ABB Relion 670 series, Technical Reference Manual, Page: 403 / 1232

7.3.1 Introduction
The Instantaneous residual overcurrent protection EFPIOC (50N) has a low transient
overreach and short tripping times to allow the use for instantaneous ground-fault
protection, with the reach limited to less than the typical eighty percent of the line at
minimum source impedance. EFPIOC (50N) can be configured to measure the residual
current from the three-phase current inputs or the current from a separate current input.
EFPIOC (50N) can be blocked by activating the input BLOCK.
7.3.2 Principle of operation
The sampled analog residual currents are pre-processed in a discrete Fourier filter
(DFT) block. From the fundamental frequency components of the residual current, as
well as from the sample values the equivalent RMS value is derived. This current value
is fed to the Instantaneous residual overcurrent protection (EFPIOC,50N). In a
comparator the RMS value is compared to the set operation current value of the
function (
Pickup ). If the residual current is larger than the set operation current a signal
from the comparator is set to true. This signal will, without delay, activate the output
signal TRIP.
There is also a possibility to activate a preset change of the set operation current via a
binary input (enable multiplier MULTPU). In some applications the operation value
needs to be changed, for example due to transformer inrush currents.
EFPIOC (50N) function can be blocked from the binary input BLOCK. The trip
signals from the function can be blocked from the binary input BLKAR, that can be
activated during single pole trip and autoreclosing sequences.
7.3.3 Function block
ANSI06000269-2-en.vsd
EFPIOC (50N)
I3P*
BLOCK
BLKAR
MULTPU TRIP
ANSI06000269 V2 EN
Figure 205: EFPIOC (50N) function block
1MRK505222-UUS C
Section 7
Current protection
397
Technical reference manual