Static Converters
Technical Information


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In a home workshop, farm, garage or small business environment there is often a requirement for the operation of machinery driven by three phase induction motors where only a single phase electricity supply is available.

The Static Converter provides an artificial means by which a three-phase motor can be operated from a single-phase supply thereby offering a cost-effective solution to this dilemma. In most instances, no modification to the machine is necessary.

The Static Converter is designed to operate three phase motors with starting characteristics and duty cycles as generally experienced on machine tool applications (ie. light to medium duty and relatively constant load conditions). This style of converter is typically used in single operator environments where only one machine is used at a time.

The use of a Rotary Converter is recommended for multi-operator and/or multi-motor working environments. Please consult the separate Rotary Converter Technical Data page.

Currently, six sizes of Static Converter are available designed to operate single motor loads between 0.37kW (0.5hp) and 7.5kW (10hp) and multi-motor loads between 1.5kW (2hp) and 11.0kW (15hp).

For applications with single motors in excess of 7.5kW (10hp) or combinations of motors in excess of 11kW, please seek further advice. Enquiries are invited from machinery manufacturers wishing to incorporate custom-built assemblies into their equipment.

For specific single motor applications where equipment has a heavy starting load or is subjected to an abnormal surge current or duty cycle an alternative range of Static Converters is recommended. Compressors, Pumps, Extractor Fans and Vehicle Hoists fall into this category. It should be noted that converters are designed for applications with a cyclic duty. Please seek advice for continuous duty applications.

TECHNICAL DATA
The converter offers no inherent overload protection to either the circuit cable or the driven machinery. Adequate overload protection for both the motors in the driven machinery and the supply circuit to the converter is the responsibility of the customer. The customer should also ensure that the electricity system and cable supplying the converter is of sufficient capacity to allow the motor to start without causing undue supply disturbances as a consequence of voltage drop.

TECHNICAL NOTES
The full load running current (flc) of an induction motor operating on a single-phase is approximately 4 amps per hp. When operated in conjunction with a Static Converter, the starting current of a three-phase motor is limited to approximately 3 times its flc. This is significantly lower than the motor starting current of an equivalent sized single-phase motor, which would typically draw between 6-8 times its flc.

As the starting characteristics of a three-phase motor supplied by a converter are similar in nature to Star/Delta starting on a three-phase supply, significant reductions in starting torque are experienced when compared with direct on line starting on a three-phase supply.

Generally when machinery is operated in conjunction with a Static Converter direct on line starting is recommended. For machinery fitted with a Star/Delta starter, the period in the star connection should be set as short as possible to ensure a successful start. This is not the case when machinery is operated on a mains three-phase supply.

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