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 The 50kA motor protection circuit breaker
 LOVATO ELECTRIC present their new range of high breaking-capacity motor protection circuit breakers. 
  
   
 In the presence of their Director Mr. Massimiliano Cacciavillani, LOVATO Electric recently presented their new SM1 range of motor protection circuit breakers with magnetic and thermal releases (0.1 – 32 A), featuring a high breaking capacity (50k A).
Fully designed at the Bergamo (Italy) production facility, the SM1 is the result of three years of studies and research work aimed at optimising operation of these breaking devices, which must be able to work in extremely heavy electrical conditions (50kA).
Safety, reliability and small size were the targets underlying the designers’ work.
The SM1 circuit-breaker has been developed in accordance with ISO9001 requisites and using state-of-the-art technologies:

  • Three-dimensional CAD design system

  • Fast prototyping thanks to stereolithography processes or with CAD-CAM systems

  • Mould-flow systems for optimising the moulds for the most critical parts

  • Dimensional checking by means of optical measuring systems with no physical contact

  • Assembly systems with laser and PLC-based checking of mechanical parameters, according to the concept of free transfer on pallets.

The solutions adopted for designing the system for the electrical arc extinction and for the control kinematics of the circuit-breaker are particularly interesting. 
Great care has beenalso taken in choosing the materials, which had to be able to withstand high thermal stresses, maintain the dimensional stability of the control-release system and meet the strict  requirements of UL standards.
SM1 motor protection circuit breakers are devices for controlling and protecting motors. 

They can be used to start motors manually or, combined with contactors, to make complete starters. In this latter case, the contactor acts as the control device, enabling remote control, while the automatic circuit-breaker takes care of protecting and disconnecting of the motor.
SM1 motor protection circuit breakers are split up into two families:
SM1A: made with 14 different ranges (from 0.1 to 32A), with 25kA breaking capacity at 32A
SM1B: made with 6 different ranges (from 9 to 32A), with 50kA breaking capacity at 32A.
The protection provided by SM1 circuit-breakers is both magnetic for short circuits and thermal for overloads. 
The magnetic protection release is tripped when the current reaches 12 times the rated operational current of the circuit breaker. 
The thermal protection release is tripped depending on how the adjustment range setting and in accordance with the requisites of IEC standard 60947-4-1 ( tripping class 10).
 Each SM1 circuit breaker is equipped with a magnetic trip indicator so that it is possible to distinguish visually between tripping due to short circuit and due to  overload. 
This arrangement makes it easy to avoid re-reclosing the circuit after it has just been cut off by the circuit breaker due to a short circuit, which would be dangerous. 
The circuit can only be closed after the system for signalling the occurrence of a short circuit has been reset.
The SM1 circuit-breaker also operates as a switch disconnector, meeting all the requirements of IEC/EN 60947 standards.  
 SM1 circuit breakers are particularly appropriate for starting, protecting and disconnecting motors that drive machine tools, pumps, compressors, fans, cranes, centrifuges, grinders and so on.  
 
To complete the SM1 Range, there is a vast range of accessories that includes:

  • Front-mount auxiliary contacts

  • Side-mount auxiliary contacts 

  • Signalling contacts

  • Undervoltage trip releases

  • Shunt trip release.

The front-mount auxiliary contacts (2NO or 1NO+1NC) are particularly innovative. 
They are equipped with high-conductivity contacts with four contact points, and are therefore suitable for operation in conditions featuring extremely low voltages and currents. 
This particular feature makes it easy, for example, to set up a reliable interface with a PLC for regulating automated systems. 
In addition, the front-mount position of these auxiliary contacts means important space saving. 
  
The add-on signalling contacts are equipped with a mechanical signalling device making it possible to distinguish between automatic tripping of the circuit breaker and manual tripping. 
When the circuit breaker is tripped automatically, the contacts require resetting before the circuit can be closed again. All the accessories are snapped into place, and can be demounted simply by pressing the retaining lever, with no need of tools.
   

   

A range of enclosures for installation is also available, which includes:

  • Wall-mount enclosures

  • Flush-mount enclosures

  • Rotary actuators for enclosures

  • Emergency stop push-button actuators.

The wall-mount enclosures are available in two versions that have different widths:

  • 100mm, able to contain the circuit-breaker, a trip release device, one front-mount and one side-mount auxiliary blocks;

  • 85mm, able to contain the circuit-breaker, a trip release device and one front-mount auxiliary block.

The degree of protection of the 100 mm enclosures is IP40. 
It can be raised to IP65 by adding the padlockable rotary actuator.
The degree of protection of the 85 mm enclosures is IP40. 
It can be raised to IP65 by adding a protective membrane or the emergency stop actuators.
One very important aspect for the correct circuit is CO-ORDINATION BETWEEN THE CIRCUIT-BREAKERS AND THE CONTACTORS. What is meant by co-ordination is the correct combination of a circuit breaker with a contactor so that, in the event of short circuit, safe tripping is obtained without causing any damage to the system - all that may be required is replacement of the contactor (type 1 co-ordination) and the possibility of resetting the system rapidly to proper working conditions without having to replace any parts (type 2 co-ordination).
SM1 motor protection circuit breakers are type 2 co-ordinated with LOVATO contactors.
The testing in this respect has been conducted by the Electromechanical Laboratory of Istituto Elettrotecnico Nazionale Galileo Ferraris in Turin (Italy).
The circuit breaker plus contactor assembly is very quickly and easily mounted thanks to the use of the connection link.
      

The SM range is completed by motor protection circuit breakers SM2 and SM3, which cover a range of motor currents up to 100 A. This means that, thanks to their wide adjustment ranges from 0.1 A up to 100 A and only four frame sizes, the SM range of circuit breakers will enable control and protection of motors of up to 45 kW (400V).
By launching this new range of motor protection circuit breakers, LOVATO Electric have further completed their wide range of products for the automation and starting of electric motors, becoming a world leader in terms of technology and know-how.

  
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