P.3.2
SEL-411L Relay Protection Manual Date Code 20151029
Protection Functions
87L Theory of Operation
➤ Switch-Onto-Fault Logic on page P.3.217
➤ Communications-Assisted Tripping Logic on page P.3.220
➤ Directional Comparison Blocking Scheme on page P.3.221
➤ Permissive Overreaching Transfer Tripping Scheme on
page P.3.224
➤ Directional Comparison Unblocking Scheme Logic on
page P.3.232
➤ Trip Logic on page P.3.237
➤ Circuit Breaker Failure Protection on page P.3.247
➤ Over/Underfrequency Elements on page P.3.257
➤ 87L Communication and Timing on page P.3.261
➤ Configuration, Monitoring, Alarming, and Logic for 87L
Channels on page P.3.279
➤ 87L Enable and Blocking Logic on page P.3.280
➤ 87L Active and Required Channel Logic on page P.3.282
➤ 87L Channel Synchronization Logic and Status on
page P.3.284
➤ 87L Channel Monitoring and Alarming Logic on page P.3.291
➤ 87L Standby Channel Switchover Logic on page P.3.297
➤ 87L Time Fallback Logic on page P.3.300
➤ 87L Master, Outstation, and Loss of Protection Logic on
page P.3.306
➤ 87L Communications Report on page P.3.308
➤ 87L Channel Recorder on page P.3.313
➤ Protection Application Examples on page P.3.315
87L Theory of Operation
Introduction
This section provides a high level overview of the line current differential
protection function (87L) in the relay. It also reviews such key 87L operating
principles as scaling, sampling, transmission, alignment, and processing of
current signals; the Alpha Plane operating characteristic; external fault
detection and built-in security; line charging current compensation; and
application with in-line transformers.
The 87L element of the relay can protect two-, three-, or four-terminal lines.
Each terminal can be connected in a dual-breaker arrangement (ring-bus,
breaker-and-a-half, or double-bus double-breaker). The relay provides proper
security for the 87L function by supporting two current inputs for individual
measurement of the two currents at each line terminal. Through the use of
SEL
OGIC
®
control equations, you can include or exclude each current input
dynamically from the differential zone, allowing such advanced applications
as breaker substitution (breaker transfer) in double-bus single-breaker or
transfer bus configurations.
To Next Page
Loading...
