Maximum Motor Rated Current; Current Limits; Motor Thermal Protection - Emerson unidrive m200 User Manual

Safety Product Mechanical
information information installation
8.2

Maximum motor rated current

Size 1 to 4:
The maximum motor rated current is the Maximum Heavy Duty Current
Rating (11.032).
The values for the Heavy Duty rating can be found in section
2.2 Ratings on page 10.
Size 5 onwards:
The maximum motor rated current allowed by the drive is greater than
the Maximum Heavy Duty Current Rating (11.032). The ratio between
the Normal Duty rating and the Maximum Heavy Duty Current Rating
(11.032) varies between drive sizes. The values for the Normal and
Heavy Duty rating can be found in section 2.2 Ratings on page 10. If the
Motor Rated Current (00.006) is set above the Maximum Heavy Duty
Current Rating (11.032), the current limits and the motor thermal
protection scheme are modified (see section 8.3 Current limits on
page 95 and section 8.4 Motor thermal protection below for further
information).
8.3

Current limits

The default setting for the current limit parameters is:
• 165 % x motor rated current for open loop mode.
• 175 % x motor rated current for RFC-A mode.
There are three parameters which control the current limits:
• Motoring current limit: power flowing from the drive to the motor
• Regen current limit: power flowing from the motor to the drive
• Symmetrical current limit: current limit for both motoring and regen
operation
The lowest of either the motoring and regen current limit, or the
symmetrical current limit applies.
The maximum setting of these parameters depends on the values of
motor rated current, drive rated current and the power factor.
With size 5 upwards, increasing the motor rated current (Pr 00.006 /
Pr 05.007) above the Heavy Duty rating (default value), will
automatically reduce the current limits in Pr 04.005 to Pr 04.007. If the
motor rated current is then set to or below the Heavy Duty rating, the
current limits will be left at their reduced values.
The drive can be oversized to permit a higher current limit setting to
provide higher accelerating torque as required up to a maximum of
1000 %.
8.4

Motor thermal protection

A time constant thermal model is provided to estimate the motor
temperature as a percentage of its maximum allowed temperature.
The motor thermal protection is modelled using losses in the motor. The
losses in the motor are calculated as a percentage value, so that under
these conditions the Motor Protection Accumulator (04.019) would
eventually reach 100 %.
Percentage losses = 100 % x [Load related losses]
Where:
Load related losses = I / (K x I
1 Rated
Where:
I = Current Magnitude (04.001)
I = Motor Rated Current (05.007)
Rated
If Motor Rated Current (05.007) ≤ Maximum Heavy Duty Current
(11.032)
Unidrive M200 / M201 User Guide
Issue Number: 4
Electrical Getting Basic Running the
installation started parameters
2
)
NV Media
Optimization
motor Card
Figure 8-1 Motor thermal protection (Heavy Duty)
1.00 1.00
0.70
K
0.00
50% of base
speed/frequency
If Pr 04.025 is 0 the characteristic is for a motor which can operate at
rated current over the whole speed range. Induction motors with this
type of characteristic normally have forced cooling. If Pr 04.025 is 1 the
characteristic is intended for motors where the cooling effect of motor
fan reduces with reduced motor speed below 50 % of base speed/
frequency. The maximum value for K1 is 1.05, so that above the knee of
the characteristics the motor can operate continuously up to 105 %
current.
Figure 8-2 Motor thermal protection (Normal Duty)
1.00 1.00
0.70
K
0.00
15% of 50% of
base speed/ base speed/
frequency frequency
Both settings of Pr 04.025 are intended for motors where the cooling
effect of the motor fan reduces with reduced motor speed, but with
different speeds below which the cooling effect is reduced. If Pr 04.025
is 0 the characteristic is intended for motors where the cooling effect
reduces with motor speed below 15 % of base speed/frequency. If
Pr 04.025 is 1 the characteristic is intended for motors where the cooling
effect reduces with motor speed below 50 % of base speed/frequency.
The maximum value for K1 is 1.01, so that above the knee of the
characteristics the motor can operate continuously up to 101 % current
When the estimated temperature in Pr 04.019 reaches 100 % the drive
takes some action depending on the setting of Pr 04.016. If Pr 04.016 is
0, the drive trips when Pr 04.019 reaches 100 %. If Pr 04.016 is 1, the
current limit is reduced to (K - 0.05) x 100 % when Pr 04.019 reaches
100 %.
The current limit is set back to the user defined level when Pr 04.019
falls below 95 %. The thermal model temperature accumulator is reset
to zero at power-up and accumulates the temperature of the motor while
the drive remains powered-up. If the rated current defined by Pr 05.007
is altered, the accumulator is reset to zero.
The default setting of the thermal time constant (Pr 04.015) is 179 s
which is equivalent to an overload of 150 % for 120 s from cold.
Advanced
Technical data Diagnostics
parameters
1.05
Pr
Pr
Base speed/
frequency
1.01
Pr
Pr
Base speed/
frequency
UL Listing
04.025
= 0
04.025
= 1
04.025
= 0
04.025
= 1
95