Safety standards for LED fluorescent tubes
At present, the application of LED in daily lighting is becoming more and more popular. From outdoor lighting to indoor lighting, you can see the footprint of LED lighting products. With the decline of LED costs, LED lighting products are no longer limited to road lighting. More LED self-ballasted lamps, LED fluorescent lamps, and other LED products that meet the purchasing power of the public have appeared on the market. The design of such products is based on The structure of the ballast fluorescent lamp and the double-ended fluorescent lamp can be easily and directly installed on the traditional household lamps without adding extra lamp purchase cost to the public. Since LED products are introduced at a faster rate, many LED products have no corresponding safety standards to follow. The safety standards of traditional lighting sources are no longer comprehensive and unsuitable. This will lead to many LED products in safe design. There are unqualified problems on the above, which affect the safety and quality of LED products.
At present, common LED fluorescent lamps are basically designed with reference to T8 and T10 fluorescent lamps in appearance and size. The main difference is that the light source uses different materials. LED fluorescent lamps have a built-in power supply (and some are designed as external power supplies) while traditional double-ended The fluorescent lamp is excited by an external ballast. From an electrical point of view, LED fluorescent lamps are not only light sources, but also very similar to lamps. It not only meets the requirements of the double-capped fluorescent lamp safety standard GB 18774-2002 for the size and heat resistance and fire resistance of the lamp holder, but also needs to meet the lamp standard GB7000.1- The 2007 standard and the GB19510.1-2009 standard have requirements for the structure, internal wiring, creepage distance and electrical clearance, insulation and electrical strength, heat resistance, fire resistance, etc. of the whole lamp and the built-in LED drive power supply.
This article will combine the contents of the two standards GB18774-2002 and GB7000.1-2007 to analyze the structure, internal wiring, protection against electric shock, insulation resistance and electrical strength, creepage distance and electrical clearance, heat resistance and fire resistance. The possible safety problems of LED fluorescent lamps.
One, structure
LED fluorescent lamps are prone to problems in the three places where the lamp cap, the screw, the basic insulation and the contact of the accessible metal parts. The lamp holder needs to meet the torque test specified in GB18774-2002 and the size requirements specified in GB2799-2001. Among them, the torque test specified in GB18774-2002 requires that both before and after the high temperature test be in compliance with the provisions of clause 2.3.1 of the standard, that is, when the torque test is applied, the rotation between the parts of the lamp cap should not exceed 6°. The high temperature condition applied by the lamp cap is (125±5)℃, and the heating time is (2000±50)h. If G13 lamp holder is used, and the lamp power is greater than 40W, the high temperature condition is: (140±5)℃. High-temperature conditions and duration are more stringent for the assessment of LED fluorescent lamps with plastic materials in the lamp cap. Using plastic lamp caps with low heat resistance, after applying such a long period of high-temperature conditions, the plastic parts are likely to have softened. If a metal lamp holder is used, it is relatively easy to meet this test condition, but the connection between the metal lamp holder and the LED fluorescent lamp body, as well as the creepage distance and electrical clearance, should also be considered.
The screws at the lamp cap of the LED fluorescent lamp mainly play the role of connection and fixing between the lamp cap and the lamp body. At present, the diameter of the screw at the base of the common LED fluorescent lamp is less than 3mm, and according to the regulations of GB 7000.1, this type of screw needs to be screwed into metal. The current common practice is to use an aluminum shell for LED fluorescent lamps, and this screw is directly screwed into the metal shell, which can also meet the requirements. However, a common problem caused by this is that after the screw is screwed into the metal shell, the screw and the live metal part of the lamp cap are too close, which easily leads to unqualified creepage distance and electrical clearance.
The internal wiring of the LED fluorescent lamp is mainly used to connect the plug of the lamp holder and the input and output of the built-in power supply. The built-in power supply is isolated from the aluminum shell by a sleeve. According to GB7000.1, the insulation between internal live parts and accessible metal parts must meet double insulation or reinforced insulation. This requires the insulation of the bushing to meet the electrical strength requirements of the reinforced insulation level.
2. Internal wiring
According to the requirements of the GB7000.1 standard, the internal wiring used by the LED fluorescent lamp needs to be evaluated in four aspects: wire diameter and insulation thickness, mechanical damage, the heating temperature of the insulation layer, and whether the insulation meets the requirements. Generally speaking, there will be no problems with the internal line in the protection of mechanical damage, and the main problems will lie in the other three aspects. According to the requirements of the GB7000.1 standard, when the normal current is less than 2A (generally the working current of the LED fluorescent lamp does not exceed 2A), the nominal cross-sectional area of the internal wire is not less than 0.4mm², and the thickness of the insulation layer is not less than 0.5mm. In addition, from the perspective of insulation, since the aluminum shell is an accessible metal part, the basic internal insulation cannot directly contact the aluminum shell. This requires the internal wire to be a double insulated wire, unless there is a relevant certificate that can prove that the insulation of the wire can meet the reinforced Insulation requirements, at this time, it is also possible to use single-layer insulated wires for internal wires. However, the internal wires used by LED fluorescent lamps on the market rarely take into account the requirements of cross-sectional area, insulation thickness and insulation wire level at the same time.
