VAMP VAMP 59, Installation, Operation And Configuration Instructions

Page: 139 / 212

Technical description 4 Measurement functions 4.9 Primary, secondary and per
unit scaling
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Example 5: 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 6: 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
4.9.2. Voltage scaling
Per unit [pu] scaling of zero sequence voltage
Zero-sequence voltage (U
0
) scaling
Voltage measurement mode = "U
0
"
secondary 
per unit
SEC
SEC
PU
U
U
U
0

per unit

secondary
SEC PU SEC
U U U
0
 
Example 1: Secondary to per unit. Voltage measurement mode
is "U
0
".
U
0SEC
= 110 V (This is a configuration value corresponding to
U
0
at full earth fault.)
Voltage connected to the relay's input is 22 V.

Per unit voltage is
U
PU
= 22/110 = 0.20 pu = 20 %