2-16
Relay Element Settings
Date Code 20060731
SEL-300G Instruction Manual
Setting Descriptions—Load Encroachment
Enable Load Encroachment (Y, N)
ELE = N
The setting ELE is available in relays with firmware
≥
R320 only.
Minimum Power Factor (OFF, 0.98 to 0.50)
MPF = 0.80
Maximum Generator Load (0.5 to 3.0 per unit)
MXLD = 1.2
The MPF and MXLD settings define the operation of a simple load encroachment
function that increases the security of the phase distance elements under heavy load. If
load encroachment security is desired, set MPF to the minimum rated generator power
factor under maximum load conditions. Set the maximum emergency generator power
output in per unit of the generator rating. If load encroachment security is not desired,
set MPF = OFF to disable the function. Also you can disable the function by setting
ELE = N. When load encroachment is disabled, the ZLOAD Relay Word bit is
inactive.
Relay Word Bits
Relay Word Bit Function
Description
Typical Applications
ZLOAD
Load encroachment element
Inhibit Phase Distance Elements
Setting Calculation
Information Needed
•
Zone 1 and Zone 2 reach apparent impedance magnitude and angle
•
Generator Step-Up Transformer Connection (only required if Zone 1 or Zone 2 mho
element is used and set to reach through the transformer)
•
Zone 1 and Zone 2 coordination time delay
•
Generator Rated Minimum Power Factor and Maximum Emergency Loading
Recommendations
The phase distance elements provide backup phase fault protection for the system, step-up
transformer, and generator. Zone 2 is typically set to reach far out onto the system. Usually, a
fault study is necessary to determine the magnitude and angle of the apparent impedance seen by
the generator relay during a system fault. Set the reach (Z
n
R or Z
n
C) equal to the apparent
positive-sequence impedance calculated by fault study for a three-phase fault at the desired reach
limit point on the system. All distance element reaches and offsets are set in secondary ohms.
Note
: For firmware versions lower than R320 (or lower than R240 for older hardware), set the
Z
n
R equal to three times the apparent impedance when Z
n
CMP = +30 or –30.
After determining the minimum reach setting required to obtain desired sensitivity with all
system breakers closed, you may wish to determine the element sensitivity when one or more
local bus circuit breakers are open. This operating contingency review shows with which relays
the Zone 2 element time delay must coordinate.
Zone 1 is usually set shorter than Zone 2, with a corresponding shorter time delay.
Summary of Contents for SEL-300G
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