Siemens 6MD85, Manual

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Definition of the Variables
The definition of the variables is important for understanding the following implementation. The reference
side 1 indicates the function with 1. This yields the reference values voltage V1, frequency f1, and phase angle
α1. The side to be synchronized indicates the function with 2. The electrical variables of side 2 are then the
voltage V2, frequency f2, and phase angle α2.
When forming the differential variables, the function is oriented to the definition of the absolute measuring
error (Δ x = measured value – real value). The reference value and hence the real value is side 1. This results in
the following calculation specifications:
Differential voltage dV = V2 – V1
A positive sign means that the voltage V2 is greater than the voltage V1. In other cases, the sign is negative.
Differential frequency df = f2 – f1
A positive result means that according to the example from
Figure 6-59 the busbar frequency is greater than
the line frequency.
Phase-angle difference dα = α2 – α1
The representation is limited to ±180
o . A positive result means that α2 leads by a maximum of 180 o . In the
case of a negative value, α2 lags by a maximum of 180 o . Figure 6-63 shows the circumstances. The phase
angle α1 was added to the zero axis as a reference system.
If asynchronous systems are present and the frequency f2 is greater than f1, the angle dα then changes from
the negative value to 0 and then to the positive value. As shown in
Figure 6-63 , the direction of rotation is
counterclockwise (mathematically positive). At f2 < f1, the direction of rotation is clockwise.
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Figure 6-63 Phase-Angle Difference Representation dα
Only positive values are permissible for the setting parameters. Inequalities are used to characterize the
setting parameters uniquely. The representation is explained with the example of differential voltage. 2
setting values are necessary to allow unbalanced settings.
The inequality V2 > V1 yields a positive value for dV. The associated parameter is
Max. voltage diff.
V2>V1
. For the 2nd setting parameter
Max. voltage diff. V2<V1
, the inequality V2 < V1 applies. It
corresponds to a negative dV.
The procedure is the same for the differential frequency and differential phase angle.
Control Functions
6.4 Synchronization Function
364 SIPROTEC 5, High-Voltage Bay Controller, Manual
C53000-G5040-C015-9, Edition 11.2017