Application of AFCI technology in the power plug o

2022-08-20
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Application of AFCI technology in air conditioning power plugs

the application of error arc breaking protection technology (AFCI Technology) in household air conditioning power plugs is very important and necessary. Since August 1st, 2004, domestic air conditioners sold in the U.S. market require power plugs with AFCI function. The application of incorrect air-conditioning power plug protection technology will directly damage the interests of consumers and air-conditioning manufacturers, and affect the safety of fire prevention. Texas Instruments has developed an air conditioning power plug with arc shield TM technology. This paper will introduce the basic content of AFCI technology, and focus on the application of AFCI technology in the power plug of household air conditioning

afci technology

afci technology is a latest circuit protection technology. Its main function is to prevent some fires caused by wrong arcs. These dangerous arcs may occur on household wiring, when plugs and sockets are connected, as well as on the harness inside household appliances or on the power line of appliances. The main cause of wrong arc is the wear of wire insulation or poor electrical connection. Numerous data from the American Consumer Product Safety Association (CPSC) and the National Fire Protection Association show that dangerous events caused by electric arcs include fires and resulting deaths

afci technology can sense abnormal phenomena in the current caused by wrong arc. Because many transient phenomena in normal operation or in the actual operation process will produce some "good" arcs (such as the disconnection and closure of contact continuity, or the instant of motor starting), AFCI technology must be able to distinguish between "good" arcs and "currently the most widely used bad arcs in single screw extruders", so as not to cause errors or misoperations. Sometimes the current signals of many loads are easily mistaken for wrong arcs. In fact, they are normal current waves (such as dimmer switches)

therefore, in addition to being able to distinguish between "good" arcs and "bad" arcs, AFCI technology also needs to be able to quickly and effectively provide protection under normal and abnormal conditions, while preventing maloperation. The key points of this technology are listed below

ul1699 standard

the application of AFCI technology in the field of household appliances is regulated by ul1699 standard, which was developed in the 1990s to identify household fires caused by arcs generated by overcurrent. The traditional circuit breaker can provide protection against overcurrent. However, the study found that in the case of no overcurrent, the wrong arc caused by small current also has enough energy to cause a fire, thus causing a fire

The ul1699 standard was originally used to regulate the application of AFCI technology in household circuit breakers, wall mounted sockets, and portable AFCI sockets. The specifications for circuit breakers can be divided into two parts: the basic requirements for branch distribution and the strict requirements for combined devices. At present, many household circuit breakers that first meet the ul1699 standard can no longer meet the current standard, because the earlier technology can no longer meet the increasingly stringent requirements of the ul1699 standard, especially for the non error arc generated by various loads, which can not have misoperation

The specification of ul1699 standard can be divided into three arc test methods: arc inspection test, malfunction test and load start test. When the ul1699 standard was initially drafted, the focus was to prevent the misoperation of ordinary loads (such as motors, lamps, electronic control systems, etc.) in the event of non erroneous arc. Nowadays, with the forced application of AFCI technology in the power plug of household air conditioner, AFCI technology should not only meet the safety specifications of ul1699 standard, but also meet the requirements of air conditioner operating conditions (we call it product applicability). However, at present, ul1699 has no requirements for product applicability, but this is very important in the actual use of products

in addition, some new loads and operating conditions that have emerged are found not to be included in the ul1699 standard, such as power line connections, fan speed controllers, and other applications. This also puts forward higher requirements for the applicability of AFCI technology

Application of AFCI technology

the application of AFCI technology in the power plug of household air conditioner should consider three design levels. First of all, it must comply with ul1699 standard. However, it is not enough to only meet the requirements of ul1699. If the product is involved in malfunction or shows unexpected characteristics under application conditions, we cannot rely on ul1699 standard to measure. According to the application and technical experience of Texas Instruments, it is very important for many applications to meet the requirements of "product applicability", especially for AFCI technology used in the field of household air conditioning

secondly, UL standard is only a safety standard and cannot cover all aspects, so the designer of a power plug product with AFCI protection needs to make sure that his design meets the "applicability" of household appliances. This includes not only testing household appliances that use AFCI plugs, but also testing when AFCI products are actually connected to household appliances

finally, from the practical point of view of a good design, the power plug with AFCI function should not only meet and exceed the standard of ul1699, but also meet the "applicability" test in the actual application process, so that such a product can bring users a safe and reliable guarantee

