5
VFD OPERATION
Special consideration must be paid
to ensure that the motor is operat-
ed within recommended guidelines
for torque and speed for the type
and size of RGZESDI motors select-
ed. Under no circumstances should
the motor be operated at frequen-
cies beyond the safe mechanical
limits shown below in this docu-
ment.
RGZESDI Constant Torque motors
provide full rated torque within their
listed speed range, without exceed-
ing their Class F temperature rating
on PWM (pulse width modulated)
inverter power. Speed ranges are
based on use with vector type IGBT
inverters, set at a minimum 3 kHz
switching frequency, and are
designed for operation at 150% of
rated torque for one minute, up to
the base speed of the motor (over-
load capacity declines as the motor
reaches maximum speed).
OPERATION
Repeated trial starts can over heat
the motor and result in motor
burnout (particularly for across the
line starting). If repeated trial starts
are made, allow sufficient time
between trials to permit heat to dis-
sipate from windings and rotor to
prevent overheating. Starting cur-
rents are several times running cur-
rents and heating varies as the
square of the current.
After installation is completed, but
before motor is put into regular ser-
vice, make an initial start as fol-
lows:
1. Check motor connections and
VFD connections against wiring
diagrams.
2. Check voltage, phase, and all
loaded drive parameters against
motor nameplate. If an auxiliary
blower is supplied, check to see
that it is wired and operating
properly. The blower should be
wired to a separate 60 hz power
source.
3. If possible, remove external load
and turn shaft by hand to ensure
free rotation. This may have
been done during installation pro-
cedure; if so, and conditions have
not changed since, this check
may not be necessary.
a. If load is disconnected, run
motor at no load long enough
to be certain that no unusual
conditions develop. Listen and
feel for excessive noise, vibra-
tion, clicking, or pounding. If
present, stop motor immedi-
ately. Investigate the cause
and correct before putting
motor in service.
b. If load is not disconnected,
interrupt the starting cycle
after motor has decelerated to
a slow speed. Carefully
observe for unusual conditions
as motor coasts to a stop.
4. When checks are satisfactory,
operate at minimum load and
look for unusual conditions.
Increase load slowly to a maxi-
mum. Check unit for satisfactory
operation.
Electric motors operating under nor-
mal conditions become quite warm.
Although some places may feel too
hot to touch, the unit may be within
operational limits. Use a thermo-
couple to measure winding temper-
ature when there is any concern.
The total temperature, not the tem-
perature rise, is the measure of
safe operation. Investigate the
operating conditions if the total
temperature measured by a ther-
mocouple placed on the winding
exceeds:
• 275°F (135°C) for class “F” insula-
tion
• 302° F(150°C) for class “H” insula-
tion
CAUTION
Electrical Overload.
May cause property damage.
To avoid the danger, guard against overloading. Overloading
causes overheating and overheating means shortened insulation
life. A motor subjected to a 10°C temperature rise above the
maximum limit for the insulation may cause the insulation life
to be reduced by 50%. To avoid overloading, be sure motor cur-
rent does not exceed nameplate current when nameplate voltage
is applied.
Maximum Safe Mechanical
Speed Limits
Direct Connected Loads
(does not imply constant horsepower
capability)
Motor
3600
1800
1200
Frame
rpm
rpm
rpm
143-184
7200
5400
2700
213-256
5400
4200
2700
284-286
5400
3600
2700
324-326
4500
3600
2700
364-365
4500
2700
2700
404-445
3600
2700
1800
447-449
3600
2250
1800
CAUTION
Electrical Overload.
May cause property damage.
To avoid damage to the motor, caution must be observed when
applying standard motors for continuous low speed, constant
torque operation. A standard motor’s self-cooling capacity
depends upon self-ventilation schemes that are greatly reduced
at decreased operating speeds.
CAUTION
Electrical Overload.
May cause property damage.
To avoid damage to the motor, it is the responsibility of the
startup personnel during commissioning of the VFD/ motor
combination to properly tune the drive to the motor for the
specific application. Application of motors which are not per
the guidelines of this document may void the warranty, if they
are not specifically approved by Siemens.
