Thytronic NC20, Manual

Page: 96 / 227

96
96 NC20 - Manual - 01 - 2015 FUNCTION CHARACTERISTICS
Residual overcurrent - 50N/51N
Preface
Three operation thresholds, independently adjustable ( I
E
>, I
E
>>, I
E
>>>) with adjustable delay ( t
E
>,
t
E
>>, t
E
>>>).
The fi rst one ( I
E
>) may be programmed with defi nite or inverse time according the IEC and ANSI/IEEE
standard.
The second and third thresholds ( I
E
>>, I
E
>>>) with independent time.
For each threshold a reset time can be set ( t
E>RES
, t
E>>RES
, t
E>>>RES
) useful to reduce the clearing
time for intermittent faults.
The fi rst threshold trip may be inhibited by start of the second and/or third threshold ( I
E
>>, I
E
>>>).
Similarly the second threshold trip may be inhibited by start of the third threshold ( I
E
>>>).
Operation and settings
The residual fundamental frequency current I
EC
, calculated from the vector sum of the three phase
currents, is compared with the setting value. Current above the associated pickup value is detected
and a start is issued. After expiry of the associated operate time a trip command is issued; if instead
the current drops below the threshold, the element is restored.
The fi rst threshold ( I
E
>) may be programmed with defi nite or inverse time according the following
characteristic curves:
Standard Inverse Time (IEC 255-3/BS142 type A or SIT): t = 0.14 · t
E
>
inv
/ [( I
EC
/ I
E
>
inv
)
0.02
- 1]
Very Inverse Time (IEC 255-3/BS142 type B or VIT): t = 13.5 · t
E
>
inv
/ [( I
EC
/ I
E
>
inv
) - 1]
Extremely Inverse Time (IEC 255-3/BS142 type C or EIT): t = 80 · t
E
>
inv
/ [( I
EC
/ I
E
>
inv
)
2
- 1]
Moderately Inverse (ANSI/IEEE type MI): t = t
E
>
inv
· {0.01 / [( I
EV
/ I
E
>
inv
)
0.02
- 1] + 0.023}
Very Inverse (ANSI/IEEE type VI): t = t
E
>
inv
· {3.922 / [( I
EC
/ I
E
>
inv
)
2
- 1] + 0.098}
Extremely Inverse (ANSI/IEEE type EI): t = t
E
>
inv
· {5.64 / [( I
EC
/ I
E
>
inv
)
2
- 1] + 0.024}
Where:
t : operate time
I
EC
: calculated residual current
I
E
>: threshold setting
t
E
>
inv
: operate time setting
For all inverse time characteristics, following data applies:
Asymptotic reference value (minimum pickup value): 1.1 I
E
>
Minimum operate time: 0.1 s
Range where the equation is valid:
[1]
1.1 ≤ I
EC
/ I
E
> ≤ 20
If I
E
> pickup ≥ 2.5 I
n
, the upper limit is 50 I
n
For all defi nite time elements the upper limit for measuring is 50 I
n
.
All residual overcurrent elements can be enabled or disabled by setting
ON
or
OFF
the
IE> En-
able
,
IE>> Enable
and/or
IE>>> Enable
parameters inside the Set \ Profi le A(or B) \ Residual
overcurrent-50N/51N \ IE> Element ( IE>> Element , IE>>> Element) \ Setpoints menus.
The fi rst overcurrent element can be programmed with defi nite or inverse time characteristic by
setting the
IE>Curve
parameter (
DEFINITE, IEC/BS A, IEC/BS B, IEC/BS C, ANSI/IEE
MI, ANSI/IEE VI, ANSI/IEE EI
) available inside the Set \ Profi le A(or B) \ Residual overcurrent-
50N/51N \ IE> Element \ Setpoints menu.
The trip of I
E
> element may be inhibited by the start of the second and/or third el-
ement ( I
E
>>, I
E
>>>) by setting
ON
the Disable IE> by start IE>>, Disable IE> by
start IE>>> (
IE>disbyIE>>, IE>disbyIE>>>
) parameters available inside the
Set \ Profi le A(or B) \ Residual overcurrent-50N/51N \ IE>> Element ( IE>>> Element) \ Setpoints
Note 1 When the input value is more than 20 times the set point , the operate time is limited to the value corresponding to 20 times the set point
•
•
•
•
•
•
•
•
•
•
t-int-F50N-51N.ai
I
EC
I
E
>> I
E
>>>
t
E
>
t
E
>>
t
E
>>>
I
E
>
t
TRIP
General operation time characteristic for the residual overcurrent elements - 50N/51N