LEESON Permanent Magnet AC Motors - Manual (Page 5)

Table 3-2 Maximum Radial Load (pounds force) @ Middle
of the Shaft Extension Length
NEMA
Frame
Motor Rated RPM
3600 1800 1200 900
182T 187 230 261 287
184T 193 237 273 301
213T 319 317 470 510
215T 327 320 480 533
254T 500 631 729 793
256T 510 631 736 820
284T - 866 990 1100
286T - 871 1005 1107
Values based on 26,280 hrs B-10 Life
For “End of Shaft” Load multiply value by 0.88
3.3.4
BELTED
The goal of any belted system is to efficiently transmit the
required torque while minimizing the loads on the bearings and
shafts of the motor and driven equipment. This can be
accomplished by following four basic guidelines:
1.
Use the largest practical sheave diameter.
2. Use the fewest number of belts possible.
3. Keep sheaves as close as possible to support bearings.
4. Tension the belts to the lowest tension that will still transmit
the required torque without slipping. V-belts may squeal
initially in high starting torque applications.
3.3.4.1 Sheave Diameter Guidelines
In general, smaller sheaves produce greater shaft stress and
shaft deflection due to increased belt tension. See Table 3-3
(next page) for recommended minimum sheave diameters.
Using larger sheaves increases the contact with belts which
reduces the number of belts required. It also increases the belt
speed, resulting in higher system efficiencies. When selecting
sheaves, do not exceed the belt manufacturer's recommended
maximum belt speed, typically 6,500 feet per minute for cast
iron sheaves. Determine belt speed by the following formula:
Figure 1
BELT SPEED (Ft/min) =
12
inches Dia Sheave x 3.14 x RPM Shaft ) (
3.3.4.2 Number of Belts
In general, use the fewest number of belts that will transmit the
required torque without slipping. See Table 3-3 (next page) for
recommended maximum number of belts. Each belt adds to
the tension in the system, which increases load on the shafts
and bearings. Belts are most efficient when operated at or
near their rated horsepower.
If the sheaves have more grooves than the number of belts
required, use the grooves closest to the motor.
3.3.4.3 Sheave Location
Install sheaves as close to the housing as possible to increase
the bearing life of the motor and driven equipment.
Figure 2
3.3.4.4 Belt Tension
WARNING: EQUIPMENT FAILURE
Excessive belt tension may lead to bearing failure and/or shaft
failure. Failure to properly tension belts may result in serious
personal injury, death, and/or property damage. Belt tension
must be adjusted using a belt tension gage. Adjusting belt
tension by "feel" (i.e., pushing on belt with fingers or hand) may
result in excessive belt tension.
In general, belt tensions should be kept as loose as possible
while still transmitting the required torque without slipping. Belt
tensions must be measured with a belt tension gage. These
inexpensive gages may be obtained through belt
manufacturers or distributors. V-belts may squeal initially in
high starting torque applications.
Proper belt tension is determined by measuring the force
required to deflect the center of the belt a given distance. The
proper deflection (in inches) is determined by dividing the belt
span in inches by 64. Calculate the proper deflection and then
see Table 3-3 (next page) for the required “Average Deflected
Force” to achieve that deflection.
After tensioning the belt, rotate the sheaves for several
rotations or operate the system for a few minutes to seat belts
into the grooves, then re-tension the belts. New belts will
stretch during use, and should be retensioned after the first
eight hours of use.
3.3.5 PERMANENT MAGNET MOTOR VFD (Variable
Frequency Drives) OPERATION
CAUTION: Power Factor Correction Capacitors
Placing power factor correction capacitors between the motor and
VFD may cause personal injury and significant damage to the
VFD. Power factor correction capacitors should never be
installed between the VFD and the motor and
should not be
installed at VFD input unless approved by VFD manufacturer.
NOTICE: MOTOR NOT SUITED FOR OPERATION ON LINE
POWER
PM motors can only be operated by a PM motor compatible VFD.
Connecting directly to line power may result in motor damage.
Consult VFD installation and operation manual for additional
instructions and safety information.