supply and con-
When altitude is expressed in feet:
nections should not be damaged.
T T Alt
RSL = RA[! - ( - 3,300)733,000] Misalignment between the motor and the driven
machine (e.g., centrifugal pump) can cause bear-
= Test
where: TRSL temperature in degrees Celsius ing failures and shaft breakage. Excessive vibra-
at sea level tions frequently indicate misalignment. All four
T RA = Temperature rise in degrees Celsius motor feet must be fastened to a flat, preferably
from tables (See NEMA Standard machined, surface. Otherwise, the frame can bend
MG-1, 1993, Section II, Par 14.04.3) when the motor is tightened down, which twists
Alt = Altitude above sea level at which the motor frame and causes misalignment. Care
machine will be operated should be taken to evenly tension mounting bolts.
If torque values are specified, follow the manu-
NEMA performance ratings are also based on facturer's recommendations.
operation at voltages within 10% of the "name- A few thick shims are preferable to many thin
plate" voltage and a frequency within 5% of the shims if it is necessary to align motor and machine
"nameplate" frequency. If both frequency and volt- (pump) shafts. Misaligned couplings create bear-
ing loading in both the motor and machine, caus-
ing high-speed distortions and also increasing
power consumption.
TABLE 12-1. Effect of Ambient Temperature on The electrical power supply s^r - .u je frequently
Electric Motors checked for proper frequency, voltage, and voltage
balance between phases. Poor and broken connec-
NEMA motor ratings are based on operating at altitudes tions of one of the supply lines are major causes
below 1,000 meters (3,300 feet) and at ambient tempera- of voltage unbalance. Overload relays for each
tures of 40°C (104°F). Variance in ambient temperature
requires rerating of motor horsepower requirements. phase will protect against extreme (greater than
5%) voltage unbalance.
Ambient Temperature Ambient Temperature The mounting should also be inspected fre-
(°C/°F) Factor
quently. If necessary, retighten bolts with the proper
-207-4 1.27 torque. If vibration is detected, one or more of the
motor feet may have to be shimmed.
0/32 1.19
Motor bearings should be greased using manu-
20/68 1.10
facturer's specified greases in concert with manufac-
40/104 1.00
turer's specified lubrication frequency and quanti-
60/140 0.88
ties. Greasing is necessary to maintain a lubricant