15
Information
Variable Speed Operation
VARIABLE SPEED INFORMATION
LEESON Electric and Lincoln Motors Vector-Duty and
Inverter Duty motors, unless otherwise stated, are rated for
continuous operation in a 40°C ambient and for altitudes up to
3300 feet (1000 meters) above sea level. Special application
considerations, such as high or low ambient, intermittent
ratings, high altitude, duty cycle rated, extended constant
horsepower range, special base speed, voltage or frequency, or
any other special requirements, should be reviewed by a factory
representative.
It is the responsibility of the startup personnel during commis-
sioning of the VFD/motor system to properly tune the drive to
the motor for the specific application. The correct voltage boost
and volts/hertz settings are application dependent and unique
to each motor design. Procedures for these adjustments should
be in your VFD user manual. Many Vector Duty and Inverter Duty
motors in this catalog are equipped with thermostats; warranty
coverage may be denied if they are not properly utilized.
Power factor correction capacitors should
never be installed between the drive and
the motor.
INVERTER DUTY OR INVERTER RATED
“Inverter Duty” (often called “Inverter Rated”) motors are suitable
for use with Variable Frequency Drives, as long as operation
is within the application guidelines published in this catalog.
In general, LEESON Electric and Lincoln Motors’ three phase,
general purpose, NEMA Design B motors are considered
“Inverter Duty”, and meet or exceed the requirements of NEMA
MG1, Part 30. As required under Federal law, these motors
comply with EISA2007 efficiencies when operating from utility
power.
Inverter Duty (Rated) motors are most often used in 10:1 speed
range, variable torque or constant torque applications. A vector
control is usually required for operation beyond 10:1 CT.
Refer to “Guidelines for Application of General Purpose, Single
Speed Three Phase Motors on Variable Frequency Drives” in
this section of this catalog for the allowable speed range and
cable length restrictions (from VFD to motor). Additional detail
regarding a specific product’s capabilities is available on its
catalog page, or by consulting your application engineer.
VECTOR DUTY
–
“Vector Duty” describes a class of motors
that are used in conjunction with Open- (without encoder) or
Closed-Loop (with encoder) Vector controls, that provide
enhanced performance under low speed operating conditions,
or in cases where torque (rather than speed) must be controlled.
“Vector Duty” motors can be applied to Volts/Hertz (scalar)
drives, as well.
LEESON Electric’s Speedmaster
®
motors and Lincoln Motors’
CTAC Motors, have been specifically designed for optimal
operation on vector or volts/hertz controls. These motors feature
a wide constant torque (up to 2000:1) and/or constant horse-
power (up to 4:1) speed range and are performance-matched
to all current technology IGBT drives. Vector Duty motors meet
or exceed the requirements of NEMA MG1, Part 31, and are
equipped with an enhanced insulation system (IRIS or Ultimate
Spike Defense) to provide many years of trouble-free service.
Consult the catalog page for each product’s capabilities and
features. As these motors are specifically designed for operation
through an inverter, they are exempt from EISA2007.
VARIABLE TORQUE LOADS
– Applications include fans,
blowers and centrifugal pumps. Torque varies as the square of
the speed, and horsepower as the cube of the speed. Operation
below base speed significantly lightens the load on the motor.
While most variable torque applications do not require the
motor to operate below half speed, the motor is fully capable of
operation to zero speed. Operation above base speed
significantly adds to the load on the motor; therefore, a factory
representative must review applications requiring variable torque
above base speed. Refer to the application chart found on page
14 for use of general purpose three phase motors on variable
frequency drives. A bypass circuit is often employed in Variable
Torque applications. If this device is intended to be used,
selection of a NEMA Design B motor is recommended, to
withstand the inrush current during across-the-line starting.
CONSTANT TORQUE LOADS
– Applications include conveyors,
elevators, hoists, extruders, positive displacement pumps, mixers
and converting equipment. Torque remains constant throughout
the range of operation, and extra care should be taken in the
proper application of motors, especially at very low speeds. Most
constant torque applications don’t require operation below 10:1
(i.e. 6 Hz operation on a 60 Hz motor), but an increasing number
of applications historically reserved for servo and/or stepper
systems are being served with motors capable of operation
beyond 20:1…even up to 2000:1 (zero speed, constant torque).
Refer to the application chart found on page 14 for use of general
purpose three phase motors on variable frequency drives.
Applications requiring greater than 20:1 C.T. are ideal for
LEESON Speedmaster
®
Inverter Duty/Vector Duty and Lincoln
Vector Duty CTAC
®
motors. These motors provide full rated
torque within their listed speed range, without exceeding a Class
F temperature rating while under inverter power (many operate at
Class B). Ratings in this catalog have been developed, based
on extensive testing on IGBT inverters, set at a minimum 3 KHz
(or equivalent) carrier frequency.
Vector Duty and Inverter Duty motors from LEESON Electric and
Lincoln Motors are designed for operation at 150% of rated load
for one minute, up to the base speed of the motor (overload
capability declines to 100% as the motor reaches maximum
constant HP speed). These motors accommodate constant
horsepower operation to 1-1/2 to 2 times base speed, subject to
the motor’s maximum safe mechanical speed limit. Refer to the
Maximum Safe Mechanical Speed Chart, as well as the perfor-
mance section for each motor’s capability.
Motors rated for zero RPM continuous duty (1000:1 or 2000:1)
must be powered by vector drives to produce rated torque
without overheating. Optimum zero speed and low-speed full
torque performance may require a closed loop vector drive (with
encoder feedback).
Continued on next page.
