Detailed knowledge of power distribution knowledge and its application
Switchgear: refers to a complete set of power distribution equipment assembled by primary equipment and secondary equipment according to a certain line scheme. It is used to control and protect the lines and equipments. It is divided into fixed and handcart type, and is pressed in and out. Line voltage levels can be divided into high voltage switchgear (fixed and handcart) and low voltage switchgear (fixed and drawer). The structure of the switchgear is generally similar, and is mainly divided into a busbar room, a circuit breaker room, a secondary control room (instrument room), and a feeder room, and steel plates are generally isolated between the rooms. Internal components include: busbars (busbars), circuit breakers, conventional relays, integrated relay protection devices, metering instruments, isolation knives, indicator lights, grounding knives, etc. 1. Incoming cabinet: Also called the receiving cabinet, it is used to receive electrical energy from the grid (from the incoming line to the bus), generally installed with circuit breakers, CT, PT, isolation knives and other components. 2, outlet cabinet: Also called feeder or distribution cabinet, it is used to distribute electrical energy (from bus to each outlet), and is generally equipped with circuit breakers, CT, PT, isolation knives and other components. 3. Busbar connection cabinet: Also called busbar breaking cabinet, it is used to connect two busbars (from busbar to busbar). In single busbar section and double busbar system, busbar contact is often used to meet the requirements or guarantees for users to choose different operating modes. There is a selective removal load in the event of a fault. 4, PT cabinet: The voltage transformer cabinet is usually installed directly on the busbar to detect the bus voltage and realize the protection function. Mainly installed voltage transformer PT, isolation knife, fuse and lightning arrester. 5, isolation cabinet: It is used to isolate the busbars at both ends or to isolate the power receiving equipment from the power supply equipment. It can provide the operator with a visible end point for maintenance and repair work. Since the isolation cabinet does not have the ability to break and switch the load current, the handrail of the isolation cabinet cannot be pushed and pulled in the case that the circuit breaker with which it is fitted is closed. In general applications, it is necessary to set the interlock between the auxiliary contact of the circuit breaker and the isolated handcart to prevent the operator from misoperation. 6, capacitor cabinet: Also called the compensation cabinet, it is used to improve the power factor of the power grid, or for reactive power compensation. The main components are the protective capacitors such as groups of capacitor banks, switching control loops and fuses connected in parallel. Generally installed side by side with the incoming line cabinet, one or more capacitor cabinets can be operated side by side. After the capacitor cabinet is disconnected from the grid, since the capacitor bank needs a period of time to complete the discharge process, it is not possible to directly touch the components in the cabinet, especially the capacitor bank; within a certain period of time after the power is cut off (according to the capacitor bank) Depending on the size of the capacity, such as: 1 minute), re-closing is not allowed to avoid overvoltage damage to the capacitor. When making automatic control functions, it is also necessary to pay attention to the reasonable number of switching times of each group of capacitor banks, so as to avoid a group of capacitors being damaged, while other groups are rarely switched. 7, measuring cabinet: Mainly used for metering electric energy (kilowatt hours), high voltage, low voltage, usually equipped with isolating switch, fuse, CT, PT, active energy meter (traditional meter or digital meter), reactive power Tables, relays, and some other auxiliary secondary equipment (such as load monitors, etc.). 8, GIS cabinet: Also known as a closed combination electrical cabinet, it is a combination of a circuit breaker, an isolating switch, a grounding switch, a CT, a PT, a lightning arrester, a busbar, etc. in a metal casing, and then a gas with good insulation performance and arc extinguishing performance (usually six Sulfur fluoride SF6) is used as an insulation measure between phases and ground. It is suitable for power distribution and control in high-voltage and high-capacity power grids. 9, circuit breaker: Under normal working conditions, the circuit breaker is in the closed state (except for special applications) and the circuit is turned on. When the automatic control or protection control operation is performed, the circuit breaker can perform the breaking or closing operation of the circuit under the control of the integrated protection device. The circuit breaker not only can cut off the normal load current, but also can withstand the short-circuit current (multiple times or even several times of the normal working current) for a certain period of time, and can break the short-circuit current and cut off the faulty line and equipment. Therefore, the main function of the circuit breaker is to break and close the circuit (including breaking and turning on the normal current, breaking the short-circuit current). Due to the inevitable arcing between the moving and stationary contacts of the circuit breaker during the breaking and closing of the circuit. In order to protect the contacts, reduce the loss of the contact material and reliably break the circuit, measures must be taken to extinguish the arc as soon as possible, one of which is to fill the moving and static contacts of the circuit breaker with different arc extinguishing media. According to the different circuit breakers of arc extinguishing medium, it can be divided into: oil circuit breaker (multi-oil, less oil), sulfur hexafluoride (SF6) circuit breaker, vacuum circuit breaker, air circuit breaker and so on. The main primary equipment in the high and low voltage switchgear that we often encounter in engineering is the circuit breaker. Since the dynamic and static contacts of the circuit breaker are generally enclosed in a container filled with arc extinguishing medium, the state of the circuit breaker can not be directly judged, generally through the auxiliary device of the circuit breaker (such as the split position pointer) Etc.) to judge. 