Some electrical equipment terms

Some electrical equipment terms

Why is the switchgear called a “complete set”, and what cabinets are they made of?

The switchgear is composed of incoming lines, metering, PT, and outgoing lines, etc. The cabinet is equipped with primary and secondary components, which must be matched at the time of purchase, so it is called “complete set”.

How many levels are there in China’s power voltage, and explain the role of the levels?

Divided into 500KV, 220KV, 110KV, 35KV, 10KV, 380V, 220V levels,etc.

Since the voltage level is related to the line loss, the higher the voltage, the lower the line loss. In this way, the farther the electricity is delivered, the higher the voltage level that needs to be delivered.

Why should the voltage be unloaded (10KV level)? What method can be used to safely discharge the voltage?

In the event of a power outage, in order to prevent the remaining power of the capacitor from injuring personnel, the voltage must be unloaded.

The method of safely unloading voltage: When opening the cabinet door or the screen, do not touch the bus directly with your hands. First use a 10KV test pencil to check whether there is electricity, then find a wire, one end is grounded, the other end is connected to the front end of the test pen, and the front end of the test pen is connected to the bus bar to discharge. Repair can be done after completion to ensure personal safety. Remember this.

What is the voltage of the 10KV test circuit? What is the difference between domestic and international standards?

Domestic: the cabinet body is 42,000 volts, and the fracture is 48,000 volts;

International: 36,000 volts

What is the function of the pressure relief channel?

If an explosion occurs in the cabinet, a strong wave of air 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.

Which main primary components should the switchgear be assembled?

Circuit breakers, contact seats, arresters, zero sequence transformers, current transformers (CT), voltage transformers (PT), high-voltage fuses, etc.

What is the function of the ring main unit? How to protect the transformer?

The function is to open and close with load, it relies on high-voltage fuse to protect the transformer.

What is the national standard for air insulation distance?

The air distance between the phases to the ground, 10KV requires 125mm.

What is the creeping distance of insulating parts?

The conduction distance from the high-voltage live side to the ground and crawling along the surface of the insulating part is called the creeping distance of the insulating part. 10KV requires 235mm.

What method is used to check whether the vacuum switch is vacuum?

Use the withstand voltage test to detect. The fracture is detected with 48,000 volts.

What are the functions of isolation plugs and isolation switches, and which cabinets are they used for?

The isolation plug is used for the handcart cabinet; the isolation switch is used for the fixed cabinet. Its function is to open and close without load, which is convenient for maintenance.

How many levels of high-voltage cabinet current is roughly divided? Which level is the load switch?

Divided into large, medium and small, namely: 3150A, 1250A, 630A three levels. The load switch is 630A level.

What is the function of high-voltage fuse?

Used for protecting transformers, PT belongs to small transformers.

What is the function of the charged display?

As an indicator, it shows whether there is high voltage in the cabinet.

What is the function of the earthing switch?

The earthing switch is installed on the outgoing line, which can prevent high-voltage power supply during maintenance and ensure personal safety.

What is the function of the shutter mechanism?

When the handcart is pulled away from the cabinet, prevent people or metal from contacting the static contact with high voltage.

Why should the busbar be rubberized?

Play an insulating role, reduce the air insulation distance, and prevent short-circuit accidents caused by small animals entering the cabinet.

What is the role of the arrester? Why is there at least one lightning arrester for each group of cabinets?

The arrester is designed according to the voltage level and must not be installed incorrectly. Some are also designed differently according to different uses. Such as: power plant output power, line operation, and capacitor.

The lightning arrester is mainly used to absorb the high voltage 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 circuit inside the cabinet; while the external power supply is already equipped with a lightning arrester when it enters the cabinet, so if the external power supply generates high voltage, it will be compared when entering the cabinet due to the protection of the lightning arrester. Safety; The lower end of the outlet cabinet is equipped with a lightning arrester, which is mainly to consider the overvoltage phenomenon when the vacuum circuit breaker is opened and closed. Therefore, a lightning arrester must be installed to replace the overvoltage absorber.

How to distinguish phase color and phase arrangement?

Yellow	Green	Red	Blue	Yellow and green
A	B	C	Neutral
Left	Middle	Right	Leftmost
Rear	Middle	Front	Forefront
Up	Middle	Down	Lowest

The role of current transformers and zero-sequence transformers?

Current transformer plays a role of metering protection;

The zero sequence transformer plays a protective role.

Can the current transformer be reversely assembled? Why?

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

What is the function of the humidity controller?

The humidity is detected by the inductive probe, and if it exceeds the normal humidity, it is adjusted by the heating plate to generate heat. There are two modes of operation: automatic and manual.

What is the role of primary scheme diagram?

Represents the original assembly and direction of the main circuit

What do PT and CT represent?

