• Analysis of working principle of transformer zero sequence current protection

    04/26/2022 at 09:10 0 comments

    Introduction to Transformers


    A transformer is a device that uses the principle of electromagnetic induction to change the AC voltage. The main components are the primary coil, the secondary coil, and the iron core (magnetic core). The main functions are voltage transformation, current transformation, impedance transformation, isolation, voltage regulation (magnetic saturation transformer), etc. According to the purpose, it can be divided into power transformers and special transformers (electric furnace transformers, rectifier transformers, power frequency test transformers, voltage regulators, mining transformers, audio transformers, intermediate frequency transformers, high-frequency transformers, impact transformers, instrument transformers, electronic transformers, reactors, transformers, etc.).

    The working principle of the transformer is composed of an iron core (or magnetic core) and a coil. The coil has two or more windings. The winding connected to the power supply is called the primary coil, and the rest of the windings are called secondary coils. It can transform AC voltage, current, and impedance. The simplest core transformer consists of a core made of soft magnetic material and two coils with different turns on the core.

    working principle

    The role of the iron core is to strengthen the magnetic coupling between the two coils. In order to reduce the eddy current and hysteresis loss in the iron, the iron core is laminated by lacquered silicon steel sheets; there is no electrical connection between the two coils, and the coils are wound by insulated copper wire (or aluminum wire). One coil connected to the AC power supply is called the primary coil (or primary coil), and the other coil connected to the electrical appliance is called the secondary coil (or secondary coil). The actual transformer is very complicated, and there is inevitably copper loss (coil resistance heating), iron loss (iron core heating) and magnetic leakage (magnetic induction line closed by air), etc. In order to simplify the discussion, only the ideal transformer is introduced here. The conditions for the establishment of an ideal transformer are: ignoring the leakage flux, ignoring the resistance of the primary and secondary coils, ignoring the loss of the iron core, and ignoring the no-load current (current in the secondary coil open circuit primary coil). For example, when the power transformer is running at full load (the secondary coil outputs rated power), it is close to the ideal transformer condition.

    Transformers are static electrical appliances made of electromagnetic induction. When the primary coil of the transformer is connected to the AC power supply, an alternating magnetic flux is generated in the iron core, and the alternating magnetic flux is represented by φ. The φ in the primary and secondary coils is the same, and φ is also a simple harmonic function, and the table is φ=φmsinωt. According to Faraday's law of electromagnetic induction, the induced electromotive force in the primary and secondary coils is e1=-N1dφ/dt, e2=-N2dφ/dt. In the formula, N1 and N2 are the turns of the primary and secondary coils. It can be seen from the figure that U1=-e1, U2=e2 (the physical quantity of the primary coil is represented by the subscript 1, and the physical quantity of the secondary coil is represented by the subscript 2), and its complex effective value is U1=-E1=jN1ωΦ, U2=E2=-jN2ωΦ, Let k=N1/N2, which is called the transformation ratio of the transformer. U1/U2=-N1/N2=-k can be obtained from the above formula, that is, the ratio of the rms value of the transformer primary and secondary coil voltages is equal to its turns ratio and the phase difference between the primary and secondary coil voltages is π.

    which leads to:

    U1/U2=N1/N2

    Under the condition that the no-load current can be ignored, there is I1/I2=-N2/N1, that is, the effective value of the primary...

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  • How Vibration Sensors Measure Vibration?

    04/09/2022 at 07:45 0 comments

    Vibration is one of the most common phenomena in nature. From the universe as small as the atomic particle, there is a vibration phenomenon. Vibration phenomena abound in the field of engineering and technology, but in many cases vibration is detrimental, such as vibration reduces machining accuracy and finish, increases fatigue and wear of structural parts, and vibration of airframe and structural parts in the field of vehicles and aviation It will not only affect the driver's operation and comfort but also cause the body and structural parts to break or even disintegrate in severe cases.

    Vibration sensors can be used for long-term monitoring of vibration and displacement in machinery, thermal expansion of rotor and casing; online automatic detection and automatic control of production lines; measurement of various micro-distances, and micro-motions in scientific research. Vibration sensors are widely used in energy, chemical industry, medicine, automobile, metallurgy, machine manufacturing, military industry, scientific research and teaching, and many other fields, and more importantly, they are used in the detection of earthquake disaster prevention.

    Vibration sensors are mainly used in gas equipment, which can sense disasters such as earthquakes and cut off gas or power in time to prevent secondary disasters. There are many ways for vibration sensors to measure vibration, but to sum up, most of the principles are as follows:

    Mechanical measurement method: Convert the variation of engineering vibration into a mechanical signal, and then amplify it by the mechanical system to measure and record. The commonly used instruments are lever-type vibrometer and Geiger vibrometer. This method measures frequency. The accuracy is poor, but the operation is very convenient.

    Optical measurement method: The variation of engineering vibration is converted into an optical signal, which is displayed and recorded after being amplified by the optical system. As the laser vibrometer is to use this method.

    Electrical measurement method: Convert the variation of engineering vibration into electrical signals, which are displayed and recorded after being amplified by the line. It first converts the mechanical vibration into electricity and then measures it. According to the corresponding relationship, the magnitude of the vibration is known. This is the most widely used vibration measurement method at present.

    It can be seen from the above three measurement methods that they are all completed through three links: a vibration sensor, a signal amplification circuit, and display recording.

  • FinFET potential and risks coexist, well-known manufacturers talk about development strategies

    03/21/2022 at 09:17 0 comments

    At Synopsys' annual user conference in Silicon Valley, industry experts who participated in a panel said that FinFETs have potential, but they also have risks, and the technology is the best time to do so. not yet reached.

    The technical director from the wafer foundry Globalfoundries pointed out that this 3D transistor architecture will bring performance improvements in the 14nm process node, and the power consumption will also be reduced by 60% compared with the current 28nm process; however, other participating experts pointed out that, This transistor architecture exacerbates some old design problems and brings new challenges due to the increased capacitance.

    Anil Jain, vice president of IC engineering at processor designer Cavium Networks, said that compared with the current 28nm process, FinFET gate capacitance per micron (micron) has increased by 66%, returning to the previous 130nm process. The level of node planar transistor architecture; he added that capacitors will limit the performance improvement and dynamic power scaling of high-end chips.

    "We have these beautiful (3D) transistors, but we can't get them to go very far," Jain points out. "The dynamic power can get out of hand." 

    Jain called on EDA suppliers to provide design tools that are better at controlling switching power and isolating electromagneTIc faults, "FinFET is not an easy technology to switch, and we will have to pay for it until the day it succeeds, so please don't. Let's go bankrupt."

    Michael Campbell, vice president of engineering at Qualcomm's chip design division, said that the FinFET architectures of different foundries are "similar, but not identical. You can only etch in a certain direction, and the etching tools are shared-- Those are the reasons for their similarities -- but each foundry actually uses different techniques for spaTIal walls and diffusion."

    Campbell pointed out that the irregular tapered walls seen in Intel's 22nm FinFET pictures could impact the defect model of planar transistors, requiring new testing techniques and a very close partners relationship in order to complete a proper testable design.

    And Campbell said Synopsys' Yield Explorer is a good tool in the EDA space, but it's still locked down to planar transistor architectures -- the company needs to introduce tools for 3D transistor architectures. He pointed out that neither Synopsys nor other EDA vendors' design tools have a serious lack of solutions to compress simple ATE graphics for backward-finding defects.