Table of Contents
Advertisement
Protection and Automation Functions
5.27 81 Frequency Protection – "f>" or "f<"
Parameter: Setting
•
Default setting: 49.5 Hz
This is the operating frequency threshold of the element. If the element is underfrequency, the element
will pickup if the frequency falls below this value. If the element is overfrequency, the element will
pickup if the frequency rises above this value. This should be set to suit the individual application.
Parameter: Hysteresis
•
Default setting: 0.1 %
This is used to set the drop-off threshold for an 81 element. If the element is underfrequency, the
element will pickup if the frequency falls below the 81-n setting and will reset when the frequency
recovers to the 81-n setting plus the 81-n hysteresis frequency. If the element is overfrequency, the
element will pickup if the frequency rises above the 81-n setting and will reset when the frequency
recovers to the 81-n setting minus the 81-n hysteresis frequency. This setting is set as a percentage of
the 81-n setting. The default setting of 0.1 % (approximately 0.05 Hz for setting around 50 Hz) is gener-
ally enough to avoid chatter of the element but consideration may be required for settings which are
close to the nominal value otherwise the element may not reset when the frequency recovers to nominal
value as the frequency is still in the hysteresis window.
Parameter: Delay
•
Default setting: 1 s
This is the time delay setting for the DTL element. This should be set to suit the individual application.
Element Inhibits
In the event of an inhibit being applied by a binary input or logic signal, an element that is picked up will be
reset. Reset of the inhibit will allow restart of the operating delay.
Frequency measurement is blocked when all phase-phase (line) voltages fall below 30 V. To allow the voltage
to stabilize this under voltage inhibit will reset 300 ms after all line voltages recover to levels above 30 V.
Frequency measurement is blocked for changes in frequency above 15 Hz/s. Very high rates of frequency
change may be indicative of a system short circuit fault that causes a sudden in the voltage vector positions.
Tripping Function
These elements can be used an alarm or monitoring function. Triggering of waveform storage must be config-
ured if required. If the element is a tripping function it must be configured to a designated trip contact to
trigger a fault record.
Settings Example
This example shows setting that could be applied for a 4-stage underfrequency application. This example
applies settings to provide automatic disconnection of load in stages depending on measurement of underfre-
quency. This could occur due to a loss of generating capacity in a network which results in an overload condi-
tion which can be managed by disconnection of the least critical loads in stages to maintain the supply of the
most critical loads whenever possible. The elements would be configured to operate 4 independent output
contacts or IEC 61850 goose which would be connected to separate circuit‑breaker tripping circuits. This
example considers device settings for the 81 elements but does not cover I/O mappings and tripping logic.
344
Reyrolle 7SR5, Overcurrent Protection Device, Device Manual
C53000-G7040-C014-1, Edition 11.2019
Advertisement
Table of Contents
