Danfoss VLT FC 103, Руководство по конструкции

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2.5.4 Mains Phase Imbalance Detection
Operation under severe mains imbalance conditions
reduces the lifetime of the motor. If the motor is operated
continuously near nominal load, conditions are considered
severe. The default setting trips the frequency converter in
case of mains imbalance (
parameter 14-12 Function at
Mains Imbalance ).
2.5.5 Switching on the Output
Adding a switch to the output between the motor and the
frequency converter is permitted. Fault messages may
appear. To catch a spinning motor, enable flying start.
2.5.6 Overload Protection
Torque limit
The torque limit feature protects the motor against
overload, independent of the speed. Torque limit is
controlled in
parameter 4-16 Torque Limit Motor Mode or
parameter 4-17 Torque Limit Generator Mode , and the time
before the torque limit warning trips is controlled in
parameter 14-25 Trip Delay at Torque Limit .
Current limit
The current limit is controlled in parameter 4-18 Current
Limit .
Speed limit
Define lower and upper limits for the operating speed
range using 1 or more of the following parameters:
•
Parameter 4-11 Motor Speed Low Limit [RPM] .
•
Parameter 4-12 Motor Speed Low Limit [Hz] and
parameter 4-13 Motor Speed High Limit [RPM] .
•
Parameter 4-14 Motor Speed High Limit [Hz] .
For example, the operating speed range can be defined as
between 30 and 50/60 Hz.
Parameter 4-19 Max Output Frequency limits the maximum
output speed the frequency converter can provide.
ETR
ETR is an electronic feature that simulates a bimetal relay
based on internal measurements. The characteristic is
shown in
Illustration 2.15 .
Voltage limit
When a certain hard-coded voltage level is reached, the
frequency converter turns off to protect the transistors and
the DC link capacitors.
Overtemperature
The frequency converter has built-in temperature sensors
and reacts immediately to critical values via hard-coded
limits.
2.5.7 Automatic Derating
The frequency converter constantly checks for critical
levels:
•
High temperature on the control card or heat sink
•
High motor load
•
High DC-link voltage
•
Low motor speed
As a response to a critical level, the frequency converter
adjusts the switching frequency. For high internal temper-
atures and low motor speed, the frequency converters can
also force the PWM pattern to SFAVM.
NOTICE
The automatic derating is different when
parameter 14-55 Output Filter is set to [2] Sine-Wave Filter
Fixed .
2.5.8 Automatic Energy Optimisation
Automatic energy optimisation (AEO) directs the frequency
converter to monitor the load on the motor continuously
and adjust the output voltage to maximise efficiency.
Under light load, the voltage is reduced and the motor
current is minimised. The motor benefits from:
•
Increased efficiency.
•
Reduced heating.
•
Quieter operation.
There is no need to select a V/Hz curve because the
frequency converter automatically adjusts motor voltage.
2.5.9 Automatic Switching Frequency
Modulation
The frequency converter generates short electrical pulses
to form an AC wave pattern. The switching frequency is
the rate of these pulses. A low switching frequency (slow
pulsing rate) causes audible noise in the motor, making a
higher switching frequency preferable. A high switching
frequency, however, generates heat in the frequency
converter which can limit the amount of current available
to the motor.
Automatic switching frequency modulation regulates these
conditions automatically to provide the highest switching
frequency without overheating the frequency converter. By
providing a regulated high switching frequency, it quiets
motor operating noise at slow speeds, when audible noise
control is critical, and produces full output power to the
motor when required.
Product Overview Design Guide
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