ABB REO 517, Applications Manual, Page: 107 / 440

97
Two step definite and inverse time
delayed phase overcurrent protection
(TOC2)
&KDSWHU
&XUUHQW
If inverse time characteristics are used with equal current and time setting for all phase
current protections in the system the selectivity is assured as long as there are more than
two bays carrying fault current to each substation. Sometimes this is however impossi-
ble due to the fault current distribution between the different lines.
If definite time characteristic is used the co-ordination between the different phase over-
current line protections is done by means of current setting.
As the phase overcurrent protection often is used as a back-up protection of lines, where
a distance protection is the main protection, relatively long operation times are accept-
able for the phase overcurrent protection.
The following formulas are valid for the inverse time characteristic:
7DEOH )RUPXODVIRUWKHLQYHUVHWLPHFKDUDFWHULVWLF
6HWWLQJRIUHOD\RSHUDWLQJFXUUHQW
If Is is the primary setting operating value of the function, then the secondary setting
current (Is
SEC
) is:
&KDUDFWHULVWLF 7LPHGHOD\V
Normal inverse
(Equation 41)
Very inverse
(Equation 42)
Extremely inverse
(Equation 43)
RI inverse
(Equation 44)
where:
I denotes (measured current)/ I>Inv and
k is a time multiplier factor, settable in the range of 0.05 to 1.10.
t
0 14
,
I
0 02
,
1
–
--------------------- k
⋅
=
t
13 5
,
I 1
–
------------- k
⋅
=
t
80
I
2
1 –
------------- k
⋅
=
t
1
0 339
,
0 236
, ( )
I
⁄ 〈 〉
–
------------------------------------------------------ k
⋅
=