Why does the above table recommend a 4.0kW Static converter for a 2.2kW motor?
The starting characteristics of a three-phase motor supplied by a TRANSWAVE converter are generally similar in nature to that of a star/delta starter. The motor starting current is inherently suppressed to approximately 3 times the full load current of the motor, significantly reducing the amount of available starting torque. This leads to starting difficulties, particularly if the maximum loading of the converter is sized close to the load of the motor. Where possible, Power Capacitors Limited recommends the use of direct-on-line starters for machinery operated in conjunction with a TRANSWAVE converter - note that the combination of a converter and a star/delta starter could compound these starting difficulties further. Generally speaking a static converter will achieve all mechanical speeds on a machine tool application provided that the synchronous speed of the motor is not exceeded. A rotary converter will overcome this problem. e.g. a Colchester Student lathe is driven by a 3hp 1400rpm motor and has  a top mechanical speed of 1200rpm, however the Harrison M300 lathe (also driven by a 3hp 1400rpm motor) has a top mechanical speed of 2500rpm. The former operates successfully from a static 4kW converter, the latter will achieve 10 of its 12 mechanical speeds. To achieve all 12 mechanical speeds of the M300 lathe, we would recommend the use of a rotary converter. Please do not hesitate to seek further advice from the company’s sales engineers if you are unsure as to which size of converter is suitable for your application.

Why does the static converter have a minimum load?
Motors driving a table rise/fall, scribing saw, feed rollers, coolant pump or table feed are invariably of a fractional horsepower nature. If operated independently from a TRANSWAVE converter, these motors would be subjected to an electrical condition, which would damage the motor windings. The minimum load reflects the minimum size of motor capable of interfacing independently with the converter, thereby establishing an acceptable artificial three-phase supply. Ancillary motors sized below the minimum loading of the TRANSWAVE should be operated in conjunction with and not independently of a larger drive motor that falls within the rating of the converter. Note that the Rotary converter does not have a minimum load.

What if my machine has a multi-speed motor? What if the application demands frequent stopping/starting?
It may be prudent to consider the use of a rotary converter for these applications. Otherwise a pilot motor may be required if the magnetic characteristics of the motor do not lend themselves to the creation of a satisfactory artificial phase. Motors with 720rpm and 960rpm windings may prove problematic. When using the standard static TRANSWAVE converter with multi-speed machines, care should be taken to ensure that the motor comes to rest before effecting a change of motor speed or rotation. Failure to do so could damage the motor and/or the converter. Please do not hesitate to seek further advice from the company’s sales engineers.

d.c. braking circuits and lighting circuits.
A wiring diagram of the braking/lighting circuit would be helpful as it may be necessary to modify the control wiring of the machine to ensure that the braking circuit is connected to the same two phases as the starter control circuit. This ensures the successful operation of the brake/light, failure to identify the need to modify the circuit could lead to malfunction of the braking mechanism or light.
 
 

1. Air & Refrigeration Compressors.The use of a dedicated SMA converter is usually recommended for compressor applications, independent of any other loads. For motor sizes in excess of 2.2kW/3hp the fitting of an off-load valve is advisable. Direct-on-line starting is essential. The use of a RT & MT rotary converter is recommended for Hydrovane-style compressors.

2. Brake Testing Equipment. As a brake tester has two motors, it is necessary to fit an additional capacitor circuit to the SMA converter to accommodate the introduction of the second motor. A control wire has to be connected via a contactor circuit to the control panel of the brake testing equipment console to ensure that the correct value of capacitor is in circuit for either the single or dual motor operation of the machine. The equipment manufacturer’s permission may be required to facilitate the accommodation of this circuit without any compromise in machine warranty. The modification enables the vehicle test to be conducted via the equipment handset, thereby not compromising the "single operator" element of the test. A surcharge would be levied for the converter modification. Alternatively, it may be possible to consider a modified RT & MT rotary converter. Further advice is available from the company’s sales engineers.

