Basic information of users
A steel rolling company manufactures 0.5mm thick steel chains. The company has 4 production lines, including 1 for 650 steel mills and 3 for 450 steel machines. The driving force is partly driven by DC brushless motors, and 3 sets of 1250KVA transformers and 630KVA . . The power supply system diagram is as follows:
Actual operating data
The average power factor of the 1250KVA transformer is PF=0.62, the working current of the 1960A and 630KVA transformer is 700KVA, the average power factor is PF=0.62, the working current is 1050A, all the transformers are overweight, and the pulse current is 5 times, the current volume change ratio is 18.5%.
Power System Situation Analysis
The main load of the DC brushless motor ballast is 6 single-pulse ballasts. The ballast equipment generates a large amount of pulse current in AC, AC, and DC operations. It is a typical pulse current source. When it is introduced into the power grid, the harmonic current The pulse current working voltage is caused to the characteristic impedance of the power network, resulting in the out-of-frame of the working voltage and current, which endangers the quality and operation safety of the switching power supply, increases the line loss and working voltage deviation, and has a negative impact on the power network and electrical equipment itself. Therefore, the compensation of the brushless DC motor should use the low-voltage reactive power compensation of the pulse current suppression filter to compensate the reactive load, improve the power factor, and will not be penalized by reactive power to increase the output of the transformer.
Filter reactive power compensation treatment plan
Governance goals
The design of filter compensation equipment meets the requirements of harmonic suppression and reactive power suppression management.
Under the 0.4KV system operating mode, after the filter compensation equipment is put into operation, the pulse current is suppressed, and the monthly average power factor is around 0.92.
High-order harmonic resonance, resonance overvoltage, and overcurrent caused by connecting to the filter compensation branch circuit will not occur.
Design Follows Standards
Power quality Public grid harmonics GB/T14519-1993
Power quality Voltage fluctuation and flicker GB12326-2000
General technical conditions of low-voltage reactive power compensation device GB/T 15576-1995
Low-voltage reactive power compensation device JB/T 7115-1993
Reactive power compensation technical conditions JB/T9663-1999 “Low-voltage reactive power automatic compensation controller” from the high-order harmonic current limit value of low-voltage power and electronic equipment GB/T17625.7-1998
Electrotechnical terms Power capacitors GB/T 2900.16-1996
Low voltage shunt capacitor GB/T 3983.1-1989
Reactor GB10229-88
Reactor IEC 289-88
Low-voltage reactive power compensation controller order technical conditions DL/T597-1996
Low-voltage electrical enclosure protection grade GB5013.1-1997
Low-voltage complete switchgear and control equipment GB7251.1-1997
Design ideas
According to the specific situation of the company, a plan for reactive power compensation of DC brushless motor filter is designed considering the load power factor and pulse current suppression, and a set of filter low-voltage reactive power compensation is installed on the 0.4kV bottom voltage side of the transformer , to suppress the pulse current, and compensate the reactive load, and improve the power factor. The ballast generates 6K-1 pulse current in the process of brushless DC motor, and uses cascaded current to dissolve the current, and the dissolved current is about 5250Hz and 7350Hz. Therefore, the reactive power compensation design of the intermediate frequency induction furnace filter should take 250Hz, 350Hz and the frequency design as the target, so as to ensure that the compensation branch of the filter can effectively suppress the pulse current compensation, and at the same time suppress the reactive load and improve the Power Factor.
design assignment
The comprehensive power factor of the 12500KVA DC brushless motor production line is compensated from 0.62 to about 0.95. The filter compensation equipment must be installed with a volume of 1100KVar, which is divided into 10 groups of automatic switching compensation to compensate for the winding on the bottom voltage side of the transformer. The 45KVAR gradually adjusts the volume to meet the output power requirements of the production line. The 630KVA transformer DC brushless motor production line The comprehensive power factor is compensated from 0.62 to about 0.95. The filter compensation device must be installed with a volume of 600KVar, and automatically disconnect the low-side winding of the transformer, and its gradually adjusted volume of 45KVAR, taking into account the voltage requirements of the production line.
Effect analysis after installation of filter compensation
In April 2010, the DC motor filtering reactive power compensation device was installed and put into operation. The device automatically tracks the load changes of DC motors and frequency converters, suppresses high-order harmonics in real time, compensates reactive power, and improves power factor. details as following:
After the filter compensation device is put into use, the power factor change curve is about 0.99 (the raised part is about 0.6 when the filter compensation device is removed)
Load operation
The current used by the 1250KVA transformer is reduced from 1960A to 1210A, a drop of 38%. The current used by the 1630KVA transformer is reduced from 1050A to 657A, a drop of 37.5%. After compensation, the power loss reduction value is WT=△Pd*(S1/S2)2*τ*[1-(cosφ1/cosφ2)2]=32×{(0.62×3000)3000}2×0.4≈15.8(kw· h) In the formula, Pd is the short-circuit loss of the transformer, which is 32KW, and the annual saving of electricity expenses is 15.8*10*30*10*0.7=33,000 yuan (based on working 20 hours a day, 10 days a month, and 10 months a year, per kwh electricity 0.7 yuan).
power factor situation
The company’s overall rights factor has increased from 0.7 to 0.95, the monthly rights factor has remained at 0.96-0.98, and the monthly salary is 3,000-4,000 yuan.
DC motor filter low-voltage reactive power compensation has the ability to suppress pulse current and compensate reactive power load, solve the problem of reactive power penalty, increase the output capacity of the transformer, reduce the loss of active power compensation, increase the output, and give The company has produced significant economic benefits, and the client has acquired the project investment for less than a year. Therefore, the company is very satisfied with the reactive power compensation of brushless DC motors and inverter filters, and will introduce some customers in the future.
Post time: Apr-14-2023