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Power Automation and Protection Division
8.1.
Phase-to-ground Units
To calculate the apparent impedance seen by the relay the following formula applies:
where x is either phase a, b or c.
The above formula is rigorous and general. However, if a quick approximation of the current required at different
angles (Ø) is desired, the following formula applies:
For forward Zone 2 trips follow the following table for currents and voltages applied and compare the calculated
impedance in the relay target data to the provided impedance in the table. The displayed value should fall within
±5%. Also make sure that the trip times are within 100 to 132 milliseconds.
Zone 2 ground (Z2G) should operate in all of the above.
For reverse Zone 2 trips follow the next table:
REL 352 Version 1.00
Zapp
=
----------------------------------------------------------------- -
2
+
I
-------------------------------------------------------- -
X
I
=
-------------------------------------------------------------------------------------- -
(
PANG φ
Z 2GF
cos
V
AG
Va = 20 ∠0
Ia = 4 ∠-75
Vb = 69 ∠-120
Ib = 0
Vc = 69 ∠+120
Ic = 0
BG
Va = 69 ∠0
Ia = 0
Vb = 20 ∠-120
Ib = 4∠+165
Vc = 69 ∠+120
Ic = 0
CG
Va = 69 ∠0
Ia = 0
Vb = 69 ∠-120
Ib = 0
Vc = 20 ∠+120
Ic = 4∠+45
V
AG
Va = 10 ∠0
Ia = 4 ∠+105
Vb = 69 ∠-120
Ib = 0
Vc = 69 ∠+120
Ic = 0
BG
Va = 69 ∠0
Ia = 0
Vb = 10 ∠-120
Ib = 4∠-15
Vc = 69 ∠+120
Ic = 0
Vxg
∠
ZR GANG-PANG
3
V
XG
ZR 1
–
) 1
–
+
--------------- -
3
I
Z app
3.0 ∠75
3.0 ∠75
3.0 ∠75
I
Z app
1.5 ∠−105
1.5 ∠-105
I.L. 40-201.9
equ (1)
equ (2)
A
P
P
E
N
D
I
X
I
I-5
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