Sel 411L - Figure 11.17 Finding Phase-To-Phase Test Quantities

P.11.35
Date Code 20151029 Protection Manual SEL-411L Relay
Testing and Troubleshooting
Checking Relay Operation
Phase-to-Phase Distance Element MBC2
The relay contains mho phase distance elements among the many protection
elements in the relay. The relay has phase distance elements to detect phase-
to-phase faults, phase-to-phase-to-ground faults, and three-phase faults. The
relay has five independent zones of mho phase distance protection; each zone
consists of phase-to-phase elements that the relay combines to produce a
particular zone output.
For example, the OR combination of MAB2, MBC2, and MCA2 produces the
Z2P Zone 2 mho phase element.
Test Current and Voltage for a Phase-to-Phase Fault
To find the test current for a phase-to-phase fault, consider Equation 11.19 for
a B-phase to C-phase fault:
Equation 11.19
The B-phase to C-phase current vector, I
BC
, is:
Equation 11.20
Choose a convenient test source current magnitude, |I
TEST
| = 2.5 A; then
|I
BC
|= 2 • |I
TEST
| = 5 A.
Find the magnitude of the test source voltage |V
TEST
|:
Equation 11.21
where relay setting Z2MP (Zone 2 Reach) substitutes for the B-phase to
C-phase impedance Z
BC
. For setting Z2MP of 9.36 , the test voltage
magnitude |V
BC
| is:
Equation 11.22
Figure 11.17 Finding Phase-to-Phase Test Quantities
I
TEST
I
B
–I
C
==
I
BC
I
B
I
C
– I
B
I
B
 + 2 • I
B
2 • I
TEST
====
V
TEST
V
BC
I
BC
• Z
BC
I
BC
• Z2MP ===
2 • I
TEST
• Z2MP=
V
TEST
2 • I
TEST
• Z2MP=
2 • 2.5 • 9.36 = 46.8 V=
β
2
=
30
˚
φ
=
–
1
50
˚
θ
= 1
50
˚
–
90
˚
90
˚
V
A
0
˚
±
1
80
˚
β
1
=
30
˚
V
B
C
V
B
V
C