Fagor APS-24, Hardware Manual

Page: 237 / 386

   Power line connection
POWER LINE CONNECTION
D
iffere
ntial brea
ker
6.
237
DDS
HARDWARE
Ref.1310
6.3 Differential breaker
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 dif-
ferential breaker.
These considerations must be taken into account if the differential break-
er only affects a machine using a FAGOR DDS servo drive system.
When several machines share the same differential breaker, bear in mind
the sum of the leak currents of all the machines involved.
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 con-
ditions.
On the filters of the FAGOR catalog, these values may vary between 27
mA (typical value) and 150 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 unbal-
anced 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 sever-
al 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.
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”, for example.
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 dif-
ferential 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 cur-
rent
must not be < 500 mA and they will have selecting switch-off.
Note. The Siemens® model “5SM3 645”, for example.
i
WARNING. Watch out for the total leak current when several machines
share a differential breaker. All of them may add up to a considerable val-
ue!