Schweitzer Engineering Laboratories, Inc. SEL-411L Data Sheet
Line Current Differential Protection
Automation and Control System
Key Features and Benefits
The SEL-411L Advanced Line Differential Protection, Automation, and Control System combines high-speed line cur-
rent differential, distance, and directional protection with complete bay control. This data sheet applies to all the model
options of the SEL-411L-0, -1, and -A relays. Table 5 details which features, functions, and applications are supported
by each of the SEL-411L models.
➤ Line Current Differential Protection. The 87L function of the SEL-411L provides protection for any transmission
line or cable with as many as three terminals over serial communications and as many as four terminals over
Ethernet communications, in three-pole or single-pole tripping modes. Each terminal can be connected in a dual
breaker arrangement.
➤ Generalized Alpha Plane. Phase-segregated (87LP), negative-sequence (87LQ), and zero-sequence (87LG)
differential elements use patented generalized alpha plane comparators. Combined with overcurrent supervision,
external fault detection, optional charging current compensation, and disturbance detection logic, these provide the
87L function with exceptional security and sensitivity. An adaptive feature increases security of the 87L function if:
➢ An external fault is detected
➢ Communications synchronization is degraded
➢ Charging current compensation is enabled but momentarily impossible because of loss-of-potential (LOP) or
other conditions
The generalized alpha plane principle is similar to the two-terminal SEL-311L. However, the SEL-311L and
SEL-411L are two completely independent hardware and firmware platforms. They are not compatible to be
applied in a line-current differential scheme.
➤ Inclusion of Power Transformers in the Protective Zone. The SEL-411L allows for in-line power transformer
applications by compensating for transformer vector group, ratio, and zero-sequence current. The 87L function
supports both harmonic blocking and/or harmonic restraint for stabilization during transformer inrush conditions.
During over-excitation conditions, the SEL-411L uses fifth-harmonic current to secure the 87L elements. The 87L
function can protect multiwinding transformers.
SEL-411L Advanced Line Differential
Protection, Automation, and Control System
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