Efficient Plant April 2022 - 24
motor maintenance
+
Reject These
Motor Myths
+
+
Have some myths replaced facts in your motor setup and
maintenance practices?
THE TONGUE-IN-CHEEK saying, " If it's in black
and white, it must be right, " is a helpful reminder that
not everything we read (or hear) is accurate or complete.
It's always best to check sources and verify facts before
accepting consequential statements as true. A similar
adage underscores the importance of this advice in the
digital age: " If it's on the internet, it must be true. " With
these things in mind, here's a selection of common
misconceptions about three-phase squirrel-cage
motors and the facts that deny them.
SOFT-STARTING MOTORS REDUCE
UTILITY DEMAND CHARGES
Soft starters typically ramp up the voltage applied to a motor over a few seconds
at start-up, reducing winding heating and starting current. This may extend the life
of the winding for motors that start frequently, but it doesn't affect utility demand
charges. That's because the electric meter averages the kilowatts consumed over each
15-to-30-min. period, not just for the few seconds that the soft starter reduces input
power to the motor.
POWER FACTOR CORRECTION CAPACITORS
CAN REDUCE MOTOR ENERGY CONSUMPTION
Applying power factor capacitors at the motor terminals increases the power factor
on the supply cables but does not change the motor's power factor. Increasing the
power factor on the supply lines reduces current in them, causing a corresponding
but typically insignificant reduction in I2
A MOTOR CAN BE LOADED UP TO ITS SERVICE
FACTOR CURRENT
An example of this would be loading a 1.15 service factor motor up to its service
factor current (typically ~1.15 x rated current). That would be a problem, according to
clause 14.37.1 of NEMA Stds. MG 1-2016: Motors and Generators (MG 1): " A motor
operating continuously at any service factor greater than 1 will have a reduced life
expectancy compared to operating at its rated nameplate horsepower. Insulation life
and bearing life are reduced by the service factor load. "
Further, the service factor only applies to Usual Service Conditions (MG 1, 14.2).
These include operation at an ambient temperature of 5 F to 104 F (-15 C to 40 C)
and at an altitude of less than 3,300 ft. (1,000 m.) when rigidly mounted in areas
or supplementary enclosures that do not seriously interfere with the machine's
ventilation.
+
This article is an excerpt from the original article by Thomas
Bishop, Bust Nine Common Motor Myths. That original
article and several other motor-maintenance publications can be
downloaded at easa.com/erc.
24 | EFFICIENTPLANTMAG.COM
OVERSIZED MOTORS, ESPECIALLY MOTORS OPERATING
BELOW 60% OF RATED LOAD, ARE NOT EFFICIENT AND
SHOULD BE REPLACED WITH APPROPRIATELY SIZED
PREMIUM EFFICIENCY (IE3) MOTORS
On the contrary, matching motor horsepower (kW) rating to the load will usually mean
a slightly lower efficiency at that load than using the next larger-sized motor. The
reason is that motors tend to peak in efficiency between 75% and 80% of rated load.
Motors that drive supply or return air fans in HVAC systems generally operate at 70%
to 75% of rated load, making them candidates for use with oversized motors. Further,
even at 60% of rated load (which more than one industrial motor study found to be
the average load level), the next higher-power-rating motor could be more efficient
at that load than the appropriately sized power rating. Some high-inertia loads also
require more HP/kW to start than to run the load. Reducing the HP/kW to match the
running load could result in the motor being unable to start the load. -Thomas H.
Bishop, P.E, Senior Technical Support Specialist, EASA Inc., St. Louis, easa.com. EP
APRIL 2022
R losses (energy) in the supply wiring. The
primary reason for reducing supply circuit current is to add electrical loads without
rewiring a facility.
