Reverse-Power Protection
Secondary Test
When performing the secondary test, note that the setting value for the reverse power refers to the machine
variables. Due to the mismatching of the current transformer, you must check with reduced currents. You can
deduce the reduction from the ratio I
rated, generator
/ I
rated, CT
. Check the reverse-power protection at rated voltage.
If the voltage transformer is not adjusted to the rated generator voltage, correct the secondary voltage, too.
Use the following ratio:
V
rated, generator
/V
rated, VT
Primary Test
For measurements on the protection current transformers and with sensitive setting of the reverse-power
protection, Siemens recommends determining the reverse power and the angle-correction values. Regardless
of the generator excitation, that is regardless of the reactive power Q, the reverse power P as a pure active
power is constant. The resulting characteristic curve is a straight line that runs parallel to the Q axis. Due to
possible angle errors of current transformers and voltage transformers, the protection device does not
measure a constant active power. The current flowing at this time, which can be assumed as being propor-
tional to the reactive power, has a substantial influence.
The deviations are determined with 3 measurements and the correcting quantity φ
corr
is determined from the
results.
To calculate the correction angle, enter the active power and reactive power measured with the device in the
following table.
Use the functional measured values P1avg and Q1avg (type averaged).
Table 11-1
Value Table for Angle Correction
State Reverse Power Reactive Power
Reactive power near zero P
0
= Q
0
=
Overexcited P
1
= Q
1
=
Underexcited P
2
= Q
2
=
[dw_RPP correction angle, 2, en_US]
Figure 11-10 Determining the Correction Angle φ
corr
CAUTION
Be careful if you operate the turbine without a certain minimum steam flow (cooling effect).
Operating the turbine without a certain minimum steam flow (cooling effect) can overheat the
turbine blades!
²
The consumption of reverse power for a turbo-generator set is only allowed for a short time!
11.14
11.14.1
11.14.2
Functional Tests
11.14 Reverse-Power Protection
1396 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017
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