Rockwell Automation 1395 Digital DC Drive FRN 5-10.10/9.30 - Manual (Page 69)

Chapter 4
Hardware Description
125 – 300 HP, 230VAC 250 – 600HP, 460VAC
4-5
SCR Cell Fuses – Each SCR cell is protected from high currents by a cell
fuse, located in each leg.
DC Contactor – Output of the armature bridge is connected to the DC
motor through the main DC contactor M1. Coil voltage to M1 is controlled
by contacts from the pilot relay PR (an external 115VAC control input
entering at TB5).
Bridge Output Connections – Bridge output connections labeled A1 and
A2 (Fig. 4.3) correspond to the NEMA standards for connection to the A1
and A2 leads of the DC motor.
Field Bridge Components A general description of the components in the field bridge (Figure 4.4)
and their operation is covered here.
Supply Voltage – The bridge requires two phases fused from an external
source. This is connected to TB8-1 and 3 as detailed in Chap. 6,
Installation.
Field Current Feedback – Current Transformer FCT provides field
current feedback information to the Feedback board at TB1-8 and 9. The
Feedback board rectifies the single phase feedback and scales the DC
voltage using a burden resistor selected by the position of Jumper J1 on the
Feedback Board before being sent to the Power Stage Interface. The DC
voltage representing field current feedback is passed directly through the
Power Stage Interface and sent to the Main Control Board.
Surge Suppression – Surge suppressor 3MOV protects the field power
bridge from line voltage spikes and line surges on the incoming AC line.
2MOV protects the motor field windings from line spikes on the output of
the field bridge.
Line Choke – Line Choke CH1 protects the field power bridge SCRs
from rapid rate of current changes (di/dt).
SCR Modules – Field bridge SCRs are contained in modules made up of
two (2) SCRs per package (PM1 and PM2).
SCR Snubbers – Each forward and reverse armature SCR combination is
protected from rapid rate of voltage changes (dv/dt) using a series
combination of a resistor and capacitor (Snubber) connected in parallel
with the two SCRs. The field SCRs do not have parallel snubbers, but have
them on the input and output of the field bridge. All snubbers are contained
on the Pulse Transformer and Snubber boards, and therefore are not shown
on the bridge schematics.
Bridge Output Connections – The output of the field bridge is connected
to TB7-1 and 3 which in turn is connected to the field leads of the motor.
The terminal labeled F+ on TB2 is connected to the F1 lead of the motor
and terminal F– to the F2 lead.