Woodward
Manual MRI3 GB
52
DOK-TD-MRI3 Rev.A
6.4.9 Checking the external blocking and reset functions
By means of the external blocking input, it is possible to block all protective functions. To give an
example, the blocking function of the phase current high set element is described.
This can be tested by first setting the parameter for the phase current high set element to „BLOC“
and then connecting the auxiliary voltage to terminals E8/D8.
The phase current low set element I> should be set to EXIT for this test. Inject a test current which
could cause a high set (I>>) tripping. Observe that there is no trip of any assigned output relay of
the high set or low set element.
Remove the auxiliary supply voltage from the blocking input. Inject a test current to trip the relay
(message „TRIP“ on the display). Interrupt the test current and apply auxiliary supply voltage to the
external reset input of the relay (terminals C8/D8). The display and LED indications should be reset
immediately.
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 5.7.1.
For this purpose, the parameter for the Block/Trip function must be set to "TR_B" (first value in the
blocking menu of the protection functions Chapter 5.7.1. The appertaining Block/Trip time should
be longer than the set tripping time tI>> (see chapter 5.4.18). Here, too, a current is impressed
which should make the short-circuit stage trip. After 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 trip-
ping time has expired.
6.4.11 Test of the CB failure protection
For testing the tripping time a test current of about 2 times the rated current to be injected. The ti-
mer is started upon tripping of the relay of a protection function (I>, I>>, I
E
>, 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 simul-
taneously. 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.