Basic information of users
The plastic products company mainly produces PE water supply pipes, metal bellows drainage pipes, etc. The company has 4 production lines, part of the driving force uses DC brushless motors and DC variable frequency drive motors, there are four sets of 400KVA, each transformer bottom pressure side Equipped with capacitance compensation box. The power supply system diagram is as follows:
Actual operating data
The DC motor of the 400KVA transformer, the high power of the inverter is 360KW, the average power factor is PF=0.7, the working current is 780A, the invalid compensation box under each transformer often trips, the capacitor expands and leaks, and the controller cannot control the abnormality, etc. Phenomena, the comprehensive rate is only 0.8, and the invalid fine is about 15,000 per month. In addition, the motors and soft starters in the production line are sometimes damaged, which affects production.
Power System Situation Analysis
The main load of DC brushless motor and inverter rectifier power supply is 6 single-pulse rectifier power supply. During the operation of rectifier equipment, AC can be converted into DC, forming a large number of pulse current sources, introducing harmonic currents in the power grid, and affecting the power grid. The characteristic impedance causes the working voltage of the pulse current, resulting in the out-of-frame of the working voltage and current, endangering the quality and operation safety of the switching power supply, increasing the line loss and working voltage deviation, and having a negative impact on 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.
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 DC brushless motor and 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
Design ideas
According to the specific situation of the company, our company designed a set of detailed DC motor and soft starter reactive power compensation filter scheme. Fully consider the load power factor and harmonic suppression, and install filters on the 0.4KV bottom voltage side of the company’s transformer for low-voltage reactive power compensation to suppress harmonics, compensate reactive power, and improve power factor. During the operation of the DC motor and inverter, the rectifier device generates 6K+1 higher harmonics. After the current is decomposed and transformed by Fourier series, 5 times of 250HZ and 7 times of higher harmonics above 350HZ are generated. Therefore, in the design of intermediate frequency electric furnace filter reactive power compensation, it is necessary to design frequencies of 250HZ, 350HZ and above to ensure that the filter compensation branch can effectively suppress harmonics while compensating reactive power and improving power factor.
design assignment
The comprehensive power of the DC motor and frequency converter production line corresponding to the 400KVA transformer is compensated from 0.7 to more than 0.95. The filter compensator needs to be set at a capacity of 380kvar, which is divided into 4 groups of capacity and automatically cut off to compensate the bending of the low-voltage side of the transformer respectively. The classified adjustment capacity is 45kvar, which can Adapt to various power requirements of the production line, so the design fully ensures that the adjusted power is above 0.9.
Effect analysis after installation of filter compensation
In July 2010, the filter reactive power compensation device for DC motors and frequency converters 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 after the filter compensation device is put into use is about 0.99 (the raised part is about 0.7 when the filter compensation device is removed)
Load operation
The current used by the 400KVA transformer is reduced from 770A to 520A, a drop of 33%. After compensation, the power loss reduction value is WT=△Pd*(S1/S2)2*τ*[1-(cosφ1/cosφ2)2]=5×{(0.7×400)400}2×0.4≈2.8(kw· h) In the formula, Pd is the short-circuit loss of the transformer, which is 5KW, and the annual saving of electricity expenses is 2.8*20*30*10*0.7=11,700 yuan (based on working 20 hours a day, 30 days a month, 10 months a year, per kwh electricity 0.7 yuan).
power factor situation
The company’s overall rights factor increased from 0.7 to 0.95, the monthly rights factor remained at 0.96-0.98, and the penalty increased from 15,000 yuan per month to 3,000-5,000 yuan per month.
The BLDC motor and soft starter filter
The reactive power compensation device has the ability to suppress the pulse current and compensate the reactive power load, solve the problem of reactive power penalty, increase the output volume of the transformer, reduce active power consumption, and increase the output, bringing obvious economic benefits to the company and return of customer project investment a year ago. 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