Siemens 6MD85, Manual

Page: 849 / 1256

Application and Setting Notes
Parameter:
Threshold
•
Default setting
(_:13231:3) Threshold
=
3.000 Hz/s
The pickup value depends on the application and is determined by power-system conditions. In most cases, a
network analysis will be necessary. A sudden disconnection of loads leads to a surplus of active power. The
frequency rises and causes a positive frequency change. On the other hand, a failure of generators leads to a
deficit of active power. The frequency drops and results in a negative frequency change.
The following relations can be used as an example for estimation. They apply for the change rate at the begin-
ning of a frequency change (approximate 1 s).
Where:
f
rated
Rated frequency
ΔP Active power change
ΔP = P
Consumption
- P
Generation
S
rated
Rated apparent power of the machines
H Inertia constant
Typical data for H:
For hydro generators (salient-pole machines)
H = 1.5 s to 6 s
For turbine-driven generators (non-salient pole rotors) H = 2 s to 10 s
For industrial turbine-driven generators H = 3 s to 4 s
EXAMPLE
f
rated
= 50 Hz
H = 3 s
Case 1: ΔP/S
rated
= 0.12
Case 2: ΔP/S
rated
= 0.48
Case 1: df/dt = -1 Hz/s
Case 2: df/dt = -4 Hz/s
Parameter:
Operate delay
•
Default setting
(_:13231:6) Operate delay
=
1.00 s
You can use the
Operate delay
parameter to avoid overfunction due to disturbing influences (for example,
switching operations). If the protection function is supposed to respond quickly, set the
Operate delay
parameter to 0 s.
For monitoring small changes (< 1 Hz/s), a small time delay is useful to avoid overfunctioning.
Parameter:
Dropout differential
•
Recommended setting value
(_:13231:4) Dropout differential
=
0.10 Hz/s
You can use the
Dropout differential
parameter to define the dropout value. The recommended value
is
0.10 Hz/s
.
7.21.4.2
Protection and Automation Functions
7.21 Rate of Frequency Change Protection
SIPROTEC 5, High-Voltage Bay Controller, Manual 849
C53000-G5040-C015-9, Edition 11.2017