Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - ForGe Control - Manual (Page 63)

Rockwell Automation Publication 7000-UM202B-EN-P - June 2014 63
Component Definition and Maintenance Chapter 3
In addition to the snubber circuit, a sharing resistor connects in parallel with the
SGCT. The sharing resistor ensures the voltage’s equal distribution among
SGCTs connected in series. Connect SGCTs in series to increase the total reverse
voltage blocking (PIV) capacity, as seen by the electrical circuit. A single SGCT
has a PIV rating of 6500V. This single device provides sufficient design margin
for electrical systems with 2400V medium voltage supply. At 4160V, connect two
SGCTs in series to provide a net PIV of 13,000V to achieve the necessary design
margin. Similarly, connect three SGCTs in series at 6.6 kV, providing a net PIV of
19,500V to achieve the necessary design margin.
To meet the cooling requirements of the SGCT, place the SGCT between two
forced air-cooled heat sinks, one heat sink on the anode and the other heat sink
on the cathode. The force on the SGCTs differs with the size of the device. The
clamp assembly on the right hand side of the inverter module generates these
forces.
The SGCTs require uniform pressure to prevent damage and to ensure low
thermal resistance. Achieve uniform pressure by loosening the heat sink
mounting bolts, tightening the clamp, then tightening the heat sink bolts.
This design directs external filtered air through the heat sink slots to dissipate
heat from the SGCTs. The door filter ensures the heat sink slots stay clear of
dust particles.
SGCT Testing
The following steps outline how to verify SGCT semiconductors and all
associated snubber components. A quick reference to the expected resistance and
capacitance values as well as a simple schematic diagram is located in the table
below. A simple schematic diagram in
Figure 41 on page 57 shows how the
snubber components are connected across an SGCT.
¹— 2400V drives will not have a sharing resistor on devices.
Table 1 - SGCT/snubber resistance values
SGCT Rating Sharing Resistor ¹ Snubber Resistor Snubber Capacitor
1500 A 80 k Ω 6 Ω (AFE Rectifier) 0.2 μf
1500 A 80 k Ω 7.5 Ω (Inverter) 0.2 μf
800 A 80 k Ω 10 Ω 0.1 μf
400 A 80 k Ω 15 Ω (AFE Rectifier) 0.1 μf
400 A 80 k Ω 17.5 Ω (Inverter) 0.1 μf
SGCT Resistance Measurement Measured Resistance
Inverter
Rectifier (AFE only)
SGCT Anode-Cathode Resistance (heat sink to heat sink) k- Ω
(Lowest) (Highest) (Lowest) (Highest)
Snubber Resistance (Test point: Heat sink above) Ω
(Lowest) (Highest) (Lowest) (Highest)
Snubber Capacitance (Test Point – heat sink on Right) μF
(Lowest) (Highest) (Lowest) (Highest)