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6 ACTUAL VALUES
DELTA-CONNECTED INSTRUMENT TRANSFORMERS:
•
ABC phase rotation:
V_0
=
N/A
∠
°
1
–
30
(
-------------------- V
V_1
=
AB
3 3
∠
1 30°
(
V_2
---------------- - V
=
AB
3 3
The zero-sequence voltage is not measurable under the Delta connection of instrument transformers and is defaulted to
zero. The table below shows an example of symmetrical components calculations for the ABC phase rotation.
Table 6–1: SYMMETRICAL COMPONENTS CALCULATION EXAMPLE
SYSTEM VOLTAGES, SEC. V *
V
V
V
AG
BG
CG
13.9
76.2
79.7
∠0°
∠–125°
∠–250°
V
V
UNKNOWN (only
1 and
2
can be determined)
*
The power system voltages are phase-referenced – for simplicity – to VAG and VAB, respectively. This, however, is a
relative matter. It is important to remember that the C70 displays are always referenced as specified under
SYSTEM SETUP
POWER SYSTEM
The example above is illustrated in the following figure.
C
C
Figure 6–3: MEASUREMENT CONVENTION FOR SYMMETRICAL COMPONENTS
GE Multilin
2
)
+
aV
+
a
V
BC
CA
2
)
a
V
aV
+
+
BC
CA
VT
CONN.
V
V
V
AB
BC
CA
84.9
138.3
85.4
WYE
∠–313°
∠–97°
∠–241°
84.9
138.3
85.4
DELTA
∠0°
∠–144°
∠–288°
FREQUENCY AND PHASE REFERENCE
SYSTEM VOLTAGES
A
A
C70 Capacitor Bank Protection and Control System
•
ACB phase rotation:
V_0
N/A
=
∠
1 30°
(
V_1
---------------- - V
=
3 3
∠
°
1
–
30
(
-------------------- V
V_2
=
3 3
RELAY INPUTS, SEC. V
F5AC
F6AC
F7AC
13.9
76.2
79.7
∠0°
∠–125°
∠–250°
84.9
138.3
85.4
∠0°
∠–144°
∠–288°
.
SYMMETRICAL
COMPONENTS
WYE VTs
B
2
DELTA VTs
B
2
827844A1.CDR
6.3 METERING
2
)
a
V
aV
+
+
AB
BC
CA
2
)
+
aV
+
a
V
AB
BC
CA
SYMM. COMP, SEC. V
V
V
V
0
1
2
19.5
56.5
23.3
∠–192°
∠–7°
∠–187°
N/A
56.5
23.3
∠–54°
∠–234°
SETTINGS
1
0
1
6
6-11
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