Chapter 4 Measurements
Accura 3300E User Guide
Page 72
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Fig 4.3 Connection with 2 PTs and 2 CTs, Wiring Mode = 3P3U (3P3W Connection)
You can use 2 or 3 PTs(Potential Transformer) in 3-phase 3-wire connection. Its installation cost
differs according to the number of PTs. However, regardless of how many PTs are used, Accura
3300E measures voltage signals in the same way. By using 3 CTs rather than 2 CTs, the residual
current can be measured by summing up three currents.
Vector Diagram
Item
Description
V
1
V
2
V
3
V
o
= V
1
+
V
2
+V
3
V
n
= V
o
/ 3
V
N
:
Voltage of floating N terminal
line to neutral
voltage sensing
▶
Sensing line to neutral voltage[V1, V2,
V3] based on floating N terminal voltage
Calculation of
Residual Voltage
▶
From sensed line to neutral voltage
Vo = V1 + V2 + V3
Calculation of
virtual center point
voltage
▶
Diving Residual Voltage by 3,
Vn = Vo/3
▶
Newly calculated virtual center point is
the center of mass of the triangle
comprised of V1, V2 and V3.
V
N
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