TB MRI(K)3-C 03.02 E
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6.4.10
Testing the external blocking with
Block/Trip function
In order to simplify things, the short-circuit stage is to be
tested here as described in Chapter 6.4.9. For this pur-
pose, the parameter for the Block/Trip function must be
set to "TR_B" (first value in the blocking menu of the pro-
tection functions Chapter 5.11.1. The appertaining
Block/Trip time should be longer than the set tripping
time tI>>. Here, too, a current is impressed which
should make the short-circuit stage trip. At the same time
the blocking input must be activated. The easiest way to
do this is to set the alarm relay to the blocking input. Af-
ter the Block/Trip time has expired, tripping will take
place. Tripping takes place when:
•
the blocking input has been set
•
a tripping stage has been excited
•
the appertaining tripping time has expired
•
the Block/trip time has expired
If the Block/Trip time is set shorter than the tripping time,
tripping will only take place after the tripping time has
expired.
6.4.11
Test of the CB failure protection
For testing the tripping time a test current of about two
times the rated current to be injected. The timer is started
upon tripping of the relay of a protection function (I>,
I>>, I
E
> or I
E
>>) and stopped as soon as the relay for
the CB failure protection has picked up. Message
"CBFP" is displayed. The tripping time ascertained by
the timer should not deviate more than 1% or, at short
trip delay, less than
±
10 ms from the set tripping time.
Alternatively, the timer can be started when the aux.
voltage and the test current are injected simultaneously.
The timer stops when the corresponding output relay for
circuit breaker failure protection trips.
In this case the previously measured tripping delay has
to be subtracted from the total tripping time measured.
6.5
Primary Test
As a rule, tests with currents at the CT primary side (real
test) can be performed in the same way as tests with
secondary currents. It is recommended to carry out pri-
mary tests only as an exception and only if it is abso-
lutely necessary (for very essential protective facilities)
because in some cases the costs involved and the strain
on the system can be rather high. Many functions of the
MRI(K)3-C
can be checked during normal operation of
the system due to the efficient fault and measuring value
indications. So it is possible, for example, to compare
the currents shown on the display with the values shown
on the ammeters in the switchboard.
6.6
Maintenance
Normally the relays are checked at regular maintenance
intervals at site. From user to user these intervals may
vary because among other things they depend on the
type of relay, the kind of application, significance of the
object to be protected, previous experience of the user
etc.
For electro-mechanical or static relays normally an an-
nual check is required. For the
MRI(K)3-C
the mainte-
nance intervals can be much longer because:
•
the
MRI(K)3-C
relays are provided with wide-ranging
self-test functions and consequently relay faults are de-
tected and indicated. It is, of course, imperative that
the internal self-supervision relay is connected to a
central display board.
•
The combined measuring functions of the
MRI(K)3-C
make
monitoring during operation possible.
•
The trip test function (TRIP-Test) allows testing of the
output relays.
Therefore a maintenance interval of two years is suffi-
cient. When servicing all relay functions incl. setting val-
ues, trip characteristics and tripping times ought to be
thoroughly checked.
