Emerson AMPGARD RVSS Instruction Booklet page 34

Instruction Booklet IB020003EN
Effective January 2021
6.2.3 Fiber optic fan-out boards
For 4160 VAC, each Power Pole has four series-parallel SCRS per
phase (see Figure 26), and requires a Fan-out Board (see Figure 28)
to distribute the SCR firing signals from the I/O board to the Gate
Driver Board, which passes them to the series SCRs in each circuit
leg.
The Fan-out Boards (one per phase) also serve as isolated power
converters for the Gate Driver Boards. Each Fan-out Board has an
on-board 48V-to-isolated-current-loop converter that provides power
to its phase's Gate Driver Boards. For more information, see the
schematic diagram Figure 11 and Figure 28, below.
J7
Current Loop to
Gate Driver toroids
J6
48 VDC
Power Supply
Input
PTC Thermistor from
Lower Gate Driver
Upper minus SCR (2-)
Lower Gate Driver
Figure 28. Fan-out board.
6.2.4 Gate driver interface boards with heat sink PTC
thermal interface
The SCR firing signals from the I/O Board are transmitted over fiber
optic cables. These signals must be converted from light to voltage
in order to gate the Power-Pole SCRs. For each Power-Pole, Gate
Driver Boards perform this conversion. In addition, the Gate Driver
boards have electronics to convert the heat sink thermistor signals
into light for fiber optic transmission to the RVSS I/O Board.
For all voltage ratings, the RVSS Power Pole uses one Gate Driver
Board to provide the heat sink thermistor signal conversion for that
phase (see Figure 11 and Figure 29).
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U25
U21
to
U18
Upper minus SCR (1-)
to
Upper Gate Driver
6.2.5 RC snubber boards
Each RVSS Power Pole includes RC snubber boards to provide dV/dT
protection of the SCRs during switching transients. The boards also
include an Overvoltage clipping circuit that fires the SCR if its anode
to cathode voltage becomes excessive. This is useful in series SCR
circuits where one device is shorted and the other healthy device
then is fired due to overvoltage, likely resulting in an Unbalance 1Ph
fault in the controller.
U29
Transmitter to I/O Board
for PTC Thermstor Temp.
U15
Upper plus SCR (1+)
U16
to
Upper plus SCR (2+)
Upper Gate Driver
to
Lower Gate Driver
AMPGARD RVSS
Reduced Voltage Soft-Starter
User Manual
Fan-out Board 58-9009
One per phase leg assembly
Three per 400 A Truck
U13
minus SCRs
Firing Signals
from I/O
Board
U8
plus SCRs
Firing Signals
from I/O
Board