CYG PRS-7367 - Three-phase thermal overload protection 49 F

Protection Functions
74 PRS-7367
No.
Name
Values(Range
)
Unit
Step
Default
Description
fault
14
50BF_ReTr_T
0.00 - 60.00
s
0.01
0.005
Delay timer for retrip
15
50BF_Op_T1
0.00 - 60.00
s
0.01
0.15
Delay timer for BF trip CB
16
50BF_BFTrBu_T
0.00 - 60.00
s
0.01
0.15
Delay timer for BF trip backup
CB
17
50BF_DeaOp_T
0.00 - 60.00
s
0.01
0.15
Delay timer for Dead Zone trip
backup CB
18
50BF_Chk_Mod
1-4
-
1
3
=1: Current check;
=2: CB status check;
=3: Current check or CB status
check
=4: Current check and CB status
check
3.8 Three-phase thermal overload protection 49F
3.8.1 49F Overview
The relay incorporates a one-stage current based thermal calculation. The heat generated within
an item of the plant, such as a cable or a transformer, is the resistive loss. Thus, heating is directly
proportional to current squared. The thermal time characteristic used in the relay is therefore
based on current squared, integrated over time. The relay automatically uses the largest phase
current for input to the thermal calculation.
If the temperature of the protected object reaches the warning level, the alarm signal is given out.
If the temperature continues to increase to the maximum allowed temperature value, the
protection issues a trip signal to the protected line.
3.8.1.1 Function Block
The function block of the protection is as below.
I3P
PTTR_49F
Clr_Therm
Str
Op
Alm
Figure 3.8-1 Function block