48
DMC3S - Manual - 08 - 2021
—
Neutral overcurrent - 51(E)
Preface
This function has two adjustable thresholds with programmable trip time.
The trip characteristic for the first threshold can be selected with definite or inverse time per IEC
60255-3/BS142.
The trip characteristic for the second threshold 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 by the start of the second threshold.
Operation and settings
The residual overcurrent protection compares the fundamental component of the residual current
(
I
E
) with the set thresholds (
I
Ne
>,
I
Ne
>>); violating a threshold starts (START) the threshold itself and
the corresponding timer (
t
ne
>,
t
ne
>>). If the threshold violation persists, when its trip time expires, the
threshold trips (TRIP), otherwise the threshold is reset.
The first threshold
I
E
> can be set to definite or inverse time with the following characteristic curves:
• IEC 255-3/BS142 type A or SIT, inverse time:
t
= 0.14 ·
t
Ne
>
inv
/ [(
I
E
/
I
Ne
>
inv
)
0.02
- 1]
• IEC 255-3/BS142 type B or VIT, very inverse time:
t
= 13.5 ·
t
Ne
>
inv
/ [(
I
E
/
I
Ne
>
inv
) - 1]
• IEC 255-3/BS142 type LTI, long time inverse:
t
= 120 ·
t
Ne
>
inv
/ [(
I
E
/
I
Ne
>
inv
) - 1]
• IEC 255-3/BS142 type C or EIT, extremely inverse time:
t
= 80 ·
t
Ne
>
inv
/ [(
I
E
/
I
Ne
>
inv
)
2
- 1]
Where:
t
:
operating time
I
Ne
>:
trip threshold
t
Ne
>
inv
:
operating time regulation
The following applies to all inverse time characteristics:
• The minimum trip current is 1.1 times the set threshold (asymptotic reference time).
• The minimum operating time
t
is 0.1 s.
• The characteristics are defined between 1.1 and 20 times the set threshold;
[1]
if threshodl regula-
tion exceeds 2.5
I
n
, the upper limit of the measurement range is 10
I
En
.
For definite time trip characteristics, the upper limit of the measurement range is 10
I
En
.
Each threshold can be enabled or disabled by setting to
ON
or
OFF
the parameter
INe> Enable
,
INe>> Enable
in the menu
Set \ Protections \ Neutral overcurrent - 51N(E) \
Threshold INe>
(
Threshold INe>>) \ Parameters
.
The first threshold can be set to definite or inverse time with parameter
INe>Curve
(
INDIPEN-
DENTE, NIT, VIT, EIT, LIT
) in the menu
Set \ Portections \ Neutral overcurrent - 51N(E) \
Threshold INe>
\ Parameters
.
In the same way, the first threshold can be inhibited by the start of the second threshold with Deac-
tivation INe> by start INe>> (
INe>>disbyIE>>
) in the menu
Set \ Protections \ Neutral overcur-
rent - 50N/51N \
Threshold IE>>> \ Parameters
.
A constant reset time can be set for each of the two thresholds
t
Ne>RES
,
t
Ne>>RES
.
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
IE
INe>>
tNe>
tNe>>
INe>
t
Trip characteristic of the thresholds of the neutral overcurrent protection - 51N(E)
TRIP
