1 Introduction
With the implementation of my country's strategy of building a resource-saving and environment-friendly society, the petrochemical industry is facing more severe situations and tasks in terms of resource protection, energy conservation, emission reduction, and safe production. The petrochemical industry has complex production technology, harsh operating conditions, and increasingly serious power quality problems. A little carelessness in the power system may cause serious safety accidents. How to improve power quality is essential to ensure the safe and stable operation of electrical equipment, improve the comprehensive energy utilization efficiency of the industry, reduce grid pollution, and implement safe production.
2 Indicators for measuring power quality in the petrochemical industry
Compared with other industries, the power quality indicators of the petrochemical industry are no different. However, the complexity of its own grid system determines that its requirements for power quality are more stringent. The indicators for measuring power quality in the petrochemical industry mainly include the following points:
Voltage deviation index
The change of reactive load causes the voltage of the power system to deviate far from its rated voltage, among which lamps such as motors and lighting are susceptible to voltage deviations.
Flicker and fluctuation of voltage
Caused by changes in active or reactive power generated by impact loads such as electric arc furnaces, arc welders, and rolling mills.
Harmonics of the grid
The ultimate root cause of harmonics when non-linear loads are generated. The sudden change of the load terminal voltage and the current in the power grid are both important factors that cause the generation of harmonics.
Unbalance of three-phase voltage
Large-capacity asymmetric loads and harmonic components in the grid system will cause negative sequence components in the grid, which are the main factors that cause three-phase imbalance.
3 Power quality analysis in petrochemical industry
The petrochemical industry has a long production line, a wide range of areas, a high degree of automation, and a degree of correlation between complex devices. Due to production needs, there are a large number of fast-changing shock loads, and the composition of electrical loads has also undergone qualitative changes. The access of a large number of non-linear loads inevitably produces many power problems: voltage flicker and fluctuation, low power factor, excessive reactive power consumption, harmonic interference, etc. Among them, the problem of harmonic interference is currently the most concerned issue of power quality in the petrochemical industry.
In the actual power supply system, due to the existence of non-linear loads, when the current flows through the load that is not linear with the applied voltage, a non-sine wave current is formed. Sudden changes in current and load terminal voltage will cause the generation of harmonics.
The main harmonic sources are: variable frequency speed regulation device of pump, uninterruptible power supply device, motor soft start equipment, new type of lighting (energy-saving lamp, fluorescent lamp with electronic ballast).
The harmonic hazards in the power grid are specifically manifested in the following aspects:
1) Grids polluted by harmonics have caused relatively increased losses in transmission and distribution lines, motors, and transformers, thereby increasing energy consumption;
2) The skin effect of wires and cables becomes larger, which accelerates the aging of the insulation layer and reduces the utilization rate of the cables;
3) The magnetic induction circulating current of the iron core of the machine increases, which increases the power consumption of the equipment, and the life of the equipment is relatively shortened; in severe cases, the machine resonates, the motor speed is unstable, and the motor burns;
4) The power system relay protection is started by mistake, tripped by mistake, refused to operate and damaged, which usually causes accidents or enlarged power outages, threatening the safe and reliable operation of the power system;
5) The computer, data transmission and automatic control system data are lost, the display screen is distorted, malfunctions, components are damaged, and the accuracy of system file processing is reduced.
4 Ankerui power quality management plan
Ankerui has been committed to the power industry for many years and has always paid attention to the power quality problems in the petrochemical industry. Aiming at the current status of the power quality problems in the petrochemical industry, it provides feasible solutions for the petrochemical industry, and the petrochemical industry operates safely and stably. First, set up filtering devices at public power points to ensure that the harmonic content of the public busbars of all levels of power grids is within the specified range; secondly, closely monitor the harmonics of the power grids at all levels and summarize and analyze them in a timely manner, and formulate and implement governance measures to ensure the petrochemical power grid The operating indicators meet the normative standards.
4.1 APMD network multi-function instrument
APMD network multi-function meters are mainly used in high-voltage important circuits and low-voltage incoming circuits. They have power parameter measurement functions and power quality analysis functions. They can continuously monitor power quality in real time and save various fault information.
Instrument function:
●Measurement function
APMD network multi-function instrument realizes the measurement of all power parameters, including real-time current, voltage, active power, reactive power, apparent power, frequency, and power factor.
