www.metrel.si 2009 VARIABLE TRANSFORMERS Single-phase Built-in Variable Transformers Three-phase Built-in Variable Transformers Motor driven Variable Transformers Desk top Variable Transformers Power Supplies Technical regulation General Three general regulations serve as a base for function, quality and safety of METREL variable transformers: European Low METREL is well known producer of variable transformers voltage directive 2006/95/EC (72/23/EEC), German standard and power supplies which are widely accepted in laborato- VDE 0552 and International standard IEC 60989. ries, industry, schools. Applications The competitiveness of these products is based on a good METREL variable transformers are applied to various products price/performance ratio. They are robust in construction, they or applications including the following: have low magnetizing current, low operating torque and no Power supplies distortion or harmonics added. Copper winding is precision Laboratory and test equipment wound on a toroidal core. Speed control devices Computer peripheral equipment Tradition with 50 years of experience in continuous production, Welding controls product control, testing, safety, permanent improvements and, Variable speed devices for large machinery customer service are fil rouge in the production of METREL Electroplating and anodising variable transformers. High-voltage electronic tube circuits Spare supply regulators in broadcast transmitters Complete information on variable transformers and complete Voltage stabilizers instrument product groups of METREL can be found on www. metrel.si. High voltage test set Meter test bench METREL variable transformers are available as: Hydro generation plants Single or poly phase types Battery chargers Autotransformer or insulated variable transformer DC motor controls Manual or motor driven variable transformer Plastic blow moulding machines Open / panel mount or enclosed construction Control of furnace transformers Air-cooled, optional oil-cooled variable transformer Lightening regulation Laboratory stirrers METREL variable transformers provide continuously adjustable AC, DC brush motors voltage from zero to 100% or 113% of the line voltage. Their High current motorized voltage regulators operation is simple and efficient. High current plastic plating operations Cooper wire is wound on a toroidal core by using high preci- sion winding machines. Technical performances Sliding trace of the winding is properly smoothed to provide low resistance and long wearing track for the carbon brush. High reliability Some models are silver plated, providing lower output imped- METREL variable transformers are practically maintenance free. ance. The core is made of strip-wound oriented silicon steel for Long-life operation is assured with: low electrical losses and high magnetic densities. The coil is in- Precision winding sulated from the core by means of a special insulation support Surface forming of winding that also prevents movement of coil turns. Variable transform- Tight tolerances in preparing sliding track ers are wound in a manner to ensure that voltage between the Deep varnishing and baking also for fixing winding structure two turns is small enough to avoid harmful sparking or exces- A spring-loaded solid carbon brush sive heating of shorted turns. Power factor Power factor of load has very little effect on the operation of a METREL variable transformer in the range from 0.5 lagging to 0.5 leading. Like any transformer, the METREL variable trans- Short duration loading former reflects the load power factor to the line with very little In (%) 600 change. 500 Only for very light loads, possibly under 10%, will the lagging Standard track Silvered track power factor of the METREL variable transformer become sig- 400 nificant due to magnetizing current. 300 High efficiency 200 METREL variable transformers have low electrical losses un- der all load conditions. 100 t (min) 0.1 1 10 100 1000 Efficiency is 98.5 percent at maximum output voltage select- ed. This efficiency remains high, even at greatly reduced load voltage. Ambient temperature METREL variable transformers are designed for continuous METREL variable transformers provide an output voltage operation in ambient of 0 C to 40 C, at full rated load. When waveform that is a precise reproduction of the applied input operated above 40 C, the output power must be derated in ac- voltage waveform. Slider is mounted on shaft but electrically cordance with diagram 1. For example, when operating model insulated from it. With a brush holder, it serves also as a heat sink. Only standard METREL variable transformers are listed in HSH 230/4 in a 60 C ambient, rated output current would be: this catalogue. 70 % x 4 A = 2.8 A. Variable Transformers