Chapter 2.1.1. – 3
EATON CORPORATION
xxxxx+xxxx-xxxxEN
Residual Current Devices
Hints for the application of our frequency converter-proof RCDs:
Frequency converters are used in a wide variety of systems and equip-
ment requiring variable speed, such as lifts, escalators, conveyor
belts, and large washing machines. Using them for such purposes in
circuits with conventional residual current devices causes frequent
problems with unwanted tripping.
The technical root cause of this phenomenon is the following: Fast
switching operations involving high voltages cause high interference
levels which propagate through the lines on the one hand, and in the
form of interfering radiation on the other. In order to eliminate this
problem, a mains-side filter (also referred to as input filter or EMC-fil-
ter) is connected between the RCD and frequency converter. The anti-
interference capacitors in the filters produce discharge currents
against earth which may cause unwanted tripping of the RCD due to
the apparent residual currents. Connecting a filter on the output side
between frequency converter and 3-phase AC motor results in the
same behaviour.
Due to the currents flowing off through the filters (designated IF), the sum of
currents through the RCD is not exactly zero, which causes unwanted tripping.
This sample tripping characteristic of a 100 mA RCD and a 300 mA
RCD shows the following: In the frequency range around 50 Hz, the
RCDs trip as required (50 - 100 % of the indicated I
Δ
n
).
In the range shown hatched in the diagram, i. e. from approx. 100 to
300 Hz, unwanted tripping occurs frequently due to the use of fre-
quency converters. Frequency converter-proof residual current
devices are much less sensitive in this frequency range than in the 50
- 60 Hz range, which leads to an enormous increase in the reliability of
systems.
Therefore, we recommend to use frequency converter-proof RCDs!
These special residual current devices can be recognised by an extension
of the type designation ("
-U
"). They meet the requirements of compatibil-
ity between RCDs and frequency converters with respect to unwanted
tripping.
These are
NOT AC/DC-sensitive
RCDs of type B !!!
Our
RCDs of type "-U"
are characterised by
SENSITIVITY TO RESIDUAL
PULSATING DC
and
SELECTIVITY
or
SHORT-TIME DELAY
.
G
S
Tripping characteristic
Protective Measures
In Austria, the ÖVE Decision EN 219 is applicable.
Under this standard
• frequency converters must be equipped with current limiting
devices in order to ensure disconnection in cause of faults or over-
load, and
• the installer of a system is obliged to make sure that additional
equipotential bonding is provided (additional inclusion of all metal
components, such as frequency converters, mains filters, motor fil-
ters, etc. into the existing equipotential bonding), in order to ensure
that the permissible touch voltage of 50 V AC or 120 V DC is not
exceeded. (In ÖVE/ÖNORM E 8001-1 the term "touch voltage" has
been omitted. There is only a fault voltage limit of 65 V AC or 120 V
DC which must not be exceeded).
In Germany, VDE 0100 is applicable, in Switzerland SEV 1000.
In case of application in any
other country
than those mentioned
take into account national rules and recommendations.
The following rules for the application of RCDs of type" -U" are only applicable in those cases where an RCD of type "-B" is not explicitly demanded in the
instructions of the manufacturer of the frequency converter.
How can you make sure that the required protective measures are in place when using RCDs type “-U” and frequency converters in one system?
Mains
RCD
RCD
Mains-side filter
Mains-side filter
F
requency
con
ver
ter
F
requency
con
ver
ter
S
c
reened motor line
Mains side filter
Motor
Motor
Frequency converter
interference range
(approx. 100 - 300 Hz)
