GE M60 Instruction Manual page 524

CONTROL ELEMENTS
The M60 is provided with optional broken rotor bar detection. This feature is specified as an option at the time
of ordering. See the Order Codes section in chapter 2 for details.
5
The broken rotor bar detection function uses the same source as other motor protection functions. This source is defined
by the
SYSTEM SETUP  MOTOR  MOTOR LINE SOURCE
bar detection function to operate:
• Phase Currents must be configured on this source for the broken rotor bar detection function
• The
AC INPUT WAVEFORMS
• The Thermal Model must be enabled.
This function monitors only phase A current.
When the broken rotor bar detection function is enabled, an alarm is initiated once the value of ratio of the broken bar
related sideband component versus the system fundamental component is greater than the pickup level for two
consecutive measurements. To reduce probability of a false alarm (caused by impairments other than a rotor bar failure),
the element is active only if the following conditions hold:
• The motor status is "Running" and the motor load is between preset minimum acceptable value and a value just below
the overload (defined by
Trying to detect the broken rotor bar during a motor start returns an incorrect result because of the rapid movement
of broken rotor bar components and a heavy change in the motor current. On the other hand, while the motor load is
small, there is not enough resolution to accurately calculate a miniscule spectral component caused by a rotor bar
failure.
• The motor load is steady.
Variations in motor load cause spectral components that can be misinterpreted as rotor bar failure. Instantaneous
motor load values are collected alongside with data for the broken rotor bar algorithm to prevent this from happening.
The average motor load and its standard deviation are calculated. If the standard deviation is greater than its
corresponding setting, the data set is discarded and the broken bar algorithm is not initiated.
• The motor current unbalance is below a corresponding setpoint.
The excessive current unbalance stresses the motor, and it can cause false broken rotor bar detection.
It is recommended that frequency tracking be enabled to avoid possible false broken rotor bar detection results when the
system frequency drifts from the nominal frequency.
The following settings are available for the broken rotor bar detection element.
5-316
BRB START BLOCK

DELAY: 60.00 s
MINIMUM MOTOR LOAD:

0.70 x FLA
MAX. LOAD DEVIATION:

0.10 x FLA
MAXIMUM CURRENT

UNBALANCE: 15.0%
BROKEN ROTOR BAR

PICKUP: -40 dB
BROKEN ROTOR BAR

RESET DLY: 1.00 s
BRB BLOCK:

Off
BROKEN ROTOR BAR

TARGET: Self-reset
BROKEN ROTOR BAR

EVENTS: Disabled
setting. The following items must addressed for the broken rotor
oscillography setting must not be "Off"
×
MOTOR FULL LOAD AMPS MOTOR OVERLOAD FACTOR
Range: 0.00 to 600.00 s in steps of 0.01
Range: 0.50 to 1.00 × FLA in steps of 0.01
Range: 0.50 to 1.00 × FLA in steps of 0.01
Range: 0.0 to 100.0% in steps of 0.1
Range: –60 to –12 dB in steps of 1
Range: 0.00 to 600.00 s in steps of 0.01
Range: FlexLogic operand
Range: Self-reset, Latched, Disabled
Range: Disabled, Enabled
).
M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
CHAPTER 5: SETTINGS