Example 3 – Rockwell Automation 23P PowerFlex DC Stand Alone Regulator and Gate Amplifier User Manual
Page 35
Rockwell Automation Publication 23P-UM001D-EN-P - July 2012
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Stand Alone Regulator Installation, Wiring and Configuration
Chapter 2
Example 3:
The only difference between Example 2 and Example 3 is the value of the burden
resistor. In this example the burden resistor is chosen as Rb = 5.0 Ohms.
In this example a standard CT ratio is chosen and the ratio no longer exceeds the
recommended CT ratio based on the gain calculation. This is due to the change
of the burden resistor from 2.5 Ohms to 5.0 Ohms.
CT, Burden Resistor and Gain Calculation
Minimum CT Primary based on IOC trip point of 2.5 x Power Module rating
Maximum CT ratio based on Gain Range of Scaling Op-Amp in the Current
Feedback circuit
Input Values
Units
Description
IdN_pm_rtg: = 226
Amp
Power module rating
Rb: = 5.0
Ohms
Jumper J5 in the “On” position
and jumper J4 in the “Off”
position. See
for jumper locations.
CT_pri: = 2000
Amp
CT_sec: = 1
Amp
Value/Calculation
Units
Description
IOC_mult: = 2.5
CT_pri_min: =
IOC_mult x IdN_pm_rtg x 0.85
0.85 is the ratio of AC to DC
current
CT_pri_min = 480
Amp
Based on IOC trip point
CT_ratio_min_based_on_ioc: = CT_pri_min / CT_sec
CT_ratio_min_based_on_ioc = 480
Based on IOC trip point
Value/Calculation
Units
Description
CT_ratio_max: = 1.2 x (IdN_rtg x Rb) / 0.612
CT_ratio_max = 2.216 x 10
3
Based on Gain <= 1.2
Value/Calculation
Units
Description
Vf_at_IdN_pm_rtg = 0.612
Volts
Fixed Value
CT_ratio: = CT_pri / CT_sec
CT_ratio = 2 x 10
3
Ib_at_IdN_pm_rtg: = IdN_pm_rtg / CT_ratio
Ib_at_IdN_pm_rtg = 0.113
Amps
Vb_at_IdN_pm_rtg: = (IdN_pm_rtg / CT_ratio) x Rb