Basic information of users
The key enterprise of a hardware and building materials company safely produces PC round steel, end plates, galvanized lines, modified material lines, 30MnSi and other commodities. The company has 4 excellent production lines, which use intermediate frequency heating and DC variable frequency drive motors, with 2000KVA2 (applied in tandem). The power supply system diagram is as follows:
Actual operating data
The specific power factor is PF=0.82, the working current is 2250A, the main pulse current is 5 times, and the total current becomes 23.6%.
Power System Situation Analysis
The main load of intermediate frequency induction furnace, intermediate frequency induction furnace and inverter rectifier power supply is the 6th pulse rectifier. The rectifier equipment produces a lot of pulse current when converting AC current into AC voltage. The harmonic current introduced into the power grid can cause pulse Current operating voltage, resulting in fluctuations in operating voltage and current, endangering the quality and operational safety of switching power supplies, increasing line loss and operating voltage deviation, and negatively affecting the power grid and the electrical equipment of the power plant itself.
The program controller computer interface (PLC) is sensitive to the harmonic distortion of the working voltage of the switching power supply. It is generally stipulated that the total pulse current working voltage frame loss (THD) is less than 5%, and the individual pulse current working voltage If the frame rate is too high, the operation error of the control system may lead to the interruption of production or operation, resulting in a large production liability accident. Therefore, the low-voltage reactive power compensation of the filter with the function of pulse current filter should be used to compensate the reactive load and improve the power factor.
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, the company designed a set of detailed reactive power compensation plans for the intermediate frequency induction furnace and the inverter power supply. Considering the load power factor and the pulse current filter, a A set of filter low-voltage reactive power compensation, filter the pulse current, compensate the reactive load, and improve the power factor.
In the whole process of the intermediate frequency induction furnace and the converter, the overall components generate 6K pulse currents, which are converted according to the current flow of the Fourier series, and the characteristic pulse currents are generated at 5250Hz and 7350Hz. Therefore, when designing filter reactive power compensation, the soft starter and 350Hz frequency design scheme ensure that the filter compensation power supply circuit is reasonable and the filter pulse current output power compensation is improved to improve the power factor so that the system software pulse current is in line with GB/T3 unanimous.
design assignment
The soft starter and soft starter power factor of each group of 2000KVA transformers are compensated from 0.8 to 0.95, the 5th pulse current is reduced from 420A to 86A, the 7th pulse current is reduced from 230A to 46A, and the filter compensation equipment needs to be installed with a volume of 1060KVar. The filter is divided into 6 groups, the filter compensation is used for soft starter and ballast switching power supply, the filter is divided into 5 times, 7 times, and the filter compensation power supply circuit is automatically converted to consider the intermediate frequency induction furnace, filter and reactive power Compensation design scheme provisions.
This design fully ensures that the harmonic control complies with the national standard GB/T 14549-93, and adjusts the power factor of the intermediate frequency furnace and frequency converter above 0.95. As shown below:
Effect analysis after installation of filter compensation
In June 2010, the intermediate frequency furnace and frequency converter filter reactive power compensation device was installed and put into operation. The device automatically tracks the load changes of the intermediate frequency furnace and frequency converter, and actually eliminates high-order harmonics to compensate reactive power and improve 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 after the filter compensation device is put into use is about 0.97 (the raised part is about 0.8 when the filter compensation device is removed)
Load operation
The current used by each set of 2000KVA transformers is reduced from 2250A to 1860A, a drop of 17%; after compensation, the power loss reduction value is WT=△Pd*(S1/S2)2*τ*[1-(cosφ1/cosφ2)2]=24 ×{(0.85×2000)/2000}2×0.4≈16(kw h) In the formula, Pd is the short-circuit loss of the transformer, which is 24KW, and the annual saving of electricity expenses is 16*20*30*10*0.7=67,000 yuan (according to Work 20 hours a day, 30 days a month, 10 months a year, 0.7 yuan per kilowatt-hour); electricity bills saved due to harmonic reduction: The loss caused by harmonic current to the transformer is mainly to increase ferromagnetic loss and copper loss, The ferromagnetic loss is related to the third power of the harmonic current frequency. Generally, 2%~5% is taken in engineering, and 2% is taken for rectified loads, that is: WS=2000*6000*0.7*0.02≈168,000 yuan, that is, the annual Save electricity (6.7+16.8)*2=47 (10,000 yuan).
power factor situation
The company’s overall rights factor has been increased from 0.8 to 0.95, and the monthly rights factor has been maintained at 0.96-0.98, with an additional reward of 6,000-10,000 yuan.
All in all, the low-voltage reactive power compensation of the MFF and VF filters has excellent filters and compensates reactive loads, solves the problem of reactive power penalties, increases the output capacity of transformers, improves power quality, improves the characteristics of applied electrical equipment, and reduces active power compensation Consumption, efficiency improvement, significant economic benefits to the company, investment with a return rate of less than a year for customers, etc. Therefore, the company is very satisfied with the compensation of the intermediate frequency induction furnace and the filter reactive load of the inverter power supply, and will introduce many customers in the future.
Post time: Apr-14-2023