ABB Relion 670 Series RES670, Technical Manual

Page: 252 / 888

2
final ref
ref
I
T
I
æ ö
Q = ×
ç ÷
ç ÷
è ø
EQUATION1167 V1 EN
(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
(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.
When the component temperature reaches the set alarm level AlarmTemp the output
signal ALARM is set. When the component temperature reaches the set trip level
TripTemp the output signal TRIP is set.
Section 8
1MRK 511 365-UUS A
Current protection
246 Phasor measurement unit RES670 2.1 ANSI
Technical manual