Section 6
1MAC050144-MB C
Supervision functions
436
615 series ANSI
Technical Manual
Table 377: Values recommended for the external resistor R
ext
Due to the requirement that the voltage over the TCM contact must be 20V or higher, the
correct operation is not guaranteed with auxiliary operating voltages lower than 48V DC
because of the voltage drop in the R
ext
and operating coil or even voltage drop of the
feeding auxiliary voltage system which can cause too low voltage values over the TCM
contact. In this case, erroneous alarming can occur.
At lower (<48V DC) auxiliary circuit operating voltages, it is recommended to use the
circuit breaker position to block unintentional operation of TCM. The use of the position
indication is described earlier in this chapter.
Using power output contacts without trip-circuit monitoring
Figure 229:
Connection of a power output in a case when TCM is not used and the
internal resistor is disconnected
Incorrect connections and usage of trip-circuit monitoring
Although the TCM circuit consists of two separate contacts, it must be noted that those are
designed to be used as series connected to guarantee the breaking capacity given in the
technical manual of the IED. In addition to the weak breaking capacity, the internal resistor
is not dimensioned to withstand current without a TCM circuit. As a result, this kind of
incorrect connection causes immediate burning of the internal resistor when the circuit
breaker is in the close position and the voltage is applied to the trip circuit. The following
picture shows incorrect usage of a TCM circuit when only one of the contacts is used.
Operating voltage U
c
Shunt resistor R
ext
48 V DC
10 kΩ, 5 W
60 V DC
22 kΩ, 5 W
110 V DC
33 kΩ, 5 W
220 V DC
68 kΩ, 5 W
Содержание 615 Series ANSI
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