Abstract: With the in-depth application of power electronics technology, the automation level of the petrochemical industry is constantly improving, and the characteristics of the load have also undergone qualitative changes. The increase in nonlinear and impulsive loads has brought about a series of power quality problems such as voltage flicker, three-phase imbalance, and harmonics, affecting the safe operation of the power grid and reducing production capacity. Therefore, continuously optimizing and improving the power quality of the petrochemical industry is an important guarantee for the economic and safe operation of the petrochemical industry.
Keywords: petrochemical industry, power quality, voltage flicker, harmonics
1 Introduction
With the implementation of my country's strategy to build a resource-saving and environmentally friendly society, the petrochemical industry faces increasingly severe situations and tasks in terms of resource security, energy conservation and emission reduction, and safe production. The petrochemical industry's production processes are complex, operating under harsh conditions, and power quality problems are becoming increasingly serious. Even slight negligence in the power system can lead to serious safety accidents. Improving power quality is crucial for ensuring the safe and stable operation of electrical equipment, increasing the industry's overall energy utilization efficiency, reducing grid pollution, and implementing safe production.
2. Indicators for measuring power quality in the petrochemical industry
While the power quality indicators for the petrochemical industry are not significantly different from those for other industries, the complexity of its power grid system dictates that its power quality requirements are more stringent. The main indicators for measuring power quality in the petrochemical industry include the following:
Voltage deviation index | Changes in reactive load can cause the voltage of the power system to deviate significantly from its rated voltage. Motors and lighting fixtures, in particular, are easily affected by voltage deviations. |
Voltage flicker and fluctuation | Caused by changes in active or reactive loads generated by impact loads such as electric arc furnaces, arc welding machines, and rolling mills. |
Harmonics of power grid | The most fundamental cause of harmonic generation under nonlinear loads is the sudden change in load voltage and the current in the power grid. |
Three-phase voltage imbalance | Large-capacity asymmetrical loads and harmonic components in the power grid system can cause negative sequence components in the power grid, which are the main factors causing three-phase imbalance. |
3 Power Quality Analysis in the Petrochemical Industry
The petrochemical industry features long production lines, a wide scope, a high degree of automation, and complex inter-unit interconnections. Due to production needs, there are numerous rapidly changing and impactful loads, resulting in a qualitative change in the composition of the electrical load. The connection of a large number of nonlinear loads inevitably generates many electrical problems: voltage flicker and fluctuations, low power factor, excessive reactive power consumption, and harmonic interference. Among these, harmonic interference is currently the most concerning issue for power quality in the petrochemical industry.
In practical power supply systems, due to the presence of nonlinear loads, when current flows through a load whose relationship with the applied voltage is not linear, a non-sinusoidal current is formed. Sudden changes in current and load terminal voltage can lead to the generation of harmonics.
The main sources of harmonics include: variable frequency speed control devices for pumps and motors, uninterruptible power supply devices, soft starters for motors, and new lighting fixtures (energy-saving lamps, fluorescent lamps using electronic ballasts).
The hazards of harmonics in power grids manifest themselves in the following ways:
1) A power grid polluted by harmonics leads to a relative increase in losses in transmission and distribution lines, motors, and transformers, which in turn increases energy consumption;
2) The skin effect of wires and cables increases, accelerating the aging of the insulation layer and reducing the utilization rate of the cables.
3) Increased magnetic induction current in the machine's iron core increases power consumption and shortens the equipment's lifespan; in severe cases, mechanical resonance occurs, motor speed becomes unstable, and the motor burns out.
4) Malfunctions, tripping, failure to operate, and damage to power system relay protection systems often cause accidents or escalate power outages, threatening the safe and reliable operation of the power system.
5) Data loss in computer, data transmission and automatic control systems, display distortion, malfunctions, component damage, and reduced accuracy of system file processing.
