Supply and fusing for the field supply
Basically, similar conditions apply for both field
supply and armature-circuit supply. Depending
on the power converter used (diode bridge, half-
controlled bridge, fully controlled 4-quadrant
bridge), some of the fault sources may not always
be applicable. Due to special system conditions,
such as supply via an autotransformer or an
isolating transformer, new protection conditions
may additionally apply.
In contrast to the armature-circuit supply, fuses
are
never
used on the DC side for the field
supply, since a fuse trip might under certain
circumstances lead to greater damage than would
the cause tripping the fuse in the first place
(small, but long-lasting overcurrent; fuse ageing;
contact problems; etc.).
Fault No. 4 can also occur in the case of field
supply units, but will not cause such a rapid and
substantial current rise as encountered with an
armature-circuit supply; this is due to the signif-
icantly higher inductance of the field winding.
If conditions similar to those for armature-circuit
supply are to apply, like for example protection
of the field supply unit and the field winding,
then a semiconductor fuse (super-quick-acting
F3.1) must be used.
The following configurations are relatively fre-
quent:
Fig 2.6/2 Configurations for field supplies
R
Possible field supply units:
- SDCS-FEX-1: uncontrolled diode bridge;
Fault:
5a, 6
- SDCS-FEX-2: half-controlled bridge, 1Q;
Fault:
1, 5a, 6
- DCF 503:
half-controlled bridge,
1Q;
Fault:
1, 5a, 6
- DCF 504:
fully controlled bridge,
4Q;
Fault:
1, 3, 4, 6
The faults listed here are described under
Aspects of fusing for the armature-circuit and
field supplies.
Note: in the case of 1, 4, and 6, the current is
limited to relatively small overcurrents due to
the ohmic content of the field winding, so that
the fuses may perhaps not be tripped.
K
See the text below in the Commutating reac-
tor section
F
The F3.2 and F3.3 fuse types serve as line
protectors and cannot protect the field supply
unit. Only pure HRC fuses or miniature circuit-
breakers may be used. Semiconductor fuses
would be destroyed, for example, by the
transformers starting current inrush.
II F 2-18
F3.3
2
2
2
F3.2
F3.1
5
.
F3.1
F3.1
)
