CYG PRS-7367 - Application Scope

Protection Functions
76 PRS-7367
the expression, one of the three phase meet the formula, the protection startup.
2
1
( ) (1 )
tt
tt
B
I
ee
kI




   

Where:
I RMS value of the max fault phase current.
K set value of 49F_K_Factor.
IB the rated current 49F_Rated_Cur
τ the set value of 49F_T_Mult
t

is the initial thermal state, if the initial thermal state is 30%, the
t

is 0.3.
t

is calculated
from the following equation:


2
2
(k )
=θ
I
I
t
B
p
. For the heat rising process, Ip is the previous current
100ms before the heat first rises; for the cooling process, the Ip is the trip current.
1t


is the trip or alarm thermal state:
Trip

(the setting value 49F_K_Tr) or
Alarm

(the setting
49F_K_Alm). For cooling process, the
1t


is the return value.
When the component temperature reaches the set alarm level 49F_K_Alm, the output signal
49F_Alm is issued. When the component temperature reaches the set trip level 49F_K_Tr, the
49F_Tr output is activated.
There is also a calculation of the present time to operation with the present current. This is only
calculated if the final temperature is calculated to be above the operation temperature.
The time to operate can be calculated as:
22
22
1
()
ln
()
tB
tB
I k I
t
I k I







The cooling time is also calculated based on the listed equation.
The temperature calculation is initiated from the value defined with the initial temperature. This is
done in case the IED is powered up, the function is turned off and back on or reset through the
49F_Clr_Therm input.
The temperature is also stored in the nonvolatile memory and restored in case the IED is
restarted.
3.8.3 49F Application Scope
If any sudden change in electrical power system, its directly impact to the operating factors of
value likes current and voltage. In such a case, if the current level of transmission line increases to