10. Isolation knife gate: Isolation knife gate (or isolation switch) can be identified as being connected or disconnected due to obvious fractures. It is mainly used to isolate the high voltage power supply to ensure the safe maintenance of the line and equipment. The current that can be disconnected is very small (generally only a few ampere). Since there is no special arc extinguishing device, it cannot be used to break the fault current and normal working current, and it is not allowed to carry out the breaking operation with load. 11, fuse: A fuse is a simple circuit protection device. The principle is that when the current flowing through the fuse reaches or exceeds a certain value for a certain period of time, the melt itself melts and cuts off the circuit. Its action principle is simple, easy to install, and generally not used alone, mainly used in conjunction with other electrical appliances. Main action characteristics: First, the current must reach a certain value, which is already done before the fuse is shipped from the factory and cannot be changed; Second, it takes a certain amount of time after the current reaches a certain value. This time is also done by the manufacturer and cannot be changed, but there are many types, including delayed action, fast action, and super fast action. Third, the body is damaged after the action, can not be reused, must be replaced; Whether the fuse is blown can be judged by the fuse indicator, or can be judged by the appearance of the melt; commonly used fuses and fuses are all in the range of such appliances. 12, load switch: The load switch has a simple arc extinguishing device. The arc extinguishing medium generally adopts air, which can switch on and off a certain current and overcurrent, but cannot break the short circuit current, and cannot be used to cut off the short circuit fault. Therefore, it is absolutely not allowed to replace the circuit breaker with a load switch alone; if a load switch is to be used, it must be used in conjunction with the aforementioned high-voltage fuses (in fact, fuses and load switches are often used in series for simple overload protection). To reduce the project cost). The load switch is similar to the isolation knife and has a clear disconnection gap, which makes it easy to determine whether the circuit is on or off. 13, transformer: Simply put, a transformer is a device that uses an alternating electromagnetic field to achieve different voltage level conversions (actually, the conversion of electrical energy), and the voltage before and after the conversion does not change in frequency. According to its use, it can be divided into many types, such as power transformers, rectifier transformers, voltage regulators, isolation transformers, and CT, PT, etc. What we often encounter at the engineering site is the power transformer. Some of the main technical parameters related to transformers include: (1) Rated capacity: refers to the rated output capacity of the transformer under rated working conditions (equal to U × I, the unit is kVA); (2) Rated voltage: the value of the terminal voltage under no-load, rated tapping (ie, the primary and secondary voltage values); (3) No-load loss: the loss of the transformer (also called iron loss) under no-load conditions; (4) No-load current: the current value flowing through the primary side coil under no-load conditions; (5) Short-circuit loss: the primary side rated current, the loss caused by the secondary short circuit (mainly caused by the coil resistance); (6) The concept of tapping (tap): In order to meet the needs of the grid operation, the high voltage side of the general transformer has taps. The voltage values ​​of these taps are expressed as a percentage of the rated voltage, the so-called tap voltage. For example, a high voltage 10kV transformer has ±5% taps, which means that the transformer can operate at three voltage levels: 10.5kV (+5%), 10kV (nominal), and 9.5kV (-5%). In general, the number of taps (tap points) of the on-load tap changer is large, such as 7-point contact (±3×2.5%) and 9-point contact (±4×2%). Since the synchronous switching of the tap changer cannot be completely ensured, the on-load tap changer is generally not able to operate in parallel. (7) Active load: A load that produces mechanical or thermal energy in a power system. However, the pure resistive load in the load only consumes active power. For example, electric power, electric furnace, lighting and other electrical loads are completely active loads. In the load of the asynchronous motor and the synchronous motor, both the active power and the reactive power are consumed, and the part of the work that produces the machine energy is the active load. The active load is supplied by the generator's active power. (8) Reactive load: The part that does not work in the electrical load. Reactive power is only consumed in inductive loads. Such as: transformers, motors, air conditioners, refrigerators, etc. Therefore, while the generator outputs active power, it also needs to provide reactive power. When the reactive power cannot meet the grid, the voltage of the system will drop. In order to meet the needs of users, a reactive power compensator should be installed in the substation to maintain the balance of reactive power, so as to maintain the voltage level. (9) Accident backup: One of the components of the spare capacity in the power system. Since the power generation equipment may have temporary or permanent failures that affect the power supply, the system must set a certain number of accident backup power sources to ensure the safety of the power facilities. (10) System unwinding: In order to prevent system out of step and accident expansion, the complete power system is decomposed into several measures that are no longer independent. After de-column, some local systems may experience insufficient power, and the frequency and voltage drop may require partial removal of the load to prevent the stability of the entire system from being destroyed. 14, PT (TV) / CT (AV): The transformer is actually a special type of transformer, which is mainly used to electrically isolate the primary circuit and the control circuit, thereby expanding the scope of use of secondary equipment (instruments, comprehensive insurance, etc.). The use of PT/CT can prevent the high voltage/high current of the primary circuit from directly entering the secondary control equipment (such as instruments, comprehensive protection devices, etc.), and can also prevent the operation of the primary circuit from being affected by the failure of the control equipment. 