Settings - Siemens SIPROTEC 7SK80 Manual

Functions
2.8 Frequency Protection 81 O/U
Pickup Values
The setting as overfrequency or underfrequency element does not depend on the parameter threshold values
of the respective element. An element can also function, for example, as an overfrequency element if its thresh-
old value is set below the nominal frequency and vice versa.
If frequency protection is used for load shedding purposes, the setting values depend on the actual power
system conditions. Normally, a time coordinated load shedding is required that takes into account the impor-
tance of the consumers or consumer groups.
Further application examples exist in the field of power stations. Here too, the frequency values to be set mainly
depend on the specifications of the power system / power station operator. The underfrequency protection safe-
guards the power station's own demand by disconnecting it from the power system on time. The turbo governor
regulates the machine set to the nominal speed. Consequently, the station's own demands can be continuously
supplied at nominal frequency.
Under the assumption that the apparent power is reduced by the same degree, turbine-driven generators can,
as a rule, be continuously operated down to 95% of the nominal frequency. However, for inductive consumers,
the frequency reduction not only means an increased current input, but also endangers stable operation. For
this reason, only a short-term frequency reduction down to about 48 Hz (for f
is permissible.
A frequency increase can, for example, occur due to a load shedding or malfunction of the speed regulation
(e.g. in an island network). In this way, the frequency increase protection can, for example, be used as over-
speed protection.
Dropout Thresholds
The dropout threshold is defined via the adjustable dropout-difference address 5415 DO differential. It
can thus be adjusted to the network conditions. The dropout difference is the absolute-value difference
between pickup threshold and dropout threshold. The default value of 0.02 Hz can usually remain. Should,
however, frequent minor frequency fluctuations be expected, this value should be increased.
Time Delays
The delay times 81-1 DELAY to 81-4 DELAY (addresses 5405, 5408, 5411 and 5414) allow the frequency
elements to be time coordinated, e.g. for load shedding equipment. The set times are additional delay times
not including the operating times (measuring time, dropout time) of the protection function.
2.8.3

Settings

Addresses which have an appended "A" can only be changed with DIGSI, under "Display Additional Settings".
Addr. Parameter
5401 FCT 81 O/U
5402 Vmin
5402 Vmin
5403 81-1 PICKUP
5404 81-1 PICKUP
5405 81-1 DELAY
5406 81-2 PICKUP
144
Setting Options
OFF
ON
10 .. 150 V
20 .. 150 V
40.00 .. 60.00 Hz
50.00 .. 70.00 Hz
0.00 .. 100.00 sec; ∞
40.00 .. 60.00 Hz
= 50 Hz) or 58 Hz (for f
N
Default Setting
OFF 81 Over/Under Frequency Protec-
tion
65 V Minimum required voltage for op-
eration
35 V Minimum required voltage for op-
eration
49.50 Hz 81-1 Pickup
59.50 Hz 81-1 Pickup
60.00 sec 81-1 Time Delay
49.00 Hz 81-2 Pickup
E50417-G1140-C344-A4, Release date 08.2010
= 60 Hz)
N
Comments
SIPROTEC, 7SK80, Manual