1MAC050144-MB C
Section 4
Protection functions
615 series ANSI
125
Technical Manual
4.1.2.4
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 long-time overcurrent protection can be described by using
a module diagram. All the modules in the diagram are explained in the next sections.
Figure 51:
Functional module diagram. I_A, I_B and I_C represent phase currents.
Level detector
The measured phase currents are compared phase-wise 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.
The pickup value multiplication is normally done when the inrush detection function
(INR) is connected to the
ENA_MULT
input.
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.
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