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Common Problems of Capacitor

Common Problems of Capacitor

1. Common failures of capacitors. When one of the following conditions of the capacitor is found, the power supply should be cut off immediately. (1) The capacitor shell is swollen or leaks oil. (2) The casing is ruptured, and flashover occurs with sparks. (3) The sound inside the capacitor is abnormal.  (4) The shell temperature rises above 55 °C, and the temperature indicator sheet falls off. 2. Fault handling of capacitors (1) When the capacitor explodes and catches fire, immediately disconnect the power supply and extinguish the fire with sand and a dry fire extinguisher. (2) When the safety of the capacitor is fused, it should be reported to the dispatcher, and the circuit breaker of the capacitor should be pulled open after obtaining consent. Cut off the power supply to discharge it, first carry out external inspection, such as whether there are flashover traces on the outside of the casing, whether the shell is deformed, whether the oil leakage and grounding device have short circuit phenomenon, etc., and shake the insulation resistance value between the poles and the pole to the ground, check whether the capacitor bank wiring is complete and firm, whether there is a phase loss phenomenon, if no fault phenomenon is found, you can replace the insurance and put in. If the safety is still blown after power transmission, the faulty capacitor should be withdrawn and power to the rest should be resumed. If the circuit breaker also tripps at the same time as the insurance blows, it cannot be forcibly sent at this time. It must be put in after the above inspection is completed and the insurance is changed. (3) The circuit breaker of the capacitor trips, and the shunt insurance is not broken, the capacitor should be discharged for three minutes, and then check the circuit breaker, current transformer, power cable and external of the capacitor. If no abnormalities are found, it may be due to fluctuations in the voltage of the external faulty bus. After inspection, it can be tested for investment; Otherwise, a thorough energization test for protection should be carried out. After the above inspection and test, if the cause cannot be found, it is necessary to follow the system and gradually test the capacitor. Before the reason is ascertained, the test investment shall not be made. 3. Safety precautions when dealing with faulty capacitors. Since the two poles of the capacitor have the characteristics of residual charge, it is necessary to try to drain the charge first, otherwise it is prone to electric shock. When dealing with faulty capacitors, the circuit breaker of the capacitor bank and its upper and lower disconnectors should be pulled apart first, and if the fuse protection is used, the fuse tube should be removed first. At this time, although the capacitor bank has been discharged by the discharge resistor, there will still be a part of the residual charge, so artificial discharge must be performed. When discharging, the grounding end of the grounding wire should be fixed with the grounding grid, and then the capacitor should be discharged multiple times with the grounding rod until there is no spark and discharge sound, and finally the grounding wire should be fixed. At the same time, it should also be noted that if the capacitor has an internal disconnection, a fuse is blown or the lead is in poor contact, there may be residual charges between its two poles, and these residual charges will not be discharged during automatic discharge or artificial discharge. Therefore, before the operation or maintenance personnel contact the faulty capacitor, they should also wear insulating gloves and short-connect the poles of the faulty capacitor with a short circuit to discharge it. In addition, capacitors using the series wire method should be discharged separately.

2023-02-27

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Capacitor selection and differentiation

