Starting Reduced voltage

Reduced-voltage starting. A reactor, resistor, or transformer is temporarily connected ahead of the motor during start to reduce the current inrush and limit voltage dip. This is accompanied by reduced starting torque. For reactor or resistor start, the torque decreases as the square of current for transformer start, the torque decreases directly with line current. The reactor, resistor, or transformer can be adjusted to give a proper balance between torque and current. 

Reduced-Voltage Starting Reduced-voltage starting is used to reduce system voltage dip. Voltage dips must be limited otherwise, they may drop other motors off the line, cause synchronous motors on the system to pull out of step, or cause objectionable lamp flicker. 

Secondary Control of Wound-Rotor Motors Wound-rotor motors may be effectively reduced-voltage-started or have their speed controlled by using external secondaiy resistance. The addition of resistance into the secondaiy circuit of a wound-rotor motor reduces the starting current and affects the speed under load conditions. 

A few common methods to achieve a reduced voltage start are described below. 

Direct on-line starting (DOL) Reduced voltage starting... 

Open-circuit transition A method of reduced-voltage starting in which power to the motor... 

Resistance starting A form of reduced-voltage starting employing resistances that are short-... 

Open versus Closed Transition. Two terms are used when discussing reduced-voltage starting open-transition and closed-transition starters.These terms are used to describe circuit continuity during the starting sequence. 

If reduced voltage starting is used, it is important that the reduced starting torque is never less than the sum of the friction and windage torque. Since the torque available to accelerate the bowl is equal to the difference between the motor torque and friction and windage torque, the motor may not reach full speed in a reasonable time, unless care is taken. 

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