Ground Leakage Current; Extreme Running Conditions; Motor Thermal Protection - Danfoss VLT Micro Drive FC 51 Design Manual

Product Overview
CAUTION
INSTALLATION AT HIGH ALTITUDE
At altitudes above 2000 m (6500 ft), contact Danfoss
regarding PELV.
3 3

3.4 Ground Leakage Current

WARNING
DISCHARGE TIME
Touching the electrical parts could be fatal - even after
the equipment has been disconnected from mains.
Also make sure that other voltage inputs have been
disconnected, such as load sharing (linkage of DC
intermediate circuit), and the motor connection for
kinetic back-up.
Before touching any electrical parts, wait at least the
amount of time indicated in Table 2.1.
Shorter time is allowed only if indicated on the
nameplate for the specific unit.
WARNING
LEAKAGE CURRENT HAZARD
Leakage currents exceed 3.5 mA. Failure to ground the
frequency converter properly can result in death or
serious injury.
•
Ensure the correct grounding of the equipment
by a certified electrical installer.
WARNING
RESIDUAL CURRENT DEVICE PROTECTION
This product can cause a DC current in the protective
conductor. Where a residual current device (RCD) is used
for protection in case of direct or indirect contact, only
an RCD of Type B is allowed on the supply side of this
product. Otherwise, apply another protective measure,
such as separation from the environment by double or
reinforced insulation, or isolation from the supply system
by a transformer. See also application note Protection
against Electrical Hazards.
Protective grounding of the frequency converter and the
use of RCDs must always follow national and local
regulations.

3.5 Extreme Running Conditions

Short circuit (motor phase-phase)
Current measurement in each of the 3 motor phases or in
the DC-link, protects the frequency converter against short
circuits. A short circuit between 2 output phases causes an
overcurrent in the inverter. The inverter is turned off
individually when the short circuit current exceeds the
allowed value (Alarm 16 Trip Lock).
24
®
VLT Micro Drive FC 51
For information about protecting the frequency converter
against a short circuit at the load sharing and brake
outputs, see chapter 6.6 Fuses.
Switching on the output
Switching on the output between the motor and the
frequency converter is fully permitted. The frequency
converter is not damaged in any way by switching on the
output. However, fault messages may appear.
Motor-generated overvoltage
The voltage in the DC link is increased when the motor
acts as a generator. This occurs in following cases:
•
•
•
The control unit may attempt to correct the ramp if
parameter 2-17 Over-voltage Control is enabled.
The frequency converter turns off to protect the transistors
and the DC link capacitors when a certain voltage level is
reached.
Mains drop-out
During a mains drop-out, the frequency converter keeps
running until the DC-link voltage drops below the
minimum stop level, which is typically 15% below the
frequency converter's lowest rated supply voltage. The
mains voltage before the drop-out and the motor load
determines how long it takes for the frequency converter
to coast.

3.5.1 Motor Thermal Protection

Motor thermal protection can be provided in 2 ways.
Using a motor thermistor, via 1 of the following:
•
•
•
The frequency converter monitors motor temperature as
the speed and load vary to detect overheating conditions.
The other method calculates motor temperature by
measuring current, frequency, and operating time. The
frequency converter shows the thermal load on the motor
in percentage and can issue a warning at a programmable
Danfoss A/S © 01/2016 All rights reserved.
The load drives the motor (at constant output
frequency from the frequency converter), 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 in the frequency converter,
the motor, and the installation.
Incorrect slip compensation setting
(parameter 1-62 Slip Compensation) may cause
higher DC-link voltage.
Thermistor input on a standard AI.
®
VLT Sensor Input MCB 114.
®
VLT PTC Thermistor Card MCB 112.
MG02K402