Sices D-PRO, Техническое руководство

Страница: 44 / 53

38 D-PRO Protection relay Technical Manual
1
0352 .
0353 .
2
−






=
P
I
P
t
I
Where I is the current in the circuit.
Please remember that the protection is carried out by performing the integral of the current
value during time; therefore, all current values over the rated threshold contribute to define the
intervention time, with their instant weight resulting from the above formula. Thus, the only way
to experimentally verify this formula is to switch instantaneously from a normal load situation
to an overload situation.
The following graph shows the used curve, with P.0353 set to 60 seconds (I is the maximum
current): Parameters P.3902
The protection is enabled only in case of absence of the disabling digital input (usually
combined to the circuit breaker status).
IEC Curve
– Extremely inverse and Very Inverse
Time-dependant current protection (it activates as much quickly as higher the current overload
is). The curves that can be used are called
EXTREMELY INVERSE and VERY INVERSE .
They are configured as genset protections as they set a limit to the thermal accumulation of
the genset when supplying. As engine protection, you must use the maximum power one,
which is independent from the load type. For further details refer to the document
EAAN005602.pdf.
The equation for the IEC curves is the following:
0353 .
1
0352 .
P
P
I
K
T
P

−






=
Where:
- I represents the current in the circuit.
- P.0353 is the time dial (TMS) set and it must have a value between 0,1 and 1.
0,1
1
10
100
1000
1 10
In
te
rv
e
n
ti
o
n
t
ime
(
s
e
c
o
n
d
s
)
I
I multiples
Intervention time