ABB Relion 670 series, Technical Manual

Page: 527 / 1432

2
final
ref
I
I
æ ö
Q = ç
÷
ç ÷
è ø
EQUATION1171 V1 EN-US
(Equation 134)
where:
I is the largest phase current
I
ref
is a given reference current
If this calculated relative temperature is larger than the relative temperature level corresponding
to the set operate (trip) current, then the pickup output signal PICKUP will be activated.
The actual temperature at the actual execution cycle is calculated as:
If
final n
Q > Q
EQUATION1172 V1 EN-US
(Equation 135)
( )
1 1
1
t
n n final n
e t
D
-
- -
æ ö
Q = Q + Q - Q × -
ç ÷
è ø
EQUATION1173 V1 EN-US
(Equation 136)
If
final n
Q < Q
EQUATION1174 V1 EN-US
(Equation 137)
( )
1
t
n final final n
e
t
D
-
-
Q = Q - Q - Q ×
EQUATION1175 V1 EN-US
(Equation 138)
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
D t is the time step between calculation of the actual and final temperature
t
is the thermal time constant of the protected circuit given in minutes. There are different time
constants depending on the cooling used. Please refer to manufacturer's manuals for details
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
1MRK 502 066-UUS B Section 8
Current protection
521
Technical manual