5-316 M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUALCONTROL ELEMENTS CHAPTER 5: SETTINGS5 The broken rotor bar detection function uses the same source as other motor protection functions. This source is definedby the SYSTEM SETUP MOTOR MOTOR LINE SOURCE setting. The following items must addressed for the broken rotorbar detection function to operate:• Phase Currents must be configured on this source for the broken rotor bar detection function• The AC INPUT WAVEFORMS oscillography setting must not be “Off”• 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 barrelated sideband component versus the system fundamental component is greater than the pickup level for twoconsecutive 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 belowthe overload (defined by MOTOR FULL LOAD AMPS × MOTOR OVERLOAD FACTOR).Trying to detect the broken rotor bar during a motor start returns an incorrect result because of the rapid movementof broken rotor bar components and a heavy change in the motor current. On the other hand, while the motor load issmall, there is not enough resolution to accurately calculate a miniscule spectral component caused by a rotor barfailure.• The motor load is steady.Variations in motor load cause spectral components that can be misinterpreted as rotor bar failure. Instantaneousmotor 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 itscorresponding 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 thesystem frequency drifts from the nominal frequency.The following settings are available for the broken rotor bar detection element. BRB START BLOCKDELAY: 60.00 sRange: 0.00 to 600.00 s in steps of 0.01 MINIMUM MOTOR LOAD:0.70 x FLARange: 0.50 to 1.00 × FLA in steps of 0.01 MAX. LOAD DEVIATION:0.10 x FLARange: 0.50 to 1.00 × FLA in steps of 0.01 MAXIMUM CURRENTUNBALANCE: 15.0%Range: 0.0 to 100.0% in steps of 0.1 BROKEN ROTOR BARPICKUP: -40 dBRange: –60 to –12 dB in steps of 1 BROKEN ROTOR BARRESET DLY: 1.00 sRange: 0.00 to 600.00 s in steps of 0.01 BRB BLOCK:OffRange: FlexLogic operand BROKEN ROTOR BARTARGET: Self-resetRange: Self-reset, Latched, Disabled BROKEN ROTOR BAREVENTS: DisabledRange: Disabled, EnabledThe M60 is provided with optional broken rotor bar detection. This feature is specified as an option at the timeof ordering. See the Order Codes section in chapter 2 for details.
