GE L90 Instruction Manual page 315

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
V_2
=
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 L90 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
L90 Line Differential Relay
• ACB phase rotation:
V_0 N/A
=
∠
1 30°
(
---------------- - V
V_1
=
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