In addition, when the internal wires are routed, care should be taken to avoid direct contact between the wires and the components that generate high internal power supply, such as transformers, filter inductors, bridge stacks, heat sinks, etc., because these components have a very high temperature when the LED fluorescent lamp is working. It may exceed the heat-resistant temperature value of the inner wire insulation material. When the internal wires are routed, do not touch the components that generate a lot of heat, which can avoid the insulation layer damage caused by the local overheating of the insulation layer, and the safety problems such as leakage or short circuit.
Three, protection against electric shock
In terms of anti-shock protection, there are generally two situations where LED fluorescent lamps may be unqualified. One is that the unreliable connection between the lamp holder and the lamp body leads to the direct removal of the lamp holder by human hands, which leads to direct contact with internal live parts in the test; The internal insulation is not done well, resulting in leakage of the shell.
4. Insulation resistance and electric strength
From the perspective of electrical classification, LED fluorescent lamps belong to class II anti-shock type, which requires the input of LED fluorescent lamps to between the accessible parts and the input to the installation surface to meet the insulation resistance and electrical strength requirements of the reinforced insulation level. At present, many LED fluorescent lamps can pass the insulation resistance test, but the dielectric strength test fails, mainly due to the selection of the transformer with the built-in power supply and the installation position of the aluminum substrate of the LED module. Many companies choose to use non-isolated transformers for the purpose of saving costs or high power supply efficiency, which will cause the built-in power supply's input and output terminals to fail to meet the electrical strength requirements of the reinforced insulation level. At the same time, because the aluminum substrate of the LED module is in direct contact with the metal shell during installation, the insulation level between the input terminal and the accessible parts cannot meet the requirements of the reinforced insulation level.
To meet the requirements of the electrical strength of the reinforced insulation level, you can choose to use an isolation transformer to electrically isolate the input and output of the built-in power supply, or use an insulating material instead of a metal shell. However, if an insulating material shell is used, it is also necessary to consider the aforementioned problem that screws with a diameter of less than 3mm need to be screwed into metal.
5. Creepage distance and electrical clearance
In the design of LED fluorescent lamps, in addition to the creepage distance and electrical clearance between the live parts of the lamp cap and the accessible parts and the live parts of different polarities, the internal driving power supply also needs to meet the GB19510.14-2009 standard due to the built-in power supply. The requirements for creepage distances and electrical clearances specified in.
Six, heat and fire resistance
There are certain differences between GB18774-2002 and GB7000.1-2007 for heat resistance and fire resistance tests. The differences are mainly concentrated on the insulating material base used in LED fluorescent lamps. The insulating material of the lamp holder is an electric shock-proof insulating part, and it is also an insulating material for fixing live parts.
The requirements of the GB18774-2002 standard for heat resistance are that the high temperature condition applied to the lamp cap is (125±5) ℃, and the heating time is 168h. If G13 lamp holder is used, and the lamp power is greater than 40W, the high temperature condition is: (140±5)℃. After the test, there should be no loosening, cracking, swelling and shrinking of the lamp holder pins, and the insulation resistance between the lamp holder pins and the accessible parts is not less than 2MΩ, and it can withstand the electric strength of 1500V (AC effective value) for 1 minute. In terms of fire resistance, it is required to withstand the glow wire test at 650°C.
The requirements of the GB7000.1-2007 standard for the heat resistance of the lamp holder insulating material are assessed by ball pressure test. The ball pressure test temperature is 25°C or 125°C higher than the maximum working temperature of the insulating component, whichever is the maximum. The test time is 1h, and whether the indentation diameter is greater than 2mm is used to determine whether it is qualified. In terms of fire resistance, since the lamp holder insulating parts are both anti-shock insulating parts and fixed live parts, it is necessary to perform the 650℃ glow wire and needle flame tests at the same time.
The two standard assessment methods have their own harsh points. At present, there is no standard that stipulates which requirements are used to assess the insulation of LED lamp holders. But in the final analysis, manufacturers are still required to focus on evaluating the heat and fire resistance of the insulating material when choosing LED fluorescent lamp holder insulation.
From the perspective of product structure, LED fluorescent lamps combine the characteristics of double-capped fluorescent lamps and lamps. When performing electrical safety assessments on LED fluorescent lamps, it is necessary to integrate the safety standards of double-capped fluorescent lamps, the safety standards of lamps and the safety standards of LED driving power supplies, and the Products undergo a more comprehensive and detailed electrical safety assessment. (The full text is selected from the seventh issue of "Semiconductor Lighting" magazine, 2011. Editor: maysoong)
references
[1] GB7000.1-2007 "Luminaires Part 1: General Requirements and Tests".
[2] GB19510.1-2009 "Light Control Device Part 1: General Requirements and Safety Requirements".
[3] GB19510.14-2009 "Lamp control devices Part 14: Special requirements for DC or AC electronic control devices for LED modules".
[4] GB18774-2002 "Safety Requirements for Double-capped Fluorescent Lamps".
[5] GB2799-2001 "Pin-type lamp holder type and size".
