ABB RELION 620 Series Technical Manual page 241

1MAC504801-IB E
620 series ANSI
Technical Manual
The operation of the negative-sequence overcurrent protection can be described using a
module diagram. All the modules in the diagram are explained in the next sections.
A070660-ANSI V1 EN
Figure 107: Functional module diagram. I
current.
Level detector
The measured negative sequence current is compared to the set Pickup value. If the
measured value exceeds the set Pickup value, the level detector activates the timer
module. If the ENA_MULT input is active, the set Pickup value is multiplied by the set
Pickup value Mult.
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.
Timer
Once activated, the timer activates the PICKUP output. Depending on the value of the
Operating curve type setting, the time characteristics are according to DT or IDMT. When
the operation timer has reached the value of Trip delay time in the DT mode or the
maximum value defined by the inverse time curve, the TRIP output is activated.
When the user-programmable IDMT curve is selected, the operation time characteristics
are defined by the parameters Curve parameter A, Curve parameter B, Curve parameter
C, Curve parameter D and Curve parameter E.
If a drop-off situation happens, that is, a fault suddenly disappears before the trip delay is
exceeded, the timer reset state is activated. The functionality of the timer in the reset state
depends on the combination of the Operating curve type, Type of reset curve and Reset
delay time settings. When the DT characteristic is selected, the reset timer runs until the set
Reset delay time value is exceeded. When the IDMT curves are selected, the Type of reset
curve setting can be set to "Immediate", "Def time reset" or "Inverse reset". The reset
curve type "Immediate" causes an immediate reset. With the reset curve type "Def time
reset", the reset time depends on the Reset delay time setting. With the reset curve type
Protection functions
represents negative phase sequence
2
Section 4
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