Rockwell Automation 23P PowerFlex DC Stand Alone Regulator and Gate Amplifier - Manual (Page 31)

Rockwell Automation Publication 23P-UM001D-EN-P - July 2012 31
Stand Alone Regulator Installation, Wiring and Configuration Chapter 2
SAR Current Feedback Calculation Examples
Example 1:
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: = 2600 Amp Power module rating
Rb:= 5.0 Ohms Jumper J5 in the “On” position
and jumper J4 in the “Off”
position. See
Figure 13 on
page 39 for jumper locations.
CT_pri: = 10000 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 = 5.525 x 10 3 Amp Based on IOC trip point
CT_ratio_min_based_on_ioc: = CT_pri_min / CT_sec
CT_ratio_min_based_on_ioc = 5.525 x 10
3
Based on IOC trip point
Value/Calculation Units Description
CT_ratio_max: = 1.2 x (IdN_rtg x Rb) / 0.612
CT_ratio_max = 2.55 x 10
4
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 = 1 x 10
4
Ib_at_IdN_pm_rtg: = IdN_pm_rtg / CT_ratio
Ib_at_IdN_pm_rtg = 0.26 Amps
Vb_at_IdN_pm_rtg: = (IdN_pm_rtg / CT_ratio) x Rb
Vb_at_IdN_pm_rtg = 1.3 Volts
Gain_Required: = Vf_at_IdN_pm_rtg /
Vb_at_IdN_pm_rtg
Gain_Required = 0.471 Note: Recommended Gain <=
1.2 (for best accuracy)