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Unidrive M702 User Guide 11
Issue Number: 3
2.3 Ratings
The drive is dual rated.
The setting of the motor rated current determines which rating applies -
Heavy Duty or Normal Duty.
The two ratings are compatible with motors designed to IEC60034.
The graph aside illustrates the difference between Normal Duty and
Heavy Duty with respect to continuous current rating and short term
overload limits.
Normal Duty Heavy Duty (default)
For applications which use Self ventilated (TENV/TEFC) induction
motors and require a low overload capability, and full torque at low
speeds is not required (e.g. fans, pumps).
Self ventilated (TENV/TEFC) induction motors require increased
protection against overload due to the reduced cooling effect of the fan
at low speed. To provide the correct level of protection the I
2
t software
operates at a level which is speed dependent. This is illustrated in the
graph below.
The speed at which the low speed protection takes effect can be
changed by the setting of Low Speed Thermal Protection Mode
(04.025). The protection starts when the motor speed is below 15 % of
base speed when Pr 04.025 = 0 (default) and below 50 % when
Pr 04.025 = 1.
For constant torque applications or applications which require a high
overload capability, or full torque is required at low speeds (e.g. winders,
hoists).
The thermal protection is set to protect force ventilated induction motors
and permanent magnet servo motors by default.
N
If the application uses a self ventilated (TENV/TEFC) induction motor
and increased thermal protection is required for speeds below 50 %
base speed, then this can be enabled by setting Low Speed Thermal
Protection Mode (04.025) = 1.
Operation of motor I
2
t protection
Motor I
2
t protection is fixed as shown below and is compatible with:
• Self ventilated (TENV/TEFC) induction motors
Motor I
2
t protection defaults to be compatible with:
• Forced ventilation induction motors
• Permanent magnet servo motors
Heavy Duty
Maximum
continuous
current (above
50% base
speed) -
Normal Duty
Maximum
continuous
current -
Heavy Duty
Motor rated
current set
in the drive
Heavy Duty
- with high
overload capability
Normal Duty
Motor total
current (Pr 04.001)
as a percentage
of motor rated
current
Motor speed as a
percentage of base speed
100%
Max. permissible
continuous
current
100%
I t protection operates in this region
2
70%
50%15%
Pr = 0
Pr = 1
04.025
04.025
Motor total
current (Pr 04.001)
as a percentage
of motor rated
current
Motor speed as a
100%
Max. permissible
continuous
current
100%
I t protection operates in this region
2
70%
50%
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