The high and low voltage complete set of equipment we are talking about, in simple terms, is a set of high and low voltage electrical equipment that is designed in advance, assembled and debugged properly to form a whole. In the power system, it is a frequent visitor, mainly used to control and protect electric energy, and is also responsible for distributing electric energy to various places. This equipment is very important to the power system. With it, the power system can run stably, and the power supply is more reliable and safer.
From the perspective of functions and usage scenarios, high and low voltage complete sets of equipment are divided into many categories. For example, switchgear, circuit breakers, and load switches are all in this category; control equipment includes contactors and relays; protection equipment includes fuses and overvoltage protectors; and there are measuring equipment, such as voltmeters and ammeters. These devices are like a team, working together to make the power system work smoothly. So what are the basic knowledge of high and low voltage complete sets of equipment, and what are the key points that need to be firmly grasped? Don’t worry, the following article has been sorted out for you, and it is recommended that everyone quickly save it and read it slowly.
- Why is the switch cabinet called a “complete set”?
The switch cabinet is composed of incoming lines, meters, PTs, outgoing lines, etc. The cabinet is equipped with primary and secondary components, which must be matched when used, so it is called a “complete set”. - How many levels are there in power voltage, and what is the role of the classification?
Answer: It is divided into 500KV, 220KV, 110KV, 35KV, 10KV, 380V, 220V and other levels.
Since the voltage is related to line loss, the higher the voltage, the lower the line loss. Therefore, the power grid often uses high-voltage transmission. The longer the distance of power transmission, the higher the voltage level. - Why do we need to discharge (10KV level)? What methods can be used to discharge safely?
Answer: When the power is cut off, in order to prevent the capacitor from having residual electricity and injuring people, the voltage must be removed.
Safe method of removing voltage: When opening the cabinet door or screen, do not touch the busbar directly with your hands. First use a 10KV test pen to check whether there is electricity, then find a wire, one end is grounded and the other end is connected to the front end of the test pen, and use the front end of the test pen to touch the busbar to discharge. After completion, maintenance can be carried out to ensure personal safety. Remember this. - What should the voltage of the 10kV test electricity be? What is the difference between domestic and international standards?
Answer: Domestic: 42kV for cabinet body, 48kV for break; International: 36kV. - What is the function of the pressure relief channel?
Answer: If the cabinet explodes, a strong air wave will be generated. At this time, if there is a pressure relief channel on the top of the cabinet, the air wave can be discharged from the top without affecting the normal operation of other parts; if there is no pressure relief channel, the air wave will rush to the weakest place. - What are the main primary components that should be installed in the switch cabinet?
Answer: Circuit breaker, lightning arrester, zero-sequence transformer, current transformer (CT), voltage transformer (PT), high-voltage fuse, etc. - What is the function of the ring network switch cabinet? How to protect the transformer?
Answer: The function is to open and close the switch with load, and it relies on high-voltage fuses to protect the transformer. - What is the national standard for air insulation distance?
Answer: The air distance between phases and relative to the ground, 10KV requires 125mm. - What is the creepage distance of insulating parts?
Answer: The conduction distance from the high-voltage live side to the ground, creeping along the surface of the insulating parts, is called the creepage distance of insulating parts. 10KV requires 235mm. - What method is used to check whether the vacuum switch is vacuum?
Answer: Use the withstand voltage test. The break is tested with 48kV. - What is the function of the isolating switch and what kind of cabinet is it used for?
Answer: The isolating switch is used for fixed cabinets. It is operated without load and provides a clear break for easy maintenance. - What is the function of the high-voltage fuse?
Answer: It is used to protect the transformer. Note: PT is a small transformer. - What is the function of the live display?
Answer: It serves as an indicator to show whether there is high voltage in the cabinet. - What is the function of the program lock?
Answer: The operation sequence of the cabinets is interlocked according to the prescribed procedure to prevent misoperation. - What is the function of the grounding switch?
Answer: The grounding switch is installed at the outlet end to prevent reverse supply of high voltage electricity during maintenance and ensure personal safety. - What is the function of the valve?
Answer: When the trolley is pulled away from the cabinet, it prevents people or metal from coming into contact with the static contact with high voltage. - Why should the busbar be covered with rubber?
Answer: It plays an insulating role, which can reduce the air insulation distance and prevent small animals from entering the cabinet and causing short circuit accidents. - What is the function of the lightning arrester? Why does each set of cabinets have at least one lightning arrester?
Answer: Lightning arresters are designed according to voltage levels and must not be installed incorrectly. Some are designed differently according to different uses. For example: power plant output, line operation, capacitors, and power stations.
