Toshiba GRL100-701B Instruction Manual page 90

At terminal A, the terminal voltage V A is taken as a reference voltage. Then, the phase angle of
the remote terminal voltage V B changes as shown in Figure 2.7.2. Out-of-step is detected when
V B moves from the second quadrant to the third quadrant or vice versa.
180°
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
OST2
Communication failure
CRT_NON_BLOCK
1587 OST_BLOCK
OST2: Element for remote 2 terminal in three-terminal application.
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
[OST]
90°
V B3
V B2
V B1
270°
Figure 2.7.2 Voltage Phase Comparison
48
&
≥1
(+)
52
&
(+)
1
Range Step
OFF/Trip/BO
 89 
V B3'
V B2'
V A
V B1'
&
[OST]
"Trip"
[OST]
&
"BO"
Default
OFF
6 F 2 S 0 8 5 0
87
OSTT
≥1
OST-TP
119
OST-BO