89
6
F
2
S
0
8
5
0
At terminal A, the terminal voltage VA is taken as a reference voltage. Then, the phase angle of
the remote terminal voltage VB changes as shown in Figure 2.7.2. Out-of-step is detected when
VB moves from the second quadrant to the third quadrant or vice versa.
90
°
180
°
270
°
VB1'
VB1
VA
VB3'
VB3
VB2'
VB2
Figure 2.7.2 Voltage Phase Comparison
In the case of a three-terminal line, this phase comparison is performed between each pair of
terminals. All the terminals can detect any out-of-step provided its locus crosses the protected
line.
Figure 2.7.3 shows a scheme logic for the out-of-step protection. The output signal of the
out-of-step element OST1 performs three-phase final tripping. The output signal is blocked
when the scheme switch [OST] is set to "OFF" or binary signal OST_BLOCK is input. The
tripping signal of the out-of-step protection can be separated from other protection tripping
signals by the switch [OST]. In this case, the switch [OST] is set to "BO" and the tripping signal
OST-BO is assigned to a desired binary output number (for details, see Section 4.2.6.9). When
the tripping signal of the out-of-step protection is not separated from other protection tripping
signals, the switch [OST] is set to "Trip".
The voltage of the out-of-service terminal is set to zero at the receiving terminal and the OST
does not function with the out-of-service terminal.
OST1
&
OST-TP
[OST]
"BO"
(+)
&
&
[OST]
"Trip"
(+)
OST-BO
Communication failure
1
OST_BLOCK
1587
52
OST2
&
≥
1
48
≥
1
OSTT
87
119
OST2: Element for remote 2 terminal in three-terminal application.
CRT_NON_BLOCK
Figure 2.7.3 Scheme Logic for Out-of-step Protection
Setting
The OST measuring element has no setting items. Only the scheme switch [OST] setting is
necessary for the out-of-step protection.
Element Range Step
Default
[OST] OFF/Trip/BO
OFF
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