Earth Leakage Current; Extreme Running Conditions - Danfoss VLT HVAC Basic Drive FC 101 Design Manual

Product Overview
30–90 kW (40–120 hp)
4 1
5
a
1 Supply (SMPS) including signal isolation of UDC, indicating
the intermediate current voltage
2 Gate drive that runs the IGBTs (trigger transformers/opto-
couplers)
3 Current transducers
4 Internal soft-charge, RFI, and temperature measurement
circuits
5 Custom relays
a Control card terminals
Illustration 3.55 Galvanic Isolation
The functional galvanic isolation (see Illustration 3.54) is for
the RS485 standard bus interface.
CAUTION
INSTALLATION AT HIGH ALTITUDE
At altitudes above 2000 m (6500 ft), contact Danfoss
regarding PELV.

3.6 Earth 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-link),
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.
MG18C702
Design Guide
3
M
2
Danfoss A/S © 04/2016 All rights reserved.
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.

3.7 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).
For information about protecting the frequency converter
against a short circuit at the load sharing and brake
outputs, see chapter 8.3.1 Fuses and Circuit Breakers.
Switching on the output
Switching on the output between the motor and the
frequency converter is allowed. 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 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.
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