Application of AC80 Frequency Inverter on Concrete Mixer

Project Overview

Overview

VEICHI has engaged in promoting industrial energy saving technology for many years and has accumulated rich experience in industrial energy saving area. In view of the high energy consumption situations in many domestic concrete production companies, VEICHI developed vector control frequency inverter that successfully realized energy-saving transformation on concrete product lines for a Guangdong company, achieving good economic benefit and social effect. In order to benefit more similar companies, we publish this application case here with hope to prompt the energy-saving transformation in this industry.

Background

That company had two concrete mixing lines and the main power utilization equipment of each production line was a 30kW inclined belt conveyor and a 2×37kW double mixer. The three motors all adopted Y-Δ starting device, when the system was in light load without material(in waiting state), the total current was 80A; when in full loads, the total current was 100~130A. On average, the system had 50% ratio in operating state and the running current was around 100A. After transformation, the power consumption was around 50KW and total 100KW for two equipments. In sum, the annual electric charge was about 100KW×20 hours×300 days×0.7RMB =420,000 RMB.

Transformation Scheme

a. Transformation methods

To adapt to market change and improve product competitiveness, adopting energy-saving production is one of the most effective ways to reduce costs. According to the actual situations of the company's concrete mixing lines, VEICHI reached agreements with client on the transformation methods. Through the cooperation of both sides, we solved many problems in the transformation process and finally finished this project, getting great economic benefits.

In this case, we adopted the advanced PLC technology and frequency inverters to replace the relays and contactor control to realize the coordinated operation between the inclined belt conveyor and dual mixer, achieving safe, energy-saving and easy-operation effect.

b. Main technical specification

(1) Mixer motor: three phase AC asynchronous motor, 4 poles, 37KW, 2 units, synchronous operation of connecting shaft.
(2) Inclined belt conveyor: three phase AC asynchronous motor, 30KW, 4 poles, 1 unit.
(3) System load rate: 50%.
(4) Motor control and operating mode: Y-Δ start and continuous operation.
(5) Total current in empty load: 80A.
(6) Total current in full load: 120A.

c. Solutions in main system control

(1) Kept the original Y-Δ starting device as a backup system;
(2) Adopted wall mounted installation due to site limitation;
(3) Adopted automatic switchover between the Y-Δ mode and inverter mode;
(4) Adopted PLC to control the two inverters according to the technical processes.
(5) Set detailed control functions, working conditions and fault signals display to facilitate monitor, control and maintenance;
(6) Completed protection functions.

d. System control points

(1) Speed control
Adopted AC80 speed control system with vector control
(2) Operations in system control such as start, stop, low speed operation, high speed operation and emergency stop could be controlled by PLC.

e. Attentions

(1) The frequency inverter was controlled by PLC, while the control conditions of PLC was determined by production process;
(2) The acceleration time, deceleration time and related parameters of frequency inverter were set on basis of actual situations.

Main Achievements

a. Remarkable energy-saving effect
After transformation, more than 30% energy can be saved in overall system.

b. Effects in Improving system stability, decreasing failure rate and reducing maintenance costs are mainly reflected on the following aspects:

(1) Extend service life.
The application of frequency inverter can achieve motor soft start and avoid impact on various equipments caused by Y-Δ staring mode, expanding motor service life.

(2) Provide powerful protection function.
The complete protection functions provide the system with protections for short circuit, overload, over-current, phase loss and under voltage, which can give maximum protections to the motor.

(3) Reduce system failure rate.
As the original system is controlled by complex contactor and relay system, the failure rate is high. The adopt of variable frequency speed regulation system has greatly simplified the control system and increase its reliability.

(4) Improve the synchronous performance of mixer's double reamers
After using one inverter to drive two reamers, the system has improved mixer's synchronous performance, reduced internal friction of dual mixers and saved great amount of electricity.

(5) Improve the power factor
Frequency inverter control has realized power factor on-site compensation and increased power factor to reach 0.95, which can not only save the electricity but also increase the power efficiency.

Conclusion

This energy saving transformation project has remained the original control system and distribution system, and it has been installed kilowatt-hour meter in the overall power system. The energy-saving effect can be directly reflected by switching variable frequency and power frequency, providing a strong basis for future industrial promotion.