FUNCTION CHARACTERISTICS
349
How to calculate resistor
Both the following conditions must be filled:
1) The circuit breaker coil must no be powered when the CB is open and an open command is issued;
2) The binary input is energized when the trip contact open.
1) If the circuit breaker is just open an unnecessary excitation must be avoided; the most critical
event arises when the TRIP contact is closed (e.g. manual or test command), so with minimal
series resistance. To avoid an unwanted excitation the series resistance must be higher than a
minimum value defined as:
R
min
=
R
TC
· (
U
AUX
-
U
TCmin
) /
U
TCmin
where:
U
TCmin
: minimum coil excitation voltage
U
AUX
: auxiliary voltage
R
TC
: coil resistance
2) To energize the binary input circuit when the TRIP contact and CB open, the series resistance
must be lowerer than a maximum value defined as:
R
max
= [(
U
AUX
-
U
DIGmin
) /
I
DIG
] -
R
TC
where:
U
DIGmin
: minimum binary input excitation voltage (18 V)
U
AUX
: auxiliary voltage
R
TC
: coil resistance
I
DIG
: binary input excitation current (0.003 A)
To satisfy the above requirements, the R value must be chosen between the
R
min
and
R
max
values;
typically the normalized value nearest the arithmetic mean:
R
= (
R
min
+
R
max
) / 2
The power dissipated by the R resistor is:
P
R
=
R
·
I
2
=
R
· [
U
AUX
/ (
R
+
R
TC
)]
2
Example
U
AUX
= 110 Vcc (auxiliary voltage)
P
TC
= 50 W (coil power)
R
TC
=
U
AUX2
/
P
TC
= 242 Ω (coil resistance)
U
TCmin
= 77 V (minimum coil excitation voltage = 70%
U
AUX
)
U
DIGmin
= 18 V (minimum binary input excitation voltage)
I
DIG
= 0.003 A (binary input excitation current)
R
min
=
R
TC
· (
U
AUX
-
U
TCmin
) /
U
TCmin
= 242 · (110 - 77) / 77 = 103.7 Ω
R
max
= [(
U
AUX
-
U
DIGmin
) /
I
DIG
] -
R
TC
= [(110 - 18) / 0.003] - 242 = 30425 Ω
R
= (
R
min
+
R
max
) / 2 = (103.7 + 30425) / 2 = 15264 Ω ~ 15 k Ω
P
R
(Power dissipated by the R resistor) =
U
AUX2
/
R
= 110
2
/ 15000 = 0.8 W
[1]
Note1 In order to limit the temperature of the resistor it should be oversized (at least double the power - 2 W)
Fun-74TCS1.ai
0
40 s
T
0
6 s
T
&
Enable (ON
≡
Enable)
74TCS Enable
RESET
TR
IP
PIN
G
M
AT
RIX
(
LE
D+R
EL
AY
S)
&
&
Block1 input (ON
≡
Block)
Block1
Start 74TCS
Start 74TCS
Trip 74TCS
Trip 74TCS
TCS1
&
Enable (ON
≡
Enable)
Block1
Binary input INx
T
0
Logic
INx
t
ON
INx
t
ON
INx
t
OFF
T
0
n.o.
n.c.
INx
t
OFF
Binary input INx
T
0
Logic
INx
t
ON
INx
t
ON
INx
t
OFF
T
0
n.o.
n.c.
INx
t
OFF
Start 74TCS
Trip 74TCS
BLK1 74TCS
74TCS-BLK1
74TCS-ST-K
74TCS-ST-L
74TCS-TR-K
74TCS-TR-L
Logic diagram concerning the trip circuit supervision with one binary inputs - 74TCS
XMR-D EQUIPMENT MANUAL
Ed. 2.9 - 02/2021
