Specifications

An alternative is to lower the ambient temperature at high
altitudes and thereby ensure 100% output current at high
altitudes. As an example of how to read the graph, the
situation at 2 km is elaborated. At a temperature of 45 °C
(T
AMB, MAX
- 3.3 K), 91% of the rated output current is
available. At a temperature of 41.7 °C, 100% of the rated
output current is available.
80
0 500
100
95
90
85
1000 1500 2000 2500 3000
Altitude (meters above sea level)*
130BB008.10
I
OUT
(%)
Illustration 8.4 Derating of Output Current Versus Altitude at
T
AMB, MAX
0 500 1000 1500 2000 2500 3000
Altitude (meters above sea level)*
30
35
40
45
(°C)
Amb. Temp.
130BB009.10
HO
NO
Illustration 8.5 Derating of Output Current Versus Altitude at
T
AMB, MAX
8.5.5 Derating for Running at Low Speed
When a motor is connected to a frequency converter, it is
necessary to check that the cooling of the motor is
adequate.
The level of heating depends on the load on the motor, as
well as the operating speed and time.
Constant torque applications (CT mode)
A problem may occur at low RPM values in constant
torque applications. A motor may overheat at low speeds
due to less cooling air from the motor integral fan.
If the motor runs continuously at an RPM value lower than
half of the rated value, additional air-cooling is needed. A
motor designed for this type of operation may also be
used.
An alternative is to reduce the load level of the motor by
selecting a larger motor. However, the design of the
frequency converter puts a limit to the motor size.
Variable (Quadratic) Torque Applications (VT)
In VT applications such as centrifugal pumps and fans,
where the torque is proportional to the square of the
speed and the power is proportional to the cube of the
speed, there is no need for additional cooling or derating
of the motor.
In Illustration 8.6, the typical VT curve is below the
maximum torque with de-rating and maximum torque
with forced cooling at all speeds.
102030405060 70 8090100 110
20
40
60
80
100
120
0
v %
T %
0
1)
130BA893.10
Illustration 8.6 Maximum Load for a Standard Motor at 40 °C
Driven by a Frequency Converter
─ ─ ─ ─
Typical torque at VT load
─•─•─•─
Max torque with forced cooling
‒‒‒‒‒
Max torque
Note 1) Over-syncronous speed operation will result in the
available motor torque decreasing inversely proportional with
the increase in speed. This must be considered during the
design phase to avoid over-loading of the motor.
Table 8.16 Legend to Illustration 8.6
8.6 Troubleshooting
A warning or alarm is signalled by the relevant LED on the
front of the frequency converter and indicated by a code
on the display.
A warning remains active until its cause is terminated.
Under certain circumstances, operation of the motor may
still continue. Warning messages are sometimes critical,
but not always.
In the event of an alarm, the frequency converter trips.
Reset alarms to restart operation once their cause has
been rectified.
General Specifications and ... VLT® HVAC Drive FC 102 Design Guide
198 MG16C102 - Rev. 2013-08-20
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