2. Low power factor;
3. Severe voltage flicker;
4. Generating higher harmonics, resulting in voltage distortion;
6. The serious three-phase imbalance of the power grid produces a negative sequence current;
Creat-Poreen's power electronic products such as Static Var Compensator (SVC), Solid-State Composite Switch (SSCS), Filter Compensator(FC) significantly improve the power quality of power supply, increase the power factor to 95% or more, and improve steel metallurgy production efficiency with the energy saving amounting to10% to 40%.
1, Fujian Qianqing Jinsheng Steel Co., Ltd. Power Quality Control Project Static Synchronous Compensator(STATCOM/SVG) Project
Project Overview: Fujian Shengqing Jinsheng Steel Company is connected to two 35kV busbars. The current equipment connected to them are mainly thethe medium-frequency furnace and refining furnace. Now the system is being updated. One 4000kVA rolling mill and one 16000kVA intermediate frequency furnace are added to the I section bus. One 14000kVA electric arc furnace and one 5000kVA rolling mill are added to the II section bus. This project installs a set of Static Synchronous Compensator(STATCOM/SVG) in the II section bus.
1. Harmonic currents and harmonic voltage exceeding the standard;
2. Voltage fluctuations and flicker exceeding the standard;
3. The power factor does not meet the requirements;
Operation effect: After SVG is put into operation, the harmonic current and the harmonic distortion rate of the bus voltage injected into the system are lower than the national standard Power Quality, Utility Grid Harmonics GB/T14549-93.The voltage fluctuation of the bus voltage meets the national standardPower Quality, Voltage Fluctuations And Flicker GB/T12326-2008. The power factor of the assessment point is above 0.95, with no over-compensation, and all indicators meet the user requirements.
2, Fujian Shunchang Hongfeng Steel Company Electric Furnace Steel-making TCR Static Var Compensator (SVC) Project
Project Overview: The power supply system of FujianShunchangHongfeng Steel Companyadds a 35kV opening and closing station in the plant area. The opening line is taken from the 35kV side line of the 110KV substation outside the plant area. The opening and closing station is providing power for two electric arc furnaces and a refining furnace. It requires the SVC’s harmonics, voltage fluctuations, flicker, and the three-phase voltage unbalance degree, after entering the operation,to meet the national limitstandard requirements: 35KV side incoming line’s averagemonthly power factorCOSΦ ≥ 0.95, without reactive power releasing.
1. Harmonic generation: The arc current of the electric furnace is in an irregularly sharp-changing state and the arc resistance is nonlinear, so the voltage and the current waveforms present an asymmetrical non-sinusoidal waveform, mainly as harmonics from 2nd-7th. During its operation, harmonics can cause heat, vibration, loss-increase, shorten service life of electrical equipment, and the malfunction of PLC and relay protection device.
2. Voltage fluctuation: During the melting period of the electric furnace, due to the frequent rising and lowering of the electrodes, the arc is frequently generated and disappeared, causing instantaneous open circuit and short circuit of the line, with a large reactive power impact. According to the previous engineering measurements of Beijing Bodian, the maximum impact load of the electric furnace can reach 1.5-2 times of the capacity of the electric furnace transformer, which will cause the rapid fluctuation and flicker of the grid voltage, and make the smelting quality unstable, thus affecting the production and product quality. .
Power factor: In the melting period of the electric furnace, the power factor is generally lower than 0.7, and at the time of short circuit, it even drops below 0.2, which not only directly affects the economic benefits of the enterprise, but also affects the power supply quality of the power grid. Negative sequence separation is generated: during the melting period of the electric furnace, especially during the well-piercing period, the arc voltage of each phase changes independently, and the phase currents of each phase change randomly. In the case of one-phase arc breaking and two-phase short-circuit, the negative sequence current will reach about 40%-60% of the rated current. This excessive negative sequence current will not only cause the negative sequence protection of the upper substation to often alarm, but also affect the output of the motor and electrical equipment in the power grid.
Operation effect: SVC effectively limits the harmonic current injected into the power grid. At the same time, it provides continuous and rapid reactive power and suppresses the voltage fluctuation and flicker level of the access point through smooth and rapid adjustment to improve the voltage stability, so that the various power quality indicators of each assessment point meet the requirements.
3, Hangzhou Steel Company High-Speed Rolling Mill 6kV TCR SVC Project
Project Overview: The Hanggang high-speed line has 6kVbusbar Section I and SectionII. According to the development requirements, the 6kV Section I busbar needs to be connected to a newly produced 220kV main transformer (220kV/35kV/6.3kV), and there are 2 LF furnace of 7000kVAon the 35kV side. Due to the impact load of the LF furnace, it will cause the voltage fluctuation of the 6kV busbar during production. Besides, the high-line load itself is a fluctuating load, which will cause the voltage fluctuation of the 6kV busbar to be large. Dynamic reactive compensation solves this problem.
1. Voltage fluctuation: Due to the special nonlinear impact load of AC steel-making arc furnace, with the increasing of the single furnace capacity and smelting power, the effect of electric furnace on the power quality of power supply system is becoming more and more serious, and arc burning in AC arc furnace operation is extremely unstable, resulting in the severe distortion of voltage and current waveforms. When the Hangzhou High-speed Line Company does not produce, the 6kV bus voltage is 7.5% higher than that of the production, that is, the voltage fluctuation of the 6kV bus is as high as 7.5%. The high voltage 6kV Section I bus load caused the voltage imbalance of 0.92% at the access point.
2. Harmonic generation: The 6kV Section I bus load of Hangzhou High SpeedCompany generates a large number of harmonics during the production process. Harmonic current generates harmonic voltage on the grid impedance, causing grid voltage distortion, and affecting power supply quality and operation safety. In addition, the large fluctuations in reactive power of the load can cause severe voltage fluctuations and flicker in the power bus.
■ Operation effect: SVC effectively limits the harmonic current injected into the power grid. At the same time, it provides continuous and rapid reactive power and suppresses the voltage fluctuation and flicker level of the access point through smooth and rapid adjustment to improve the voltage stability, so that the various power quality indicators of each assessment point meet the requirements.