http://www.easa.com/erc
http://www.easa.com
http://www.EFFICIENTPLANTMAG.COM
Efficient Plant April 2022
Table of Contents for the Digital Edition of Efficient Plant April 2022
Efficient Plant April 2022 - Cover1
Efficient Plant April 2022 - Cover2
Efficient Plant April 2022 - 1
Efficient Plant April 2022 - 2
Efficient Plant April 2022 - 3
Efficient Plant April 2022 - 4
Efficient Plant April 2022 - 5
Efficient Plant April 2022 - 6
Efficient Plant April 2022 - 7
Efficient Plant April 2022 - 8
Efficient Plant April 2022 - 9
Efficient Plant April 2022 - 10
Efficient Plant April 2022 - 11
Efficient Plant April 2022 - 12
Efficient Plant April 2022 - 13
Efficient Plant April 2022 - 14
Efficient Plant April 2022 - 15
Efficient Plant April 2022 - 16
Efficient Plant April 2022 - 17
Efficient Plant April 2022 - 18
Efficient Plant April 2022 - 19
Efficient Plant April 2022 - 20
Efficient Plant April 2022 - 21
Efficient Plant April 2022 - 22
Efficient Plant April 2022 - 23
Efficient Plant April 2022 - 24
Efficient Plant April 2022 - 25
Efficient Plant April 2022 - 26
Efficient Plant April 2022 - 27
Efficient Plant April 2022 - 28
Efficient Plant April 2022 - 29
Efficient Plant April 2022 - 30
Efficient Plant April 2022 - 31
Efficient Plant April 2022 - 32
Efficient Plant April 2022 - Cover3
Efficient Plant April 2022 - Cover4
https://www.nxtbook.com/atp/MaintenanceTechnology/efficient-plant-jan-feb-2024
https://www.nxtbook.com/atp/MaintenanceTechnology/efficient-plant-april-2022
https://www.nxtbook.com/atp/MaintenanceTechnology/efficient-plant-october-2021
https://www.nxtbook.com/atp/MaintenanceTechnology/efficient-plant-june-2021
https://www.nxtbook.com/atp/MaintenanceTechnology/epapril2021
https://www.nxtbook.com/atp/MaintenanceTechnology/epmarch2021
https://www.nxtbook.com/atp/MaintenanceTechnology/epjanfeb2021
https://www.nxtbook.com/atp/MaintenanceTechnology/epjulyaug2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epjune2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epmay2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epapril2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epmarch2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epfeb2020
https://www.nxtbook.com/atp/MaintenanceTechnology/epjan2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epnovdec2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epseptoct2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epmay2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epapril2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epmarch2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epfebruary2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epjanuary2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epdecember2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epnovember2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epoctober2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epseptember2019
https://www.nxtbook.com/atp/MaintenanceTechnology/epaugust2018
https://www.nxtbook.com/atp/MaintenanceTechnology/0818schneider
https://www.nxtbook.com/atp/MaintenanceTechnology/epjuly2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epjune2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epmay2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epapril2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epmarch2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epfebruary2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epjanuary2018
https://www.nxtbook.com/atp/MaintenanceTechnology/epdecember2017
https://www.nxtbook.com/atp/MaintenanceTechnology/epnovember2017
https://www.nxtbook.com/atp/MaintenanceTechnology/epoctober2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtsept2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtaugust2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjuly2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjune2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtmay2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtapril2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtmarch2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtfebruary2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjanuary2017
https://www.nxtbook.com/atp/MaintenanceTechnology/mtdecember2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtnovember2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtoctober2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtseptember2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtaugust2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjuly2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjune2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtmay2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtapril2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtmarch2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtfebruary2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtjanuary2016
https://www.nxtbook.com/atp/MaintenanceTechnology/mtdecember2015
https://www.nxtbook.com/atp/MaintenanceTechnology/mtnovember2015
https://www.nxtbook.com/atp/MaintenanceTechnology/mtoctober2015
https://www.nxtbook.com/atp/MaintenanceTechnology/mtseptember2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTAugust2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTJuly2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTJune2015
https://www.nxtbook.com/atp/MaintenanceTechnology/M
https://www.nxtbook.com/atp/MaintenanceTechnology/0415endress
https://www.nxtbook.com/atp/MaintenanceTechnology/MTApril2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTMarch2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTFebruary2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTJanuary2015
https://www.nxtbook.com/atp/MaintenanceTechnology/MTDecember2014
https://www.nxtbook.com/atp/MaintenanceTechnology/MTNovember2014
https://www.nxtbook.com/atp/MaintenanceTechnology/MTOctober2014
https://www.nxtbook.com/atp/MaintenanceTechnology/MTSeptember2014
https://www.nxtbook.com/atp/MaintenanceTechnology/MTAugust2014
https://www.nxtbook.com/atp/MaintenanceTechnology/MTJuly2014
https://www.nxtbookmedia.com