ABB REL 356

ABB REL 356 Current Differential Protection
5-18
Testing
Phase to Phase Units
To calculate the fault impedance seen by the relay system the following formula applies:
where x is either phase a, b, or c and y is the next lagging phase.
The above formula is rigorous and general. However, if a quick approximation of the minimum trip current required at
different angles (q) is desired, the following formula applies:
where x is either phase a, b, or c and y is the next lagging phase.
Zone 2 Phase-Phase Element
10. Forward Internal Faults
For forward Zone 2 Phase-Phase Internal faults use the Table 5-10 of voltages and currents. In each case apply the 3-
phase voltage to the relay system first then suddenly apply the currents listed. Compare the relay system trip target
data to the applied fault values. The target data should be within +/- 10% on magnitude and +/- 3 degrees on phase. Trip
time should fall within 100-132 milliseconds.
Table 5-10. Zone 2 Phase-Phase Forward Internal Faults: Z2P = 4.5 Ohms
Volts
∠
Angle
I
Amps
∠
Angle
Fault Z
Ohms
∠
Angle
Relay System
Operation
AB at MTA 90% of reach fault
Va = 17.3
∠
0 Ia = 3.7
∠
-75 (285) 4.05
∠
75
Vb = 17.3 ∠ -120 (240) Ib = 3.7 ∠ -225 (135)
Vc = 69 ∠ -240 (120) Ic = 0
Z2T Trip
Fault trip AB
Z2G Unit
Trip time 100-132 mS
BC at MTA 90% of reach fault
Va = 69 ∠ 0 Ia = 0 4.05 ∠ 75
Vb = 1.73
∠
-120 (240) Ib = 3.7
∠
-165 (195)
Vc = 1.73
∠
-240 (120) Ic = 3.7
∠
-345 (15)
Z2T Trip
Fault trip BC
Z2G Unit
Trip time 100-132 mS
CA at MTA 90% of reach fault
Va = 17.3 ∠ 0 Ia = 3.7 ∠ -105 (255) 4.05 ∠ 75
Vb = 69
∠
-120 (240) Ib = 0
Vc = 17.3
∠
-240 (120) Ic = 3.7
∠
-285 (75)
Z2T Trip
Fault trip CA
Z2G Unit
Trip time 100-132 mS
Z fault =
Vxy
Ix Iy
-
--------------
V
XG
Z2P (cos (PANG - q))
---------------------------------------------------------
-
lxg =