The main transformer of the rolling mill power distribution system is a rectifier transformer with a voltage of 0.4/0.66/0.75 kV, and the main load is a DC main motor. Because the power transmission and distribution of the user’s extruder rectifier device generally uses two types of six-pulse rectifier technology, which generates a certain amount of pulse current (6N+1) in different degrees on the low-voltage side, and mainly (6N+1) on the high-voltage side. 12N+1) Display twelve single-pulse rectifier mode.
The damage of power engineering harmonics to the power grid depends on the harm of the harmonic working voltage to the machinery and equipment in the power grid, that is, the harmonic working voltage exceeds the level that the machinery and equipment can bear. The power supply party is responsible for the pulse current working voltage of the power supply network, and the power consumer is responsible for introducing the harmonic current of the system software.
According to the engineering experience of our company’s traditional rolling mills to deal with harmonics, in the work, in the user’s low-voltage power distribution system, the 5th harmonic current content reaches 20%~25%, the 7th harmonic current reaches 8%, and the harmonic current is injected into the high voltage The harmonic content in the power system increases rapidly, which causes the waveform distortion of the supply voltage, increases the loss of wiring and power equipment, brings additional energy consumption, affects the normal operation of other power equipment in the power grid, and reduces the power quality of the power grid. , which affects the power security of the power grid and brings security risks to the safe operation of equipment.
In order to ensure the normal operation of the equipment, reliable power supply and energy saving of the power supply system, it is necessary to take technical measures to suppress the harmonic current of the equipment and consider the compensation of the fundamental reactive power. According to the quality standards of working voltage products in my country’s power grid and the scientific research results of pulse current control in various countries in the world, the technical specifications of bottom voltage filtering and dynamic compensation are adopted, and the filter control loops are respectively set for the characteristic pulse currents caused by the rectifier to digest and absorb harmonic currents. In addition, it has the functions of compensating the fundamental wave reactive load and saving electromagnetic energy.
The anti-harmonic equipment produced by Zhejiang Hongyan Electric Co., Ltd. has the characteristics of dynamic change with the load. While effectively improving the power quality, power factor and energy saving of the power grid, it can also improve the reliability of the overall operation of the power system and the operation efficiency of equipment, and reduce operating costs and Reduce equipment maintenance costs, prolong equipment life, and bring obvious economic benefits to users.
DC rolling mills generally use DC motors, and the power factor during rolling is very low, generally around 0.7. One of its major features is short working cycle, fast speed, impact load, and large invalid fluctuations. Power squeezers can also cause strong fluctuations in grid voltage, causing lights and TV screens to flicker, causing visual fatigue and irritation. In addition, they will also affect the smooth operation of thyristor components, instruments or production equipment, and even cause safety accidents. General capacitor bank compensation cannot track load changes in real time to maintain reasonable compensation. Mechanical equipment contact points are affected due to frequent switching, which has a great impact on the power grid.
The DC rolling mill adopts the electric transmission of thyristor rectification technology. According to the number of rectification pulses, it can be divided into 6-pulse rectification, 12-pulse to 24-pulse. In addition to low power factor, high-order harmonics will be generated during work. Generally, domestic DC rolling mills The 6-pulse rectification technology is used, so the high-order harmonics generated by the single low-voltage winding side of the rectifier transformer are mainly 11 and 13 in the low-voltage side of the transformer with 2 windings do and yn joint method, the 5th and 7th High-order harmonics can be offset on the high-voltage side, so the 11th and 13th high-order harmonic components are mainly displayed on the high-voltage side. The main impacts of high-order pulse currents on the power grid include heating and vibration of electrical equipment, increased loss, shortened service life, communication impact, thyristor operation error, operation error of some relay protection devices, aging and damage of electrical insulation layer, etc.
Solutions to choose from:
Solution 1 Centralized management (applicable to low-power hosts, left and right volumes)
1. Adopt harmonic control branch (3, 5, 7 filters) + reactive power regulation branch. After the filter compensation device is put into operation, the harmonic control and reactive power compensation of the power supply system meet the requirements.
2. Use a bypass circuit that suppresses the ineffective compensation of harmonics, and after connecting the filter compensation device, make the power factor meet the requirements
Option 2 Local treatment (applicable to 12-pulse rectifier transformer low-voltage side treatment and high-power main engine and winding machine installed separately)
1. Adopt anti-harmonic bypass (5th, 7th, 11th order filter), automatic tracking when the rolling mill is running, solve harmonics on site, do not affect the operation of other equipment during production, and the harmonics do not reach the standard after being put into operation.
2. Using active filter (filtering dynamic harmonics) and filter bypass (5th, 7th, 11th order filtering), the harmonics after switching on are not up to the standard.
Post time: Apr-13-2023