2 Functions
120
7UM61 Manual
C53000-G1176-C127-3
The following relations can be used as an example for estimation. They apply for the
change rate at the beginning of a frequency change (approx. 1 second).
Significance:
f
N
Nominal Frequency
∆P Active power change
∆P = P
Consumption
– P
Generation
S
N
Nominal apparent power of the machines
H Inertia constant
Typical values for H are:
for hydro-electric generators (salient-pole machines) H = 1.5 s to 6 s
for turbine-driven generators (cylindrical-rotor machines) H = 2 s to 10 s
for industrial turbine-generators H = 3 s to 4 s
Example:
f
N
= 50 Hz
H = 3 s
Case 1: ∆P/S
N
= 0.12
Case 2: ∆P/S
N
= 0.48
Case 1: df/dt = -1 Hz/s
Case 2: df/dt = -4 Hz/s
The default settings are based on the above example. The four stages have been set
symmetrically.
Time Delays The delay time should be set to zero wherever the protection function is supposed to
respond very quickly. This will be the case with high setting values. For the monitoring
of small changes (< 1Hz/s), on the other hand, a small delay time can be useful to
avoid overfunctioning. The delay time for stage 1 is set at address 4504 T df1/dt,
and the time set there is added to the protection operating time.
Release by the Fre-
quency Protection
The parameter df1/dt & f1 (Address 4505) is used to set the release of the stage
from a certain frequency threshold on. For this the pertinent frequency stage of the fre-
quency protection is queried. In the setting example this is stage f1. To exclude cou-
pling of the two functions, the parameter can be set to OFF (default setting).
Advanced Parame-
ters
The advanced parameters allow to set for two stages each (e.g. df1/dt and df2/dt) the
dropout difference and the measuring window. These parameters can only be set with
the DIGSI communication software.
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