60
DMC3S - Manual - 08 - 2021
—
Maximum directional current - 67
Preface
This function has four adjustable thresholds with programmable trip time.
The trip characteristic for the first two thresholds can be selected with definite or inverse time per
IEC 60255-3/BS142.
The trip characteristic for thresholds
I
>>> and
I
>>>> is definite time.
A constant reset time can be set for each threshold, to reduce the time for eliminating intermittent
faults (while being no less than the protection start time).
Each protection threshold can be enabled or disabled.
The first threshold can be inhibited when at least one of the three thresholds starts, just as the sec-
ond threshold can be inhibited when the third threshold starts and the third when the fourth starts.
The protection includes a voltage memory which, should all three voltages be lower than 2%
U
n
,
saves the phase shift of the currents relative to the voltages prior to the fault for at least 1 s.
Operation and settings
If the current
I
L2
is not available, it is reconstructed vectorially.
The trip characteristic for thresholds
I
PD
>,
I
PD
>> can be selected with definite or inverse time per the
following characteristic curves:
• IEC 255-3/BS142 type A or SIT, inverse time:
t
= 0.14 ·
t
PD
>
inv
/ [(
I
PD
/
I
PD
>
inv
)
0.02
- 1]
• IEC 255-3/BS142 type B or VIT, very inverse time:
t
= 13.5 ·
t
PD
>
inv
/ [(
I
PD
/
I
PD
>
inv
) - 1]
• IEC 255-3/BS142 type LTI, long time inverse:
t
= 120 ·
t
PD
>
inv
/ [(
I
PD
/
I
PD
>
inv
) - 1]
• IEC 255-3/BS142 type C or EIT, extremely inverse time:
t
= 80 ·
t
PD
>
inv
/ [(
I
PD
/
I
PD
>
inv
)
2
- 1]
Where:
t
:
operating time
I
PD
>
inv
:
trip threshold (
I
PD>inv,
I
PD>>inv
) for the first and second threshold
t
PD
>
inv
:
trip threshold regulation (
t
PD>inv,
t
PD>>inv
) for the first and second threshold
The trip characteristic for the third and fourth thresholds (
I
PD>>>def,
I
PD>>>>def
) is definite time.
The following applies to all the above inverse time characteristics:
• The minimum trip current is 1.1 times the set threshold (asymptotic reference time).
• The characteristics are defined between 1.1 and 20 times the set threshold;
[1]
if threshold regula-
tion exceeds 2.5
I
n
, the upper limit of the measurement range is 30
I
n
.
• The minimum operating time
t
is 0.1 s.
• For definite time trip characteristics, the upper limit of the measurement range is 30
I
n
.
Two separate detection criteria are available:
• Violation of the phase current threshold
(modulus mode
)
• Violation of the projection of the phase current along the characteristic axis (
projection mode
).
For both criteria, the polarising parameter used as a reference for the measurement of the current
phase shift in each of the three phases is the phase-to-phase voltage relative to the two remaining
phases (phase-to-phase voltage delayed by 90° relative to the current when the electrical system
power factor is one).
Note 1 For input values greater than 20 times the threshold, the operating time is limited to the value corresponding to 20 times the threshold
t-int-F67.ai
IPD
IPD>>
IPD>>>
IPD>>>>
tPD>
tPD>>
tPD>>>
tPD>>>>
IPD>
t
Trip characteristic of the four thresholds of the maximum directional current protection - 67
TRIP
NO TRIP
