Thytronic DMC3S - Neutral Current Unbalance - 51(SQL)

52
DMC3S - Manual - 08 - 2021
— Neutral current unbalance - 51(SQL)
Preface
Neutral unbalance current protection between the star centres of two capacitor arrays with an ad-
justable threshold with programmable operating time.
The trip characteristic can be selected with definite or inverse time per IEC 60255-3/BS142.
A constant reset time can be set to reduce the time for eliminating intermittent faults (while being no
less than the protection start time).
The threshold can be enabled or disabled.
Operation and settings
The protection compares the fundamental component of the residual current (I
SQL
) with the set
threshold (I
SQL
>); violating the threshold starts (START) the threshold itself and the corresponding
timer (t
SQL
>). If the threshold violation persists, when its trip time expires, the threshold trips (TRIP),
otherwise the threshold is reset.
The first threshold 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
SQL
>
inv
/ [(I
SQL
/I
SQL
>
inv
)
0.02
- 1]
• IEC 255-3/BS142 type B or VIT, very inverse time: t = 13.5 · t
SQL
>
inv
/ [(I
SQL
/I
SQL
>
inv
) - 1]
• IEC 255-3/BS142 type LTI, long time inverse: t = 120 · t
SQL
>
inv
/ [(I
SQL
/I
SQL
>
inv
) - 1]
• IEC 255-3/BS142 type C or EIT, extremely inverse time: t = 80 · t
SQL
>
inv
/ [(I
SQL
/I
SQL
>
inv
)
2
- 1]
Where:
t: operating time
I
Eeme
>: trip threshold
t
Eeme
>
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 regulation
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
.
The threshold can be enabled or disabled by setting to ON or OFF the parameter IEeme> Ena-
ble in the menu Set \ Protections \ Residual emergency overcurrent - 51N(Eme) \ Threshold IEeme>
\ Parameters.
The first threshold can be set to definite or inverse time with parameter IEeme>Curve (INDIP-
ENDENTE, NIT, VIT, EIT, LIT) in the menu Set \ Portections \ Residual emergency overcur-
rent - 51N(Eme) \ Threshold IEeme> \ Parameters.
In the same way, the first threshold can be inhibited by the start of the second threshold with Deacti-
vation INe> by start INe>> (INe>>disbyIE>>) in the menu Set \ Protections \ Residual emergen-
cy overcurrent - 51N(Eme) \ Threshold IEeme> \ Parameters.
A constant reset time can be set for each of the thresholds t
Eeme>RES
.
Shrink time
If the threshold is programmed with definite time characteristic you can set the contracted time by
setting to ON the parameter EnTcIEeme>def and regulating the contracted time (tcIEeme>-
def) and the operating time (tatcIEeme>def).
Once the breaker closes, during the operating time (e.g.: tatcIEeme>def), the value of the trip
time (e.g.: tEeme>def ) is replaced by the contracted time (e.g.: tcIEeme>def ); when the oper-
ating time expires the trip time is reset (e.g.: tEeme>def ).
The related parameters are available in the menu Set \ Protections \ Residual emergency overcur-
rent - 51N(Eeme) \ Threshold IEeme>\ Definite time.
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
ISQL
tSQL>
ISQL>
t
Trip characteristic of the threshold of the neutral unbalance overcurrent protection - 51N(SQL)
TRIP