Fluke performs power quality testing for the distribution system of the three total transformer substation of a steel mill in Hubei
The power supply and distribution system of a large steel company in Hubei consists of a 220 kV total drop, self-supplied thermal power plant and three 110 kV substations.
The hot rolling main drive of the steel mill adopts a new type of high-voltage and high-power frequency conversion equipment, which causes serious problems of high-order harmonics and voltage fluctuations in the power distribution system, affecting the safe operation of the system, excessive distribution voltage and reactive power flow. The economic operation level is not high. The main power supply and distribution problems reflected by the steel mill include: high-frequency whistling during the hot-rolling main drive operation of the hot-rolling main drive power supply transformer and switchgear; about 90 A current fluctuation during operation; 110 kV cold-rolled substation /63 MVa power supply transformer has abnormal vibration sound; 220 kV, 110 kV, 35 kV and part of 10 kV bus line harmonic voltage exceeds the national standard limit.
In order to solve the above problems, the steel plant power supply and distribution system is safe, reliable, high-quality and efficient operation. The steel plant has established a comprehensive test and evaluation of the power quality of the power supply and distribution system, and has given solutions to the problems existing in the distribution network. Specific requirements:
• Background harmonics and power quality testing
• Power quality testing of existing nonlinear loads
• Calculation of the allocation of power quality indicators;
• Testing and diagnosis of existing SVC
• Propose power quality governance solutions and recommendations
• Submit system analysis and assessment reports;
• The development of follow-up management methods and the measures to be taken.
(Note: SVC is an advanced high-voltage power grid dynamic power factor compensation device. It saves a lot of power by increasing the power factor, while at the same time reducing the harmonics of the power grid, stabilizing the voltage, and improving the quality of the power grid.)
Test evaluation analysis
(1) Fundamental power flow diagram, as shown in Figure 1.
(2) Analysis of 33 kV bus voltage variation of 220 kV total drop LF furnace.
(3) 35 kV harmonic analysis of main drive of 220 kV total hot rolling
4.1 Main problems in power supply and distribution systems
The main power quality problems affecting the safe, reliable, high-quality and efficient operation of the steel plant's power supply and distribution system are:
(1) The distribution voltage of 35 kV bus and most 10 kV busbars is too high, which seriously affects the economic operation of the system.
(2) The voltage of the 10 kV III section busbar is changed frequently during cold rolling, and the number of voltage changes greater than 1% is more than 13000 times, which is likely to cause mechanical resonance of transformers, motors and other equipment.
(3) More than 50 abnormal high harmonics generated by the hot rolling main drive cause the harmonic voltage of the 220 kV, 110 kV, 35 kV, 33 kV and part of the 10 kV power supply bus of the whole plant to exceed the specified limit, resulting in Harmonic losses are severe.
(4) The total load of 33 kV steel rolling, 10kV I section, 10kV II section, 10kV III section and 5kV section of cold rolling variable 10 kV is low, resulting in serious reactive power loss.
4.2 Solution
In view of the problems in the power supply and distribution system of the steel plant, the following technical measures should be taken:
(1) Adjust the distribution voltage of 10 kV and 35 kV so that the voltage deviation is within ±3 %.
(2) Set the RC high-pass filter on the 35 kV bus to filter out the harmonic currents from 50 to 97 times, so that the harmonic voltage and harmonic current are controlled within the specified limits.
(3) Solve the problem of reactive over-compensation of some branches of 10 kV system, and set the reactive power compensator for each 10 kV busbar with low power factor, especially to solve the voltage fluctuation caused by the reactive impact of LF furnace. Flicker problem.
(4) Solving the problem of excessive voltage variation of the 10 kV III section busbar in cold rolling from the rolling process and the power supply and distribution system
Benefits after project implementation
After the project is implemented, the local power supply bureau will organize on-site effect detection and harmonic control assessment. The conclusions are as follows:
(1) After on-site inspection, the total distortion rate of harmonic voltage decreased from 8.94% before treatment to 2.7%, which was lower than 5% of the national standard requirement. The harmonic current injected into the common connection point meets the standard requirements.
(2) The power factor is above 0.9, and the power factor of the 10 kV green line is greatly improved.
(3) The economic benefits of users are more obvious, and the electricity expenses are reduced by nearly 60,000 yuan per month.
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