Operation Principle; Application - ABB RELION REX640 Technical Manual

Section 4
Protection functions
4.3.8.5
4.3.8.6
722
in this document. The configuration can be written to the protection relay once the
mismatch is corrected.

Operation principle

The function can be enabled and disabled with the Operation setting. The
corresponding parameter values are "On" and "Off".
The operation of MHZPDIF can be described using a module diagram. All the
modules in the diagram are explained in the next sections.
I_A
I_B
I3P
I_C
BLOCK
GUID-714A65DA-AAAC-4EC2-9706-AC919F204DC9 V1 EN
Figure 400: Functional module diagram
Level detector
This module compares the three-phase differential currents to the set Operate value.
If any of the differential currents ID_A, ID_B or ID_C exceeds the set Operate value,
the Level detector module sends an enable signal to the Timer module to start the
definite timer (DT).
Timer
Once activated, the Timer activates the START output. The Timer characteristic is
according to DT. When the operation timer has reached the value set by Minimum
operate time, the OPERATE output is activated. If the fault disappears before the
module operates, the reset timer is activated. If the reset timer reaches the value set by
Reset delay time, the operation timer resets and the START output is deactivated.
The Timer calculates the start duration value START_DUR, which indicates the
percentage ratio of the start situation and the set operation time. The value is available
in the Monitored data view.
The activation of the BLOCK signal resets the Timer and deactivates the START and
OPERATE outputs.

Application

MHZPDIF provides the winding short circuit and earth-fault protection for motors.
The high-impedance or flux-balance principle has been used through many years for
differential protection due to the capability to manage through-faults with a heavy
current transformer (CT) saturation.
Timer
Level
t
detector
1MRS759142 C
OPERATE
START
Technical Manual
REX640