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Snubber capacitance (sgct device), Scr testing, Snubber capacitance (sgct device) scr testing – Rockwell Automation 7000L PowerFlex Medium Voltage AC Drive (C-Frame) - ForGe Control User Manual

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Rockwell Automation Publication 7000L-UM301D-EN-P - June 2014

Chapter 4

Commissioning

Snubber Capacitance (SGCT Device)

Turn the multimeter from the resistance to capacitance measurement mode.
Proceed to verify the snubber capacitor by measuring from the test point to the
chill block adjacent to the right.

Figure 184 - Snubber Capacitor Test

The capacitance measured is actually affected by the snubber capacitor and other
capacitance in the circuit, including capacitance from the Gate Driver circuit.
You are actually looking for a consistent reading for all devices.

If the capacitor is found to be out of tolerance, refer to

Component Definition

and Maintenance on page 265 (Chapter 5)

for detailed instructions on how to

replace the snubber capacitor.

SCR Testing

The following steps outline how to verify SCR 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 below:

Table 7 - SCR Snubber Circuit Resistance and Capacitance Values

Drive Rating

Sharing

Resistance

Snubber

Resistance

Snubber

Capacitance

3300 to 6600V

80 kΩ

90 Ω

0.5 μf

Snubber Test Point

Measure capacitance
between cathode
chillblock and testpoint