Eaton EDR-5000 Nstallation, Operation And Maintenance Manual page 678

81UR – Underfrequency and Rate of Change of Frequency (df/dt)
With this setting, the frequency element supervises if the frequency falls below a set pickup threshold and if the
frequency gradient exceeds a set threshold at the same time.
In the selected frequency parameter set 81[X], an underfrequency pickup threshold f<, a frequency gradient df/dt, and a
tripping delay can be set.
Whereby:
Positive df/dt = the frequency element detects an increase in frequency;
•
Negative df/dt = the frequency element detects a decrease in frequency; and
•
Absolute df/dt (positive and negative) = the frequency element detects both, increase and decrease in frequency.
•
81OR – Overfrequency and Rate of Change of Frequency (df/dt)
With this setting, the frequency element supervises if the frequency exceeds a set pickup threshold and if the frequency
gradient exceeds a set threshold at the same time.
In the selected frequency parameter set 81[X], an overfrequency pickup threshold f>, a frequency gradient df/dt, and a
tripping delay can be set.
Whereby:
Positive df/dt = the frequency element detects an increase in frequency;
•
Negative df/dt = the frequency element detects a decrease in frequency; and
•
Absolute df/dt (positive and negative) = the frequency element detects both, increase and decrease in frequency.
•
Working Principle
The frequency element supervises the three phase voltages » VA« , » VB« and » VC« . If any of the three phase voltages
is below 15% Vn, the frequency calculation is blocked. According to the frequency supervision mode set in the Device
Planning (81UR & df/dt or 81OR & dt/dt), the evaluated phase voltages are compared to the set frequency pickup
threshold and the set frequency gradient (df/dt) threshold. If in any of the phases, both the frequency and the frequency
gradient exceed or falls below the set thresholds and if there are no blocking commands for the frequency element, an
alarm is issued instantaneously and the tripping delay timer is started. When the frequency and the frequency gradient
still exceed or are below the set threshold after the tripping delay timer has elapsed, a tripping command will be issued.
EDR-5000
(Please refer to block diagram on next page.)
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