Operation Principle - ABB REB650 Technical Manual

Section 7
Current protection
7.3.7
104

Operation principle

The sampled analog phase currents are pre-processed and for each phase current the
true RMS value of each phase current is derived. These phase current values are fed to
the Thermal overload protection, two time constants (TRPTTR, 49).
From the largest of the three phase currents a relative final temperature (heat content)
is calculated according to the expression:
2
æ ö
I
Q = ç
÷
ç ÷
final
I
è ø
ref
EQUATION1171 V1 EN
where:
I
I
ref
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
Table continues on next page
is the largest phase current
is a given reference current
n
æ ö
D
t
)
-
× -
t
1 e
ç ÷
-
n 1
è ø
n
D
t
)
-
- Q ×
e t
-
n 1
1MRK 505 277-UUS C
(Equation 17)
(Equation 18)
(Equation 19)
(Equation 20)
(Equation 21)
Technical Manual