65
DMC3S - Manual - 08 - 2021
—
Ground directional overcurrent - 67N
Preface
This function has five 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
ED
>>
b
,
I
ED
>>> and
I
ED
S
b
is definite time.
There are also protection functions against intermittent arcs and evolving faults, based on measur-
ing the directional ground current and residual voltage, implementing the logics described below.
A constant reset time can be set for each of the thresholds.
Each protection threshold can be enabled or disabled.
Operation and settings
Two separate detection criteria are available:
• Violation of the residual current threshold
(modulus mode
)
• Violation of the projection of the residual current along the characteristic axis (
projection mode
).
The first and second thresholds
I
ED
>,
I
ED
>>
b
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
ED
>
inv
/ [(
I
ED
/
I
ED
>
inv
)
0.02
- 1]
• IEC 255-3/BS142 type B or VIT, very inverse time:
t
= 13.5 ·
t
ED
>
inv
/ [(
I
PD
/
I
ED
>
inv
) - 1]
• IEC 255-3/BS142 type LTI, long time inverse:
t
= 120 ·
t
ED
>
inv
/ [(
I
ED
/
I
ED
>
inv
) - 1]
• IEC 255-3/BS142 type C or EIT, extremely inverse time:
t
= 80 ·
t
PD
>
inv
/ [(
I
ED
/
I
ED
>
inv
)
2
- 1]
Where:
t
:
operating time
I
ED
>
inv
:
trip threshold (
I
ED>inv,
I
ED>>ainv
) for the first and second threshold
t
ED
>
inv
:
trip threshold regulation (
t
ED>inv,
t
ED>>ainv
) for the first and second threshold
The trip characteristic for thresholds
I
ED
>>
b
,
I
ED
>>> and
I
EESb
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 0.5
I
En
, the upper limit of the measurement range is 10
I
En
.
• The minimum operating time
t
is 0.1 s.
• For definite time trip characteristics, the upper limit of the measurement range is 10
I
En
.
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-F67N.ai
IED
IED>>a
IED>>b
IED>>>
tED>
tED>>a
tED>>b
tED>>>
tEDSb
IED>
IEDSb
t
Trip characteristic of the thresholds of the ground directional overcurrent protection - 67N
TRIP
