5 Product Features
5.1 Automated Operational Features
Automated operational features are active when the drive
is operating. Most of them require no programming or set-
up. The drive has a range of built-in protection functions
to protect itself and the motor when it runs.
For details of any set-up required, in particular motor
parameters, refer to the
programming guide
.
5.1.1 Short-circuit Protection
Motor (phase-to-phase)
The drive is protected against short circuits on the motor
side by current measurement in each of the 3 motor
phases. A short circuit between 2 output phases causes an
overcurrent in the inverter. The inverter is turned off when
the short circuit current exceeds the allowed value (
Alarm
16, Trip Lock
).
Mains side
A 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 if
there is component break-down inside the drive (1
st
fault).
Mains side fuses are mandatory for UL compliance.
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 drive is protected from a short circuit in the brake
resistor.
Load sharing
To protect the DC bus against short circuits and the drives
from overload, install DC fuses in series with the load
sharing terminals of all connected units.
5.1.2 Overvoltage Protection
Motor-generated overvoltage
The voltage in the DC link is increased when the motor
acts as a generator. This situation occurs in following cases:
•
The load rotates the motor at constant output
frequency from the drive, that is, the load
generates energy.
•
During deceleration (ramp-down) if the inertia
moment is high, the friction is low, and the ramp-
down time is too short for the energy to be
dissipated as a loss throughout the drive system.
•
Incorrect slip compensation setting causing
higher DC-link voltage.
•
Back EMF from PM motor operation. If coasted at
high RPM, the PM motor back EMF can
potentially exceed the maximum voltage
tolerance of the drive and cause damage. To help
prevent this situation, the value of
parameter 4-19 Max Output Frequency
is automat-
ically limited based on an internal calculation
based on the value of
parameter 1-40 Back EMF at
1000 RPM
,
parameter 1-25 Motor Nominal Speed
,
and
parameter 1-39 Motor Poles
.
NOTICE
To avoid motor overspeeds (for example, due to
excessive windmilling effects), equip the drive with a
brake resistor.
The overvoltage can be handled either using a brake
function (
parameter 2-10 Brake Function
) and/or using
overvoltage control (
parameter 2-17 Over-voltage Control
).
Brake functions
Connect a brake resistor for dissipation of surplus brake
energy. Connecting a brake resistor allows a higher DC-link
voltage during braking.
AC brake is an alternative to improving braking without
using a brake resistor. This function controls an over-
magnetization of the motor when the motor is acting as a
generator. Increasing the electrical losses in the motor
allows the OVC function to increase the braking torque
without exceeding the overvoltage limit.
NOTICE
AC brake is not as effective as dynamic braking with a
resistor.
Overvoltage control (OVC)
By automatically extending the ramp-down time, OVC
reduces the risk of the drive tripping due to an
overvoltage on the DC-link.
NOTICE
OVC can be activated for a PM motor with all control
core, PM VVC
+
, Flux OL, and Flux CL for PM Motors.
NOTICE
Do not enable OVC in hoisting applications.
Product Features
Design Guide
MG38C202
Danfoss A/S © 01/2018 All rights reserved.
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