Schweitzer Engineering Laboratories SEL-700G Series, Инструкция по эксплуатации

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4.78
SEL-700G Relay Instruction Manual Date Code 20170814
Protection and Logic Functions
Group Settings (SET Command)
Single-Blinder Scheme
The single-blinder scheme, shown in Figure 4.46, consists of mho element
78Z1, right blinder 78R1, and left blinder 78R2.
Figure 4.46 Single-Blinder Scheme Operating Characteristics
This scheme detects an out-of-step condition by tracking the path of positive-
sequence impedance trajectories that pass through the protection zone. If the
relay detects an out-of-step condition, it asserts the following Relay Word bits:
➤
Relay Word bit SWING picks up when the positive-sequence
impedance moves from the load region into Area A (left blinder
78R2 and mho element 78Z1 assert).
➤
Relay Word bit OOS picks up when the impedance trajectory
advances to Area B between the two blinders (right blinder
78R1, left blinder 78R2, and mho element 78Z1 assert).
➤
At the time the impedance trajectory exits the mho circle via
Area C, the rising-edge triggered timer with 78TD pickup delay
and 78TDURD dropout-delay starts timing. Relay Word bit
OOST remains picked up for 78TDURD seconds after the
pickup delay time 78TD expires.
➤
The previous description is only for trajectories traveling from
right to left. Out-of-step trajectories traveling from left to right
traverse the protection zone in the reverse sequence (that is, from
Area C to B to A). The Relay Word bits assert in the same way,
whether trajectories travel from right to left or from left to right.
The single-blinder scheme distinguishes between short-circuit faults and out-
of-step conditions by tracking the path of the impedance trajectory. During
short-circuit faults, the impedance moves from the load region to inside the
mho element and between the two blinders almost instantaneously, preventing
the out-of-step function from picking up.
Figure 4.47 shows the logic diagram for the single-blinder scheme. In the
figure, the states of 78R1 and 78R2 are latched on the rising edge of SWING
to determine if the swing has entered the 78Z1 mho circle from the right or the
left. (For an OOST to occur, the swing must exit the 78Z1 mho circle in the
opposite direction from which it entered.) The latched states of 78R1 and
Diameter of 78Z1 = (78REV + 78FWD)
78R2
Pickup 78R1
Pickup
78R1
Right Blinder
R
78R2
Left Blinder