TB XRW1-4 04.01 E
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7.4.7
Checking the relay operating time of
the over/underfrequency functions
The operating time of the over/underfrequency func-
tions can be tested in the similar manner as in chapter
7.4.5 for over/undervoltage functions.
7.4.8
Checking the tripping and reset va-
lues of the df/dt stages
The df/dt function can only be tested with a frequency
generator which is capable of producing a defined li-
near frequency gradient. The step speed of the fre-
quency generator must be < 10 ms. The tripping value
of the frequency gradient can be tested with the follo-
wing setting values.
Set all frequency stages to "EXIT"
df = 0.5 Hz/s, dt = 10, f
N
= 50 Hz,
UB = 40 % of Un
First of all a measuring voltage is applied the value of
which must be higher than the voltage threshold for fre-
quency measuring and the df/dt measuring. After 5 s
the df/dt supervision is released (refer to Chapter 4.7).
The frequency generator should now run through a fre-
quency ramp from 50 Hz to 48.6 Hz within 2.0 s
which corresponds to a frequency-change speed of –
0.7 Hz/s. If the frequency change during the set time
dt = (T+1') x 20 ms is greater than the set trip value df,
tripping will take place. In this case that means after
120 ms with a permissible tolerance of +/- 20 ms.
Tripping will also take place if the frequency ramp from
50 Hz to 51.4 Hz within 2 s (+0.7 Hz/s). If the fre-
quency ramp is set from 50 Hz to 49.4 Hz within 2 s
(0.3 Hz/s), there must not be any tripping.
7.4.9
Checking the external blocking and
reset functions
The external blocking input is free programmable by
the user.
To test the blocking function apply auxiliary supply
voltage to the external blocking input of the relay (ter-
minals C1/C1L or C1/C1H). Inject a test voltage
which could cause tripping for the tested functions. Ob-
serve that there is no trip and alarm for those functions.
Remove the auxiliary supply voltage from the blocking
input. Return the test voltages to the same condition.
The display should show “TRIP” now. Remove the test
voltages and apply auxiliary supply voltage to the ex-
ternal reset input of the relay (terminals C2/C2L or
C2/C2H). The display and LED indications should be
reset immediately.
7.5
Primary injection test
Generally, a primary injection test could be carried out
in the similar manner as the secondary injection test de-
scribed above. With the difference that the protected
power system should be, in this case, connected to the
installed relays under test „on line“, and the test volt-
ages should be injected to the relay through the volt-
age transformers with the primary side energized.
Since the cost and potential hazards are very high for
such a test, primary injection tests are usually limited to
very important protective relays in the power system.
Because of its powerful combined indicating and
measuring functions, the
XRW1-4
relay may be tested
in the manner of a primary injection test without extra
expenditure and time consumption.
In actual service, for example, the measured voltage
and frequency values on the
XRW1-4
relay display
may be compared phase by phase with the concerned
indications of the instruments of the switchboard to ver-
ify that the relay works and measures correctly.
