The operation of electric motors using variable frequency speed control has gradually become a defining symbol of the modern era. In the context of Synchronous Motors, this speed control method specifically refers to the application of AC variable frequency drives to regulate the speed of machinery—such as fans, pumps, and similar equipment characterized by square-law torque loads—within industrial production processes. Variable frequency speed control enables the achievement of optimal process results while delivering substantial benefits in terms of energy conservation and cost reduction.
- Energy-Saving Effects:
In traditional systems, mechanical equipment driven by brushless-excited synchronous motors—such as fans, pumps, and compressors—typically operates at utility frequency with a constant power output. However, when process requirements necessitate adjustments to flow rates or pressure levels, significant energy waste often ensues. This is because, as the load varies, the flow rate changes in direct proportion to the motor speed, whereas the required power changes in proportion to the *cube* of the motor speed. Consequently, in a practical scenario where the required flow rate is only 80% of the rated flow, employing modern variable frequency automatic speed control can save over 45% more electrical energy compared to traditional regulation methods.
- Process Control for Variable Frequency Operation:
Variable frequency speed control operates as a standalone control system. While the operational sequence for variable frequency speed control is fundamentally similar to that of the variable frequency soft-start process, there are distinct differences. The key distinction lies in the initial phase: after the central control room issues the preparatory command for variable frequency operation, a barring motor (turning gear) begins to rotate the synchronous motor. Once the synchronous motor reaches a rotational speed equivalent to 1% of its rated speed—and in accordance with the pre-programmed logic—the control system initiates the excitation sequence. Upon successful engagement of the excitation system, the central control room issues an "Authorization to Engage" signal, thereby triggering the closure of the high-voltage switch associated with the variable frequency soft-start operation. Simultaneously, acting upon this signal, the central control room immediately closes the main high-voltage switch within the soft-start control circuit, thereby placing the synchronous motor into the active soft-start operational state under variable frequency control.