- 340 -
Frequency protection (FRQ/DFRQ)
The frequency protection (FRQ and DFRQ) functions have six frequency elements (stages) to
detect frequency-deviations and frequency-changes, respectively. If the deviations or changes
are appeared, the FRQ and DFRQ function can issue a trip signal (or an alarm signal) in
response to the degree of the frequency-deviation and the frequency-change.
With respect to monitoring the frequency-deviation, either an under-frequency element
(UF) or an over-frequency element (OF) is used to monitor a frequency. The user can set the
degree of frequency deviation at each frequency. Generally, the UF element is applied to
monitor the balance between the power generation capability and the loads. The OF element
is used monitor the frequency to be within the normal range by load shedding; the OF element
is used to protect synchronous machines from possible damage owing to over-frequency
conditions.
With respect to monitoring the frequency-changes, either a frequency-rise element
(RISE) or a frequency-down element (DOWN) is used to monitor the frequency-change. To
monitor the frequency-change, the user should select either the RISE element or the DOWN
element at respective frequencies. The DFRQ is used to ensure the operation of load shedding
promptly when the change of frequency is very rapid.
To simplify the description, only stage 1 is discussed, but is applicable to the other stages;
hence, read the express for stage 1 as the other stages unless a special explanation or
instruction has been produced.
─────────────────────────────────────────────────────────────────
Note: Several IED models do not have frequency protection features. To determine whether
the features are implemented in the IED or not, locate the IED ordering number; and check
the order number at “G&T position” referring to the comparison table below. For more
information, see
Appendix: Ordering
.
Table 2.26-1 Comparative table in respective ordering numbers
✓: Applicable NA: Not applicable
To Next Page
Loading...
