LED lamps are operated at low voltages and contained a number of delicate semiconductor elements, which are more susceptible to power surge damages than conventional lamps. And further, different with A-style bulb that mainly used in residential environment, the tube lamps are mainly used in commercial and especially industrial environments where electrical grids are relatively unstable, damages to LED tubes caused by power surge are more common.
What is Power Surge?
Power surge, in simple words, is a sudden spike in electricity in your electrical circuits. Even though surges in general can last for as little as a fraction of a second, it can take massive toll on all electrical devices that connected to the utility grid. Surges will cause wires and components to overheat, melt and lead to short circuits, all of which are destructive LED components. An LED light can last well over 50,000hrs, with some going over 70,000hrs but an power surge can end that life in less than a second.
Common Causes of Electrical Surge
Power surges have several causes. For example, lightning discharges that directly strike the distribution line of a building, or its lightning rod, can induce electromagnetic fields that generate voltage spikes in nearby lighting installations. Long outdoor distribution power lines are highly susceptible to the direct effects of lightning strikes, with large currents from the lightning being conducted in the power lines. It’s also common for non-weather phenomena to cause voltage spikes in adjacent lines — for instance, switching devices (contactors) inside electrical cabinets, or the disconnection of transformers, motors and other inductive loads or high power equipment (generators, welders) coupling energy on shared branch circuits connected to sensitive electronic equipment.
Surge Immunity Test
The aim of the surge immunity test is to provide a model to simulate the surges and then check if the product can survive. The lightning surge tests are conducted by IEC 61000-4-5 and ANSI/IEEE C62.41. The test can be divided into differential mode (DM) and common mode (CM) transient.
Two selected voltage/current waveforms are identified as representative of typical electrical environments:
1. Combination wave: conducted by IEC 61000-4-5, which simulated a unipolar pulse that occurs most often outside a facility (e.g., a lightning strike). Two waveforms are defined rise time and duration as 1.2×50µs open circuit voltage and 8×20µs short circuit current;
2. 100 kHz Ring wave: conducted by ANSI/IEEE C62.41, which simulated an oscillating waveform that occurs most often inside a facility. The amplitude and available energy of the standard waveforms are dependent upon location within a facility;
Compliance Related to Surge Immunity
In the US, ANSI/IEEE C62.41 is a very important specification to consider, because it is either the primary or secondary reference for surge immunity testing. This standard defines three lighting location categories and associated transient surge testing requirements. The categories correspond to the physical location of the LED light whether located indoors or outdoors.
Category C (outdoor) is the region outside the building that includes external conductors, and it extends inside to the load center main circuit breaker or service entrance disconnect breaker;
Category B (indoor) is a zone within a building that extends at least 30 ft (10 m) from the service entrance disconnect breaker along feeders or branch circuits to electrical receptacles or outlets. The most probable sources of surges within this zone are the on/off switching of electric motors or motor driven appliances;
Category A (indoor) is the zone farthest from the disconnect breaker. It is defined as the zone within the building where the branch circuits extend to all outlets that are more than 30 ft (10 m) from Category B outlets, and more than 60 ft (20 m) from the service entrance disconnect breaker located in the Category C zone;
IEEE also has defines three exposure levels that characterize the rate of surge occurrence versus voltage level at an unprotected site. The three exposure categories include:
- Low exposure: applications known for low lightning activity, little load switching;
- Medium exposure: systems and geographical areas known for medium to high lightning activity or with significant switching transients or both;
- High exposure: those rare installations that have greater surge exposure than those defined as low or medium.
Below table is a summary of the ANSI/IEEE C.62.41-1991 surge levels and where they apply
Surge Immunity of LED Tubes
The tube lamps are mainly used in commercial and especially industrial environments where electrical grids are relatively unstable, damages to LED tubes caused by power surge are more common.
LED tubes are grouped into four categories: Type A (Ballast Compatible), Type B (Ballast Bypass), Type C (External Driver), and Type A+B (Dual Mode). Either Type A or Type C tubes are work with external fluorescent ballast or LED driver, which are designed well specifically to protect lamps and fixtures against power surge. While the tiny internal driver of Type B or Type A+B tubes are weak due to size and cost limitation, therefore a power surge may overwhelm such lamps when your building experiences any strong jump in electrical output. Think of external ballast or drivers as cruise ships and internal drivers of Type B tubes as life jackets. Both keep you above the water, but cruise ship does it much better.
Surge Immunity of Type B Tube
Some manufacturers generally design Type B or Type A+B tube lamps according Energy Star Program requirements, which defines a 0.5μs 2.5kV 100kHz ring wave with 30Ω source impedance transient test. In addition, some manufacturers adopt 500V 1.2×50µs / 8×20µs combination waves for product immunity test. It is clearly that such design guideline is just aligned to ANSI/IEEE C.62.41 Category A Low exposure level. That is ok for A-style bulb that mostly used in residential environment but is far away for linear replacement lamp that mostly used in commercial and industrial environments.
One pieces of advice is checking the surge immunity level of Type B or Type A+B tube lamps before making a quantity purchase. The least surge test level for tube lights should be 1kV combination waves with 2Ω source impedance (differential mode) and 2kV combination wave with 12Ω source impedance (common mode) per IEC61547.
2 thoughts on “Lightning Surge Immunity of LED Tube”
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