ANNEX 1 THERMAL IMAGE UNIT
GEK-106273L
MIF Digital Feeder Protection
11-3
Obviously, the derived equation describes the temperature evolution for both, a heating process and a cooling
process.
The final temperature value
θ
∞
, for a permanent current I
∞
, will be (according to [2]):
In equation [2], solving for time, you get:
Introducing the following variable change:
that implies to refer temperatures to the steady state value, equations [2] and [4] can be written as :
where I’ represents the current value in per unit, based on the permanent current, this is:
To compute the tripping time, substitute in [7], with
θ
’ = 1, and you get:
It is necessary that I > 1.
Equation [9], can also be written as a function of current, in p.u., if it has been maintained permanently (in other case,
it is necessary to compute the equivalent current), that is represented by the letter “
v
”:
Equation [10], represents the basic tripping algorithm for a thermal image relay, that for a given
τ
and I
∞
, can be
drawn, in general using a logarithm plane, using “v” as the parameter, as shown in figures A-1.1 and A-1.2.
[3]
[4]
[5]
[6]
[7]
[8]
[9]
[10]
α
θ
∞
∞
=
I
⎥
⎦
⎤
⎢
⎣
⎡
−
−
=
θ
α
θ
α
τ
*
*
ln
*
2
0
2
I
I
t
∞
=
′
θ
θ
θ
/
(
)
τ
τ
θ
θ
/
'
0
/
2
*
1
*
t
t
e
e
I
−
−
+
−
′
=
′
⎥
⎦
⎤
⎢
⎣
⎡
−
−
=
'
'
'
ln
*
2
0
2
θ
θ
τ
I
I
t
∞
=
I
I
I
/
'
⎥
⎦
⎤
⎢
⎣
⎡
−
−
=
1
'
'
ln
*
2
0
2
I
I
t
θ
τ
⎥
⎦
⎤
⎢
⎣
⎡
−
−
=
1
'
'
ln
*
2
2
2
I
v
I
t
τ
Summary of Contents for GEK-106273L
Page 19: ...GETTING STARTED 1 12 MIF Digital Feeder Protection GEK 106273L ...
Page 95: ...SETTINGS 5 38 MIF Digital Feeder Protection GEK 106273L ...
Page 101: ...I O CONFIGURATION 6 44 MIF Digital Feeder Protection GEK 106273L ...
Page 127: ...KEYPAD AND DISPLAY 8 26 MIF Digital Feeder Protection GEK 106273L ...
Page 147: ...INSTALLATION AND MAINTENANCE 10 2 MIF Digital Feeder Protection GEK 106273L ...
Page 199: ...ANNEX 5 HARMONIC FILTERING 15 4 MIF Digital Feeder Protection GEK 106273L ...