1MAC050144-MB C
Section 6
Supervision functions
615 series ANSI
435
Technical Manual
to flow through the monitored coil and the actual coil current is a sum of all TCM currents.
This must be taken into consideration when determining the resistance of R
ext
.
Trip-circuit monitoring with auxiliary relays
Many retrofit projects are carried out partially, that is, the old electromechanical relays are
replaced with new ones but the circuit breaker is not replaced. This creates a problem that
the coil current of an old type circuit breaker can be too high for the protection IED trip
contact to break.
The circuit breaker coil current is normally cut by an internal contact of the circuit breaker.
In case of a circuit breaker failure, there is a risk that the protection IED trip contact is
destroyed since the contact is obliged to disconnect high level of electromagnetic energy
accumulated in the trip coil.
An auxiliary relay can be used between the protection IED trip contact and the circuit
breaker coil. This way the breaking capacity question is solved, but the TCM circuit in the
protection IED monitors the healthy auxiliary relay coil, not the circuit breaker coil. The
separate trip circuit monitoring relay is applicable for this to supervise the trip coil of the
circuit breaker.
Dimensioning of the external resistor
Under normal operating conditions, the applied external voltage is divided between the
relay’s internal circuit and the external trip circuit so that at the minimum 10 V (3...10 V)
remains over the relay’s internal circuit. Should the external circuit’s resistance be too high
or the internal circuit’s too low, for example due to welded relay contacts, the fault is
detected.
Mathematically, the operation condition can be expressed as:
(Equation 51)
(Equation 52)
V
c
Operating voltage over the supervised trip circuit
I
c
Measuring current through the trip circuit, appr. 1.0 mA (0.85...1.20 mA)
R
ext
external shunt resistance
R
s
trip coil resistance
If the external shunt resistance is used, it has to be calculated not to interfere with the
functionality of the supervision or the trip coil. Too high a resistance causes too high a
voltage drop, jeopardizing the requirement of at least 20 V over the internal circuit, while
a resistance too low can enable false operations of the trip coil.
Setting the TCM function in a protection IED not-in-use does not typically
affect the supervising current injection.
V
R
R
I
V
AC DC
C
ext
int
s
c
−
+
+
× ≥
(R
)
/
20
V
R
R
I
V DC
c
ext
s
c
−
+
× ≥
(
)
10
Содержание 615 Series ANSI
Страница 1: ...Relion Protection and Control 615 series ANSI Technical Manual ...
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Страница 29: ...1MAC050144 MB C Section 615 series ANSI 22 Technical Manual ...
Страница 389: ...Section 4 1MAC050144 MB C Protection functions 382 615 series ANSI Technical Manual ...
Страница 485: ...Section 6 1MAC050144 MB C Supervision functions 478 615 series ANSI Technical Manual ...
Страница 635: ...Section 10 1MAC050144 MB C Other functions 628 615 series ANSI Technical Manual ...
Страница 707: ...Section 15 1MAC050144 MB C Applicable standards and regulations 700 615 series ANSI Technical Manual ...
Страница 711: ...Section 16 1MAC050144 MB C Glossary 704 615 series ANSI Technical Manual ...
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