SPEED CONTROL OF THREE PHASE INDUCTION MOTOR BY USING CYCLOCONVERTER
SPEED CONTROL.pptx (Size: 1.08 MB / Downloads: 274)
It is a singly excited ac machine in the sense that it is supplied power from a single ac source.
Its stator winding is directly connected to ac source whereas its rotor winding receives its energy from stator by means of INDUCTION (Transformer action.)
It has good speed regulation and high starting torqe.
It consists of two parts:
Curve of the behaviour of the Induction Machine
During start up. Normally draws up to seven times the rated current.
Normally delivers approximately 1.5 the rated torque, when starting
When operating at base speed if the load is increased, the motor will start slowing down and the slip will increase.
But if the load is increased beyond the break down torque, the machine wont be able to recover.
V/Hz Theory Background
The induction motor draws the rated current and delivers the rated torque at the base speed.
As mentioned before, the motor can take up to 2.5 load increase with 20% drop in the speed.
Cycloconverter is a device which converts input power at one frequency to output power at different frequency with one stage conversion , thus it is a one stage frequency changer.
Cycloconverter eliminates the use of flywheel because the presence of flywheel in machine increases torsional vibration and fatigue in the component of power transmission system
A cycloconverter is a type of power controlled in which an alternating voltage at without any intermediate d.c stage.
A cycloconverter has the facility for continuous and independent control over both its output frequency and voltage. This frequency is normally less than 1/3 of the input frequency.
APPLICATION OF CYCLOCONVERTER IN INDUCTION MOTOR
Speed control of high power AC drive
Static VAR compensation
For converting variable speed alternator voltage to constant frequency output voltage for use as power supply in aircraft or shipboard.
How cycloconverters are used in speed control of 3 phase induction motor?
A cycloconverter converts regular 50 or 60 Hz AC power to a frequency that is less half of the input frequency. They essentially work by passing selected portions of the input waveform directly to the load. For motor speed control, the voltage is reduced by the same percentage that the frequency is reduced. The minimum frequency for motor speed control is probably 5 or 10 percent of the input frequency. In recent years, cycloconverters have been used to control motors in the power range of a few megawatts (thousands of horsepower) and above.