Siemens 7SJ82, Manual

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General Functionality
Description
Logic of the Function
[lo_RPP general functionality, 2, en_US]
Figure 6-236 Logic Diagram of the Cross-Stage Functionality
Calculating the Reverse Power
The reverse-power protection calculates the active power from the symmetrical components of the funda-
mental components of the voltages and currents. It generates the average value of the active power over a
fixed number of cycles. Since positive-sequence variables are used for evaluation, the reverse power is deter-
mined independently of unbalance in currents or voltages. The frequency-tracking sampled values are used for
calculation. The determined reverse power corresponds to the load on the driving-power side. The calculated
active-power value corresponds to the total active power.
Taking the phase-displacement angle of the voltage and current transformers into account, the function calcu-
lates the exact active power even with a high apparent power and a small cos φ. A constant correction angle
φ
corr
makes correction possible. The influence of the current-transformer angle error is predominant here.
Determine this constant correction angle when you commission the protection device in the plant and adjust
it as specified in the table (see
Table 11-1 ).
Power Calculation and Angle Correction
To satisfy the high measuring-accuracy requirements, the power measured value is additionally averaged over
16 cycles before it is supplied to the protection function. The active power is calculated from the symmetrical-
component vectors of voltage V1 and current I1. The total power is evaluated as power. The complex apparent
power results from the following relationship. The real component is the active power:
S = 3V
1
⋅ I
1
* = 3V
1
e j
ϕ
V ⋅ I
1
e -j
ϕ
I = 3V
1
I
1
e j(
ϕ
V-
ϕ
I)
P = 3V
1
I
1
cos(φ
V
-φ
I
)
6.38.3
6.38.3.1
Protection and Automation Functions
6.38 Reverse-Power Protection
810 SIPROTEC 5, Overcurrent Protection, Manual
C53000-G5040-C017-8, Edition 07.2017