Fagor QC-PDS, Руководство по оборудованию

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Power line connection
6.
POWER LINE CONNECTION
D
iffere
ntial brea
ker
214
Ref.2003
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QC-PDS
HARDWARE
6.3 Differential breaker
On a QC-PDS 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.
These considerations must be taken into account if the differential breaker
only affects a machine using a QC-PDS system.
When several machines share the same differential breaker, always take
into account the sum of the leak currents of all the machines involved.
Note that most of the leak current is due to the mains filter. Thus, the role
of the filter is to discharge to ground the noise coming from mains. On the
other hand, the leak current of the filters varies depending on mains
conditions.
In the filters of the FAGOR catalog, these values may vary between 27
mA (typical value) and 600 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 several
differential breakers are to be installed.
 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® type-B 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 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 are usually valid for QC-PDS systems with a FAGOR filter. The off
current must not be lower 500 mA and should have a selective switch-off.
Note. The Siemens® type-A model "5SM3 745-8", 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
value !