PoE照明设备的雷击防护策略与合规标准分析

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本报告专注于"Power over Ethernet (PoE)"供电设备(PSE)中的雷电浪涌保护实施策略。PoE是一种将数据通信和电源通过双绞线同时传输的技术，广泛应用于网络摄像头、无线接入点等设备。在设计和部署PoE PSE时，考虑到环境因素至关重要，比如建筑物的地理位置、周围电子设备的密集程度以及可能遭受雷击的风险。实施浪涌保护的必要性取决于PSE的使用环境。如果设备将置于高风险地区，如靠近高压线或风暴多发区，那么保护措施就显得尤为关键，以防止雷击引发的过电压对设备造成损害。PSE的内置隔离特性也可能影响保护需求，如是否具备内置浪涌保护器或依赖于外部保护方案。报告指出，针对不同的产品类型，包括电源供应器和传统电话系统，有众多国际和行业标准来规范浪涌保护水平。这些标准如UL 60950-1（信息技术设备的安全）和IEC 60335（家用电器的电气安全）等，设定了严格的测试条件，以确保设备能在极端情况下保持功能并保护用户安全。报告深入研究了这些标准，重点关注与PoE PSE应用相关的测试条件，例如瞬态电压抑制、浪涌吸收能力和保护级别。它提供了实用的建议，帮助设计者和工程师选择合适的保护组件，确保其满足雷电防护等级（如IEC 61000-4-2）的要求，以及可能存在的其他标准，如IEEE 802.3bt PoE++标准中的保护措施。总结来说，对于PoE PSE设备，浪涌保护不仅关乎设备性能和稳定性，还涉及法规遵从性和用户安全。通过理解并符合相关的标准，可以确保在面对雷电等自然灾害时，这些设备能够有效地抵御冲击，减少潜在的故障风险，从而提升整个系统的可靠性。

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Determining the Peak Surge Current

SLUA818–February 2017

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Lightning Surge Considerations for PoE Power Sourcing Equipment Devices

As seen in Figure 3, eight 200-Ω resistors are used along with eight coupling elements, typically gas

arrestors, to couple the surge from the generator output to each line of the eight-wire cable

simultaneously. The 200-Ω value of the resistors is compliant with the 250-Ω maximum defined in the IEC

61000-4-5:2005 standard. The parallel combination of the eight 200 Ω resistors provides an equivalent

resistance of 25 Ω which would be in series with the internal 15 Ω resistance associated with the surge

generator. This total resistance satisfies the 40-Ω effective output impedance and peak short-circuit

requirements discussed in Section 2.

The IEC 61000-4-5:2005 standard also specifies a 1.2/50-µs generator for use in performing lightning

surge tests on power lines and short-distance signal applications. Some PSE applications may fall under

the short-distance category where the tests are performed using the 1.2/50-µs generator instead of the

10/700-µs to 5/320-µs combination wave generator. The 1.2/50-µs generator is commonly referred to as a

1.2/50-µs to 8/20-µs combination wave generator, because it is a short-circuit current waveform has an 8-

µs virtual front time and a 20-µs virtual time to half value.

Another physical consideration of PoE is discussed on page seven of theElectrical Transient Immunity for

Power-Over-Ethernet[2] application report:

On a twisted-pairs cable, the two wires of each pair are twisted together, but there is no twisting between

pairs at all (in fact, each pair is well separated from its neighbors). Consequently, a differential-mode

transient between P and N is likely with that type of cable, and this tandem of pairs can be considered as

an unbalanced line as far as the test voltages are concerned.

The implication is that the unbalanced circuit and lines category is also applicable for PoE as is the 1.2/50-

µs combination wave generator. Under these assumptions, Table 2 outlines several test scenarios using

both an eight-wire and four-wire coupling-decoupling network (CDN).

Table 2. PoE PSE Test Scenarios

TEST CONDITION EIGHT-LINE CDN FOUR-LINE CDN

Common mode (line-earth) 8-wires to earth 4-wires to earth

Single wire differential 1-wire shorted to earth with surge applied

to 7-wires

1-wire shorted to earth with surge applied

to 3-wires

Single pair differential 1-PoE pair shorted to earth with surge

applied to other 3-pairs

1-PoE pair shorted to earth with surge

applied to other pair

3 Determining the Peak Surge Current

The peak current per line needs to be considered when selecting the surge current rating of components

within the PSE, including any surge protection devices (SPDs). The path of the surge must be understood

to determine whether the component will see the current associated with one line or an additive current

associated with multiple lines. Additionally, there could be other worst case scenarios such as when only

one line or one twisted pair is subjected to the surge with the other lines open. It should be noted, that the

surge test is not normally performed with some of the lines open; rather the differential surges will be

applied as described in Table 2. Other examples include extending the surge voltage to levels above 4kV

and testing only four lines instead of eight.

Table 3 and Table 4 show the per-wire currents for both the 10/700-µs and 1.2/50-µs waveforms. The

green columns are for four-wire and the orange for eight-wire conditions. Generally speaking,

configuration one yields higher per-wire currents than configuration two and the four-wire test generates

higher currents than the eight-wire test. In most cases too, the 10/700-µs waveform yields higher peak

current with the exception of the eight-wire test in configuration two due to the maximum per-line series

resistance of 250 Ω.

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