Rockwell Automation 865 Differential Protection Relay - Manual (Page 117)

Measurement Functions 5-7
865-UM001A-EN-P – July 2009
Example 6: Per unit to secondary for residual current.
Input is I
01
or I
02
.
CT
0
= 50/1
The relay setting is 0.03 pu = 3 %.
⇒ Secondary current is
I
SEC
= 0.03x1 = 30 mA
Example 7: Secondary to per unit for residual current.
Input is I
0Calc
.
CT = 750/5
Currents injected to the relay's I
L1
input is 0.5 A.
I
L2
= I
L3
= 0.
⇒ Per unit current is
I
PU
= 0.5/5 = 0.1 pu = 10 %
Example 8: Per unit to secondary for residual current.
Input is I
0Calc
.
CT = 750/5
The relay setting is 0.1 pu = 10 %.
⇒ If I
L2
= I
L3
= 0, then secondary current to I
L1
is
I
SEC
= 0.1x5 = 0.5 A