The main function of the lightning arrester is to absorb the overvoltage generated in a certain section of the line to achieve the purpose of safe operation of the line. For example, the incoming cabinet has a set of lightning arresters to protect the safety of the lines in the cabinet; the external power supply has been equipped with a lightning arrester when entering the cabinet, so if the external power supply generates high voltage, it is safer when entering the cabinet because of the protection of the lightning arrester; the lower end of the outgoing cabinet is equipped with a lightning arrester, mainly considering that the vacuum circuit breaker will generate overvoltage when opening and closing, so the lightning arrester must be installed instead of the overvoltage absorber.
- Talk about the functions of current transformer and zero-sequence transformer.
Answer: Current transformer plays the role of measurement, metering and protection; zero-sequence transformer plays the role of protection. - Can the current transformer be assembled in reverse? Why?
Answer: The normal flow direction is L1→L2. If it is from L2→L1, the secondary line design needs to be modified. - What is the function of the humidity controller?
Answer: The humidity is detected by the induction probe. If it exceeds the normal humidity, it is adjusted by heating the heating plate. There are two operation modes: automatic and manual. - What is the function of the primary scheme diagram?
Answer: It represents the components and directions installed on the main circuit line - What do the terms PT and CT stand for?
Answer: PT—voltage transformer, CT—current transformer - What do AC and DC stand for?
Answer: AC—alternating current, DC—direct current - What is the function of a vacuum circuit breaker?
Answer: It can open and close the circuit breaker with load, and extinguish the arc by using a vacuum arc extinguishing chamber (vacuum bubble). - Classification of circuit breakers:
Answer: (1) Vacuum circuit breaker: uses vacuum (vacuum degree is less than 100,000 columns of mercury) as arc extinguishing medium and main insulating medium. The moving and static contacts of arc extinguishing are sealed in the vacuum arc extinguishing chamber. The main voltage levels are 10VK and 35KV.(2) Sulfur hexafluoride circuit breaker: It was introduced relatively late. It was not widely used until the early 1970s. It is now an advanced equipment in the power system. It uses SF6 gas as the arc extinguishing medium. The breaking capacity is about 10 times higher than that of ordinary circuit breakers. The arc voltage is low. The arcing time is short, the contact burns less, and it can be operated frequently. Disadvantages: SF6 is expensive. A recovery device is required, and the structure is more complicated. my country has manufactured a fully enclosed combination electrical appliance with an attendance rate of 220KV and SF6 as the main body. The circuit breaker, disconnector, transformer, lightning arrester, busbar and other main equipment of the substation are all installed in a sealed container filled with SF6 gas, which greatly reduces the space occupied by the substation. It is the main development direction of ultra-high voltage electrical appliances. It has been widely used abroad.(3) Circuit breaker: Compressed air is used as arc extinguishing medium. It is currently the main product in the field of ultra-high voltage. China produces 380KV. Foreign countries have produced 765KV.(4) Self-produced circuit breaker: The fixed medium is decomposed into gas by the arc to blow the arc to extinguish the arc. The voltage is low and the interruption current is small. It is suitable for agricultural electronic systems.(5) Magnetic blow circuit breaker: The magnetic field is used to blow the arc into the arc extinguishing grid. - Power transformer
Answer: A transformer is an electrical device that converts voltage (current). It cannot convert power.
Basic structure: It mainly consists of a closed iron core and two coils (i.e. windings) with different turns and insulated from each other. In order to reduce eddy current and hysteresis loss, the iron core is made of silicon steel sheets with good magnetic conductivity and coated with insulating paint and a thickness of 0.35-0.5mm. It constitutes the closed magnetic circuit in the transformer. The primary coil is called the thick coil primary side, and the secondary coil is called the secondary coil. The three-phase transformer group connected by three single-phase transformers is the three-phase transformer. - Current transformer
Answer: The basic structure is the same as that of ordinary transformers, which is also composed of primary winding, iron core and secondary winding. When in use, the primary side is connected in series with the load of the circuit to be measured, and the secondary side is connected in series with a 5A ammeter and protection circuit. The primary side uses thick wires with only one or a few turns, and the secondary side wires are very thin with many turns. According to the operating principle of the transformer: the ratio of the primary and secondary currents of the current transformer should be inversely proportional to the ratio of the primary and secondary turns: IN1/IN2=N2/N1, (IIN1, IN2 are the primary and secondary currents respectively, N1, N2 are the primary and secondary coil turns respectively). - Voltage transformer
Answer: Basic structure: It is a special transformer that expands the voltage range. Its basic structure is the same as that of an ordinary transformer. Therefore, the voltage ratio of the primary and secondary sides of the voltage transformer is U1/U2=N1/N2 (N1 and N2 are the number of turns of the primary and secondary coils, respectively). - High-voltage insulators
Answer: The function of high-voltage insulators is to support and fix the busbar and the live conductor, and to ensure that there is sufficient distance and insulation between the live conductors or between the conductor and the ground; the insulation of the insulator is obtained by the surface shape. Insulators of different voltage levels have different effective heights and different surface conditions. The surface is made into high and low concave and convex skirts to increase its surface length.
