VAMP 50 - Page 147

Technical description 4 Measurement functions 4.11 Primary, secondary and per uni
t
scalin
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147
Example 1: Secondary to per unit for phase currents excluding
ArcI>.
CT = 750/5
I
mode
= 525 A
Current injected to the relay's inputs is 7 A.
 Per unit current is
I
PU
= 7x750/(5x525) = 2.00 pu = 2.00 xI
mode
= 200 %
Example 2: Secondary to per unit for ArcI>.
CT = 750/5
Current injected to the relay's inputs is 7 A.
 Per unit current is
I
PU
= 7/5 = 1.4 pu = 140 %
Example 3: Per unit to secondary for phase currents excluding
ArcI>.
CT = 750/5
I
mode
= 525 A
The relay setting is 2xI
mode
= 2 pu = 200 %.
 Secondary current is
I
SEC
= 2x5x525/750 = 7 A
Example 4: Per unit to secondary for ArcI>.
CT = 750/5
The relay setting is 2 pu = 200 %.
 Secondary current is
I
SEC
= 2x5 = 10 A
Example 5: Secondary to per unit for residual current.
Input is I
01
.
CT
0
= 50/1
Current injected to the relay's input is 30 mA.
 Per unit current is
I
PU
= 0.03/1 = 0.03 pu = 3 %
Example 6: Per unit to secondary for residual current.
Input is I
01
.
CT
0
= 50/1
The relay setting is 0.03 pu = 3 %.
 Secondary current is
I
SEC
= 0.03x1 = 30 mA