Page 267 - contactors_motor_protection_for_rolling_stock_application

Contactors for DC switching applications

DC-1, DC-3, DC-5 applications according to IEC 60947-4-1

The circuit switching on DC is more difficult than on AC, as Operational voltage
alternating current go to zero according to the frequency of the – The higher the operational voltage value is, the more difficult

supply source while DC current has a continuous value. it is to break the arc.
The main parameters to be considered for selecting a contac- – The use of main poles connected in series will allow to in-
tor are the current, the voltage and the L/R time constant of the crease the value of switched voltage.
controlled load. However, the maximum switched voltage must be within the
max operational voltage of the contactor. 3
Time constant and utilization categories All the poles required for breaking must be connected in
In DC applications, the nature of load to switch (resistor, induc- series between the load and the source polarity not linked to
tance or a combination) is characterized by the ratio of the in- earth (or chassis) (see recommended connection diagrams).
ductance to the resistance (L (inductance of operated circuit) / R
(resistance of operated circuit) = mH/Ω = ms) ABB offer a large choice of possibilities for DC switching
This ratio L/R is called the time constant of the circuit. applications (see selection tables):
– AF..(Z)B 3-pole or 4-pole contactors with either 1- pole
DC current utilization categories are defined according to breaking or breaking with poles connected in series.
IEC 60947-4-1: – GAF75..RT designed for DC breaking with permanent
– DC-1 non inductive or slightly inductive loads, resistance magnets fitted on the main poles for use with the 3 poles
furnaces (L/R ≤ 1 ms) connected in series and considered as 1-pole devices.
– DC-3 shunt motors: starting, plugging, inching, dynamic – The 3 poles are connected in series via two supplied and
breaking of DC motors (L/R ≤ 2 ms) fitted insulated connections (25 mm²).
– DC-5 series motors: starting, plugging, inching, dynamic
breaking of DC motors (L/R ≤ 7.5 ms). Selection tables
The enclosed selection tables will guide your choice through
The higher the time constant value is, the more difficult it is to all contactor variants according to utilization category, for op-
break the arc. erational voltage up to 1000 V DC-1 and operational current up
The addition of a resistor in parallel with an inductive winding helps to 520 A in ambient temperatures from -25 °C up to 40 °C.
in the elimination of the arcs, by reducing the time constant.

Connection diagrams
Recommended connection
In the example below, the 3 poles are connected in series without the load in between.
This connection is recommended in systems according to the following configurations.

+ -

Indirect earthed system Direct earthed system Centre earthed system
(isolated system)
Load

Points to consider Polarity:
The above relates to power circuit switching. The SCPD (Short For all GAF75..RT types, connection polarities must be re-
Circuit Protection Device) must comply with applicable protec- spected.
tion rules. (See instruction leaflet and see markings on the main terminals
or the contactor front)
1SBC100193S0201

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