GE 869, Instruction Manual

Page: 411 / 606

CHAPTER 4: SETPOINTS MONITORING
869 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL 4–279
START OF BRB OFFSET
Range: -12.00 to 11.99 Hz Step: 0.01 Hz
Default: 0.40 Hz
This setting defines the beginning of the frequency range where the spectral component
due to a rotor bar failure, is searched.
The setting must be set to a value equal to:
fstart_offset = 2*s* f1 – max(0.3, min(2*s* f1 – 0.4, 1.0))
where:
f1 = system frequency
s = the motor slip at full load
max = returns the largest of its arguments
min = returns the smallest of its arguments.
For example, if the full load slip is 0.01, set this setting to: 2*0.01*60 – 0.8 = 0.40 Hz, for a
60 Hz power system.
END OF BRB OFFSET
Range: -12.00 to 11.99 Hz Step: 0.01 Hz
Default: 2.00 Hz
This setting defines the end of the frequency range where the spectral component due
to a rotor bar failure, is searched.
This setting must be set to a value equal to:
fend_offset = 2*s* f1 + max(0.3, min(2*s* f1 – 0.4, 1.0))
where:
f1 = system frequency
s = the motor slip at full load
max = returns the largest of its arguments
min = returns the smallest of its arguments.
For example, if the full load slip is 0.01, set this setting to: 2*0.01*60 + 0.8 = 2.00 Hz, for a
60 Hz power system.
START BLOCK DELAY
Range: 0.00 to 600.00 s Step: 0.01 s
Default: 60.00 s
This setting specifies the time for which the broken rotor bar detection algorithm is
blocked after the motor status has changed from “Stopped” to “Running”. This ensures
that the broken rotor bar element is active only when the motor is running.
MINIMUM MOTOR LOAD
Range: 0.50 to 1.00 x FLA Step: 0.01
Default: 0.70 x FLA
This setting is used to block the data acquisition of the Broken Rotor Bar detection
function, as long as the motor load is below this setting. The Broken Rotor Bar detection
algorithm cannot accurately determine the BRB spectral component when a motor is
lightly loaded.
MAXIMUM LOAD DEVIATION
Range: 0.00 to 1.00 x FLA Step: 0.01
Default: 0.10 x FLA
This setting is used to block the data acquisition of the Broken Rotor Bar detection
function, as long as the standard deviation of the motor load is above this setting. The
Broken Rotor Bar detection algorithm cannot accurately determine the BRB spectral
component when the motor load varies.