ABB REG316 4 Series Operating Instructions Manual page 122

ABB Switzerland Ltd
Multiplier 'k1-Setting'
The multiplier 'k1-Setting' enables the IDMT characteristic
chosen by the setting of parameter c to be shifted without
changing its shape. This is used for grading the operating times
of a series of IDMT relays along a line to achieve discrimination.
For example, in the case of the "very inverse" characteristic, the
constant c = 1 and the factor k1 £ 13.5. The operating time t is
given by the equation
k 1
=
t
I
-
1
I
B
Assuming a grading time of 0.5 s at 6 times the base current I
required, the factor k1 for each of the relays is given by
k1 = 5 t
This produces for operating times between 0.5 and 2.5 s the
following settings for k1:
t [s]
0.5
1
1.5
2
2.5
The characteristics according to BS 142 are set as follows:
"normal inverse"
"very inverse"
"extremely inverse"
"long time earth fault"
Typical settings:
IB-Setting
I-Start
c-Setting
k1-Setting
t-min
3-84
REG 316*4 1MRB520049-Uen / Rev. F
k1 [s]
2.5
5
7.5
10
12.5
: k1 = 0.14 s
: k1 = 13.5 s
: k1 = 80 s
: k1 = 120 s.
corresponding to load current of the pro-
tected unit
1.1 IB
according to desired characteristic for the
protected unit
according to the time grading calculation
0.00
is
B