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Date Code 20010625
Setting the Relay
9-37
SEL----311L Instruction Manual
A
PPLICATION
S
ETTINGS
Application settings are available in order to reduce the number of settings to be made for
applications that may not require the full features of the SEL-311L Relay.
By setting APP = 311L, all the settings are shown. If APP is set equal to 87L, 87L21, or 87L21P,
then a reduced group of settings are selected.
Section 14: Application Settings for SEL-311L
Relays
contains the settings sheets for APP = 87L, 87L21, and 87L21P. The following list
contains summaries for each APP setting.
•
87L—Basic line current differential and overcurrent backup, including tapped load
coordination. All settings related to elements requiring potentials applied to the relay are
hidden. Some SEL
OGIC
control equations, programmable displays, and advanced
functions are also hidden. M
IRRORED
B
ITS
communications are enabled.
•
87L21—Includes all of the elements of the 87L application setting as well as three zones
of distance protection. SEL
OGIC
control equations and programmable display points are
also enabled.
•
87L21P—Includes all the elements of the 87L21 application setting plus
communications-assisted tripping schemes.
S
ETTINGS
E
XAMPLE
: 230
K
V T
RANSMISSION
L
INE WITH
T
APPED
L
OAD
Use the SEL-311L Relay to protect a transmission line with transformer tapped load. Figure 9.11
shows a 230 kV transmission line with SEL-311L Relay protection at Stations S and R. A tap
midway between Stations S and R supplies power to a large industrial load. This example
explains the calculation of settings for the SEL-311L Relay at Station S that protects the 230 kV
circuit between substations S, R, and the transformer bank at bus T. Note that this same scheme
may be used on lower voltage applications such as 69 kV.
The primary protection is differential overcurrent with tapped load total overcurrent elements
(T50/T51). High-speed differential elements (87L) provide torque control for the tapped load
elements; T50/T51 elements are blocked until the corresponding 87L element asserts. Backup
step distance and single-ended time overcurrent elements operate for faults on the 230 kV line.
Zone 1 provides instantaneous protection while Zone 2 provides torque control for the phase
time-overcurrent element. This time overcurrent is coordinated with the load transformer
protection. Zone 3 provides the overreaching backup protection usually provided by Zone 2.
In this example, maximize line security (trip saving) while still providing adequate line
protection. Backup overcurrent settings provide protection for faults on the 230 kV system only.
The differential elements assure that the fault is in the protected line or on the tap. Tapped load
overcurrent elements are set to coordinate with primary protection on the tap transformers. To
achieve high speed tripping with T50 elements over the entire protected line, accept a small risk
of tripping for a fault between the transformer breakers and bushings. The 230 kV delta/13.8 kV
grounded wye transformers on the tap assure that zero-sequence quantities seen by the SEL-311L
Relay are due to transmission system faults. This example assumes that the transformer
secondaries are not paralleled for normal operation.
To avoid the compromises that must be made with tapped lines, such as loss of sensitivity and
delayed tripping, install a third SEL-311L Relay and communications at the tap point even if no
breaker is present. A third SEL-311L Relay provides high-speed, high-sensitivity, protection of
the transmission line without overreaching for faults on the tap. This example considers two
terminal protection only.
Содержание SEL-311L
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