Siemens SIPROTEC 4 7UT6 Series Manual page 241

Generally, turbine-driven generators can be continuously operated down to 95 % of nominal frequency
provided that the apparent power is reduced proportionally. However, for inductive consumers, the frequency
reduction not only means greater current consumption but also endangers stable operation. Therefore, a
shortterm frequency reduction down to approx. 48 Hz (at f
16,7 Hz) is permitted.
A frequency increase can, for example, occur due to a load shedding or malfunctioning of the speed control
(e.g. in an island network). A frequency increase protection, e.g. as speed control protection can be used here.
The setting ranges of the frequency stages depend on the set rated frequency. The three underfrequency
stages are set under addresses
Stage
f< stage
f<< stage
f<<< stage
f> stage
By means of setting an underfrequency stage to 0, it can be deactivated. If the overfrequency stage is not
required, set it to ∞.
Durch Einstellung einer Unterfrequenzstufe auf 0 können Sie diese unwirksam stellen. Benötigen Sie die Über-
frequenzstufe nicht, stellen Sie diese auf ∞ ein.
The delay times can be set under addresses 5641 T f<, 5642 T f<<, 5643 T f<<< and 5644 T f>. Hereby,
a grading of frequency stages can be achieved or the required switching operations in the power station
sector can be triggered. The set times are pure additional delay times that do not include the operating times
(measuring time, drop-out time) of the protective function. If a delay time is set to , this does not result in a
trip, but the pickup will be indicated.
Setting example:
The following example illustrates a setting of the frequency protection for a generator that indicates a delayed
warning at approx. 1 % decreased frequency. In case of a further frequency decrease, the generator is discon-
nected from the network and finally shut down.
Changes to CPU
modules
Stage
Warning
f<
Disconnection
from the
f<<
network
Shutdown
f<<<
Warning and trip 52.00 Hz
f>
Minimum Voltage
The frequency protection is blocked on undershooting the minimum voltage U MIN. The recommended value
is approx. 65 % U
of the main protected object, the value must be set as reference value under address 5652 U MIN, e.g. 0.65.
When assigned to a measuring location the value of phase-phase voltage must be set under address 5651
Umin in Volt , e.g. 71. V at U
by setting this address to 0. However, no frequency measuring is possible below approx. 5 V (secondary) so
that the frequency protection can no longer function.
SIPROTEC 4, 7UT6x, Manual
C53000-G1176-C230-5, Edition 09.2016
Address at f =
N
50 Hz
5611
5612
5613
5614
Setting at f =
N
50 Hz
49.50 Hz
48.00 Hz
47.00 Hz
. The setting value is based on phase-phase voltages. If the frequency protection of one side
N
= 110 V (65 % of 110 V). The minimum voltage threshold can be deactivated
Nsec
= 50 Hz) or 58 Hz (at f
N
60 Hz 16.7 Hz
5621 5631
5622 5632
5623 5633
5624 5634
60 Hz 16.7 Hz
59.50 Hz 16.60 Hz
58.00 Hz 16.00 Hz
57.00 Hz 15.70 Hz
62.00 Hz 17.40 Hz
2.16 Frequency Protection
= 60 Hz) or 16 Hz (at f
N
Parameter name
f<
f<<
f<<<
f>
Delay
20.00 s
1.00 s
6.00 s
10.00 s
Functions
=
N
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