VAMP 259 - Voltage Scaling

Technical description
4 Measurement functions
4.11 Primary, secondary and per unit
scaling
VM259.EN007
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199
Example 5: Secondary to per unit for residual current.
Input is I
0Calc
.
CT = 750/5
Currents injected to the device'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 device 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
4.11.2. Voltage scaling
Primary/secondary scaling of line-to-line voltages
secondary  primary
SEC
PRI
SECPRI
VT
VT
UU  3
primary  secondary
PRI
SEC
PRI
SEC
VT
VT
U
U 
3
Example 1: Secondary to primary.
VT = 12000/110
Three phase symmetric voltages connected to the device's
inputs Ua, Ub and Uc are 57.7 V.
 Primary voltage is U
PRI
= 3x58x12000/110 = 10902 V
Example 2: Primary to secondary.
VT = 12000/110
The device displays U
L12
= U
L23
= U
L31
= 10910 V.
 Symmetric secondary voltages at Ua, U
b
and U
c
are
U
SEC
= 10910/3x110/12000 = 57.7 V4