ABB REG650 Technical Manual page 186

Section 7
Current protection
180
If
(
Q = Q + Q - Q
-
n n 1 final
EQUATION1173 V1 EN
If
(
Q = Q - Q
n final final
EQUATION1175 V1 EN
where:
Q
n
Q
n-1
Q
final
Dt
t
The calculated transformer relative temperature can be monitored as it is exported
from the function as a real figure HEATCONT.
When the transformer temperature reaches any of the set alarm levels Alarm1 or
Alarm2 the corresponding output signals ALARM1 or ALARM2 are activated.
When the temperature of the object reaches the set trip level which corresponds to
continuous current equal to ITrip the output signal TRIP is activated.
There is also a calculation of the present time to operation with the present current.
This calculation is only performed if the final temperature is calculated to be above
the operation temperature:
æ
Q
t
= - × ç final
t ln
ç
operate Q
è
final
EQUATION1176 V1 EN
The calculated time to trip can be monitored as it is exported from the function as a
real figure TTRIP.
Q
EQUATION1172 V1 EN
æ ö
D
t
)
-
× -
1 e t
ç ÷
-
n 1
è ø
Q
EQUATION1174 V1 EN
D
t
)
-
- Q ×
e t
-
n 1
is the calculated present temperature
is the calculated temperature at the
previous time step
is the calculated final (steady state)
temperature with the actual current
is the time step between calculation of the
actual and final temperature
is the set thermal time constant Tau1 or
Tau2 for the protected transformer
ö
- Q
operate
÷
÷
- Q
ø
n
1MRK 502 034-UEN -
> Q
final n
(Equation 46)
(Equation 47)
< Q
final n
(Equation 48)
(Equation 49)
(Equation 50)
Technical Manual