What Is a Power Distribution Unit?

The section of the power system that exports from the step-down distribution substation (high-voltage distribution substation) to the user end is called the power distribution system. The power distribution system is a power network system that consists of a variety of power distribution equipment (or components) and power distribution facilities to convert voltages and directly distribute electrical energy to end users.

Traditionally, the power system is divided into three major systems: power generation, transmission, and distribution.

The power generated by the power generation system is transmitted by the power transmission system, and finally distributed to various users by the power distribution system.

Generally, the section of the power system that exports from the step-down distribution substation (high-voltage distribution substation) to the user end is called the power distribution system.

The power distribution system is a power network system that consists of a variety of power distribution equipment (or components) and power distribution facilities to convert voltages and directly distribute electrical energy to end users. ^[1]

In China, the power distribution system can be divided into high-voltage power distribution

The safe operation management of transformers is the focus of our daily work. Through the summary of the experience of abnormal operation conditions and common fault analysis of transformers, it will help to timely and accurately judge the cause and nature of the fault, and take effective measures in time to ensure the safe operation of the equipment. .

Transformers are extremely important electrical equipment in the power transmission and distribution system. According to the operation and maintenance management regulations, transformers must be inspected regularly in order to understand and grasp the operation of the transformer in a timely manner, take effective measures in a timely manner, and strive to eliminate the fault in the bud state. Ensure the safe operation of the transformer. The abnormal operation and common faults of the transformer are as follows:

1. The sound of the transformer is abnormal.

2. Under normal load and normal cooling mode, the transformer oil temperature keeps rising.

Third, the transformer insulation oil color changes significantly.

Fourth, the oil pillow or explosion-proof pipe is sprayed.

Fifth, three-phase voltage imbalance occurs.

Sixth, the operation of the relay protection.

7. Flashover and explosion of insulating porcelain casing.

8. Failure of the tap-changer. ^[1]

According to the various protection methods and terminologies defined by the IEC, the low-voltage power distribution system is divided into three categories according to the different grounding methods, namely TT, TN, and IT systems, as described below.

TT method

The power supply and distribution systems in China and enterprises have a huge waste of power. The problems are manifold. The main problems and solutions are as follows.

Current grid capacity and load do not match

With the economic development and the improvement of people's living standards, the power consumption has increased rapidly. The equipment and wires of the original distribution network did not match the power consumption. Many places were overloaded, which not only affected the safety of power supply, but also greatly Increased losses in the power distribution system. The way to save energy is to update the lines and equipment.

Unreasonable power supply voltage

In some areas and many larger power consumption units, the supply voltage is low. For example, in the past, the line voltage of enterprises should be 6,000 volts, and multiple voltage reductions were required in the middle, which required more construction funds and increased the power of the system. loss. Properly increasing the power supply voltage and reducing the original two or even three voltage drops to one can greatly reduce the equipment and line losses of the power supply system.

The layout is not reasonable

In many areas, electricity consumers and enterprises use electrical equipment far away from the power distribution center, which makes the low-voltage (0.4 kV) transmission distance too long, causing great line losses and voltage drops. This situation is common in the old large and medium-sized enterprises, because the design stipulated that the power distribution center should be built at the end of the company's incoming power. The improvement measures are to keep the distance between the power distribution center and the power equipment as close as possible under the premise of safety, and change the original low-voltage long-distance power transmission to high-voltage long-distance, low-voltage short-distance power transmission, which can greatly reduce the power transmission line. loss.

Reactive power shortage

With the economic development, the inductive load in the power supply and distribution system has increased rapidly.

DC screen of power distribution system

DC screen is short for DC power operating system. Commonly known as intelligent maintenance-free DC power screen, referred to as DC screen, the general model is GZDW. Simply put, a DC screen is a device that provides stable DC power. (When the input has 380V power, it will be directly converted to 220V. When there is no input from mains and backup power, it will be directly converted to battery power-DC 220V: it can actually be said to be an industrial emergency power supply. The power operating power sources in power plants and substations are currently using DC power supplies, which provide power for controlling loads and dynamic loads, as well as DC accident lighting loads, etc., and are the basis of contemporary power system control and protection. The DC screen consists of AC power distribution unit, charging module unit, step-down silicon chain unit, DC power feeding unit, power distribution monitoring unit, monitoring module unit and insulation monitoring unit. It is mainly used in small and medium-sized power plants, hydropower stations, various types of substations, and other users using DC equipment (such as petrochemicals, mines, railways, etc.). Electrical protection and fault lighting.

The DC screen is a new type of DC system with digital control, protection, management and measurement. The monitoring host part is highly integrated and adopts a single board structure (All in one), which includes insulation monitoring, battery inspection, ground selection, battery activation, silicon chain voltage stabilization, and microcomputer central signal. The host is equipped with a large LCD touch screen, and various operating states and parameters are displayed in Chinese characters. The overall design is convenient and concise, and the human-machine interface is friendly, which is in line with user habits. The DC screen system provides powerful functions for remote detection and control, and has remote control, remote adjustment, remote measurement, remote signaling functions and remote communication interfaces. The operating parameters of the DC power supply system can be obtained remotely through the remote communication interface, and the operating status and setting values can be set and modified through this interface to meet the requirements of unmanned substations for power automation and power systems; Line interface and Ethernet interface can be easily incorporated into the power station automation system.

Microcomputer protection of power distribution system

The microcomputer protection device is a relay protection composed of a microcomputer, which is the development direction of power system relay protection (now basically realized, and needs to be developed). It has high reliability, high selectivity and high sensitivity. The hardware of the microcomputer protection device includes a microprocessor (Single Chip Microcomputer) as the core, with input and output channels, human-machine interface and communication interface. The system is widely used in power, petrochemical, mining, railway, and civil buildings. The hardware of the microcomputer is universal, and the performance and function of protection are determined by software.

The digital core of the microcomputer protection device is generally composed of CPU, memory, timer / counter, Watchdog, etc. At present, the mainstream of digital cores is embedded microcontrollers (MCUs), commonly known as single-chip microcomputers. The input and output channels include analog input channels (analog input conversion circuits (converting the quantities measured by CT and PT into lower Internal A / D conversion voltage amount, ± 2.5V, ± 5V or ± 10V), low-pass filter and sampling, A / D conversion) and digital input and output channels (man-machine interface and various alarm signals, trip signals) And electrical pulses, etc.). ^[2]