STPMC1 Datasheet, PDF (31/77 Pages) STMicroelectronics – Programmable poly-phase energy calculator IC

STPMC1
Theory of operation
9.10.2
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
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.
Doc ID 15728 Rev 6
31/77