4. Acrel Power Quality Management Solution
Acrel has been dedicated to the power industry for many years, consistently focusing on power quality issues in the petrochemical sector. Addressing the current state of power quality problems in the petrochemical industry, Acrel provides feasible solutions to promote its safe and stable operation. Firstly, filtering devices are installed at common power sources to ensure that the harmonic content of the common busbars at all levels of the power grid is within specified limits. Secondly, harmonics in power networks at all levels are closely monitored and analyzed in a timely manner, and mitigation measures are formulated and implemented to ensure that the operational indicators of the petrochemical power grid meet the required standards.
4.1 APMD Network Multifunctional Meter
APMD network multifunction meters are mainly used in high-voltage critical circuits and low-voltage incoming circuits. They have power parameter measurement and power quality analysis functions, and can monitor power quality continuously in real time and save various fault information.
Instrument Functions:
● Measurement function
APMD network multifunction meters enable the measurement of all electrical parameters, including real-time current, voltage, active power, reactive power, apparent power, frequency, and power factor.
●Power quality analysis function
Total voltage harmonics, total current harmonics, 2nd to 31st order voltage and current harmonics, voltage crest factor, telephone waveform factor, current K coefficient, voltage and current vector analysis, voltage and current imbalance analysis, voltage and current sequence quantity, waveform tracking.
It is equipped with RS485 communication interface, industrial Ethernet, Profibus and other interfaces to meet the needs of communication network management, and to centrally upload monitoring information to meet the needs of real-time monitoring.
Continuous precision machining production lines in the petrochemical industry are extremely sensitive to interference in the power distribution system. Even a fraction of a second of abnormal power supply can disrupt production, resulting in incalculable losses. Real-time monitoring of power quality via APMD network power meters, issuing alarms or control commands, prevents problems before they occur and ensures the safe and efficient operation of the petrochemical industry's power system. Therefore, the necessity of continuous power quality monitoring is self-evident.
4.2 ANAPF Active Filter Device
The ANAPF active power filter can dynamically filter out harmonic currents generated by nonlinear loads in the power supply system, reduce voltage harmonic distortion rate, and effectively eliminate the impact of harmonics on transformers, capacitors and precision equipment.
The principle of the ANAPF active power filter is as follows: It is connected to the power grid in parallel. By monitoring the harmonic and reactive components of the load in real time, it uses PWM converter technology to generate a reverse component corresponding to the current harmonic and reactive components from the converter and injects it into the power system in real time, thereby achieving harmonic control and reactive power compensation.
4.2.1 Key Technical Features of ANAPF
● This machine is multifunctional, capable of compensating for both harmonics and reactive power.
●DSP+FPGA fully digital control method with extremely fast response time;
● It has comprehensive bridge arm overcurrent protection functions;
● Advanced main circuit topology and control algorithm, high precision and stable operation.
4.2.2 Compensation Capacity Calculation
Harmonic current can be estimated from the transformer capacity, but the transformer load rate needs to be considered. Specifically, it can be estimated using the following formula:
K1 is the load factor: that is, the ratio of the load to the rated capacity of the transformer, which is usually taken as 0.6~0.8, and is taken as 0.6 here;
K2 is the harmonic coefficient. In centralized compensation applications, it is suitable for situations where overall harmonic pollution is not high but is relatively dispersed, and is set to 12%.
ST represents the rated capacity of the transformer, in kVA.
US is the low-voltage system voltage, typically 0.4.
According to the above formula, for a transformer with a capacity of 2000kVA, the harmonic current on the output side is ITHD = 206A, and an active power filter cabinet with a harmonic compensation capacity of 200A can be selected for compensation.
4.2.3 Compensation Method
In the power supply system of the petrochemical industry, the ANAPF active power filter can adopt three filtering compensation methods.
● Centralized compensation is implemented on the transformer outgoing line side.
When there are many nonlinear loads, their distribution is relatively dispersed, and the harmonic distortion rate is not too high, an ANAPF (Active Power Filter) device can be centrally installed on the low-voltage distribution bus side of the transformer for centralized compensation. This is suitable for lighting load transformers with many energy-saving lamps or gas discharge lamps. This compensation method can effectively improve the transformer's operating performance and enhance the overall power quality of the system.
