ABB REG670 - Page 411

( )
1
t
n final final n
e
t
D
-
-
Q = Q - Q - Q ×
EQUATION1175 V1 EN (Equation 74)
where:
Q
n
is the calculated present temperature
Q
n-1
is the calculated temperature at the previous time step
Q
final
is the calculated final (steady state) temperature with the actual current
Dt
is the time step between calculation of the actual and final temperature
t
is the set thermal time constant Tau1 or Tau2 for the protected transformer
The calculated transformer relative temperature can be monitored and 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 signal ALARM1 or ALARM2 is 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 time to operation with the present current. This
calculation is only performed if the final temperature is calculated to be above the
operation temperature:
ln
final operate
operate
final n
t t
æ ö
Q - Q
= - ×
ç ÷
ç ÷
Q - Q
è ø
EQUATION1176 V1 EN (Equation 75)
The calculated time to trip can be monitored and it is exported from the function as an
integer output TTRIP.
After a trip there can be a lockout to inhibit reconnecting the tripped circuit. The output
lockout signal LOCKOUT is activated when the temperature of the object is above the
set lockout release temperature setting ResLo.
The time to lockout release is calculated by the following cooling time calculation.
_
_
ln
final lockout release
lockout release
final n
t t
æ ö
Q - Q
= - ×
ç ÷
ç ÷
Q - Q
è ø
EQUATION1177 V1 EN (Equation 76)
In the above equation, the final temperature is calculated according to equation 70.
The calculated component temperature can be monitored as it is exported from the
function as a real figure, TRESLO.
1MRK502052-UEN B Section 8
Current protection
405
Technical manual