3RW443. datasheet(7/40 Pages) SIEMENS

7 / 40 page

Soft start-up with voltage ramp and current limiting

What are the benefits of settable

current limiting?

More and more power supply companies

request compliance with specific current

limit values during start-up to minimize

the load on the power supply systems

posed by high starting currents. This

requirement can be perfectly met with

the settable current limiting of our soft

starters.

Is an external bypass contactor

required?

No. Thanks to integrated bridging

contact systems, bypass contactors

are unnecessary while the power

semiconductors’ power loss is

nevertheless sustainably minimized.

What are the advantages of the

inside-delta circuit?

With inside-delta circuits, the soft

starter’s phases are switched in series

with the individual motor windings,

thanks to which the soft starter merely

has to conduct the delta current, i. e.

58% of the nominal motor current

(conductor current).

Automatic recognition of the circuit type

by our soft starters partially facilitates

the application of considerably smaller

devices.

Do all three phases have to be

controlled?

No, this is not required for operational

switching. Also for smooth motor start

using our soft alternative, two controlled

phases are sufficient with standard soft

starters. Moreover, our solution not only

saves costs, but also space in the control

cabinet. However, the third controlled

phase is required for inside-delta circuits.

Are there further options for soft

motor starting?

Soft motor starting can also be realized

with a frequency converter. However, this

is only reasonable if the motor’s speed

is to be influenced also during operation

in addition to the starting phase – which

increases the costs.

Rated current I of the starter corresponds to the

nominal motor current

3 cables to the motor

Rated current I of the starter corresponds to 58%

of the nominal motor current I

6 cables (as with wye-delta* starters) to the motor

Standard circuit

Inside-delta circuit

Phase control angle principle of the line voltage

with soft starters using semiconductor elements

= Phase control angle

I = 100 A

I = 58 A

Q11

I = 100 A

with voltage ramp

US: Starting voltage

IS:

Starting current

IB:

Limiting current

with current limiting

* star-delta

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