Functionality
24 USER MANUAL FPC 200 - 3/2017
Negative sequence/unbalance overcurrent protection - ANSI code 46
Uneven distribution of currents is caused by asymmetrical loads, single or two phase earth faults, line disconnections or
irregular switching operations. Negative sequence/unbalance overcurrent protection function calculates negative
sequence current of symmetrical components in three phase system.
2.2.3.1 Functionality
Function is used for detecting unbalanced loads in the
power system. Negative sequence value is defined by
the asymmetry of power system. Asymmetrical faults
selectivity is achieved by considering negative sequence
value.
In order to prevent malfunction of the protection and to
achieve better selectivity additional operational
conditions must be applied:
All phase currents have to be below the set
Maximum current value and
At least one phase current has to be above the
set Minimum current value
Protection selectivity is further improved with trip delay
time value set higher than the one set in main
protections (e.g. Overcurrent protection).
The trip time characteristics can be selected to be
Instantaneous, definite time (DT) or inverse definite
minimum time (IDMT). When instantaneous operation
mode is selected the trip signal is stated as the DT
characteristic with zero trip delay parameter.
The selection of pickup value, pickup delay as well as
drop-out ratio and drop-out delay helps the user to fine
tune the protection according to the project
specifications.
Definite time
46 Negative sequence
Mode:
Enabled:
IDMT coeficient:
0.05
Yes
Pickup value: 0.1In
Trip delay: 1.5s
A B
Figure 2.20 Example of parameter settings on HMI.
2.2.3.2 Delays
Function includes following delays explained in Chapter
2.1:
Pickup delay
Trip delay
Drop-out delay
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