GE 339

6–34 339 MOTOR PROTECTION SYSTEM – INSTRUCTION MANUAL
S3 PROTECTION CHAPTER 6: SETPOINTS
S3 Protection
Figure 6-14: Main protection menu
Motor Thermal Model
The primary protective function of the 339 motor relay is motor thermal protection.
The 339 thermal protection consists of seven key elements:
• Start Protection - accounts for the rapid heating that occurs during starting
• Unbalance Current Biasing - accounts for negative sequence heating
• Hot/Cold Biasing - accounts for normal temperature rise
• RTD Biasing - accounts for ambient variation and cooling problems
• Cooling Rate - accounts for heat dissipation
• Thermal Protection Reset - controls recovery from thermal trips/lockouts.
Each of these elements is described in detail in the sections that follow.
S3 PROTECTION
MOTOR THERMAL MOD
SHORT CIRCUIT
MECHANICAL JAM
UNDERCURRENT
CURRENT UNBAL
LOAD INCR ALARM
GROUND FAULT
NEUTRAL IOC
PHASE TOC
NEUTRAL TOC
PHASE UV 1
PHASE UV 2
PHASE OV 1
PHASE OV 2
NEGATIVE SEQ OV
POSITIVE SEQ UV 1
POSITIVE SEQ UV 2
UNDERFREQUENCY1
UNDERFREQUENCY2
OVERFREQUENCY1
OVERFREQUENCY2
UNDERPOWER
PHASE REVERSAL
ACCELERATION
RTD PROTECTION
TWO SPEED MOTOR
NTRL DIR
DIRECTIONAL POWER 1
DIRECTIONAL POWER 2
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