Datasheet

STPMC1 Theory of operation
Doc ID 15728 Rev 7 31/77
Example 6: 3-ph system - BCS = 1
Let us consider a three-phase, four wires system where:
I
R
= 5 A
I
S
= 5 A
I
T
= 3.2 A
I
N
= 0 A
The tamper is evaluated because
I
R
+ I
S
+I
T
+I
N
= 13.2 A > 0,703125 A = I
MAX
/ 256
In this case
sIRMS = 0,449901 A > 0,4125 A = (I
R
+ I
S
+I
T
+I
N
) / 32
Then BCS = 1.
Example 7: 1-ph system - BCS = 0
Let us consider a single phase systems with only S and T wires connected where
I
S
= 5 A
I
T
= 4 A
I
MAX
= 180 A
In this case the criterion for tamper evaluation is verified since:
(I
S
+ I
T
) = 9 A > 0,703125 A = I
MAX
/ 256
But BCS = 0 because
7/9 I
T
= 3.11 A < I
S
= 5 A < 9/7 I
T
= 5.14 A
and
7/9 I
S
= 3.88 A < I
T
= 4 A < 9/7 I
S
= 6.43 A
Example 8: 1-ph system - BCS = 1
Let us consider the case in which:
I
S
= 5 A
I
T
= 3 A
I
MAX
= 180 A
Also in this case the criterion for tamper evaluation is verified:
(I
S
+ I
T
) = 8 A > 0,703125 A = I
MAX
/ 256
Now BCS = 1 because
7/9 I
S
= 3.88 A > I
T
= 3 A
9.10.2 Phase sequence is wrong (status bit BSF )
One tamper condition is that phase sequence is not correct. A 3-ph phase status bit BSF
checks the sequence of phases, which, in a three phase system is one of the following:
● R → S → T
● S → T → R
● T → R → S
In one of the above cases
BSF is cleared, otherwise bit BSF is set.