●Power quality analysis function
Voltage total harmonics, current total harmonics, 2-31 sub-harmonics of voltage and current, voltage crest factor, form factor, current K factor, voltage and current vector analysis, voltage and current unbalance analysis, voltage and current sequence quantity, waveform track.
With RS485 communication interface, industrial Ethernet, Profibus and other interfaces, it is used to meet the needs of communication network management and centrally upload monitoring information to meet the needs of real-time monitoring.
The continuous finishing production line of automation equipment in the petrochemical industry is extremely sensitive to interference in the power distribution system. An abnormal power supply of a fraction of a second may cause confusion in production, and the loss is incalculable. Real-time monitoring of power quality is achieved through APMD network power meters, alarms or control instructions are issued to prevent problems before they occur, and to ensure the safe operation of power systems in the petrochemical industry. Therefore, the necessity of continuous monitoring of power quality is self-evident.
4. 2 ANAPF active filter device
ANAPF active power filter device can dynamically filter the harmonic current generated by the nonlinear load in the power supply system, reduce the voltage harmonic distortion rate, and the impact of harmonics on transformers, capacitors and precision equipment.
The principle of the ANAPF active filter device: connect to the grid in parallel, monitor the harmonic and reactive components of the load in real time, and adopt the PWM converter technology to generate one corresponding to the current harmonic components and reactive components from the converter. The reverse component is injected into the power system in real time, so as to realize harmonic control and reactive power compensation.
4.2.1 Main technical features of ANAPF
●One machine has multiple functions, which can not only compensate harmonics, but also compensate reactive power;
●DSP+FPGA full digital control mode, with extremely fast response time;
●Has perfect bridge arm overcurrent and protection functions;
●The main circuit topology and control algorithm have high precision and stable operation.
4.2.2 Compensation capacity calculation
Harmonic current can be estimated from the transformer capacity, and the load factor of the transformer needs to be considered. Specifically, it can be estimated according to the following formula:
K1 is the load factor: the ratio of the load to the rated capacity of the transformer, usually 0.6 to 0.8, here 0.6;
K2 is the harmonic coefficient. The centralized compensation field is suitable for occasions where the overall harmonic pollution is not high but relatively dispersed, and 12% is taken;
ST is the rated capacity of the transformer, in kVA;
US is the low-voltage system voltage, generally 0.4.
According to the above calculation, a transformer with a capacity of 2000kVA, the outgoing side harmonic current ITHD=206A, 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, ANAPF active power filter devices can use three filter compensation methods.
●Concentrated compensation on the transformer outlet side
When the number of nonlinear loads is large, the distribution is relatively scattered, and the harmonic distortion rate is not too high, ANAPF active power filter devices can be installed on the transformer low-voltage distribution bus side for centralized compensation, such as energy-saving lamps, gas Lighting load transformer with many discharge lamps. This compensation method can improve the operating performance of the transformer and improve the overall power quality of the system.
Centralized compensation
●Partial compensation for specific branch
When the non-linear equipment is concentrated on some specific branches, ANAPF active filter devices can be installed on the branches for partial compensation.
Partial compensation
●On-site compensation for specific equipment
A single non-linear petrochemical equipment with large capacity and stable operation, non-linear loads with obvious spectral characteristics, low natural power factor, and harmonics generated by harmonic sources are more concentrated in consecutive three or less (such as 3rd, The 5th, 7th) harmonic control can be used to compensate the harmonic sources on-site, such as rectifier equipment, frequency conversion equipment, welding equipment, etc. This method can achieve very good compensation and energy-saving effects, and will not affect the branch circuit. And the entire system.
On-site compensation
When designing a harmonic control plan, the above three harmonic control methods can be flexibly adopted according to the harmonic monitoring data of the distribution network, which can better control the harmonic pollution of the petrochemical industry, and make the power supply system hidden. The impact of wave pollution on the power grid system and equipment of the petrochemical industry is minimized to avoid affecting the normal operation of important equipment.
5 Conclusion
Based on the analysis of power quality problems in the petrochemical industry, this paper proposes that harmonics are one of the important indicators of power quality. Explains Ankerui's power quality management plan in the petrochemical industry, solves actual power problems, improves economic benefits, and contributes to the construction of a resource-saving society.