Uniform clamping pressure – Rockwell Automation 7000 PowerFlex Medium Voltage AC Drive (B Frame) - ForGe Control (PanelView 550) User Manual
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Rockwell Automation Publication 7000-UM151E-EN-P - January 2013
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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 6500 V. This single device provides sufficient design margin
for electrical systems with 2400 V medium voltage supply. At 4160 V, connect
two SGCTs in series to provide a net PIV of 13000 V to achieve the necessary
design margin. Similarly, connect three SGCTs in series at 6.6 kV, providing a net
PIV of 19500 V to achieve the necessary design margin.
To meet the cooling requirements of the SGCT, place the SGCT between two
forced air-cooled heatsinks, one heatsink on the anode and the other heatsink 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 heatsink mounting
bolts, tightening the clamp, then tightening the heatsink bolts. See
for instructions.
This design directs external filtered air through the heatsink slots to dissipate heat
from the SGCTs. The door filter ensures the heatsink slots stay clear of dust
particles.
Uniform Clamping Pressure
Always maintain proper pressure on the thyristors. Follow this procedure
whenever changing devices or loosening the clamp completely.
1. Apply a thin layer of Electrical Joint Compound (Alcoa EJC No. 2 or
approved equivalent) to the clamp head pressure pad face.
2. Torque the heatsink bolts to 13.5 N-m (10 ft-lb.), then loosen each bolt
two complete turns.
3. Tighten the clamp to the proper force until you can turn the indicating
washers by the fingers with some resistance.
4. Torque the heatsink bolts to 13.5 N-m (10 ft-lb.) starting with the center
heatsink and moving outward alternating left to right.
5. Check the clamp indicating washer.