Synchronism Check Element - Synchrocheck (25) - GE F650 Instruction Manual

5 SETTINGS 5.5 CONTROL ELEMENTS

5.5.4 SYNCHRONISM CHECK ELEMENT - SYNCHROCHECK (25)

Note: The Switchgear element used in the F650 synchronism element is the one configured in the Number of Switchgear
setting inside Breaker settings, at "Setpoint > System Setup > Breaker > Breaker Settings".
WARNING
When testing this function do not forget that the relay must detect an open breaker to operate.
The synchronism element is used for monitoring the connection of two parts of the circuit by the close of a breaker. This
element verifies that voltages (V1 and V2) at both sides of the breaker are within the magnitude, angle and frequency limits
set by the user. V1 and V2 are the line and busbar voltage values measured by the relay.
Synchronism check (25) is defined as the comparison of the voltage difference of two circuits with different sources to be
either linked through an impedance element (transmission line, feeder, etc.), or connected through parallel circuits of
defined impedance (Figure 5–22:) The voltage comparison between both sides of a breaker is performed before closing the
breaker, in order to minimize internal damage that could occur due to the voltage difference, both in magnitude and angle.
This is extremely important in steam generating plants, where reclosing output lines with angle differences could lead to
severe damage to the turbine axis.
V
s
V
r
52
s
52
r 5
Z
line
C/2
C/2
Z
Parallel
Figure 5–22: SYNCHRONISM CHECK ELEMENT
The difference in voltage level and phase angle in a given moment is the result of the existing load between remote sources
connected through parallel circuits (load flux), as well as a consequence of the impedance of those elements connecting
them (even if there is no load flux in parallel circuits, or because sources to be connected are completely independent and
isolated from one another).
In interconnected systems, the angle difference between both ends of an open breaker is usually negligible, as its sources
are remotely connected through other elements (equivalent or parallel circuits). However, in isolated circuits as in the case
of an independent generator, the difference in angle, voltage levels and relative slip of voltage phasors can be very
important. It may happen that the relative slip of voltage values is very low or null so that they will rarely be in phase.
Luckily, due to the changing conditions of a power system (connection-disconnection of loads, sources, and new inductive-
capacitive elements) the relative slip between phasors is not null and they can be synchronized.
In the first case, even if we must take into consideration the length of the line whose ends (sources) will be connected for
determining the angle difference between them, this is not enough to fix the synchronism conditions before closing the
breaker. Experience tells us that the window of angle difference between voltage phasors must be fixed to a value of 15º-
20º.
GEK-106310AB F650 Digital Bay Controller 5-89