Point-on-Wave Motor Switching Reduces Torque Pulsation
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Solution Overview
Problem
The starting of induction motors results in severe torque pulsations and high surge currents due to the sudden connection of supply, leading to mechanical stress and protection issues, which existing technologies struggle to mitigate effectively.
Innovation Solution
Implementing a point-on-wave (POW) switching method where at least one winding is connected to a phase-shifted supply voltage at a controlled point, with the remaining windings connected after a controlled delay, to reduce or eliminate torque pulsation and surge current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If all three phase contacts are closed simultaneously during motor starting, then the motor starts up quickly, but severe torque pulsations and surge currents occur causing mechanical stress and protection issues
Solution Approach 1:
The patent segments the simultaneous closing of three phase contacts into a sequential process. Two contacts are closed first when the line voltage between two phases is at its peak value, and the third contact is closed a quarter of a cycle later. This segmentation eliminates the severe torque pulsations and surge currents that occur with simultaneous closing while maintaining quick motor startup.
2Device complexity
If traditional simultaneous contact closure is used, then the control system is simple, but the mechanical stress on drive train components is excessive
Solution Approach 1:
The patent applies preliminary action by monitoring the supply voltage waveform and timing the closing of contacts based on the voltage phase. Two contacts are closed at the peak of the line voltage between two phases, and the third contact is closed a quarter cycle later. This preliminary timing action reduces mechanical stress on drive train components while keeping the control system relatively simple.
3Quantity of substance
If conventional starting method is used, then the motor draws expected locked rotor current, but surge current can reach eighteen times full load current complicating protection settings
Solution Approach 1:
The patent changes the timing parameter of contact closure relative to the supply voltage waveform. By closing two contacts when the line voltage between two phases is at its peak value and the third contact a quarter of a cycle later, the surge current is reduced from eighteen times full load current to acceptable levels, simplifying protection relay and breaker settings while maintaining adequate starting current.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach significantly reduces surge currents by up to a factor of two and peak torques by 50%, allowing for safer and more reliable motor operation with reduced maintenance and improved system uptime.
Implementation Method 1
connection is made at a controlled point selected to occur when an induced back electro-motive force (e.m.f.) in the machine is substantially in phase with the supply voltage
Data Source
AI summary
A method of starting and apparatus for starting a multiphase electrical machine is disclosed. The aim is to reduce oscillatory pulsation in torque generated by the motor and inrush current that occurs shortly after start-up. The starting method comprises the steps of first connecting at least one, but less than all, of a plurality of windings to a respective phase-shifted supply voltage at a controlled point in the supply phase. Then, after a controlled delay following the first connection, connecting the or each remaining winding of the machine a respective phase-shifted supply voltage. The invention has particular application to multiphase (most usually, 3-phase) motors. However, it can also be applied to other electrical machines, such as generators and transformers. The method can be performed at initial start-up or, in the case of application to a motor, at Y-delta switchover.