Missing Motor Phase Detection; Line Phase Imbalance Detection; Switching On The Output; Overload Protection - Danfoss VLT AQUA Drive FC 202 Design Manual

Product Overview
Overvoltage control (OVC)
OVC reduces the risk of the adjustable frequency drive
tripping due to an overvoltage on the DC link. This is
managed by automatically extending the ramp-down time.
NOTICE!
OVC can be activated for PM motors (PM VVC
Brake functions
Connect a brake resistor for dissipation of surplus brake
energy. Connecting a brake resistor prevents excessively
high DC link voltage during braking.
An AC brake is an alternative to improve braking without
using a brake resistor. This function controls an overmag-
netization of the motor when running as a generator
creating extra energy. This function can improve the OVC.
Increasing the electrical losses in the motor allows the OVC
function to increase the braking torque without exceeding
the overvoltage limit.
NOTICE!
AC braking is not as effective as dynamic braking with a
resistor.

2.5.3 Missing Motor Phase Detection

The missing motor phase function (4-58 Missing Motor Phase
Function) is enabled by default to avoid motor damage in
the case that a motor phase is missing. The default setting
is 1000 ms, but it can be adjusted for a faster detection.

2.5.4 Line Phase Imbalance Detection

Operation under severe line power imbalance conditions
reduces the lifetime of the motor. Conditions are
considered severe if the motor is operated continuously
near nominal load. The default setting trips the adjustable
frequency drive in case of line imbalance (14-12 Function at
Mains Imbalance).

2.5.5 Switching on the Output

Adding a switch to the output between the motor and the
adjustable frequency drive 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 4-16 Torque Limit Motor Mode or 4-17 Torque
Limit Generator Mode and the time before the torque limit
MG20N622
Design Guide
warning trips is controlled in 14-25 Trip Delay at Torque
Limit.
Current limit
The current limit is controlled in 4-18 Current Limit.
Speed limit
Define lower and upper limits for the operating speed
+
).
range using the following parameters:
•
•
•
For example, the operating speed range can be defined as
between 30 and 50/60 Hz.
4-19 Max Output Frequency limits the maximum output
speed the adjustable frequency drive can provide.
ETR
ETR is an electronic feature that simulates a bimetal relay
based on internal measurements. The characteristic is
shown in Figure 2.18.
Voltage limit
The adjustable frequency drive turns off to protect the
transistors and the DC link capacitors when a certain hard-
coded voltage level is reached.
Overtemperature
The adjustable frequency drive has built-in temperature
sensors and reacts immediately to critical values via hard-
coded limits.

2.5.7 Automatic Derating

The adjustable frequency drive constantly checks for
critical levels:
•
•
•
•
As a response to a critical level, the adjustable frequency
drive adjusts the switching frequency. For high internal
temperatures and low motor speed, the adjustable
frequency drives can also force the PWM pattern to SFAVM.
NOTICE!
The automatic derating is different when 14-55 Output
Filter is set to [2] Sine-Wave Filter Fixed.
Danfoss A/S © 09/2014 All rights reserved.
4-11 Motor Speed Low Limit [RPM] or
4-12 Motor Speed Low Limit [Hz] and 4-13 Motor
Speed High Limit [RPM], or
4-14 Motor Speed High Limit [Hz]
High temperature on the control card or heatsink
High motor load
High DC link voltage
Low motor speed
2 2
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