Danfoss VLT DriveMotor FCM 106, Design Manual

Page: 34 / 66

3.5.5 Extreme Running Conditions
Short Circuit (Motor Phase – Phase)
The frequency converter is protected against short circuits
by current measurement in each of the 3 motor phases or
in the DC link. A short circuit between 2 output phases
causes an overcurrent in the inverter. The inverter turns off
when the short circuit current exceeds the permitted value
(Alarm 16 Trip Lock).
Switching on the Output
Switching on the output between the motor and the
frequency converter is permitted. Fault messages can
appear. To catch a spinning motor, enable flying start.
Motor generated overvoltage
The voltage in the intermediate circuit is increased when
the motor acts as a generator. This voltage increase occurs
in the following cases:
1. The load drives the motor at constant output
frequency from the frequency converter. That is,
the load generates energy.
2. During deceleration ("ramp-down") when the
moment of inertia is high, the friction is low, and
the ramp-down time is too short for the energy
to be dissipated as a loss in the frequency
converter, the motor, and the installation.
3. Incorrect slip compensation setting can cause
higher DC link voltage.
4. Back-EMF from PM motor operation. When
coasted at high RPM, the PM motor back-EMF can
potentially exceed the maximum voltage
tolerance of the frequency converter and cause
damage. To help prevent this risk of damage, the
value of
4-19 Max Output Frequency is automat-
ically limited based on an internal calculation,
based on the values of
•
1-40 Back EMF at 1000 RPM ,
•
1-25 Motor Nominal Speed
•
1-39 Motor Poles .
When the motor risks overspeed (for example,
due to excessive windmilling effects) then use of
a brake resistor is recommended.
The control unit can attempt to correct the ramp
(
2-17 Over-voltage Control ).
The inverter turns off to protect the transistors and the
intermediate circuit capacitors when a certain voltage level
is reached.
Select the method used for controlling the intermediate
circuit voltage level via
•
2-10 Brake Function and
•
2-17 Over-voltage Control
NOTICE
OVC cannot be activated when running a PM motor (that
is, when
1-10 Motor Construction is set to [1] PM non-
salient SPM ).
Mains Drop-out
During a mains drop-out, the frequency converter keeps
running until the DC-link voltage drops below the
minimum stop level. The minimum stop level is typically
15% below the lowest rated supply voltage of the
frequency converter. The mains voltage before the drop-
out and the motor load determines how long it takes for
the inverter to coast.
Static Overload in VVC plus mode
When the frequency converter is overloaded, the control
reduces the output frequency to reduce the load.
If the overload is excessive, a current can occur that makes
the frequency converter cut out after approx. 5–10s.
3.6 Ambient Conditions
3.6.1 Humidity
Although the frequency converter can operate properly at
high humidity (up to 95% relative humidity), condensation
must always be avoided. There is a specific risk of conden-
sation when the frequency converter is colder than moist
ambient air. Moisture in the air can also condense on the
electronic components and cause short circuits. Conden-
sation occurs to units without power. It is advisable to
install a cabinet heater when condensation is possible due
to ambient conditions. Avoid installation in areas subject
to frost.
Alternatively, operating the frequency converter in stand-
by mode (with the unit connected to the mains) reduces
the risk of condensation. However, ensure the power
dissipation is sufficient to keep the frequency converter
circuitry free of moisture.
The frequency converter complies with the following
standards:
•
IEC/EN 60068-2-3, EN 50178 9.4.2.2 at 50
°
C
•
IEC600721 class 3K4
3.6.2 Temperature
Minimum and maximum ambient temperature limits are
specified for all frequency converters. Avoiding extreme
ambient temperatures prolongs the life of the equipment
System Integration
VLT
®
DriveMotor FCP 106 and FCM 106 Design Guide
32 MG03M102 - 08/2015
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