Introduction to voltage levels in power system

In the previous article, we introduced the components of the power system, mainly including, the power source, the power network and the power load center. The power network is further divided into transmission system and distribution system. This article mainly introduces the voltage levels commonly used in transmission and distribution systems.

Various power devices in the power system have their own rated voltages, which constitute the voltage level of the entire power system. The voltage used for transmission is higher than the distribution voltage. The division of transmission and distribution voltage boundaries is not fixed and varies with the area covered by the grid and the size of its capacity.

The domestic power system voltage levels are 220/380V (0.4 kV), 3kV, 6kV, 10kV, 20kV, 35kV, 66kV, 110kV, 220kV, 330kV, 500kV.

Common transmission voltage classification:

High voltage power transmission: ≤ 220KV;

Ultra-high voltage power transmission: 330 ~ 765 KV; (commonly used 330KV, 500KV, 750KV)

UHV power transmission: ≥1000KV (AC) / ±800KV (DC)

Distribution voltage classification:

Low voltage distribution voltage: 220V/380V

Medium voltage distribution voltage: 10KV(20KV)

High voltage distribution voltage: 35~110KV

In some countries, the high-voltage distribution voltage is also called the secondary transmission voltage, the medium-voltage distribution voltage is also called the primary distribution voltage, and the low-voltage distribution voltage is also called the secondary distribution voltage.

The power supply mode of the power distribution system is divided into AC power supply and DC power supply.

Commonly used AC power supply methods:

① Three-phase three-wire system. Divided into delta connection (0.4kv motor and lighting) and star connection (for low-voltage three-phase 0.23kv industrial lighting distribution and 0.23kv three-phase motor).

② Three-phase four-wire system. It is used for 0.4kv/0.23kv low-voltage power and lighting hybrid power distribution.

③ Single-phase single-wire system 27.5kv. Commonly used in electric railway traction power supply.

④ Single-phase two-wire system 0.23kv (obtained by three-phase four-wire system). Mainly supply residential electricity.

Commonly used DC power supply methods:

① Two-wire system. It is used for power supply of urban trolleybuses, subway locomotives, mine traction locomotives, etc.

② Three-wire system. Supply power plants, substations, and distribution stations for their own use and secondary equipment, as well as electricity for electrolysis and electroplating.

Various voltage levels of the power system are converted by power transformers, so the substations are divided into step-up and step-down.

High and low voltage distribution cabinet

The high and low voltage power distribution cabinet is the power distribution equipment used for power distribution, control, measurement and connection of cables in the power supply system. Generally, power supply bureaus and substations use high-voltage power distribution cabinets, which are then stepped down by transformers to low-voltage switchgears, and then to each power distribution board, control box, and switch box. Inside is a power distribution device that meets the design functional requirements by assembling some switches, circuit breakers, fuses, buttons, indicator lights, meters, wires and other protective devices into one. 

Low-voltage switchgear is suitable for power plants, petroleum, chemical industry, metallurgy, textile, high-rise buildings and other industries, as power transmission, distribution and power conversion.

For equipment selection, energy-saving complete sets of equipment and stereotyped products are given priority, which are economical and reliable.

Xichi Electric provides customers with complete sets of high and low voltage equipment. Advanced equipment, technical processing and assembly by skilled workers, and good testing conditions ensure the quality of the complete set of equipment. 

Following are complete sets of equipment we provide:

KYN28-12 Indoor Metal Armored Withdrawable Switchgear

GCS-Low Voltage Withdrawable Switchgear

GGD-AC Low Voltage Power Distribution Cabinet

MNS-Low Voltage Combined Withdrawable Switchgear

GGJ-Low Voltage Reactive Power Compensation Cabinet

CGC-High Voltage Soft Grid-connected Device