PT—voltage transformer, CT—current transformer

What do the names of AC and DC stand for?

AC—Alternating Current, DC—Direct Current

How many operating mechanisms does the circuit breaker have?

Magnetic attraction for manual and automatic power distribution, magnetism, springs, and contactors. Such as: low pressure air switch with manual

CD10 or CD17 (electromagnetic mechanism) for high-voltage vacuum switch, CT8 or CT19 (spring mechanism)

What is the function of the air switchgear, and what does it rely on to protect the transformer?

Its function is vacuum arc extinguishing, which can be opened and closed with load for power transmission, and the transformer is protected by the current transformer and the instrument to cut off the current. Other components can also be installed for other purposes.

What role does the vacuum circuit breaker play?

It can open and close with load, and use vacuum to extinguish arc.

Classification of circuit breakers:

(1) Vacuum circuit breaker: Use vacuum (vacuum degree below 100,000 Hg) as the arc extinguishing medium and the main insulation medium. The static and dynamic contacts of the arc extinguishing chamber are sealed in the vacuum arc extinguishing chamber. There are mainly 12kV, 24kV, 40.5kV voltage level.

(2) SF6 circuit breaker: It was widely used in the early 1970s, and it is now 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 general circuit breakers. The arc voltage is low. The arcing time is short, the contact burns less, and it can be operated frequently. Disadvantages: SF6 circuit breaker is more expensive. A recovery device is required, and the structure is more complicated. Our country has manufactured 220KV fully enclosed combined electrical appliances with SF6 circuit breakers as the main body. The main equipment of the substation such as circuit breaker, isolating switch, transformer, arrester, busbar, etc. are all installed in a sealed container filled with SF6 gas, which greatly reduces the space occupied by the substation and is the main direction for the development of ultra-high voltage electrical appliances. It has been widely used abroad.

(3) Circuit breaker: use compressed air as the arc extinguishing medium. In terms of ultra-high pressure, it is currently the main producer. China produces 380KV. 765KV has been produced abroad.

(4) Self-produced circuit breaker: Use a fixed medium to be decomposed into gas by the arc to blow the arc to extinguish the arc. The voltage is low and the current is small. Suitable for agricultural electronic systems.

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

Power Transformer

A transformer is an electrical device that transforms voltage (current). It cannot convert power.

Basic structure: It is mainly composed of a closed iron core and two coils (ie windings) with different turns and insulated from each other on the iron core. In order to reduce the eddy current and hysteresis loss, the iron core is coated with insulating paint. It is composed of 0.35-0.5mm silicon steel sheets with good magnetic permeability. It forms the closed magnetic circuit in the transformer. The primary coil is called the thick coil type primary side, and the secondary coil is called the secondary coil type secondary side, which is connected by a three-way single-phase transformer. The completed three-phase transformer group is a three-phase transformer.

Current transformer

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

The basic structure is the same as the ordinary voltage transformer, which is also composed of the iron core and the primary and secondary coils wound on the iron core. When in use, the primary side of the main is connected in series with the load of the circuit under test, and the secondary side is connected in series with a 5A ammeter and a protection relay current coil. The primary side uses a thick wire, the number of turns is only one or a few turns, but its electric cathode is small, the voltage is very low, and it does not change the compensation current after it is connected to the circuit under test. The secondary side wire is very thin and the turns There are many, but its induced potential is not high (only a few volts). The secondary side ammeter and relay coil resistance are very small. When working, the secondary side can be regarded as a short-circuit state.

According to the operating principle of the transformer: the ratio of the primary current of the electric charging transformer should be inversely proportional to the number of turns: L1/L2=W2/W1 or L1=W2/W1L2. W2/W1=K2 transformation ratio.

Voltage transformer

Basic structure: It is a special transformer that expands the voltage range, and the basic structure is the same as that of an ordinary transformer. Therefore, the voltage relationship between the primary side of the voltage transformer and the auxiliary power is U1/U2=W1/W2.

Lightning arrester

Basic principle: When an overvoltage is transmitted. The internal and external gaps S1 and S2 break down at the same time. The strong lightning current flows into the ground through the grounding device to limit the amplitude of the overvoltage.

One of the largest lightning accidents in China: August 12, 1989, a huge fire at the Huangdao Oil Depot in Shandong. 19 people were killed and 78 people were injured. 36,000 tons of crude oil was bypassed by the fire. Direct losses of hundreds of millions of yuan.

High voltage insulator

High-voltage insulator function: used to support and fix the bus bar and the live conductor, and make the live conductor or between the conductor and the earth, there is sufficient distance and insulation; the insulator insulation is obtained by the surface shape.

Insulators of different voltage levels have different effective heights, and their surface conditions are also different. The surface is made of high and low uneven skirts to increase the surface length.