10/05 AWB8230-1541GB
Connection to power supply
19
Residual current circuit-breakers
To protect persons and domestic animals, residual current circuit-
breakers (RCCBs; also called earth-leakage circuit breakers or
ELCBs) must be used. For the protection of persons, systems with
frequency inverters must be fitted with universal current sensitive
ELCBs conforming to EN 50178 and IEC 755.
The Frequency inverters contain a built-in mains rectifier. On a
frame fault, this can cause a fault DC to inhibit tripping of the AC
or pulse-current sensitive residual-current circuit-breaker, thereby
preventing it from fulfilling its protective function. We therefore
recommend the use of:
• pulse-current sensitive RCCBs with a rated fault current f
30 mA for frequency inverters with a single-phase supply;
• universal RCCBs with a rated fault current f 300 mA for
frequency inverters with a three-phase supply.
The approximate fault current values of the DF51 frequency
inverters and their assigned radio interference filters are listed in
the appendix, paragraph “RFI filters”, page 208.
Spurious tripping of a residual-current circuit breaker can be
caused by the following:
• capacitive compensation currents in the cable screens,
particularly with long, screened motor cables,
• simultaneous connection of multiple frequency inverters to the
mains supply,
• the use of additional chokes and filters (radio interference
filters, line filters).
Mains contactor
The mains contactor is connected to the mains side input cables
L1, L2, L3 or L and N (depending on its type). and allows the DF51
frequency inverter on the supplying network to be switched on and
off during operation and to be disconnected in the event of a fault.
Mains contactors and their assignment to the DF51 frequency
inverters are listed in the appendix, paragraph “Mains
contactors”, page 210.
Current peaks
In the following cases, a relatively high peak current can occur on
the primary side of the frequency inverter (i.e. on the supply
voltage side), which, under certain conditions, can destroy the
frequency inverter’s input rectifier:
• Imbalance of the voltage supply greater than 3 %.
• The maximum power output of the point of supply must be at
least 10 times greater than the maximum frequency inverter
rating (about 500 kVA).
• If sudden voltage dips in the supply voltage are to be expected,
for example when:
– a number of frequency inverters are operated on a common
supply voltage.
– a thyristor system and a frequency inverter are operated on a
common supply voltage
– power factor correction devices are switched on or off
In these cases, a mains choke with about 3 % voltage drop at
rated operation should be installed.
Line reactor
The line reactor (also called commutating or mains choke) is
connected to the mains side input cables L1, L2 and L3, or L and N
(depending on type). It reduces the harmonics and therefore cuts
the apparent mains current by up to 30 %.
A mains reactor also limits any current peaks caused by potential
dips (for example caused by p.f. correction equipment or earth
faults) or switching operations on the mains.
The mains reactor increases the lifespan of the DC link capacitors
and consequently the lifespan of the frequency inverter. Its use is
also recommended in the following cases:
• with single-phase supplies (DF51-322),
• with derating (temperatures above +40 °C, sites of installation
more than 1000 m above sea level),
• for parallel operation of multiple frequency inverters on a single
mains supply point,
• for DC link coupling of multiple frequency inverters
(interconnected operation).
Mains chokes and their assignment to the DF51 frequency
inverters are listed in the appendix, paragraph “Line reactors”,
page 212.
Identification on the residual-current circuit-breakers
Logo
Type Alternating-
current sensitive
(RCD, Type AC)
Pulse-current
sensitive
(RCD, Type A)
universal current
sensitive
(RCD, Type B)
Caution!
Residual-current circuit breakers must be installed only on
the primary side between the incoming supply and the
frequency inverter.
Warning!
Use only cables, residual-current circuit-breakers and
contactors with the permissible rating. Otherwise there is
a danger of fire.
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