Voltage Scaling - Allen-Bradley Rockwell Automation 857 User Manual

Voltage Scaling

Table 5.17 – Primary/Secondary Scaling of line-to-line Voltages
Voltage measurement mode
= "2LL+Uo"
secondary ⇒ =
U U
PRI
primary
primary ⇒
=
U U
secondary
SEC
Example 1 – Secondary to primary. Voltage measurement mode
is "2LL+Uo"
VT = 12000/110
Voltage connected to the device's input U
⇒ Primary voltage is U
Example 2 – Secondary to primary. Voltage measurement mode
is "3LN"
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
Example 3 – Primary to secondary. Voltage measurement mode
is "2LL+Uo"
VT = 12000/110
The device displays U
PRI
⇒ Secondary voltage is U
Example 4 – Primary to secondary. Voltage measurement mode
is "3LN"
VT = 12000/110
The device displays U
12
⇒ Symmetric secondary voltages at Ua, U
U = 10910/√3x110/12000 = 57.7 V4
SEC
Measurement Functions
Line-to-line voltage scaling
Voltage measurement mode
= "3LN"
VT
⋅
PRI
U
SEC
PRI
VT
SEC
VT
⋅
SEC
U
PRI SEC
VT
PRI
or U
a
= 100x12000/110 = 10909 V
PRI
= √3x58x12000/110 = 10902 V
PRI
= 10910 V.
= 10910x110/12000 = 100 V
SEC
= U = U = 10910 V.
23 31
and U
b
5-15
VT
= 3 ⋅ ⋅
PRI
U
SEC
VT
SEC
VT
U
= ⋅
PRI SEC
VT
3
PRI
is 100 V.
b
are
c
857-UM001A-EN-P – July 2009