VAMP 52 - Per unit [pu] scaling of line-to-line voltages

Technical description 4 Measurement functions 4.11 Primary, secondary and per uni
t
scalin
g
VM50.EN004 VAMP 24h support phone +358 (0)20 753 3264
149
Example 4: Primary to secondary. Voltage measurement mode
is "1LN".
VT = 12000/110
The relay displays U
12
= U
23
= U
31
= 10910 V.
 Secondary voltage is
U
SEC
= 10910/3x110/12000 = 57.7 V4
Per unit [pu] scaling of line-to-line voltages
One per unit = 1 pu = 1xU
N
= 100 %, where U
N
= rated voltage
of the VT.
Line-to-line voltage scaling
Voltage measurement mode =
"1LL"
Voltage measurement mode =
"1LN"
secondary  per
unit
SEC
SEC
PU
VT
U
U 
SEC
SEC
PU
VT
U
U  3
per unit 
secondary
SECPUSEC
VTUU


3
SEC
PUSEC
VT
UU 
Example 1: Secondary to per unit. Voltage measurement mode
is "1LL".
VT = 12000/110
U
N
= VT
PRI
Voltage connected to the relay's input is 110 V.
 Per unit voltage is
U
PU
= 110/110 = 1.00 pu = 1.00xU
MODE
= 100 %
Example 2: Secondary to per unit. Voltage measurement mode
is "1LN".
VT = 12000/110
Phase-to-neutral voltage connected to the relay's input is 63.5
V.
 Per unit voltage is
U
PU
= 3x63.5/110x12000/11000 = 1.00 pu = 1.00xU
N
=100 %
Example 3: Per unit to secondary. Voltage measurement mode
is "1LL".
VT = 12000/110
The relay displays 1.00 pu = 100 %.
 Secondary voltage is
U
SEC
= 1.00x110x11000/12000 = 100.8 V