Parameters
92 M-Max Series Adjustable Frequency Drive MN04020003E—October 2013 www.eaton.com
Motor Heat Protection (P8.6–P8.9)
The motor temperature protection is based on a calculated
temperature model and uses the motor current set in
parameter P7.1 to determine the motor load. It does not use
a temperature measurement in the motor.
The calculated temperature model cannot protect the motor
if the cooling flow to the motor is influenced, for example, by
a blocked air entry-way.
The temperature model is based on the assumption that the
motor achieves a winding temperature of 284°F (140°C) at
rated speed and an ambient temperature of 104°F (40°C),
with 105% rated load.
The cooling efficiency, without external cooling, is a function
of the speed (corresponding with the output frequency of the
frequency inverter). When the motor is stationary (zero
frequency), heat is also dissipated through the housing surface.
When the motor is under a great load, the current required by
the motor can be higher than the rated operational current.
The current provided by the frequency inverter can be higher
than the rated operational current of the motor. If the load
requires this much current, there is a danger of a thermal
overload. This is especially the case at lower frequencies
(<25 Hz). Here, the cooling effect (speed of the motor fan)
and the load rating of the motor (see data sheet of the motor)
are reduced similarly with lower frequencies. On motors that
are equipped with an external fan, there is less of a load
reduction at lower speeds.
With parameters P8.6 to P8.9, a motor temperature protection
can be set for the M-Max frequency inverter which protects
the motor from overheating. The temperature protection is
calculated. A direct temperature measuring in the windings
of the motor (see thermistor protection) offers great protection.
The reaction of the M-Max frequency inverter to a
detected thermal overload can be set via parameter P8.6.
At parameter P8.8 you can set the cooling output (P
Cool
)
on the motor at zero frequency (standstill). Note the
specifications of the motor manufacturer.
Possible setting values are 0–150% of the cooling output at
the rated frequency f
N
(see nameplate of the motor = P7.6).
If the protection function is deactivated (P8.6 = 0), the
temperature model of the motor is reset to zero.
The thermal current I
th
corresponds with the load current at
maximum thermal load rating on the motor. In continuous
operation, at rated frequency (f
N
= P7.6) and rated loading,
the value of I
th
corresponds with the rated operational
current of the motor (see the motor rating plate = P7.1).
Motor Cooling Power
The time constant for the motor temperature (P8.9) defines
how long it takes until the temperature has achieved 63% of
its end value in the motor. In practice, this temperature time
is constant depending on the type and design of the motor. It
varies between the different design sizes at the same shaft
power and between the different motor manufacturers.
The larger a motor is, the greater the time constant. The
factory set value (P8.9 = 45 min) can be set in the range
between 1 and 200 minutes. The guide value is twice t
6
time
of a motor. The t
6
time defines the time in seconds in which
a motor can be operated safely at six times the rated
operational current (see data sheet of the motor,
manufacturer specifications).
If the drive is stopped, the time constant is increased
internally to three times the set parameter value (P8.9).
Calculation of Motor Temperature
Notes
Motor current I/I
T
.
Trip value shut-off (error message) or warning according to P8.6.
Calculated value for the motor temperature Q = (I/I
T
)
2
x (1 - e
-t/T
).
Motor temperature
M
(example).
P8.9 = Motor temperature time constant (T).
P7.6
f
N
P8.8
100%
150%
P
Cool
P7.1
I
th
f (Hz)
t
105%
P8.9
P8.6
M
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