Allen-Bradley Rockwell Automation 857 User Manual page 186

5-14
Measurement Functions
857-UM001A-EN-P – July 2009
Example 3 – Per unit to secondary for feeder mode and ArcI>
CT = 750/5
The device setting is 2 pu = 200 %.
⇒ Secondary current is
I = 2x5 = 10 A
SEC
Example 4 – Per unit and percent to secondary for phase
currents in motor mode excluding ArcI>
CT = 750/5
I = 525 A
MOT
The device setting is 2xI
⇒ Secondary current is
I = 2x5x525/750 = 7 A
SEC
Example 5 – Secondary to per unit for residual current
Input is I or I .
01 02
CT = 50/1
0
Current injected to the device's input is 30 mA.
⇒ Per unit current is
I = 0.03/1 = 0.03 pu = 3 %
PU
Example 6 – Per unit to secondary for residual current
Input is I or I .
01 02
CT = 50/1
0
The device setting is 0.03 pu = 3 %.
⇒ Secondary current is
I = 0.03x1 = 30 mA
SEC
Example 7 – Secondary to per unit for residual current
Input is I .
0Calc
CT = 750/5
Currents injected to the device's I
I = I = 0.
L2 L3
⇒ Per unit current is
I = 0.5/5 = 0.1 pu = 10 %
PU
Example 8 – Per unit to secondary for residual current
Input is I .
0Calc
CT = 750/5
The device setting is 0.1 pu = 10 %.
⇒ If I
= I = 0, then secondary current to I
L2 L3
I = 0.1x5 = 0.5 A
SEC
= 2 pu = 200 %.
MOT
input is 0.5 A.
L1
is
L1