At present, LED application 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 in the cost of LED, LED lighting products are no longer limited to road lighting, the market began to appear more LED self-ballasted lamps, LED tubes and other LED products in line with the public purchase ability, the design of such products refer to the self-ballasted fluorescent lamp, double-ended fluorescent lamp structure, can be easily installed directly on the traditional home lamps. It will not add additional lighting purchase costs to the public. Due to the speed of LED product innovation is relatively fast, many LED products have no corresponding safety standards to follow, the use of traditional lighting source safety standards to assess has not been comprehensive, is not suitable, which will lead to many LED products in the safety design of unqualified problems, affecting the safety quality of LED products.
At present, the common LED lamp, the appearance of the size of the basic reference to T8, T10 fluorescent lamp design, the difference is mainly in the light source material is different, LED lamp has a built-in power supply (also does not rule out some design into the external power supply) and the traditional double-ended fluorescent lamp by external ballast excitation. From an electrical point of view, the LED lamp is both a light source, and very similar to the lamp, it must meet the double-ended fluorescent lamp safety standard GB 18774-2002 on the lamp part size and heat and fire resistance requirements, It also needs to meet the requirements of the lighting standard GB7000.1-2007 standard and GB19510.1-2009 standard for the whole lamp and the built-in LED drive power supply on structure, internal line, creepage distance and electrical gap, insulation and electrical strength, heat resistance, fire resistance and so on.
This paper will combine the content of GB18774-2002 and GB7000.1-2007 two standards, from the structure, internal wiring, anti-shock protection, insulation resistance and electrical strength, creepage distance and electrical gap, heat and fire resistance of the LED tube may exist in the safety problems.
1. Structural aspects
The three places where LED tubes are prone to problems are the lamp head, screws, basic insulation and the contact of accessible metal parts. The lamp holder shall comply with the torque test specified in GB18774-2002 and the size requirements specified in GB2799-2001. Among them, the torque test required by GB18774-2002 must meet the provisions of the 2.3.1 clause of the standard before and after the high temperature test, that is, when the torque test is applied, the rotation between the components of the lamp head does not exceed 6° . The high temperature conditions applied to the lamp holder are (125± 5) ℃, heating time is (2000± 50)h. If the G13 lamp holder is used, and the lamp power is greater than 40W, the high temperature condition is: (140± 5) ° C. High temperature conditions and duration for the lamp holder using plastic material LED tube assessment is relatively harsh, the use of heat resistance is not good plastic lamp holder, after applying such a long time of high temperature conditions, it is likely that the plastic parts have softened. If a metal lamp holder is used, it is relatively easy to meet this test condition, but it is also necessary to consider the connection between the metal lamp holder and the LED lamp body, as well as the creepage distance and electrical gap.
The screw at the lamp head of the LED lamp mainly plays the connection and fixing role between the lamp head and the lamp body. At present, the diameter of the screw at the head of the common LED lamp is less than 3mm, and according to the provisions of GB 7000.1, such screws need to be screwed into the metal. At present, the common practice is that the LED tube uses an aluminum housing, and this screw is directly screwed into the metal housing, which can also meet the requirements. However, a common problem resulting from this is that after the screw is screwed into the metal housing, the screw is too close to the live metal part of the lamp head, which easily leads to unqualified creepage distance and electrical gap.
The internal wiring of the LED lamp tube is mainly used to connect the input and output of the lamp socket and the built-in power supply, and the built-in power supply is separated from the aluminum housing through the sleeve. According to the provisions of GB7000.1, the insulation between the internal live parts and the accessible metal parts shall meet the requirements of double insulation or reinforced insulation. This requires the insulation of the casing to meet the electrical strength requirements of the strengthened insulation grade.
Two, internal wiring
According to the requirements of the GB7000.1 standard, the internal wiring used by the LED tube needs to be assessed mainly in four aspects: wire diameter and insulation thickness, mechanical damage, insulation layer heating temperature, and whether the insulation meets the requirements. In general, the internal line will not have a problem in the protection of mechanical damage, and the main problem will be in the other three aspects. According to the requirements of the GB7000.1 standard, when the normal current is lower than 2A (the working current of the general LED lamp will not exceed 2A), the nominal cross-sectional area of the internal wire is not less than 0.4mm² The insulation layer thickness is not less than 0.5mm. And, from the insulation point of view, because the aluminum shell belongs to the accessible metal parts, the internal basic insulation can not be in direct contact with the aluminum shell, which requires the internal wire to be double-insulated wire, unless there is a relevant certificate to prove that the insulation layer of the wire can meet the requirements of strengthening insulation, then the internal line can use single-layer insulated wire. However, the internal lines used by LED tubes on the market at present rarely take into account the requirements of cross-sectional area, insulation layer thickness and insulation line grade.
