Fagor DDS Series Hardware Manual page 229

6.3 Differential breaker
i
On a DDS system, fault DC current, practically flat, may come up besides
the AC currents and pulsating DC currents. This requires the use of a
differential breaker.
MANDATORY. Install a universal type B breaker (valid for AC, pulsating DC
and flattened DC currents) and selective switch-off (delayed switch-off).
Note. The Siemens® model "5SZ6 468-0KG00", type B for example.
These considerations must be taken into account if the differential breaker
only affects a machine using a FAGOR DDS system.
WARNING. It is not recommended to use differential breakers sensitive to
pulsating currents and, overall, general purpose differential breakers. In this
cases, undesired stops might occur due to the high sensitivity of those
devices to pulsating currents. Therefore, never use AC type differential
breakers!
INFORMATION. As an alternative, type A differential breakers may be used
with selective switch-off. They are more economical than type B ones and
usually valid for DDS systems with a FAGOR filter. The off current must not
be < 500 mA and they will have selecting switch-off.
Note. The Siemens® model "5SM3 745-8", type A for example.
When several machines share the same differential breaker, bear in mind
the sum of the leak currents of all the machines involved.
WARNING. Watch out for the total leak current when several machines share
a differential breaker. All of them may add up to a considerable value!
Note that most of the leak current is due to the mains filter. Hence, it is up to
the filter to discharge to ground the noise coming from mains. On the other
hand, the leak current of the filters varies depending on mains conditions.
On the filters of the FAGOR catalog, these values may vary between 27 mA
(typical value) and 130 mA (maximum value). They practically do not vary
with temperature because their components are stable and certified.
The main reason for the variation of the leak current has to do with
unbalanced mains voltage or with too many harmonics.
Bear in mind these considerations when installing differential breakers for
several machines.
 Verify that the differential breaker to be installed is more immune and
admits higher leak currents.
 Distribute the machines connected to each line when installing several
differential breakers.
 Use fewer mains filters. Install one filter common to several machines
instead of one for each machine. Verify that the machines connected to
the same filter do not generate disturbances between them and meet the
current regulations.
   Power line connection
6.
HARDWARE
Ref.1912
DDS
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