Although the fault-location computation takes several seconds, faults in quick succession, such
as occur in a reclosing sequence, are handled. This is because the fault data are stored, and
subsequently processed in turn. As an example, suppose three faults occur within a few
seconds. The data from them are stored as they occur. The fault-location computations begin
with the first (oldest) fault and proceed until all three faults are processed. Each of the
summary event reports is transmitted as soon as the corresponding fault location is available.
Shunt capacitance of the transmission line is not taken into account. The capacitance causes
the fault location to appear more remote by, approximately, a factor of 1/cos(bL), where bL
is the line length in radians at 60 Hz. One wavelength at 60 Hz is 3100 miles. For example,
the line length of a 100-mile line in radians is calculated:
The indication neglecting capacitance is about cos (0.2027) = 0.98 times the actual location,
or about 2 miles short for a fault at the far end of a 100-mile line.
When compensation using shunt reactors is employed, and when the measured current equals
the reactor current plus the line current, the shunt reactors reduce the errors due to neglecting
the shunt capacitance of the transmission line.
(100/3100) * 2 * 3.14159 = 0.2027 radians.
DIRECTIONAL ELEMENTS
The SEL-267D relay contains three directional elements, applied as shown below:
Fault Type
Criterion
Directional Element
ABC
AB, BC, CA,
ABG, BCG, CAG
50A3 + 50B3 + 50C3
Phase directional (32PQ)
AG, BG, CG
Depends on 32IE, and 32QE
Zero-sequence or
negative-sequence
settings only
The directional elements are phasor-product derived. For the negative-sequence element, the
product is negative-sequence voltage times negative-sequence current, adjusted by the
maximum torque angle (MTA) setting.
For the zero-sequence element, the product is the residual current adjusted by the MTA
setting times the sum of the residual voltage plus polarizing current shifted in phase by the
MTA setting.
2-24
Specifications
SEL-267D/167D Instruction Manual
Date Code 920326
Содержание SEL-167D
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