In addition, when the internal wire is running, it is also necessary to pay attention to avoid direct contact between the wire and the internal power supply with large heating components, such as transformers, filter inductors, bridge piles, heat sinks, etc., because these components work in the LED tube, the temperature is likely to exceed the heat resistance temperature value of the internal wire insulation material. When the internal wire is routed, it does not contact the parts with large heat, which can avoid the insulation layer damage caused by local overheating of the insulation layer, resulting in leakage or short circuit and other safety problems.
Protection against electric shock
In terms of anti-shock protection, Xing Yuan laboratory reminds you that there may be two kinds of unqualified situations, one is that the lamp head and the lamp body are not reliably connected leading to the direct removal of the lamp head, resulting in the test can directly touch the internal live parts; Second, the internal insulation is not well done, resulting in shell leakage.
Four, insulation resistance and electrical strength
From the electrical classification point of view, the LED lamp belongs to the class II anti-shock type, which requires the LED lamp input between the accessible parts, as well as the input to the installation surface need to meet the insulation resistance and electrical strength requirements to strengthen the insulation level. At present, many LED tubes can pass the insulation resistance test, but the electrical strength test can not pass, mainly because of the transformer selection of the built-in power supply and the installation position of the aluminum substrate of the LED module. Many enterprises choose to use non-isolated transformers for the purpose of cost savings or high power efficiency, which will cause the input and output of the built-in power supply to fail to meet the electrical strength requirements of the strengthened insulation level. At the same time, because the aluminum substrate of the LED module is in direct contact with the metal housing during installation, the insulation level between the input end and the accessible part cannot meet the electrical strength requirements of the strengthened insulation level.
To meet the electrical strength requirements of the reinforced insulation grade, 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 housing instead of a metal housing. However, if the insulating material housing is used, it is also necessary to consider the metal screw with a diameter of less than 3mm as described above.
5. Creepage distance and electrical clearance
In the design of the LED lamp, in addition to the need to consider the creepage distance and electrical gap between the live parts of the lamp head and the accessible parts and the live parts of different polarity, due to the built-in power supply, the internal drive power supply also needs to meet the requirements of the creepage distance and electrical gap specified in the GB19510.14-2009 standard.
Six, heat and fire resistance
For heat and fire resistance tests, there are certain differences in the provisions of GB18774-2002 and GB7000.1-2007, and the differences are mainly concentrated on the insulating materials used in LED lamps. The insulation material of the lamp head part belongs to the anti-shock insulation part, and also belongs to the insulation material of the fixed live parts.
The heat resistance requirements of GB18774-2002 standard are that the high temperature conditions applied to the lamp holder are (125± 5) ℃, heating time is 168h. If the G13 lamp holder is used, and the lamp power is greater than 40W, the high temperature condition is: (140± 5) ° C. After the end of the test, the lamp socket should not be loose, cracked, bulging or crumpled, and the insulation resistance between the lamp socket and the accessible part should not be less than 2MΩ It can withstand the electrical strength of 1500V (AC RMS value) for 1 minute. In terms of fire resistance, it is required to withstand 650℃ hot wire test.
GB7000.1-2007 standard for lamp head insulation material heat requirements are assessed through the ball pressure test, the ball pressure test temperature is the highest working temperature of the insulation parts of 25 ° C or 125 ° C, the two take 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 head insulation is both an anti-shock insulation part and an insulation part belonging to a fixed live part, it is necessary to carry out a 650℃ hot wire and needle flame test at the same time.
The two standard assessment methods have their own harsh places, and there is no standard provision that is in accordance with which requirements to assess LED lamp head insulation. However, in the final analysis, manufacturers are required to focus on the heat and fire resistance of the insulation material when choosing LED lamp head insulation.
