
81 Frequency Protection – "f>" or "f<"
Elements can be mapped to operate for frequency measurement on the 3 phase voltage inputs or the single
phase input V4. The 3 phase function can be tested by application of 1P or 3P voltage. For over-frequency, the
elements with the highest setting should be tested first and for under-frequency the elements with the lowest
settings should be tested first. The elements with other settings can then be tested without need to disable
the elements already tested. Note that the relay is designed to track the gradual changes in power system
frequency and that sudden step changes in frequency during testing do not reflect normal system operation.
Normal, instantaneous, operation of the frequency element is 140 ms to 175 ms in line with the
Technical
Data
. Application of sudden step changes to frequency can add additional delay which can produce
misleading test results.
Gradually increase/decrease applied voltage frequency until 81-n operation occurs. Elements set for more
extreme frequency fluctuation should be tested first with lesser elements disabled.
If the 81-n
Delay
setting is long it will be advantageous to map the function to temporarily drive the relevant
pickup output in the
Pickup Config
sub-menu in the
Output Config
menu as this will allow the
Pickup
LED to operate for the function. If the delay setting is short the operation of the element can be easily checked
directly.
The frequency should then be gradually decreased/increased until the element resets. The reset frequency can
be used to check the
Hysteresis
setting.
Apply setting fre0.5 Hz for over-frequency or -0.5 Hz for under-frequency and record operating time.
Starting with the element in the operated condition, gradually increase or decrease the applied voltage until
the element resets. Measure the reset voltage level to check the 81
Hysteresis
setting.
Freq
(Hertz)
U/O
Delay
(sec)
Hyst.
D.O.
(calc.)
P.U. Freq
(Hz)
D.O.
Freq.
(Hz)
Operate
Time @ ±
0.5 Hz
UV
Guard
Notes
Element Blocking
The U/O frequency elements can be blocked by
Binary Input Inhibit
. This functionality should be
checked.
Element
BI Inhibits
81-1
81-2
81-3
81-4
81-5
81-6
Check correct indication, trip output, alarm contacts, waveform record.
When testing is complete reinstate any of the disabled functions.
87GH Restricted Earth Fault Protection – High-Impedance
The setting resistance should be measured and the value compared to that specified in the settings data. Both
values should be recorded.
Settings Data Resistor Value
Measured
The high value of setting resistance
R
will often prevent secondary current injection when using a digital test
set. It is normal practice in these cases to short out the series resistor to allow testing, the shorting link should
be removed after testing.
9.10.21
9.10.22
Functional Tests
9.10 Protection Functional Tests
446
Reyrolle 7SR5, Transformer Protection Device, Device Manual
C53000-G7040-C015-1, Edition 11.2019