GE M60 Instruction Manual page 309

CHAPTER 5: SETTINGS
This element receives current inputs from the source selected by the
setting. Generally, this element compares the ratio of motor negative sequence current (I_2) to the positive
LINE SOURCE
sequence current (I_1) times an adjustment factor to compensate for the actual motor load to a set threshold. The
adjustment factor is used to prevent nuisance alarms at light loads. If the motor is operating at an average current level
equal to or greater than the programmed full load current (FLA, as selected by the
setting) the adjustment factor is one. If the motor is operating at an average current level less than the
FULL LOAD AMPS
programmed full load current (as selected by the
adjustment factor is the ratio of average current to full load current. It is intended that the Amp Unbalance 1 element is
used to generate an alarm and Amp Unbalance 2 element is used to generate a trip.
A declaration of a "single-phasing" condition is made two seconds after the unbalanced current level exceeds 40%, or the
average current is above 25% of FLA and the current in any one phase is less than 2% of FLA.
— This setting selects the level of unbalanced current that generates a stage 1 (intended to alarm)
AMP UNBAL 1(2) PICKUP
output. Note that a supply voltage unbalance of 1% creates a current unbalance of 6% in a typical three-phase induction
motor; a supply voltage unbalance of 2% creates a current unbalance of 12%. As a 2% voltage unbalance is common in
most applications, a setting of 0.15 is often used as the alarm level, and
higher.
AMP UNBAL 1(2) PICKUP DELAY
motor stress in a shorter period; a reasonable setting is 3 to 10 seconds.
— This timer can be used to maintain the output until other equipment or an operator can
AMP UNBAL 1(2) RESET DELAY
react to the unbalance condition.
5.7.3.5 Mechanical jam
SETTINGS  GROUPED ELEMENTS  SETTING GROUP 1(6)  MOTOR  MECHANICAL JAM
 MECHANICAL JAM

M60 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
AMP UNBAL 1 EVENTS:

Disabled
SYSTEM SETUP  MOTOR  MOTOR FULL LOAD AMPS
— The alarm delay is often set from 5 to 10 seconds. A higher level of unbalance causes
Figure 5-93: AMP unbalance logic
MECHANICAL JAM

FUNCTION: Disabled
MECH JAM OVERCURRENT

PICKUP: 2.00 x FLA
Range: Disabled, Enabled
SETTINGS  SYSTEM SETUP  MOTOR  MOTOR
SYSTEM SETUP  MOTOR  MOTOR
is usually set to this level or
AMP UNBAL 1 PICKUP
Range: Disabled, Enabled
Range: 1.00 to 10.00 x FLA in steps of 0.01
GROUPED ELEMENTS
setting) the
5
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