Basic information of users
A cement factory produces various construction concrete. The company has 3 production lines. The switching power supply uses inverter drive motors, 2000KVA2, 630KVA transformers, and each transformer is equipped with a capacitor compensation cabinet on the bottom pressure side. The power supply system diagram is as follows:
Actual operating data
The output power of the soft starter for 2000KVA transformer is 1720KVA, the average power factor is PF=0.83, the working current is 2500A, the power is 530KVA630KVA transformer, the average power factor is PF=0.87, and the working current is 770A. The reactive power compensation cabinet under each transformer often has power trips, capacitor oil leakage, and control panel display information that does not allow abnormal operations. Therefore, the comprehensive power factor is only 0.84, and the reactive power penalty is about 20,000 in January. And production line motors and soft starters can sometimes disrupt manufacturing.
Power System Situation Analysis
The main load of the converter ballast is 6 single-pulse ballasts. The ballast equipment produces a large amount of pulse current in the work of converting AC to DC. It is a typical pulse current source and is input into the power grid. Harmonic currents cause pulsed current working voltage to the characteristic impedance of the power grid, resulting in frame loss of working voltage and current, endangering the quality and operation safety of switching power supplies, increasing line loss and working voltage deviation, and causing negative effects on the power grid and power plants themselves Influence.
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.
When the reactive power compensation capacitor bank is put into operation, because the pulse current characteristic impedance of the capacitor bank is small, a large amount of pulse current is introduced into the capacitor composition, and the current amount expands rapidly, seriously affecting its service life. On the other hand, when the pulse current capacitor of the capacitor bank is equivalent to the equivalent pulse current inductor of the system software, the increase in harmonic current (2-10 times) will cause the capacitor to overheat and destroy it, and the pulse current will cause the frequency of the output power to change. The sinusoidal waveform is out of frame, resulting in a saw-tooth-shaped sharp wave, and will cause partial discharge of the insulating layer material, thereby accelerating the embrittlement of the insulating layer material, and causing damage to the capacitor. Therefore, the capacitor reactive power compensation cabinet cannot be used for inverter power compensation, and a filter with pulse current suppression function should be selected for low-voltage reactive power compensation.
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
concept of design
According to the specific situation of the company, the power factor and pulse current suppression are considered in the filter compensation of the inverter power supply, and the filter failure compensation equipment is set on the 0.4kV bottom voltage side of the transformer, which can suppress the pulse current and compensate for the improvement of the power factor.
In the converter, the ballast generates 6K-1 advanced pulse currents according to the Fourier series current flow, and then generates 5 advanced pulse currents, each at about 250Hz and 7350Hz. Therefore, when designing reactive power compensation for intermediate frequency induction furnaces, it is necessary to design frequencies around 250Hz and 350Hz to ensure that the filter compensation branch can effectively suppress pulse currents, compensate reactive loads at the same time, and improve power factor.
design assignment
The comprehensive power factor of the paired inverter power line of the 2000kV AC transformer is compensated from 0.8 to 0.95. The filter compensation equipment must be equipped with a volume of 760kV, and automatically converted into 8 sets of volumes, and one set cooperates with the winding compensation on the bottom voltage side of the transformer. The workload of class adjustment is 45KVAR, which can meet various power requirements of the production line. The comprehensive power factor of the 630kV transformer paired converter line has been compensated, and the compensation range is from 0.8 to 0.95. The filter compensation equipment must be equipped with 310kV volume, which is automatically converted into four sets of volumes, and one set cooperates with the winding resistor on the bottom voltage side of the transformer for compensation. The workload of class adjustment is 26KVAR, which can meet various power requirements of the production line. The scheme design fully guarantees that the power factor exceeds 0.95.
Effect analysis after installation of filter compensation
In July 2010, the inverter filtering reactive power compensation device was installed and put into operation. The device automatically tracks the load change of the inverter, suppresses high-order harmonics in real time, compensates reactive power, and improves the power factor. details as following:
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 2000KVA transformers is reduced from 2500A to 2120A, a drop of 15%; the current used by 630KVA transformers is reduced from 770A to 620A, a drop of 19%. After compensation,thepowerlossreductionvalueisWT=△Pd*(S1/S2)2*τ*[1-(cosφ1/cosφ2)2]=50×{(0.85×4500)/4500}2×0.4≈34(kw h) In the formula, Pd is the short-circuit loss of the transformer, which is 50KW, and the annual saving of electricity expenses is 34*20*30*10*0.7=142,800 yuan (based on working 20 hours a day, 30 days a month, 10 months a year, 0.7 yuan per kWh).
power factor situation
The company’s overall power engineering index has increased from 0.8 to 0.95, and the monthly power engineering index has remained at 0.96-0.98, rising from more than 20,000 yuan per month to more than 6,000-10,000 yuan per month.
The low-voltage reactive power compensation of the frequency conversion filter has the ability to suppress the pulse current and compensate the reactive 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 bring benefits to the company Obvious economic benefits have been produced, and the customer’s project investment is less than one year’s acquisition of project investment. Therefore, the company is very satisfied with the reactive power compensation of the inverter filter, and will introduce some customers in the future.
Post time: Apr-13-2023