Capacitor selection and differentiation

The characteristics of capacitors are mainly DC through AC (in the circuit, blocking DC current, through the action of AC current), often used for interpole coupling, filtering, decoupling, bypass and signal tuning. 1. In the power supply circuit, the rectifier circuit turns the AC into pulsating DC, and after the rectifier circuit, a larger capacity electrolytic capacitor is connected, and its charge-discharge characteristics are used to make the pulsating DC voltage after rectification become a relatively stable DC voltage. In practice, in order to prevent the power supply voltage of each part of the circuit from changing due to load changes, electrolytic capacitors of tens to hundreds of microfarads are generally connected to the output end of the power supply and the power input end of the load. Since large-capacity electrolytic capacitors generally have a certain inductance, they cannot effectively filter out high-frequency and pulse interference signals, so a capacitor with a capacity of 0.001--0.lpF is connected in parallel at both ends to filter out high-frequency and pulse interference. 2. Coupling effect: In the process of transmission and amplification of low-frequency signals, in order to prevent the static working points of the front and rear two-stage circuits from affecting each other, capacitor coupling is often used. In order to prevent excessive loss of low-frequency components in the signal, electrolytic capacitors with larger capacity are generally used. The main indicator of capacitance 1. The nominal capacity of the capacitor - the capacitance value indicated on the capacitor. 2. The allowable error of the capacitor (1) There is always a certain deviation between the actual capacity of the capacitor and the nominal capacity, which is called the error. Because this error is within the allowable range specified by the national standard, it is called the allowable error. The allowable error is divided into 5 levels: ±1% (00 level), ±2% (0 level), ±5% (I.), ±10% (II.), ±20% (III.). (2) When the value on the capacitor is tens, hundreds, and thousands, the unit is pF. For example, 3300 means 3300pF. 3. The rated working voltage of the capacitor (1) The DC voltage value of the capacitor that works for a long time without causing any damage to the dielectric electrical properties, also known as withstand voltage. When the capacitor is operating, the maximum value of the actual applied voltage cannot exceed the rated operating voltage. If an AC voltage is added across the capacitor, the maximum AC voltage applied must not exceed its rated operating voltage. (2) Some capacitors use three digits to indicate the nominal capacity, where the first two digits represent the significant digits of the capacitance, and the last digit word indicates how many zeros are added after the significant digits, and the unit is also pF. 4. Quality parameters of capacitors: (1) Voltage: DC rated withstand voltage value (2) Peak voltage: the peak of DC voltage that can be withheld (3) Capacity: the capacitance of the electrolytic capacitor (4) Deviation: the positive and negative deviation value of the capacity (5) Leakage current: leakage current under rated withstand voltage (6) Ripple current: The allowable ripple current at a frequency of 120Hz at a certain temperature (such as 40°C) is equivalent to the internal resistance of the electrolytic capacitor (7) Temperature: working temperature range (such as -55~+105°C)

2023-02-27

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What are the types of capacitors?

What are the types of capacitors?

(1) Fixed capacitance As the name suggests, a fixed capacitor is a type of capacitor that creates a fixed-capacity capacitor. This means that it can only store a predetermined amount of charge in it. Further fixed capacitors can be classified according to the dielectric materials used between the conductive plates, such as paper capacitors, plastic capacitors, ceramic capacitors, etc. (2) Variable capacitors Capacitors whose capacitance value can be changed electronically or mechanically are called variable capacitors. A variable capacitor consists of a fixed plate and a variable plate. By changing the distance between the two plates, the capacitance can be changed. These capacitors are used in antennas for impedance matching. Specifically, it is divided into: (1) Polarized capacitors Polarized capacitors are capacitors with predefined pin polarity. Before connecting a polarity capacitor to a circuit, the polarity of the capacitor pin must be kept in mind. The most common polarized capacitors are electrolytic capacitors. (2) Non-polarizing capacitors Non-polar capacitors can be connected directly to the circuit regardless of the polarity of the pins. This means that non-polar capacitors do not have any assumed pin polarity. They are also known as bipolar capacitors. (3) Tuned capacitors A tuning capacitor or tuning capacitor consists of a stator, a rotor, and a rack. The stator is a fixed component and the rotor moves with the help of a movable shaft. When the rotor blades enter the stator slot, they act like capacitor plates. The capacitance value is maximum when the moving vane is attached to the stator groove, and the minimum capacitance value when the moving vane is away from the groove. The capacitance values of tuned capacitors range from a few picofarads to tens of picofarads. They are mainly used in LC circuits in radio receivers.

2023-02-27

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The principle of operation of the capacitor dielectric

The principle of operation of the capacitor dielectric

How does the dielectric increase the capacitance of the capacitor? Dielectrics contain polar molecules, which means they can change direction depending on the charge on both plates. Thus, the molecules are aligned with the electric field in such a way that more electrons are attracted to the negative plate while repelling more electrons out of the positive plate. So, once it is fully charged, if we remove the battery, it will maintain the charge for a long time, playing the role of energy storage. Now, if we shorten the two ends of the capacitor by the load, the current will begin to flow through the load. The accumulated electrons from the first plate will begin to move to the second plate until both plates return to electrical neutrality.

