2.0 Various Electrical switchgear knowledge

20. What is the function of lightning arrester? Why does each cabinet have at least one lightning arrester?

The lightning arrester is designed according to the voltage level and must not be installed incorrectly. Some are also designed differently based on different purposes. For example, power plants that output electricity, those with line operation, and those with capacitors.

Lightning arrester is mainly used to absorb excessive voltage generated in a certain section of the line to achieve the goal of safe operation of the line. For example, the incoming cabinet has a set of lightning arresters that can protect the safety of the lines inside the cabinet; When the external power supply enters the cabinet, it is already equipped with a lightning arrester, so if the external power supply generates high voltage, it is safer to enter the cabinet due to the protection of the lightning arrester; The lower end of the outgoing cabinet is equipped with a lightning arrester, mainly considering the overvoltage phenomenon that may occur during the opening and closing of the vacuum circuit breaker. Therefore, a lightning arrester must be installed to replace the overvoltage absorber.

22. Describe the functions of current transformers and zero sequence transformers.

The current transformer plays a metering protection role;

The zero sequence transformer plays a protective role.

23. Can the current transformer be reassembled? Why?

The normal flow direction is L1 → L2. If it changes from L2 to L1, the secondary line design needs to be modified.

24. What is the difference between VE cabinet and ring network cabinet?

VE cabinet (manual vehicle) is opened with a circuit breaker to protect the transformer for 0.2 seconds

High voltage fuse protection transformer for loop main cabinet (fixed type) for 0.02 seconds

25. What is the function of the humidity controller?

Detect the humidity through an induction probe, and if it exceeds normal humidity, adjust it by heating the heating plate. There are two modes of operation: automatic and manual.

26. What is the purpose of a plan diagram?

Represents the components and direction assembled on the main circuit line

27. What do PT and CT terms represent?

PT - Voltage Transformer, CT - Current Transformer

28. What do AC and DC terms represent?

AC-alternating current, DC-direct current

29. How many operating mechanisms are there for circuit breakers?

Magnetic suction for manual, automatic power distribution, magnetic, spring, and contactor. For example, the low-pressure air switch is manually operated

CD10 or CD17 (electromagnetic mechanism) for high-pressure vacuum switches

Using CT8 or CT19 (spring mechanism)

30.What is the function of the air switch cabinet and how does it protect the transformer?

Its function is vacuum arc extinguishing, which can be opened and closed with load for power transmission. The transformer is protected by cutting off current through current transformers and instruments. Other components can also be installed for other purposes.

31. What does a vacuum circuit breaker do?

Capable of opening and closing with load, using vacuum arc extinguishing.

32. What should be the stroke of the vacuum switch?

Stroke: 11 ± 1 Spring compression: 4 ± 1 VE: 8 ± 0.5

33. Classification of circuit breakers:

(1) Vacuum circuit breaker: Use vacuum (with a vacuum degree below 100000 mercury) as the arc extinguishing medium and main insulation medium. The dynamic and static contacts for arc extinguishing are sealed in the vacuum arc extinguishing chamber. Mainly 10VK. 35KV voltage level.

(2) Sulfur hexafluoride circuit breaker: came out relatively late. It was widely used in the early 1970s and is currently an advanced equipment in the power system, using SF6 gas as the arc extinguishing medium. The cutting capacity is about 10 times higher than that of a typical circuit breaker. Low arc voltage. Short arcing time, less contact damage, and can be operated frequently. Disadvantage: SF6 is more expensive. Requires a recycling device with a complex structure. China has manufactured fully enclosed composite electrical appliances with a attendance rate of 220KV and SF6 as the main component. Turn on the circuit breaker and isolation switch. Transformer, lightning arrester. The main equipment of the substation, such as busbars, are all installed in sealed containers filled with SF6 gas, greatly reducing the space occupied by the substation. It is the main direction for the development of ultra-high voltage electrical appliances. It has been widely used abroad.

(3) Circuit breaker: uses compressed air as the arc extinguishing medium. Currently, it is the main producer in terms of ultra-high pressure. I produce 380KV domestically. 765KV has been produced abroad.

(4) Self produced circuit breakers: use fixed media to decompose into gas under the action of an arc for arc blowing to extinguish the arc. Low voltage and low interruption. Suitable for agricultural electronic systems.

(5) Magnetic blowing circuit breaker: Use a magnetic field to blow an arc into the arc extinguishing grid.

34. Power Transformer

A transformer is an electrical device that converts voltage (current). It cannot change power.

Basic structure: It mainly consists of a closed iron core and two coils (i.e. windings) wound on the iron core with different turns and insulated from each other. In order to reduce eddy current and hysteresis losses, the iron core is made of silicon steel sheets coated with insulation paint, with a thickness of 0.35-0.5mm and good magnetic conductivity. It forms the closed magnetic circuit in the transformer. The primary coil is called the thick coil type primary edge, and the secondary coil is called the secondary coil type secondary edge, A three-phase transformer group formed by connecting a three-phase single-phase transformer is a three-phase transformer.

35. Current transformer

Basic structure: A current transformer is a converter used to expand the range.

The basic structure is the same as that of an ordinary voltage device, which is also composed of an iron core and an original and auxiliary coil wound on the iron core. When used, the primary side of the main device is connected in series with the load of the circuit under test, and the auxiliary side is connected in series with the 5A ammeter and the current coil of the protective relay. Because its primary side uses a thick wire, its turns are only one or several, so its cathode is small and the voltage is very low. After being connected in series with the circuit under test, the supplementary current is not changed. The secondary side wire is very thin and the turns are many, But its induced potential is not high (only a few volts), and the resistance of the secondary ammeter and relay coil is very small. When working, the secondary side can be considered as a short circuit state. According to the operating principle of the transformer, the ratio of the primary side current of the charging transformer should be inversely proportional to the number of turns:

L1/L2=W2/W1 or L1=W2/W1L2. W2/W1=K2 transformation ratio.

36. Voltage transformer

Basic structure: It is a special transformer that expands the voltage range, and the basic structure is the same as that of a regular transformer. Therefore, the voltage relationship between the primary and secondary sides of the voltage transformer U1/U2=W1/W2.

37. Lightning arrester

Basic principle: When overvoltage is transmitted. Simultaneous breakdown of internal and external gaps S1 and S2. The strong lightning current flows into the ground through the grounding device, limiting the amplitude of overvoltage.

One of the largest lightning accidents in China: a major fire at the Huangdao Oil Depot in Shandong on August 12, 1989. 19 people died and 78 were injured. 3. 60000 tons of crude oil were swept away by the fire. Direct losses of tens of millions of yuan.

38. High voltage insulators

High voltage insulator function: used to support and fix the busbar and live conductors, and ensure sufficient distance and insulation between live conductors or between conductors and the earth; Insulator insulation is obtained by surface shape.

Insulators of different voltage levels. Except for having different effective heights. The surface condition is also different. The surface is made into high and low concave and convex skirt edges. To increase its surface length.

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