17
Recorded data
and fault analysis
The information stored in the registers of the
protection relay can be used for analysing fault
situations and situations during normal opera-
tion.
Register 1 stores the highest current value meas-
ured on one of the phases L1, L2 or L3, as a
multiple of the rated value of the relay. If the
module performs tripping, the current value at
moment of tripping is memorized. Any new trip
resets the old recorded value and updates the
register. The same thing happens if the meas-
ured current exceeds the previous recorded value.
The data stored in register 1 show the agreement
between the setting values and, on the one hand,
the actual current values that occur in a fault
situation and, on the other hand, the operation
values in normal situations.
If a short circuit occurs on the feeder, the over-
current module records the current value at the
moment of tripping and stores the value in
register 1. The level of the current indicates how
close the fault location is and also whether it is
a two-phase or three-phase fault. In addition,
the indicators on the front plate of the overcur-
rent module show in which phases the current
has exceeded the setting value of the tripping
stage.
Auxiliary register 1 of register 1 indicates the
current measured at the last tripping. A re-
corded value is reset only by a new trip that
simultaneously enters the new value into the
register.
A connection inrush current has a very short
duration, but the current level may be high
enough to start the relay and the value conse-
quently stored in register 1. In this case the
current value recorded at the previous tripping
is also stored in auxiliary register 1 and available
for the analysis of the fault situation.
The level of the fault current is directly indicated
by the register values. If, for instance, the value
is 5.0 after tripping, the highest value for a
separate phase at the moment of tripping was
five times the rated primary current of the
current transformers.
The number of starts of the various operation
stages, registers 2 and 3, illustrates the occur-
rence of the the overcurrents. Frequent starts on
a feeder may, for instance, be due to too low
setting values of the relay, connection inrush
currents or a concealed fault, e.g. a defective
insulator.
Registers 4 and 5 show the duration of the latest
start situation of the operation stages, as a per-
centage of the preset operate time or, when
inverse time characteristic has been selected, of
the calculated operate time. A new start always
resets the counter that starts counting from zero
again. When the stage trips, the register value is
100.
Registers 4 and 5 contain information about the
duration of, for instance, the connection inrush
current or the safety margin of the grading times
of the selective protection. If register 4 of the
busbar overcurrent relay operating as back-up
protection for an outgoing feeder has the value
75 when the overcurrent module of the feeder
has performed tripping, the selective protection
has a safety margin of 25% of the operate time
of the low-set stage of the busbar overcurrent
protection.