2023-02-27

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Are capacitors and capacitors the same?

Are capacitors and capacitors the same?

It is generally considered that capacitors and capacitors are the same. What people usually call capacitance refers to capacitors. A capacitor consists of an insulating dielectric sandwiched between two metal electrodes. Capacitance is a physical quantity that describes the performance of a conductor or conductor system to hold an electric charge. The capacitance of the isolated conductor charges the charge Q to the isolated conductor, its potential U is proportional to Q, Q/U has nothing to do with Q, only depends on the shape and size of the isolated conductor, it reflects the ability of the isolated conductor to hold the charge, so it is defined as the capacitance of the isolated conductor, expressed by C, C = Q/U. The capacitance of an isolated conductor is equal to the amount of electricity required for the conductor to raise its unit potential. The international unit of capacitance is the farad, abbreviated as the method, which is denoted by F and is a very large unit. If the Earth is considered an isolated conductor, its capacitance is only 709×-6 method, so it is usually measured in μF (=-6F) or pF (=10-12F). If another negatively charged conductor is moved closer to an isolated conductor, the potential of the latter decreases, and it can be seen that the potential of a non-isolated conductor is not only related to the amount of electricity it carries, but also depends on the relative position of other surrounding conductors. Capacitor If the charged conductor A is surrounded by a closed conductor cavity B, the potential difference between AB is not affected by the charged body outside the cavity due to the shielding effect of the cavity, and the amount of electricity carried by A is proportional to the potential difference between A and B. In fact, the limit of cavity sealing is not too high, even if the two conductors A and B are a pair of conductor plates (coaxial cylindrical or parallel planar plates) that are not much apart, if QA is the amount of electricity on the side opposite conductor B on conductor A, the above proportional relationship remains unchanged. This pair of conductors insulating each other forms a capacitor, and this pair of conductors is called a pair of plates of the capacitor. Connect the voltage U to a pair of plates of the capacitor, and they obtain a charge of equal magnitude and opposite signs±Q, and the potential difference UA-UB=U defines the capacitance of the capacitor as C=Q/U. Capacitance is the characteristic constant of the capacitor, which depends on the shape, size and relative position of the two conductors; When the conductors are filled with insulating material, the capacitance of the capacitor is also related to the relative passivity εr of the insulating material. If εr is related to the strength of the electric field, the capacitance C will change with the applied voltage U, and this capacitor is called a nonlinear capacitor. The reciprocal of the capacitance 1/C=U/Q=S is called the inverted capacitance. The capacitance formula for a simple capacitor is shown in the table.　Parallel and series connection of capacitors n capacitors are connected in parallel as shown in Figure A, their voltages are equal to u, and the charged charges are Q1, Q2 、...、 QN. The total charge q= obtained by this parallel combination is C=, i.e. the total capacitance of the shunt capacitor bank is equal to the sum of the capacitors. 　n capacitors are connected in series as shown in Figure B, they are charged with equal charge Q, and the voltages are U1, U2、...、un, respectively. The total voltage u=of this series combination is S=, i.e. the total inverted capacitance of the series capacitors is equal to the sum of the respective inverted capacitors. Performance parameters and uses of capacitors Capacitance is one of the main performance parameters of capacitors. In addition, the performance parameters of the actual capacitor are withstand voltage (or operating voltage), loss and frequency response, which depend on the breakdown field strength, medium loss and frequency response of the charged medium, respectively. There are many types of actual capacitors and different uses. Large power capacitors are mainly used to improve the power factor of power equipment to reduce transmission losses and give full play to the efficiency of power equipment. Capacitors are widely used in electronics to provide AC bypass stabilized voltage, as interstage AC coupling, and as filters, phase shifters, oscillators, and so on.

2023-02-27

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Various capacitor applications

Various capacitor applications

No polarity variable capacitor Production process: the rotatable moving piece is a ceramic film plated with metal film on the surface, and the fixed piece is a ceramic bottom plated with metal film; The moving piece is a coaxial metal sheet, and the fixed piece is an organic film sheet as the medium Advantages: easy to produce, low technical content. Disadvantages: large volume, small capacity...

2023-02-27

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