Basic information of users
A steel rolling company mainly produces hot-rolled round steel with a specification of 16mm~φ150mm. The power part of the company’s production line is driven by a DC motor and equipped with two 3150KVA transformers. The power supply system diagram is as follows:
Actual operating data
The average power factor of the 3150KVA DC brushless motor is PF=0.75, the working current is 2650A, the main pulse current is 5 times, 7 times, and the current conversion ratio is 19.5%.
Power System 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.
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” High-order harmonic current limit value from 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 filter reactive power compensation must be designed for 250Hz, 350Hz and other frequencies to ensure that the filter compensation circuit can effectively filter out the pulse current output power, improve the power factor, and make the system pulse current comply with GB/T3.
design assignment
The comprehensive power factor of the 3150KVA transformer is compensated from 0.72 to about 0.95. The filter compensation equipment must be installed with 2100KVar, and divided into 6 groups of control switches to compensate the bottom pressure side winding of the transformer, and adjust the volume to 95KVAR, taking into account the output power requirements of the production line.
Effect analysis after installation of filter compensation
In April 2011, the DC motor filter reactive power compensation device was installed and put into operation. The device automatically tracks the load changes of the DC motor, and actually filters out high-order harmonics to compensate reactive power and improve the power factor. details as following:
Harmonic spectrum distribution diagram
Load Waveform
After the filter compensation device is put into use, the power factor change curve is about 0.98 (the raised part is about 0.7 when the filter compensation device is removed)
Load operation
The power factor of the 3150KVA transformer is above 0.95, the 5th harmonic is reduced from 510A to 102A, the 7th harmonic is reduced from 300A to 60A, and the current used is reduced from 2650A to 2050A, a drop of 23%. After compensation, the power loss reduction value is WT=△Pd*(S1/S2)2*τ*[1-(cosφ1/cosφ2)2]=35×{(0.72×3150)/3150}2×0.66≈33(kw h) In the formula, Pd is the short-circuit loss of the transformer, which is 35KW, and the annual saving of electricity expenses is 33*20*30*10*0.7*2=280,000 yuan (based on working 20 hours a day, 30 days a month, and 10 months a year , 0.7 yuan per kilowatt-hour of electricity); due to the reduction of harmonics, the electricity bill saved: The loss of the transformer caused by the harmonic current is mainly to increase the ferromagnetic loss and copper loss. The ferromagnetic loss is related to the third power of the harmonic current frequency. Engineering Generally, 2%~5% is taken. For rectification load, 2% is taken, that is, WS=4300*6000*0.7*0.03≈360,000 yuan, that is, the annual saving of electricity costs is 28+36=64 (10,000 yuan).
power factor situation
The company’s overall rights factor has increased from 0.72 to around 0.95, the monthly rights factor has remained at 0.96-0.98, and the monthly remuneration has ranged from more than 100,000 yuan to 15,000 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 the brushless DC motor filter, and will introduce some customers in the future.
Post time: Apr-14-2023