1. Severe reality of electrical fires and defects in traditional inspections

Since the reform and opening up, China’s economic construction has made remarkable achievements. However, with the rapid economic development, the fire has been plaguing people. According to statistics, between 1999 and 2001, there were 119,029 electrical fires in the country with direct economic losses of 3.43 billion yuan. The proportion of electrical fires in the national fire has been on the rise: 7.2% in 1982, 27.5% in 1998, and more than 40% in some provinces and cities. In recent years, there have been some major fires: On December 8, 1994, a fire broke out at the Friendship Hall in Karamay, Xinjiang, killing 323 people and injuring 130 people, direct economic losses of 2.09 million yuan, and Beijing’s Longfu Building and Quanjude Roast Duck Restaurant. Hualong Lighting City and other fires are caused by electrical reasons. Therefore, how to detect electrical fire hazards early, reduce electrical fire damage, and establish a systematic and standardized electrical fire prevention system are particularly urgent. To this end, Beijing, Shanghai, Sichuan and other provinces and municipalities are based on the "Fire Law of the People's Republic of China," "Fire Supervision and Inspection Regulations," "Code for Fire Protection of Architectural Design" (GBJ16-87), and "Code for Design of Fire Protection of High-rise Civil Buildings" (GB50045). -95) and other relevant laws and regulations as well as IEC related standards, formulated the "Electrical Fire Safety Testing Technical Specifications", and formed a system of electrical fire safety testing, and introduced measures to conduct electrical fire detection intermediary services for buildings. This is an urgent need to protect the lives and property of the country and people, as well as an important means of preventing electrical fires.

The traditional electrical fire safety inspection is a simple and easy way to directly find out the fire hazard of electrical installations by relying on the experience of electrical instruments and people's five functions (visual inspection, oral measurement, auscultation, touching, smelling). Traditional methods cannot detect the hidden dangers of local overheating or spark discharge in electrical installations. Moreover, since China does not have a relatively comprehensive system of comprehensive electrical fire safety inspection standards, inspections relying only on these traditional methods cannot accurately diagnose and evaluate the potential hazards of electrical systems, resulting in some electrical lines and devices being exposed to harsh conditions for a long period of time. run. Although the initiation of a fire is random, under certain conditions, these hidden dangers may cause catastrophes and cause heavy losses. It is an important issue to prevent the occurrence of electrical fires by means of which methods can be used to accurately find local overheating and spark discharge that are not easily found by traditional means, and to establish a systematic and standardized system for diagnosing fire hazards in electrical systems. At present, electrical fire safety testing institutions use high-tech infrared and ultrasonic technologies and can quickly and safely detect equipment and loads under load using point thermometers, thermal imaging cameras, and ultrasonic probes. Over-temperature hot spots and sparks can visually see the fire hazard image display, which plays an important role in determining the fire safety of the distribution system operation.

Because of the tightness of the public security fire department and the detection methods, it is difficult to find "point-to-point" hidden dangers of electrical fire hazards during project acceptance and daily supervision and inspection. For example, in Mianyang City, Sichuan Province, the area is 20,249 square kilometers and the population is 5.2 million, of which the urban area is 50 square kilometers and 600,000 people, while the Mianyang detachment has only 83 cadres and only 42 fire protection cadres, obviously only relying on the fire department. The strength of one party is not enough, and the fire safety inspection agency service organization can organize professional and technical personnel to conduct a comprehensive search for the hidden dangers of building electrical safety, thus becoming an important part of the public security fire prevention department to effectively prevent electrical fire accidents.

2. Establishment and service scope of electrical fire safety testing agencies

2.1 Establishment of an institution

The professional organization for electrical fire safety testing is composed of senior and middle-level technicians in electrical and fire safety. It is equipped with testing equipment that meets standards. It is approved by a provincial-level fire monitoring agency after a strict qualification review in accordance with the law, and has an independent legal personality. The intermediary (third party) service functions defined in the "Enterprise Law" are supervised by public security fire control agencies in business and their test results must be fair and reliable.

