Automated Operational Functions; Short Circuit Protection; Overvoltage Protection; Mg20N622 - Danfoss VLT AQUA Drive FC 202 Design Manual

Product Overview
Feedback conversion
2 2
In some applications, it is useful to convert the feedback
signal. One example is using a pressure signal to provide
flow feedback. Since the square root of pressure is propor-
tional to flow, the square root of the pressure signal yields
a value proportional to the flow, see Figure 2.17.
Figure 2.17 Feedback Conversion

2.5 Automated Operational Functions

Automated operational features are active as soon as the
adjustable frequency drive is operating. Most of them
require no programming or set-up. Understanding that
these features are present can optimize a system design
and possibly avoid introducing redundant components or
functionality.
For details of any set-up required, in particular motor
parameters, refer to the Programming Guide.
The adjustable frequency drive has a range of built-in
protection functions to protect itself and the motor it is
running.

2.5.1 Short Circuit Protection

Motor (phase-phase)
The adjustable frequency drive is protected against short
circuits on the motor side by current measurement in each
of the three motor phases or in the DC link. A short circuit
between two output phases causes an overcurrent in the
inverter. The inverter is turned off when the short circuit
current exceeds the permitted value (Alarm 16 Trip Lock).
Line power side
An adjustable frequency drive that works correctly limits
the current it can draw from the supply. Still, it is
recommended to use fuses and/or circuit breakers on the
supply side as protection in case of component break-
down inside the adjustable frequency drive (first fault). See
chapter 7.7 Fuses and Circuit Breakers for more information.
26
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VLT AQUA Drive FC 202
NOTICE!
To ensure compliance with IEC 60364 for CE or NEC 2009
for UL, it is mandatory to use fuses and/or circuit
breakers.
Brake resistor
The adjustable frequency drive is protected from a short
circuit in the brake resistor.
Load sharing
To protect the DC bus against short circuits and the
adjustable frequency drives from overload, install DC fuses
in series with the load sharing terminals of all connected
units. See chapter 2.3.5 Load Sharing for more information.

2.5.2 Overvoltage Protection

Motor-generated overvoltage
The voltage in the intermediate circuit is increased when
the motor acts as a generator. This occurs in the following
cases:
•
•
•
•
NOTICE!
To avoid motor overspeeding (for example, due to
excessive windmilling effects or uncontrolled water flow),
equip the adjustable frequency drive with a brake
resistor.
The overvoltage can handled by either using a brake
function (2-10 Brake Function) or using overvoltage control
(2-17 Over-voltage Control).
Danfoss A/S © 09/2014 All rights reserved.
The load drives the motor (at constant output
frequency from the adjustable frequency drive),
for example, the load generates energy.
During deceleration (ramp-down) if 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 adjustable frequency
drive, the motor, and the installation.
Incorrect slip compensation setting may cause
higher DC link voltage.
Back EMF from PM motor operation. If coasted at
high RPM, the PM motor back EMF may
potentially exceed the maximum voltage
tolerance of the adjustable frequency drive and
cause damage. To help prevent this, the value of
4-19 Max Output Frequency is automatically
limited via an internal calculation based on the
value of 1-40 Back EMF at 1000 RPM, 1-25 Motor
Nominal Speed, and 1-39 Motor Poles.

MG20N622