Woodward High PROTEC MRU4, Руководство пользователя

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Protective Elements
f< and DF/DT – Underfrequency and DF/DT
With this setting the frequency element supervises the frequency and the absolute frequency difference during a
definite time interval.
In the selected frequency parameter set f[X], an underfrequency pickup threshold f<, a threshold for the absolute
frequency difference (frequency decrease) DF and supervision interval DT can be set.
f> and DF/DT – Overfrequency and DF/DT
With this setting the frequency element supervises the frequency and the absolute frequency difference during a
definite time interval.
In the selected frequency parameter set f[X], an overfrequency pickup threshold f>, a threshold for the absolute
frequency difference (frequency increase) DF and supervision interval DT can be set.
Working principle f< and DF/DT | f> and DF/DT
(please refer to block diagram on next page)
The frequency element supervises the three voltages (depending on if the voltage transformers are wired in Star or
Delta connection »
VL12«, »VL23« und »VL31« oder »VL1«, »VL2« und »VL3«).
If any of the three phase voltages is e.g. below 15% Vn, the frequency calculation is blocked (settable via parameter
»
V Block f«). According to the frequency supervision mode set in the Device Planning (f< and DF/DT or f> and
DF/DT), the evaluated phase voltages are compared to the set frequency pickup threshold and the set frequency
decrease or increase threshold DF.
If in any of the phases, the frequency exceeds or falls below the set pickup threshold and if there are no blocking
commands for the frequency element, an alarm is issued instantaneously. At the same time the timer for the
supervision interval DT is started. When, during the supervision interval DT, the frequency still exceeds or is below
the set pickup threshold and the frequency decrease/increase reaches the set threshold DF, a tripping command
will be issued.
Working Principle of DF/DT Function
(Please refer to f(t) diagram after the block diagram)
Case 1:
When the frequency falls below a set f< threshold at t1, the DF/DT element energizes. If the frequency difference
(decrease) does not reach the set value DF before the time interval DT has expired, no trip will occur. The
frequency element remains blocked until the frequency falls below the underfrequency threshold f< again.
Case 2:
When the frequency falls below a set f< threshold at t4, the DF/DT element energizes. If the frequency difference
(decrease) reaches the set value DF before the time interval DT has expired (t5), a trip command is issued.
408 MRU4 DOK-HB-MRU4-2E