2.2 Specific service scope

Testing of building electrical fire safety is done, testing technical data and documented reports are issued, inspection basis is provided for the fire supervision department, and the safety of the electrical facilities of the building is regularly tested, and the technical status of the use of these facilities is reported for the fire supervision department. According to the requirements of the fire supervision department, conduct special inspections on the electrical fire safety of individual places.

3, the main content of electrical fire safety testing intermediary services and commonly used testing equipment

3.1 The inspection work is mainly divided into two aspects:

On the one hand, it is checked whether the electrical installation complies with the regulations; on the other hand, testing equipment and instruments such as infrared and ultrasonic instruments are used for the detection of thermal images, hot spots, and electrical contact conditions on the lines and facilities with loads. Electrical fire safety inspections should take into account various fire protection measures. The measures taken from the aspects of building structure, electrical operation, insulation protection, and heat limitation are all objects and contents of testing.

3.2 Commonly used instruments:

Infrared thermometer, ultrasonic multi-function detector, grounding resistance tester, AC and DC clamp

Dual-use watches and so on.

4. To carry out the science and role of the intermediary service for electrical fire safety testing

The development of modern high-tech such as infrared, ultrasonic sensors and computers provides opportunities and possibilities for online detection and diagnosis of electrical devices overheating and spark discharge external characterization signals. The infrared detection method and the ultrasonic detection method can enable us to perform non-contact quick detection under the normal operating state of the electrical system and discover the overheating and spark discharge parts of the system.

4.1 Infrared detection method

In nature, all objects whose absolute temperature is higher than 0K will generate infrared radiation. The infrared radiation characteristics of objects, the size of radiation energy and their distribution according to wavelength are closely related to the surface temperature of objects. By measuring the infrared radiation energy of the measured object, the surface temperature of the object can be accurately determined. This is the basic principle of infrared temperature measurement.

4.1.1 Infrared spot thermometer is an instrument made by measuring the infrared radiation energy of the target as a function of temperature. The schematic diagram is shown in Figure 1:

During work, the infrared radiation energy of the measured target converges through the lens of the instrument and enters the infrared detector through the infrared filter. The detector converts the radiation energy into a power signal, which is then amplified by the amplifier, processed by the electronic circuit, and displayed by the liquid crystal display. The surface temperature of the measured object. This instrument is a non-contact, non-scanning infrared radiation temperature measurement device.

4.1.2 Infrared thermal television is a thermal imaging scanning device using the principle of thermoelectricity effect. It converts the infrared radiation on the surface of the target object to a video signal. The principle is shown in Figure 2.

The size of the signal current of the infrared thermal television is proportional to the target temperature change law dT/dt. In other words, thermal image cannot be established without change, or thermal image disappears quickly when the target is not moving. Therefore, infrared thermal television must be modulated to achieve image creation. There are three types of modulation methods:

(1) Translational Modulation - The working mode of translational modulation is to make relative motion between the measured object and the instrument. Therefore, when panning and modulating a hot TV, it is necessary to shake the instrument to establish an image and maintain an image. Due to constant shaking, the accuracy and positioning of the temperature measurement are affected, and at the same time the image is smeared, resulting in image distortion and low definition. ;

(2) Chopper wave modulation - Chop wave modulation is a method of periodically cutting off the incident infrared radiation of the measured target, and the motor-driven modulation disk is added in the instrument. The image is stable, clear, no smearing, no distortion, accurate temperature measurement, and convenient positioning. It is technologically advanced and practically advanced. The disadvantage is that the mechanical modulation and synchronous tracking technology is relatively complicated, prone to failure, and the price is high. ;

(3) Transient Modulation - Transient Modulation works by using the electronic shutter for photography and uses a thermal image of the target being shot. Its feature is to freeze the image and measure the temperature at any point on the image. The image is stable, without smearing, and the accuracy of temperature measurement is high. The disadvantage is that it cannot be continuously tracked and cannot continuously capture images.

