Siemens 7SR242 Duobias - 2.11 Under;Over Frequency (81)

7SR242 Duobias Commissioning & Maintenance Guide
©2010 Siemens Protection Devices Limited Chapter 6 Page 43 of 57
2.11 Under/Over Frequency (81)
Figure 2-13 Under/Over Frequency
Voltage Inputs: V
1
(V
X
)
Current Inputs: n/a apply zero current to stabilize other functions
Disable:
Map Pickup LED: 81-n - Self Reset
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 140-175ms in line with the
Performance Specification. 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 Pick-up LED to
operate for the function. If the delay setting is short the operation of the element can be easily checked directly.