Rockwell Automation Publication 7000-UM202D-EN-P - May 2018 67
Power Component Definition and Maintenance Chapter 2
In addition to the snubber circuit, a sharing resistor connects in parallel with
the SGCT. The sharing resistor ensures the equal distribution of the voltage
among the 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 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.
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.
SGCT Testing
The following sections 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 43 on page 61
shows how
the snubber components are connected across an SGCT.
SGCT Rating Sharing Resistor
(1)
(1) 2400V drives will not have a sharing resistor on devices.
Snubber Resistor Snubber Capacitor
1500 A 80 kΩ 6 Ω (AFE rectifier) 0.2 µf
1500 A 80 kΩ 7.5 Ω (Inverter) 0.2 µf
800 A 80 kΩ 10 Ω 0.1 µf
400 A 80 kΩ 15 Ω (AFE rectifier) 0.1 µf
400 A 80 kΩ 17.5 Ω (Inverter) 0.1 µf
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