ABB RET670 - Application

3.7.3.1 Application
In many applications, when fault current is limited to a defined value by the object
impedance, an instantaneous ground-fault protection can provide fast and selective
tripping.
The Instantaneous residual overcurrent EFPIOC (50N), which can operate in 15 ms (50
Hz nominal system frequency) for faults characterized by very high currents, is
included in the IED.
3.7.3.2 Setting guidelines
The parameters for the Instantaneous residual overcurrent protection EFPIOC (50N)
are set via the local HMI or PCM600.
Some guidelines for the choice of setting parameter for EFPIOC (50N) is given.
The setting of the function is limited to the operate residual current to the protection
(Pickup).
The basic requirement is to assure selectivity, that is EFPIOC (50N) shall not be
allowed to operate for faults at other objects than the protected object (line).
For a normal line in a meshed system single phase-to-ground faults and phase-to-phase-
to-ground faults shall be calculated as shown in figure 188 and figure 189. The residual
currents (3I
0
) to the protection are calculated. For a fault at the remote line end this
fault current is I
fB
. In this calculation the operational state with high source impedance
Z
A
and low source impedance Z
B
should be used. For the fault at the home busbar this
fault current is I
fA
. In this calculation the operational state with low source impedance
Z
A
and high source impedance Z
B
should be used.
~
~
Z
A
Z
B
Z
L
A B
IED
I
fB
Fault
ANSI09000022-1-en.vsd
ANSI09000022 V1 EN
Figure 188: Through fault current from A to B: I
fB
1MRK504116-UUS C Section 3
IED application
419
Application manual