I. Introduction
According to 2009 statistics of the Chinese Ministry of Public Security in Shenyang, of major electrical fire, the 58.44% is caused by the failure of electrical wiring, and increasing year by year, with the continuous development of society, increasing the degree of electrification, the more circuit protection The more important it is.
The fault arc energy in the electric is large, the temperature is high, the hazard is extremely great, and it is very easy to cause a fire. However, the traditional circuit breaker can only protect against leakage, overcurrent and short circuit, and many serious fire accidents are caused by fault arc below rated current. The traditional circuit breaker can never detect or prevent such fault. . Accidents caused by arc faults become more and more convex
Obviously, we need to use AFCI technology to prevent and monitor fire hazards in electrical circuits.
Second, a general introduction to AFCI
What is AFCI?
AFCI is the abbreviation of English ArcFaultCircuitInterrupt, which can be translated into "arc fault circuit breaker". As we all know, the traditional circuit breaker only protects against short circuit and overcurrent. The common leakage protection switch RCD (GFCI) is only for "phase/ground". Or “Zero/Ground†has a protective effect and cannot protect the fault arc between “phase/zeroâ€.
AFCI technology is a state-of-the-art circuit protection technology that protects against fault arcs between “phase/zero†and “phase/ground†based on conventional circuit breakers. These dangerous arcs can occur in electrical On the wiring, plug and socket connection points, and on the wiring harness inside the household appliance or on the power line of the appliance, when a faulty arc occurs, the arc can generate a high temperature of about 4,000 degrees in an instant, and it is easy to ignite nearby flammable materials. , causing electrical fires.
US Electrical Fire and AFCI Situation
In the United States, according to 1998 statistics CPSC (ConsumerProductSafetycommission CPSC), every year due to aging distribution lines cause a fire caused by arcing over 40,000 cases, resulting in US $ 1.68 billion in direct economic losses.
The National Association of Fire Protection Directors National Association (NASFM) also pointed to the "Fault Arc" in the subsequent investigation report on electrical fire causes, accounting for 83% of electrical fires.
Therefore, in order to effectively reduce electrical fires, the US Electrical Code (NEC2002) 210-12(A)(B) requires the installation of such AFCI circuit breakers and AFCI wall sockets in the bedrooms of new buildings and old buildings. All air conditioners must be fitted with AFCI sockets. .
Because of the obvious effect after installation, NEC2008 increases the scope of use of AFCI, and (210-12(B)) almost branch circuits require the installation of fault arc breaker AFCI.
The National Fire Protection Association (NFPA) concluded in 2003 about the economics of installing AFCI: AFCI can protect against approximately 75%-80% of electrical line fires, and NFPA estimates that the US home furnishing AFCI contains 20 years of old houses (per The average cost of homes is $175, the cost and the casualties and property that are expected to occur when there is no installation.
Compared with the loss, the total society (1.9 million homes in the United States) can save almost double the cost of input during the AFCI lifespan (20-30 years), which can save the country double the funds and bring huge Social benefits.
Electrical fire situation in China
According to the statistics of Shenyang Institute of Public Security of China in 2009, in the five years from 2003 to 2007, the proportion of electrical fires in the total number of fires in each year was 23%, 20.7%, 21.9%, 23.1% and 28.3%, respectively. 58.44% is caused by the failure of electrical lines, and is increasing year by year, the form is quite severe.
According to the statistics of our relevant departments, China's electrical fires are three times as many as those in the United States. Fires caused by aging of circuits account for the highest proportion of all fire accidents. The distribution of electrical lines in China is unreasonable, and there are many fake and inferior electrical appliances, which are prone to electrical fires. China's voltage is 220V, the United States' voltage is 110V, and the high voltage is more prone to fault arcing, which is a hidden danger of electrical fires.
Third, electrical arc knowledge
Arc:
When the electrical line insulation is aging, damaged, the connector is connected, the line is connected, and the short circuit will cause a fault arc. (Arc discharge) Even if it is within the rated current range, an arc will occur, and an arc will generate heat at the same time (more than 3000). Degree) is sufficient to ignite nearby combustibles.
The arc on the line can be divided into two types, one is the normal operating arc, also known as "good arc", and the other is the fault arc, called "bad arc".
1, "Good arc" refers to the arc generated when the motor rotates, such as electric drills, vacuum cleaners, etc. In addition, when people switch electrical appliances, the arc generated when plugging and unplugging electrical appliances is also "good arc."
2, "bad arc" is a fault arc, the type of fault arc can basically be divided into three categories. Class A, Class B and Class C. Class A is called a string arc, and Class B is called a parallel arc. The figure is as follows:
Class C is the fault arc (leakage) of the live and neutral to ground. Since our electrical protection generally has a leakage protector, Class C arc can be effectively prevented. (in case of good grounding)
3, the wire is on fire (0.5-1s)
Introduction to the US UL1699 standard
UL1699 is a US standard that regulates AFCI. UL1699 was developed in the early 1990s to identify home fires caused by overcurrent and short circuit arcs. However, the study found that a fault arc caused by a small current without an overcurrent also has enough energy to cause a fire and cause a fire.
The UL1699 specification can be divided into three arc test methods: arc test, misoperation test, and load start test. When the initial UL1699 was drafted, the focus was on preventing malfunctions of ordinary loads (such as motors, lights, electronic control systems, etc.) in the event of non-false arcs. Nowadays, with the application of AFCI technology on the household air conditioner power plug, the AFCI technology must meet the safety requirements of UL1699, and at the same time meet the requirements of air conditioning operating conditions (we call it product suitability), but currently UL1699 There is no requirement for product suitability, but it is very important in the actual use of the product.
According to the UL1699 standard, AFCI should identify "good arc" and "bad arc" on the AC line. When the AFCI detects the fault arc "bad arc" signal for 8 and a half weeks in 0.5 seconds, the circuit breaker performs tripping. Cut off the AC line in time.
In addition, when "good arc" occurs, such as electric drill, motor start, no malfunction, the 2008 edition of UL1699 has been published.
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