Operation Principle - ABB RELION 620 Series Technical Manual

Section 4
Protection functions
4.1.1.4
140
In the DT mode, the function trips after a predefined trip time and resets when the fault
current disappears. The IDMT mode provides current-dependent timer characteristics.
The function contains a blocking functionality. It is possible to block function outputs,
timers or the function itself, if desired.

Operation principle

The function can be enabled and disabled with the Operation setting. The corresponding
parameter values are "Enable" and "Disable".
The operation of three-phase non-directional overcurrent protection can be described by
using a module diagram. All the modules in the diagram are explained in the next sections.
A070552-ANSI V1 EN
Figure 61: Functional module diagram. I_A, I_B and I_C represent phase currents.
Level detector
The measured phase currents are compared phasewise to the set Pickup value. If the
measured value exceeds the set Pickup value, the level detector reports the exceeding of
the value to the phase selection logic. If the ENA_MULT input is active, the Pickup value
setting is multiplied by the Pickup value Mult setting.
Do not set the multiplier setting Pickup value Mult higher than necessary.
If the value is too high, the function may not trip at all during an inrush
followed by a fault, no matter how severe the fault is.
The pickup value multiplication is normally done when the inrush detection function
(INR) is connected to the ENA_MULT input.
1MAC504801-IB E
620 series ANSI
Technical Manual