The starting load of the ball mill is large, and the VFD starting current is 3-5 times smaller than that of the working frequency(For example, The power frequency starting current of the 132kW motor is about 1300A,VFD starting current is about 300A).As the starting current is so large that pull down the voltage of the power grid, which leads to the trip or failure of other device. After the use of VSD, the failure rate is greatly reduced.

The load fluctuation of the ball mill is large, and the over current, overvoltage, overload, lost phase, overheating and other protective functions of the VSD reduce the damage rate of the devices.In the power frequency operation,the motor should be repaired or replaced within at least one year, and the normal running time of the motor can reach 3 years or even longer when VSD control. Due to their electrical energy consumption and throttling losses, such as valves, dampers and baffles, as well as maintenance and repair costs, these costs consume between 7% and 25% of their production costs.

The ball mill uses frequency conversion speed to search the best working speed, which can grind the particles more evenly with less times, and the grain qualified rate is higher at one time.

FRECON inverter built-in simple PLC, multi-speed operation mode can reduce the input current under the state of below the power frequency, set the different operating frequency and running time in different time periods under the conditions of meeting the equipment process requirements, can achieve a good energy-saving effect, energy-saving rate can generally reach 7-18%.

**Note:** A 110kw ball mill uses FRECON FR500A series 132kw inverters to run for 19 hours every day. The conservative saving rate is estimated to be 9.3%, saving about 5,000 dollars in electricity bills a year. The following is a power-saving calculation example analysis:

**Factory introduction:**

The main motor power of the ball mill is 110KW, the rated speed is 1440 rpm, the rated current is 210A, and the rated voltage is 380V. Auxiliary motor rated voltage is 380V, rated current is 32A, rated speed is 1440 rev / min.The barrel rotation speed is 12N/min.

According to the work characteristics of the ball mill, the impact load requires a higher starting torque. Therefore, it is recommended that the power amplifier should be selected, and FRECON FR500A-4t-132g /160P will be configured.

The following is the V/F curve picture when the motor starts:

**Power consumption analysis of work frequency :**

A ball needs to run for 19 hours. first start the auxiliary motor to run 20 cycles, and then switch to the main motor work.The main motor is started by the way of buck up, the starting current is 1300A, and the starting time is 20S. After starting, the main motor's working current is about 250A. After two hours of work, the current drops to 190A, until the end.

Power consumed at startup:

*P1=1.732*380*1300*0.8÷1000=684.5KW*

Starting time is 20 seconds, and the power consumption is:

**685*20÷3600=3.8KWH**

Power consumption for grinding one ball at power frequency (19 hours):

The power consumption of startup impact is:

**3.8kwh+2*1.732*380*250*0.8÷1000+17*1.732*380*190*0.8÷1000=1967.8KWh**

A ball mill works 30 days a month, 10 months per year, and the annual consumption is as follows:

**30*10*1967.8KWh=590340 KWh **

**Power consumption analysis of frequency conversion :**

Using the FR500A series 132kw inverter, the ball is required to run for 19 hours, starting with the auxiliary motor running 20 cycles and switching to frequency changer until one bucket is finished.According to the process of the equipment, the VSD is required to set different speeds at different times.

The frequency and current of the five section speed in the frequency conversion state are measured as follows:

After using VSD for process transformation, the impact current is about 300A, This five-steps current recording is based on the initial operating current of each step, The longer the grinding time, the finer the grinding body, the smaller the current, so there will be some differences in calculations. But the impact on energy efficiency is not huge.

Power consumption for 19 hours in inverter:

*1.732*380*0.8÷1000（2*208+4*188+4*182+4*171+5*162）=1785KWh*

A ball mill works 30 days a month, 10 months per year, and the annual consumption is as follows:

**30*10*1785KWh=535500KWh**

Investment and recovery:

From the analysis of the above-mentioned power frequency and frequency converter's power consumption, the energy-saving rate after using the VSD can be calculated:

Power saving rate:**（590340-535500）/590340x100%=9.3%**

**The energy saving amount after one year of VSD using is: 590340x9.3%=54830 KWh**

Each kilowatt-hour is charged at $0.1, saving for a year: 54830KWh x0.1= $5,483.

The investment for each inverter is calculated at 2,000 dollars and the investment cost can be recovered in half a year. The serve life of the inverter is generally 10 years. According to the conservative power-saving rate of 9%, it is a pure payback period after half a year. The annual power-saving income is more than 5,000 dollars. If it is a high-power ball mill, energy-saving effect is more obvious.