4.1.3 The working principle of the optical imaging scanning system is to scan the target from left to right and from top to bottom. The target is divided into pixels and the thermal image properties and degree of the measured object will be decomposed. The pixel in the position is once ingested and converted into different bright, continuously-realistic images in less than 0.2 seconds and sent to an infrared detector.

4.2 Ultrasound detection

In the hidden dangers of electrical fire, the spark discharge formed by the virtual connection of wires, insulation leakage, insufficiency of joint contact, or the increase of local electric field intensity is highly concealed. If it cannot be eliminated in time, local overheat will be formed, which will ignite the flammable surrounding. Things. Because the spark discharge will emit ultrasonic waves higher than 20000Hz, the ultrasonic detector can catch the ultrasonic signal emitted by the spark discharge and convert the sound that can be heard by adults, thereby achieving the purpose of accurately diagnosing the hidden state of the spark discharge.

4.3 Comprehensive diagnostic methods for electrical fire hazards

Due to the complexity of the electrical system and the environment in which it is located, we must combine modern high-tech and traditional inspection methods to form a comprehensive set of general methods for electrical fire safety testing. We must cross-check and diagnose certain parts from different angles. The correct understanding and judgment of the location, nature, cause, and risk level of hidden dangers are made.

4.4 Diagnosis and implementation process of electrical fire hazards

The identification of potential fire hazards is a rigorous procedural process. Figure 4 is a block diagram of the process of diagnosis and implementation of electrical fire hazards.

According to the logical thinking process in the figure is summarized as follows: 1) In the field, the testing personnel should fully apply the traditional and modern detection methods, use audio and video, text, graphics and other carriers, widely collecting immediate status hidden information. 2) After the departure, the inspection company made full use of computer storage, data processing and image analysis and diagnostic functions to analyze the hidden danger signal. 3) Based on the relevant national electrical fire safety standards and standards, identify potential types, locations, and possible trends in forecasting. Prepare rectification reports with drawings and texts to send to the inspected units and report them to the fire protection supervision department for record. 4) After the unit under inspection completes rectification of the hidden danger, the inspection company conducts a re-inspection. After passing the re-inspection, it reports to the fire control department for acceptance of the inspected unit.

5. The feasibility of carrying out electrical fire safety inspection and intermediary services

From the perspective of laws and regulations, the first is that the current building design fire protection code has related regulations for power supply, lighting, lamps, etc.; the second is established by the former Ministry of Water Resources and Electric Power, the Ministry of Broadcasting and Television, the Ministry of Energy, the Ministry of Construction, and the Ministry of Chemical Industry. The series of electrical design specifications have corresponding fire protection requirements for distribution transformers, lines, lighting, and fire protection, and requirements for installation, protection, lightning protection, and grounding have been written into the fire code provisions. . From the perspective of practical operability, the fire supervision authorities cannot assign inspection services in accordance with the supervision function and police force allocation granted by the Fire Protection Law. Each power user is not limited by its nature, business scope, scale, funds, and personnel quality. It is possible to invest special funds to purchase these expensive equipment and provide services for the electrical fire prevention and safety of the company (department). The most feasible way is to establish service organizations that specialize in electrical fire safety testing. The principle of who is responsible for and responsible for the implementation of firefighting work and how to protect the safety of people’s lives and property is of course the responsibility of all government agencies, groups, enterprises, institutions, employees, and leaders at all levels. Therefore, it is necessary for the responsible persons to ref In the case of fire, he was enlightened and scientifically accepted the new thing of electrical fire detection. With the help of professional personnel and testing equipment of inspection agencies, he found hidden dangers of electrical fire and ensured fire safety.

In a word, the electrical fire safety inspection intermediary service is a professional job born in the process of China's reform and opening up, and may encounter work resistance. Therefore, it needs the meticulous guidance of the fire supervision authority, and the community supports and cooperates with it. The testing agency will make due contributions to prevent electrical fires.