CHAPTER 6: ACTUAL VALUES
METERING
L60 LINE PHASE COMPARISON SYSTEM – INSTRUCTION MANUAL
6-15
6
DELTA-connected instrument transformers
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
* The power system voltages are phase-referenced – for simplicity – to V
AG
and V
AB
, respectively. This, however, is a
relative matter. It is important to remember that the L60 displays are always referenced as specified under
SETTINGS
SYSTEM SETUP
POWER SYSTEM
FREQUENCY AND PHASE REFERENCE
.
The example above is illustrated in the following figure.
Figure 6-5: Measurement convention for symmetrical components
•
ABC phase rotation:
•
ACB phase rotation:
SYSTEM VOLTAGES, sec. V *
VT conn. relay INPUTS, sec. V
SYMM. COMP, sec. V
V
AG
V
BG
V
CG
V
AB
V
BC
V
CA
F5ac
F6ac
F7ac
V
0
V
1
V
2
13.9
∠
0°
76.2
∠
–125°
79.7
∠
–250°
84.9
∠
–313°
138.3
∠
–97°
85.4
∠
–241°
WYE
13.9
∠
0°
76.2
∠
–125°
79.7
∠
–250°
19.5
∠
–192°
56.5
∠
–7°
23.3
∠
–187°
UNKNOWN (only
V
1
and
V
2
can be determined)
84.9
∠
0°
138.3
∠
–144°
85.4
∠
–288°
DELTA
84.9
∠
0°
138.3
∠
–144°
85.4
∠
–288°
N/A
56.5
∠
–54°
23.3
∠
–234°
