Guizhou electrical equipment factory analyzed that the surge has different degrees of harm to electrical equipment, surge failure is inevitable, but through effective protective measures to reduce its harm to electrical equipment. This paper will discuss the surge protection of electrical equipment room.

1. Overview

With the continuous progress of society, the construction speed and construction scale of highway, railway, bridge and other engineering projects continue to grow, which greatly promotes the development of China's economy. The safety protection of electrical equipment room is of practical significance for the healthy development of China's transportation industry. For electrical equipment, surge is a relatively common phenomenon. According to the relevant statistics at home and abroad, the degree of harm caused by surge is different, but the accumulation of different degrees of harm will have a destructive impact. According to the statistics of our country, 63% of the faults of electrical equipment in the warranty period are caused by surge. This paper will discuss the harm and protection of surge.

2. Surge and its harm

2.1 concept of surge the phenomenon that the instantaneous voltage of electrical equipment exceeds the normal working voltage during operation is called surge, which can also be referred to as transient pulse voltage, transient overvoltage or surge. The time of surge is very short, usually one millionth of a second.

2.2 the main causes of surge are external causes and internal causes. The external causes are mainly due to lightning, while the internal causes are due to operational errors.

2.2.1 lightning causes surge. There are many reasons for the surge, but the lightning surge is the most harmful. When the lightning discharge occurs, dangerous overvoltage will occur within the radius of 1.5-2km. The surge caused by lightning stroke belongs to single pulse type with huge energy. It takes only a few microseconds for external surge voltage to rise from normal value to 2KV high voltage state, and the transmission distance is long. Specifically, there are four types of lightning induced surge, and their main characteristics are shown in Table 1.

2.2.2 surge caused by operation. When the power equipment is operated, the operation parameters of the system will be affected, which will lead to the transition of electromagnetic energy conversion (transmission) within the power system, thus causing the surge in the power system. As far as the causes of the surge are concerned, the following are the main reasons for the surge: the input and removal of large power load; the input or removal of inductive load; the input or removal of power factor compensation container; the transfer and removal of power factor compensation container; Short circuit fault. In the above reasons, more than 80% of them are caused by electrical load. The main characteristic of surge caused by power system is oscillation type, which oscillates between transformer, inductive load and capacitor, and the content of high-order harmonic component is relatively high. When it is in the peak of power consumption, the performance of this kind of surge is more prominent.

2.3 the harm of surge. The causes of surge are complex. Once the electrical equipment encounters overvoltage, it may cause data loss or damage, and in serious cases, it may affect the normal operation of the equipment. Lightning is the most destructive to electrical equipment, which is also the focus of electrical equipment room in road and bridge engineering. According to the damage degree, it can be divided into destructive hazard and cumulative hazard. For example, the insulation voltage of a 220 V motor is generally 1500 v. when the over-voltage caused by the change of external environment exceeds this value, the insulation layer will be broken down, causing disaster; when the over-voltage value is small, the small surge accumulation effect will affect the performance of the components in the electrical equipment, and then induce failure or shorten the life of the equipment.

3. Surge protection

3.1 protection principle surge is inevitable, and the energy contained in it is extremely strong, which can not be prevented. It is an ideal protection strategy to use advanced technology to separate the surge and sensitive electrical equipment. The best surge protection device should have no impact on the power system. Only when the voltage reaches a certain limit, it will act and shunt excessive energy into the ground. Mov technology can meet this requirement. The principle of MOV technology is as follows: under normal conditions, it will be hung on the power line, without any impact on the normal operation of the power supply. When there is a surge, it will react immediately to protect the power supply from being damaged. Generally, the voltage value of the equipment is preset. When the working voltage reaches this set value, MOV will react immediately, and the time is only 1-3 nanoseconds. The instantaneous resistance of the protector decreases from the complete value to nearly zero ohm, which almost causes a short circuit to the electrical equipment, and the instantaneous high voltage enters the ground from MOV, so as to achieve the purpose of protecting the electrical equipment.

3.2 analysis of surge protection measures for electrical equipment room

3.2.1 protection of electrical equipment beyond the protection scope of lightning arrester. The main function of lightning protection equipment is to prevent the direct effect of lightning on the electrical equipment room, and to protect all kinds of metal pipelines and electrical equipment within the protection scope of the lightning arrester. The scope of the protection equipment has certain limitations, which can not protect the metal wires or electrical equipment outside the protection range of the lightning arrester, and can not prevent the direct lightning Damage to electrical equipment caused by induced lightning. Therefore, surge protector should be installed in the electrical equipment room to ensure the safety of internal power supply and data line.

3.2.2 the grounding of machine room cannot replace surge protection. Electrical equipment grounding is the requirement of normal operation of equipment. The main function of machine room grounding is to eliminate the accumulation of static electricity and protect the safety of electrical equipment and personnel. But the grounding of computer room does not have the function of lightning protection