4.14
SEL-749M Relay Instruction Manual Date Code 20080918
Protection and Logic Functions
Basic Motor Protection
Figure 4.5 Load-Jam Element Logic
Undercurrent
(Load Loss) Elements
The relay arms the load-loss detection logic a settable time after the motor
starts, as defined by the undercurrent start delay time setting (LLSDLY) (see
Figure 4.6). Set this delay to allow pumps or compressors to reach normal
load. Once armed, this function issues a warning or trip if phase current drops
below warn or trip level for the specified time delay.
Figure 4.6 Undercurrent (Load-Loss) Logic
Load-Jam Alarm and Trip Pickup
Positive-Sequence Current Magnitude
Motor is Running
Load-Jam Alarm and Trip Delay
Load-Jam Alarm and Trip
Full Load Amps Setting
LJAPU, LJTPU =
I1 =
RUNNING =
LJADLY, LJTDLY =
JAMALRM, JAMTRIP =
FLA =
| I1 |
LJAPU = Off
LJTPU = Off
(LJAPU) (FLA)
(LJTPU) (FLA)
RUNNING
JAMALRM
LJADLY
0
JAMTRIP
LJTDLY
0
Relay
Word
Bits
Relay
Word
Bit
Setting
Setting
Settings
Table 4.11 Undercurrent Settings
Setting Prompt Setting Range Setting Name := Factory Default
UC TRIP LEVEL Off, 0.10–1.00 xFLA LLTPU := OFF
UC TRIP DELAY 0.4–120.0 sec LLTDLY := 5.0
UC WARN LEVEL Off, 0.10–1.00 xFLA LLAPU := OFF
UC WARN DELAY 0.4–120.0 sec LLADLY := 10.0
UC START DELAY 0–1500 sec LLSDLY := 0
Load Loss Trip Pickup Setting
Load Loss Alarm Pickup Setting
Motor Is Starting
Motor Is Running
Load Loss Trip
Load Loss Alarm
LLTPU =
LLAPU =
STARTING =
RUNNING =
LOSSTRIP =
LOSSALRM =
Positive-Sequence Current Magnitude
Full Load Amps Setting
Load Loss Trip Delay Setting
Load Loss Start Delay Setting
Load Loss Alarm Delay Setting
I1 =
FLA =
LLTDLY =
LLSDLY =
LLADLY =
| I1 |
| I1 |
LLTPU = Off
LLAPU = Off
(LLTPU) (FLA)
RUNNING
STARTING
RUNNING
Load Loss Start
Delay Timer
Rising
Edge Detect
Load Loss Trip
Delay Timer
Load Loss Alarm
Delay Timer
(LLAPU) (FLA)
LOSSTRIP
LLTDLY
0
LLSDLY
0
LOSSALRM
LLADLY
0
Relay
Word
Bits
Relay
Word
Bits
Setting
Setting
Settings
Courtesy of NationalSwitchgear.com
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