1. Control the Starting Current of the Motor

When a motor is started directly at line frequency, it generates 7 to 8 times its rated current. This high current significantly increases electrical stress on the motor windings and produces heat, which can reduce the motor's lifespan.

With variable frequency drive (VFD) speed control, the motor can start from zero speed and zero voltage. Once the frequency and voltage relationship is established, the VFD can operate the load using V/f or vector control methods. Using VFDs for speed control greatly reduces starting current, enhances winding durability, and ultimately lowers maintenance costs while extending motor life—this is especially beneficial for heating supply enterprises.

2. Reduce Voltage Fluctuations in Power Lines and Improve Grid Quality

During direct-on-line (DOL) motor startup at line frequency, the surge in current causes significant voltage fluctuations. The extent of the voltage drop depends on the motor power and the capacity of the distribution grid. Such voltage drops may cause sensitive equipment on the same power network to trip or malfunction—for example, DCS systems, PCs, and contactors may all be affected. With VFD-based speed control, the motor starts gradually from zero frequency and zero voltage, minimizing voltage drops.

3. Lower Power Demand During Startup

Motor power is proportional to the product of current and voltage. Direct starting of motors consumes significantly more power than starting with a VFD. For example, a 315kW circulation pump started directly may generate a current surge that seriously affects other equipment—even causing overcurrent tripping of transformers—and could result in warnings from the utility provider. In contrast, using a VFD for motor start-up avoids such issues entirely.

4. Adjustable Acceleration and Deceleration Functions

Operating Speed and Torque Limitation – VFDs allow users to freely set acceleration and deceleration times based on specific needs, and also choose the acceleration/deceleration method, such as linear or S-shaped profiles. This prevents violent vibrations in motor shafts or gears connected to the system, thereby reducing mechanical wear and fatigue. Additionally, smooth speed adjustments can be achieved via external potentiometers or manual controllers. After VFD speed control, torque limits can be set to protect mechanical components from damage, ensuring continuous production processes and product reliability. Modern VFD technology allows adjustable torque limits with control accuracy reaching approximately 3% to 5%.

5. VFD Application in Water Pump Pipelines

In heating supply enterprises, water pumps are among the most frequently used devices, and water hammer effect is the most critical issue to address in heating pipelines.

When an electric water pump starts under full voltage, the startup time is less than one second. Within this short period, the flow rate in the pipeline increases rapidly from zero to the rated flow. This abrupt change in fluid flow generates high or low pressure impacts inside the pipe, potentially causing cavitation phenomena.

The pressure impact against the pipe wall creates noise similar to a hammer striking the pipe—known as the "water hammer effect." This phenomenon not only produces noise but can also cause physical damage. Excessive pressure may rupture pipes, while low pressure may cause them to collapse. Cavitation can lead to intense fluid agitation, eroding the inner walls of pipes and causing liquid vaporization. Additionally, water hammer can damage valves and fasteners. When stopping directly, the potential energy of the liquid overcomes the inertia of the motor, causing sudden stoppage and generating pressure surges and water hammer effects.

With VFD control, acceleration and deceleration times can be set according to requirements, reducing the rate of flow change within the piping system to acceptable levels. This effectively eliminates the water hammer effect completely—offering a simple yet highly effective solution.

Sunye Electric Co., Ltd. (Changsha Sunye Electric Co., Ltd. was established in 2010; Shenzhen Sunye Electric Co., Ltd. was established in 2002) is a national high-tech enterprise integrating R&D, manufacturing, and sales of inverters, industry-specific all-in-one machines, servo drives, and new energy products.

Sunye Electric owns independent intellectual property rights. Its products have passed inspections and certifications by national authoritative institutions and have obtained multiple software copyrights and IP certificates. It invests heavily every year in researching new technologies and developing new products, with many patents and software copyrights granted. The company possesses core platform technologies such as construction hoist drivers, high-performance vector inverters, servos, and permanent magnet synchronous motor controls. Low- and medium-voltage inverters and servo drives are widely used in industries such as lifting equipment, stone processing, HVAC, machine tools, metal products, wire and cable, plastics, printing and packaging, textile and chemical fibers, building materials, metallurgy, coal mining, municipal services, and automotive applications. Guided by the philosophy of "innovation, technology, and strength," and driven by the corporate spirit of "unity, progress, pragmatism, and innovation," the company adheres to the business principle of "honesty and excellence, mutual benefit and coexistence." With a quality policy of "implementing total quality management and continuous improvement to pursue zero defects," Sunye Electric is committed to providing premium products to customers across various industries.

Address: Sunye Electric Industrial Park, No. 669 Xinsheng Road, High-Tech Zone, Changsha City

Tel/Fax: 0731-89932666 0731-89932688

Business Phone: 400-0755-731

Technical Support: 400-0755-731