1) The characteristics of current transformers (CT, AV) are: The primary side winding N1 is thick and small, the secondary side winding N2 is thin and numerous, and the secondary side rated current I2 is generally 5A (the primary side current I1 can be approximated according to N1I1=N2I2, or the corresponding ratio can be selected according to the primary side current I1) Current transformer). Since the primary winding and the secondary winding are respectively connected in series in the primary circuit and the secondary control circuit when the CT is in operation, according to the characteristic U1I1=U2I2 of the transformer, the working voltage of the secondary side during operation is obtained. When opening the road, it is very large, so CT is absolutely not allowed to open the road. According to the purpose, it can be divided into CT for protection and measurement. When the CT is short-circuited in the primary circuit, it is easy to saturate to limit the secondary current (secondary winding side current I2) to be too large to protect the comprehensive protection device; and the protection CT should not be short-circuited in the primary circuit. A protective phenomenon occurs to ensure reliable operation of the integrated protection device. 2) Ratio: The ratio of the number of turns of the high-voltage side winding to the low-voltage side of the transformer is called the ratio, which can be expressed by the ratio of the rated voltage of the high-voltage side to the low-voltage side. 3) The characteristics of voltage transformers (PT, AV) are: The number of turns of the primary winding is more than N1, and the number of turns of the secondary winding is less than N2, which is equivalent to a step-down transformer (the secondary side rated voltage is generally 100V). Since the primary winding and the secondary winding are respectively connected in parallel to the primary loop and the secondary control loop voltage coil during operation, the current on the secondary side of the PT is very small due to the large impedance of the voltage coil, and the secondary winding is approximated. In the empty load state; but the impedance of the secondary winding itself is very small, so if the secondary winding is shorted, it will result in a very large secondary current (N1I1 = N2I2). Therefore, the secondary winding of the PT must not be short-circuited. 15, handcart / drawer: The handcart and the drawer are respectively part of the high voltage switchgear and the low voltage switchgear, and the components such as the high voltage circuit breaker and the low voltage circuit breaker and their relays are respectively installed. The hand-operated switchgear (high-voltage) and the drawer-type switchgear (low-voltage) are thus divided. They are basically the same function as the fixed switchgear. The main difference is that it is convenient for maintenance and overhaul (handcarts and drawers can pass through the machine). The operating mechanism shakes the handle to push and pull out). Handcarts and drawers generally have three position states: work (normal operation), test (for trial operation and field test), and exit (for maintenance and inspection). 16, grounding knife: The grounding knife (also called the grounding switch) is mainly used for grounding to ensure the safety of personnel when the line and equipment are inspected; secondly, it can be used to artificially cause the system to be short-circuited to the ground to achieve the purpose of control and protection. The first role is well understood and will not be introduced. The second function is as follows: the grounding knife is usually connected to the high voltage side of the step-down transformer. When the power receiving end fails or the internal fault of the transformer occurs, the grounding knife switch should be automatically closed, causing a short circuit to the ground, forcing the power transmitting end ( The upper end of the circuit breaker acts quickly and cuts off the fault, so this is a personal ground short circuit fault. The purpose is to ensure that the circuit breaker at the power transmitting end can move quickly. 17, contactor: The contactor is an electrical appliance for frequently switching on and off the AC/DC main circuit and the large-capacity control circuit at a long distance. The main control object is an electric motor, an illumination, a capacitor bank, etc., and an AC contactor and a DC contactor. Compared with circuit breakers, the difference is that the operating frequency is very high (thus requiring its electrical and mechanical life is long enough); it has a high breaking and switching capacity, but is generally used at voltage levels of 1kV and below. It cannot be compared with tens of kilovolts and hundreds of kilovolts of circuit breakers. 18, relay: The relay is used to control other electrical appliances (usually an electrical main equipment) in the control loop or as a protection and signal conversion in the main circuit. It is only suitable for long-distance disconnection and switching on small-capacity control loops. For example, AC/DC current relays, voltage relays, time relays, intermediate relays, thermal relays, etc. 19. Test Common tests include: 1) Type test: A test performed on one or more devices or equipment manufactured in accordance with a design requirement to verify that the design requirements meet certain specifications. 2) Routine test: Also called the factory test, the test carried out during or after the completion of each device or device to determine whether the device or device meets a certain standard. 3) Medium test: It is a general term for various tests for testing the electrical properties of a medium, including: insulation, static electricity, and withstand voltage. Sampling test: Several samples randomly selected from a batch of products are tested to determine whether the sample meets certain criteria. 4) Life test: A test to determine the life expectancy of a product under specified conditions, or a test to evaluate the life characteristics of an analytical product, is a destructive test. 5) Tolerance test: Tests performed on products, such as repeated operations, short circuits, overvoltages, vibrations, shocks, etc., under specified conditions, including specific operations taken for a certain period of time, are destructive tests. 6) Commissioning test: The test carried out on the product at the site to prove that the installation is correct and the product operation is normal. T Series Pluggable Connectors,Custom Pluggable Connectors,T Branch Parallel Connectors,Quick Splice Connector Jiangmen Krealux Electrical Appliances Co.,Ltd. , https://www.krealux-online.com