Maximum Motor Rated Current; Current Limits; Motor Thermal Protection - Nidec Unidrive M200 User Manual

Safety Product Mechanical
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8.2

Maximum motor rated current

Size 1 to 4:
The maximum motor rated current is the Maximum Heavy Duty Current
Rating (Pr 77).
The values for the Heavy Duty rating can be found in the Power
Installation Guide.
Size 5 onwards:
The maximum motor rated current allowed by the drive is greater than
the Maximum Heavy Duty Current Rating (Pr 77). The ratio between the
Normal Duty rating and the Maximum Heavy Duty Current Rating (Pr 77)
varies between drive sizes. The values for the Normal and Heavy Duty
rating can be found in the Power Installation Guide. If the Motor Rated
Current (Pr 06) is set above the Maximum Heavy Duty Current Rating
(Pr 77), the current limits and the motor thermal protection scheme are
modified (see section 8.3 Current limits on page 54 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 torque producing current for open loop mode.
• 175 % x motor rated torque producing 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 06 /
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
Where:
I = Current Magnitude (Pr 88)
I = Motor Rated Current (Pr 06)
Rated
If Motor Rated Current (Pr 06)  Maximum Heavy Duty Current (Pr 77)
54
Electrical Getting Basic
installation started parameters
2
)]
Rated
Running the 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
base speed/
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
accumulates the temperature of the motor while the drive remains
powered-up. By default, the accumulator is set to the power down value
at power up. If the rated current defined by Pr 06 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.
Onboard Advanced
Diagnostics
PLC parameters
1.05
Base speed/
frequency
1.01
50% of Base speed/
base speed/ frequency
frequency
Unidrive M200 / M201 Control User Guide
Issue Number: 2
UL Listing
Pr 04.025 = 0
Pr 04.025 = 1
Pr 04.025 = 0
Pr 04.025 = 1