ABB RED650 Technical Manual page 215

1MRK 505 394-UEN A
Line differential protection RED650 2.2 IEC
Technical manual
2
æ ö
I
Q = ×
ç ÷ T
ç ÷
final ref
I
è ø
ref
EQUATION1167 V1 EN-US
where:
I is the largest phase current,
I is a given reference current and
ref
T is steady state temperature rise corresponding to I
ref
The ambient temperature is added to the calculated final temperature. If this
temperature is larger than the set operate temperature level, TripTemp, a START
output signal is activated.
The actual temperature at the actual execution cycle is calculated as:
(
Q = Q + Q - Q
-
n n 1 final
EQUATION1168 V1 EN-US
where:
is the calculated present temperature,
Q
n
is the calculated temperature at the previous time step,
Q
n-1
is the calculated final temperature with the actual current,
Q
final
is the time step between calculation of the actual temperature and
Dt
is the set thermal time constant for the protected device (line or cable)
t
The actual temperature of the protected component (line or cable) is calculated by
adding the ambient temperature to the calculated temperature, as shown above. The
ambient temperature can be taken from a separate sensor or can be given a constant
value. The calculated component temperature is available as a real figure signal,
TEMP.
When the component temperature reaches the set alarm level AlarmTemp the
output signal ALARM is set. When the component temperature reaches the set trip
level TripTemp the output signal TRIP is set.
There is also a calculation of the present time to operate with the present current.
This calculation is only performed if the final temperature is calculated to be above
the operation temperature:
ref
æ ö
D
t
)
-
× -
t
1 e
ç ÷
-
n 1
è ø
Section 8
Current protection
(Equation 30)
(Equation 31)
209