How can designers of AFCI technology fulfill these requirements? For the power plug of household air conditioner, it is necessary to comply with ul1699 standard. We can find that there are many patents related to arc detection. In fact, arc detection is very easy to work, but the real challenge is how to distinguish between "good" and "bad" arcs without misoperation. Ideally, the sensitivity of AFCI algorithm can not only meet the basic requirements of ul1699 standard, but also have enough ability to provide the fastest detection of unsafe arcs. Due to the strict requirements for the induction ability of different arcs and the discrimination ability of harmful arcs, at present, many AFCI technologies only partially meet the requirements of ul1699 standard. Although some AFCI technologies can pass the ul1699 standard, in the process of practical application, the detection of different arcs may not be stable enough or can not provide the fastest detection of harmful arcs, which is very "fragile"

therefore, the power plug with AFCI function can not only meet the ul1699 standard, but also be suitable for the design of different household air conditioners and air conditioning manufacturers. This is a very serious challenge. It exceeds the ul1699 standard, but it is very important in practical use. The designers of AFCI power plugs should not only be very familiar with the working principle and conditions of household appliances, but also consider the numerous models and specifications of different appliance manufacturers. First of all, the designer of an AFCI power plug must refer to the ul1699 standard and decide what test items to adopt to replace the load of the air conditioner. Please remember that the standard ul1699 test item has nothing to do with household air conditioners, even though NEC standard requires all manufacturers of household air conditioners to provide AFCI protection for the air conditioner power plugs produced by them after August 1st, 2004 (refer to ul484 standard). To complete this task, it is logical to use some standard loads instead of household air conditioners to do the test of ul1699. For example, Texas Instruments re adopts different ul1699 test items for air conditioners to replace specific loads of household air conditioners (such as vacuum cleaners). Because the signal parameters of different air conditioners vary greatly, Texas Instruments Corporation of the United States tests air conditioners of different specifications produced by different manufacturers. The current range includes 15A ~ 35A @ 115VAC/240VAC, and the refrigerating capacity includes 6000btu ~ 14500. When the pendulum cannot be hung or the plug cannot be detached, the relevant parts can be removed and the BTU can be cleaned with kerosene

in addition, Texas Instruments has worked with many air conditioning manufacturers to understand any situation that may affect the performance of AFCI power plugs. Through this cooperation, we learned that the arc ("good" arc) generated when changing the position of the mechanical control switch of the air conditioner will cause the misoperation of some AFCI devices to cut off the power supply and automatically shut down the air conditioner. This is because each time the switch changes position, a series of contact opening and closing actions will occur, resulting in an arc ("good" arc). The size of the air conditioning power is directly related to how to judge the AFCI plug without misoperation when the control switch rotates. We found that even for low-power air conditioners, when the speed control switch is rotated quickly (just like when you enter a room with high temperature in summer, the air conditioner will be turned on to the maximum), some other AFCI products will malfunction. This makes it easy for air conditioner users to mistakenly think that there is a problem with the air conditioner and ask for repair or return

we also learned from some air conditioning manufacturers that many of the arcs generated in the air conditioner (and lead to fire) are related to the wiring in the air conditioner. At present, the technology provided in ul484 cannot provide protection for this kind of arc in the air conditioner. They only provide integrated protection for the electrical harness; AFCI technology can provide such arc protection. The arc shield TM algorithm developed by Texas Instruments can well protect the arc generated at the wiring in the air conditioner

during the development of AFCI, another requirement comes from the ability to resist electromagnetic interference (EMI), such as the electromagnetic interference that may be caused by some power communication equipment in many families. In order to eliminate these concerns, the arc shield TM algorithm developed by Texas Instruments will not be affected by electromagnetic interference or other similar signals

the design of reliability should also consider the performance of AFCI and the electronic and mechanical properties of the power plug. The arc shield TM algorithm developed by Texas Instruments can meet all the test requirements of AFCI technology, including: arc detection, anti-interference ability against misoperation beyond the provisions of ul1699 standard, and compatibility with new loads that may be added to the new version of ul1699 standard

for example, the arc shield TM power plug developed by Texas Instruments can detect small arcs like 0.5A. In addition, AFCI technology can also ensure that there is no misoperation for two different new fan speed controller loads, and some current household AFCI circuit breakers have found misoperation for these loads. It is expected that the new version of ul1699 standard will require that AFCI devices cannot malfunction under such loads. It is precisely because the mainstream of Texas Instruments in the United States and Japan is the systematic research of 2.5 ~ 2.7mm instrument company on technology, application, standards and other aspects, which makes our AFCI algorithm more reliable and practical

in addition, the electrical and mechanical properties of the power plug should also be more reliable. Therefore, we need to pay special attention to the mechanical contact system of AFCI power plug (part of the tripping device). Poor mechanical contact system will lead to the failure of the power plug, especially when the plug is required to repeatedly break the point contact test of high current (cut off the power line test) and similar arc test, the performance of the mechanical contact system should be fully taken into account. If the mechanical contact system is not designed well, these large currents may cause the contact to stick and corrode, and even

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