ABB Relion Technical Manual page 244

Section 8
Current protection
238
If this calculated relative temperature is larger than the relative temperature level
corresponding to the set operate (trip) current a pickup output signal PICKUP is activated.
The actual temperature at the actual execution cycle is calculated as:
Q > Q
If
final
EQUATION1172 V1 EN
(
Q = Q + Q - Q
-
n n 1 final
EQUATION1173 V1 EN
Q < Q
If
final
EQUATION1174 V1 EN
(
Q = Q - Q
n final final
EQUATION1175 V1 EN
where:
is the calculated present temperature
Q
n
is the calculated temperature at the previous time step
Q
n-1
is the calculated final (steady state) temperature with the actual current
Q
final
is the time step between calculation of the actual and final temperature
Dt
is the set thermal time constant Tau1 or Tau2 for the protected transformer
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:
n
æ D ö
t
)
-
× -
1 e t
ç ÷
-
n 1
è ø
n
D
t
)
-
- Q ×
t
e
-
n 1
1MRK 502 048-UUS A
(Equation 57)
(Equation 58)
(Equation 59)
(Equation 60)
Technical manual