Centralized compensation
●Local compensation for specific branch lines
When nonlinear devices are concentrated in certain specific branches, ANAPF active filters can be installed on the branches for local compensation.
Local compensation
●On-site compensation for specific equipment
For single, large-capacity, stable-operating nonlinear petrochemical equipment, nonlinear loads with obvious spectral characteristics and low natural power factors, and harmonic sources whose harmonics are concentrated in three or fewer consecutive harmonics (such as the 3rd, 5th, and 7th orders), on-site compensation can be performed on harmonic sources, such as rectifiers, frequency converters, and welding equipment. This method can achieve very good compensation and energy-saving effects without affecting branch circuits or the entire system.
Local compensation
When designing harmonic mitigation solutions, the above three harmonic mitigation methods can be flexibly adopted based on the harmonic monitoring data of the power distribution network. This can effectively control harmonic pollution in the petrochemical industry, eliminate potential hazards in the power supply system, minimize the impact of harmonic pollution on the power grid system and equipment in the petrochemical industry, and avoid affecting the normal operation of important equipment.
5. Conclusion
This paper analyzes the power quality problems in the petrochemical industry and proposes that harmonics are one of the important indicators of power quality. It elaborates on Acrel's power quality management solution for the petrochemical industry, effectively solving practical power problems, improving economic efficiency, and contributing to the construction of a resource-saving society.
6. Company Profile
Acrel Electric Co., Ltd. [Stock Code: 300286.SZ] is one of the few leading domestic companies that provides intelligent power monitoring, power management, and electrical safety system solutions for smart grid users.
Since its establishment in June 2003, the company has focused on the research, development, production and sales of smart power meters for users. Its product line covers low-voltage power signal acquisition, measurement, metering, monitoring, protection and system integration for smart grid users. The main products include network power meters, smart motor controllers, DIN rail mounted energy meters, power sensors, photovoltaic combiner boxes, active filters, medical cleanroom power cabinets and other products, as well as system solutions such as smart power monitoring and energy management, building energy consumption analysis and management, electrical fire monitoring, data center power monitoring, photovoltaic power station monitoring, and ZigBee (Internet of Things) wireless power management.
The company possesses a Jiading District-level technology center and is a high-tech enterprise and software enterprise. It has participated in the drafting or compilation of several national and industry standards for power meters, including GB/T22264-2008 "Installation-type Digital Electrical Measuring Instruments", JB/T10736-2007 "Low-voltage Motor Protectors", GB/T15576-2008 "Low-voltage Complete Reactive Power Compensation Devices", and GB/T22387-2008 "Residual Current Operated Relays". As of December 2011, the company held over 100 authorized patents and over 70 computer software copyrights; its ACR network power meter was listed as a national key new product, and the company was designated as one of the key smart grid enterprises by the Shanghai Municipal Commission of Economy and Information Technology.
In 2007, the company's production base in Jiangyin, Jiangsu Province, was completed and put into operation. The first phase of the factory covered an area of 10,000 square meters and was the first enterprise in the intelligent power meter industry to adopt lead-free SMT production technology, providing a guarantee for the industrialization and large-scale implementation of the company's products. In March 2010, the company underwent technological upgrades, including anti-static renovations to the workshop, further improving the production environment. Simultaneously, an MES management system was introduced, with barcode scanning at each stage of the process, enabling control over the entire production progress and process. This essentially achieved paperless management, saving production costs and improving management efficiency.
Ankerui's trademarks and products have been recognized as famous trademarks and brand-name products in Shanghai. Its products have been widely used in major domestic and international projects such as the Shanghai World Expo, the Guangzhou Asian Games, the Costa Rica National Stadium, the Beijing-Tianjin High-Speed Railway power monitoring, the Dunhuang 10MW photovoltaic demonstration power station, the Bank of China Pudong Data Center, and the India 500,000-ton coking plant, winning a good market reputation.
References
[1] Acrel Electric Co., Ltd. Product Manual. January 2013 Edition.
[2] Factors affecting power quality and methods to improve it, Chen Lei. Shanghai: 2008.
Source: *Electrical Technology*, Issue 1, 2014
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