3. Car Ramps. Ensure that you advise the motor size and type of car ramp (electro-mechanical or hydraulic). The cost-engineered SMA range is usually recommended for this type of application. The SMA is a dedicated solution for the particular ramp, the capacitor values within the converter are sized according to information given by the customer. Bear in mind that the power regulator switch fitted to the converter may have to be adjusted in line with a variation in load. Even though the ramp may have a 3 tonne capacity mechanically, the artificial nature of the supply created by a converter may result in one power setting to lift a Ford Escort and another to lift a Land Rover. The operation of the equipment in conjunction with a converter may involve some operator discipline. The RT & MT rotary converter may offer a better solution.

4. Copy Lathes. The traverse motor of a copy lathe is usually controlled via either a hydraulic or electronic circuit. If the lathe has a separate hydraulic pump motor, it may be necessary to consider a single phase pump motor to overcome the sequential starting problem outlined above. The use of a rotary converter would eliminate this anomaly. Lathes with an electronic traverse (dc motor) can invariably be operated in conjunction with a static converter as the dc circuit is normally connected to a 240-volt phase & neutral supply.

5. Edgbanders, Routers, Shoe Repair Machinery, Guillotines (paper/card), Cutting Presses (fabric, leather) and Clicking Presses.The use of a rotary converter is recommended for these applications.

6. Extractor Fans. It may be necessary to consider a dedicated SMA to accommodate the load characteristics of the extractor fan motor, particularly for applications sized in excess of 2.2kW/3hp.

7. Printing Machinery. Machines without an inching facility can be operated directly from a suitably rated static converter. Applications requiring an inching facility must be operated in conjunction with a rotary converter to avoid electrical damage to the motor windings. Japanese printing machines (e.g. Ryobi) often incorporate 200 volt three phase motors, connected to a mains supply via a three phase 200/415 volt transformer. To ensure successful operation of the machine, the use of a rotary converter is recommended, together with a means of isolation between the converter output and the three phase transformer.

8. Produce Conveyors, Grading and Potting Equipment. Care should be taken to ensure that the TRANSWAVE converter rating is high enough to enable the motor to start under a load condition. Be wary of multi-motor applications where it may be necessary to consider a rotary converter or to ensure that one motor is running constantly to allow fractional horsepower ancillary motors to switch on and off at will. Other solutions to minimise this impracticality are available using individual capacitor circuits. Motors sized below the minimum loading of the converter will be damaged if operated independently from any converter other than the rotary. Please seek further advice from the company’s sales engineers if unsure as to which converter to order.

9. Pump applications (slurry/dirty water - irrigation/clean water), aerators and mixers. As most installations are controlled remotely, rather than via an operator, the majority of converters manufactured for this type of application are custom-built. The recommended SMA converter rating is determined by the duty cycle of the motor - i.e. cyclic or continuous - the application and the nominal motor speed. On-site commissioning by a PCL engineer or qualified electrician is recommended; technical assistance is available if required.

10. Welding Equipment. Both three-phase and two-phase 415 volt welding sets can be operated from a single-phase supply in conjunction with a modified rotary converter. The modification incorporates a hand/auto switch, which bypasses the automatic boost circuit. As the welding set has no motor (the load is resistive as opposed to inductive) it is necessary to use a rotary converter to develop the voltage in the "artificial" third phase, independently of the welder. The motor should be of sufficient capacity to maintain the voltage on the artificial phase when the welder is operated at its maximum current rating. A guide to the recommended size of rotary converter is given below.

Converter Size = RT5.5KW (7.5hp);  Welding Current = 160A
Converter Size = RT7.5KW (10hp);  Welding Current =  230A
Converter Size = RT11KW (15hp);  Welding Current =  300A

Note that the modified converter still offers the facility for standard motor applications as well as welding applications. There is a price surcharge for the modification.

Do not hesitate to contact the manufacturers for further advice, clarification or assistance.