ABB Relion RES670, Technical Manual

Page: 254 / 934

From the largest of the three-phase currents a final temperature is calculated according
to the expression:
2
final ref
ref
I
T
I
æ ö
Q = ×
ç ÷
ç ÷
è ø
EQUATION1167 V1 EN-US
(Equation 23)
where:
I
is the largest phase current,
I
ref
is a given reference current and
T
ref
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 trip temperature level,
TripTemp , a PICKUP output
signal is activated.
The actual temperature at the actual execution cycle is calculated as:
( )
1 1
1
t
n n final n
e t
D
-
- -
æ ö
Q = Q + Q - Q × -
ç ÷
è ø
EQUATION1168 V1 EN-US
(Equation 24)
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 temperature with the actual current,
D
t is the time step between calculation of the actual temperature and
t is the set thermal time constant for the protected device (line or cable)
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.
Section 8
1MRK 511 408-UUS A
Current protection
248 Phasor measurement unit RES670 2.2 ANSI
Technical manual