52BT Setting (52BT) And Switch-Onto-Fault Protection
The relay includes switch-onto-fault logic for use during line testing. This logic allows you to
enable selected elements for a short duration after line breaker closure. Switch-onto-fault
logic permits instantaneous line breaker tripping for end-of-section faults which would
normally be cleared in Zone 2 time.
Switch-onto-fault protection is provided through elements selected in the MTO logic mask,
typically non-time delay overreaching elements. The 52BT time delay setting dictates the
interval during which these elements are enabled for tripping.
The 52BT bit is an inverted time delayed follower of the 52A input. When the 52A input
changes from the asserted (breaker closed) to deasserted state (breaker open), the 52BT bit
remains low for 52BT time. After the 52BT timer expires, the 52BT bit changes from logic
state
"
0
"
to
"
1.
"
When the breaker is closed (from an open state), 52BT remains high for
52BT time, then deasserts. While the 52BT bit is high, elements selected in the MTO logic
mask are enabled to trip. Thus, for 52BT time after breaker closure, assertion of any element
selected in the MTO logic mask causes the relay to close the TRIP output contacts. This
logic provides Switch-Onto-Fault (SOTF) protection.
Figure 5.2 illustrates the timing relationship of the 52A input and 52BT element.
Figure 5.3: 52A Input and 52BT Timing Diagram
MTO logic is enabled during the time period shown for Regions 1 and 2. During Region 1,
the MTO logic is enabled to protect the open line breaker. For line breaker tank faults, the
relay can issue the trip signal required for breaker failure schemes. Any time delay associated
with the circuit breaker auxiliary contact opening occurs during the time shown in Region 1.
Region 2 shows the time period where MTO logic is performing true switch-onto-fault
transmission line protection. The 52BT element serves as a permissive signal for elements set
in the MTO mask.
For example, the circuit shown in Figure 5.4 has a phase-phase fault close to Breaker 2.
Suppose that Breaker 1 is the preferred source for testing the line (Breaker 2 is to remain
open until Breaker 1 energizes the line). If standard time-stepped distance protection is
employed without SOTF protection, the fault would have to be cleared in Zone 2 time. Using
the relay MTO logic, the instantaneous Zone 3 phase elements detect the fault and issue a trip
5-22
Applications
SEL-221F, -1 Instruction Manual
Date Code 920508
Содержание SEL-221F
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Страница 170: ...Figure 6 2 Horizontal Front and Rear Panel Drawings Date Code 920508 Installation 6 7 SEL 221F 1 Instruction Manual ...
Страница 174: ...Figure 6 8 Dc External Connection Diagram Typical Date Code 920508 Installation SEL 221F 1 Instruction Manual 6 11 ...
Страница 228: ...APPENDICES TABLE OF CONTENTS Parts Placement Diagram Date Code 920508 Table of Contents SEL 221F 1 Instruction Manual i ...
Страница 229: ...SEL 200 Series Relay Main Board Troubleshooting Test Points and Jumper Locations ...