Danfoss VLT 380-500 V Design Manual page 18

Product Features
Power
kW (hp)
250 (300)
315 (350)
355 (400)
400 (400)
500 (500)
560 (600)
630 (650)
710 (750)
800 (950)
5 5
900 (1050)
1000 (1150)
Table 5.2 Carrier Frequency Operational Ranges for 525–690 V
5.1.4 Automatic Derating for
Overtemperature
Automatic overtemperature derating works to prevent
tripping the frequency converter at high temperature.
Internal temperature sensors measure conditions to protect
the power components from overheating. The frequency
converter can automatically reduce its carrier frequency to
maintain its operating temperature within safe limits. After
reducing the carrier frequency, the frequency converter
can also reduce the output frequency and current by as
much as 30% to avoid an overtemperature trip.
5.1.5 Auto Ramping
A motor trying to accelerate a load too quickly for the
current available can cause the frequency converter to trip.
The same is true for too quick of a deceleration. Auto
ramping protects against this scenario by extending the
motor ramping rate (acceleration or deceleration) to match
the available current.
5.1.6 Current Limit Control
If a load exceeds the current capability of the frequency
converter normal operation (from an undersized frequency
converter or motor), current limit reduces the output
frequency to slow the motor and reduce the load. An
adjustable timer is available to limit operation in this
condition for 60 s or less. The factory default limit is 110%
of the rated motor current to minimize overcurrent stress.
5.1.7 Short-circuit Protection
The frequency converter provides inherent short-circuit
protection with a fast acting fault-trip circuit. Current is
measured in each of the 3 output phases. After 5–10 ms, if
the current exceeds the permitted value, all transistors in
the inverter turn off. This circuit provides the most rapid
current sensing and the greatest protection against
16
®
VLT Parallel Drive Modules
Switching frequency
Hz
3000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
Danfoss A/S © 6/2016 All rights reserved.
Minimum Maximum
Hz Hz
2000 8000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
1500 6000
nuisance trips. A short circuit between 2 output phases can
cause an overcurrent trip.
5.1.8 Ground Fault Protection
After receiving feedback from current sensors, the control
circuitry sums up the 3-phase currents from each drive
module. If the sum of all 3 output phase currents is not 0,
it indicates a leakage current. If the deviation from 0
exceeds a predetermined amount, the frequency converter
issues a ground fault alarm.
5.1.9 Power Fluctuation Performance
The frequency converter withstands mains fluctuations
such as
•
Transients.
•
Momentary dropouts.
•
Short voltage drops.
•
Surges.
The frequency converter automatically compensates for
input voltages ±10% from the nominal to provide full rated
motor voltage and torque. With auto restart selected, the
frequency converter automatically powers up after a
voltage trip. And with flying start, the frequency converter
synchronizes to motor rotation before starting.
5.1.10 Motor Soft Start
The frequency converter supplies the right amount of
current to the motor to overcome load inertia and bring
the motor up to speed. This action avoids full mains
voltage being applied to a stationary or slow turning
motor, which generates high current and heat. This
inherent soft start feature reduces thermal load and
mechanical stress, extends motor life, and provides quieter
system operation.
Factory Setting
Hz
3000
2000
2000
2000
2000
2000
2000
2000
2000
2000
2000
MG37N102