38 Basic application
Disadvantages The auxiliary supplies are de-energised by the main contactor. This causes a turn on
delay of approximately 0.75 secs while the synchronisation circuits establish a lock onto the supply prior to
the application of power to the motor. Also the field cannot remain energised after contactor drop out w hich
prohibits dynamic braking and/or condensation prevention in standby field mode.
4.3.3 Main contactor isolating DC armature
Advantages The auxiliary supplies are permanently energised. This allows the synchronisation
circuits to lock onto the supply prior to the application of po wer to the motor. This results in a fast release of
current to the armature because it avoids the synchronisation delay. Also the field can remain energised after
contactor drop out allo wing dynamic braking and/or condensation prevention in standby field mode.
Disadvantages The field winding is not electromechanically isolated by the main contactor, which
may contravene safety codes without additional measures. The field standby level may not be set to a lo w
enough level by the user and could cause overheating of the field winding.
The A C supply is permanently connected to the PL/X unless further provision is made to isolate the supplies.
Note. The armature must be connected to the remote sense terminals T41 and T43. This
ensures that the PL/X can measure the armature voltage even when the contactor is open.
It is dangerous to utilise a DC contactor when field weakening is employed without also
connecting T41 and T43 to the motor armature.
See also 6.5 CH ANGE PARAMETERS / STOP MODE RA MP and 6.5.1.1 Block diagram of contactor control.
T4 1 + T43 -
A V sensing inputs
only used with DC
side contactors
Line
reactor
L1 L2 L3
EL1 EL2
EL3
Main
Contactor
With aux
contact
F- F +
Auxiliary
Fuses
Motor
Field
Main
Fuses
A + A-
Motor
Arm
DC Semiconductor fuse fo
regenerative applications
Wire the auxiliary N/O contact in series
with RUN (T31) and + 24 V (T35)
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