Let-Through Voltage #06 - controlledpwr.com

1 APPLICATION NOTES SureImage - # 06. Vlet-thruappnotes 17 June 2009. Voltage Let-Through General Voltage Let-Through can be a con- microelectronic circuits has There are many devices that are fusing subject, especially since increased, problems related to designed to suppress transients different manufacturers of power transients have also increased to safe values. One well known treatment devices vary their rating tremendously. Surges up to 6,000 device is the transient Voltage techniques. Voltage Let-Through volts can appear at the power surge suppressor (TVSS) or refers to the amount of transient outlets inside medical facilities. surge protection device (SPD).

2 Voltage passed through a power These surges may cause medical Other devices, such as power conditioning device to the load. equipment to malfunction and conditioners and shielded often cause component damage. isolation transformers, provide a A transient is a high amplitude, significant amount of transient short duration spike or surge Energy is a function of Voltage suppression and are often used in superimposed on the normal and current over a period of time. conjunction with TVSS or a SPD, waveform. It is often caused by The ability of a transient to cause thus providing a more complete switching electrical loads, switch- disruption or damage depends on power conditioning solution.

3 Mode power supplies or lightning the energy contained in the effects. As the use of transient. ANSI/IEEE and UL 1449. The Institute of Electrical and lists the different waveforms with A suppressor that has a let- Electronics Engineers (IEEE) which to test a surge suppressor. through Voltage of 330 volts when standard indicates that There are three categories (A, B, tested with a category A3. 6,000 volts is the largest transient and C), each having three sub- waveform may not be any better that the interior of a commercial categories (1, 2, and 3). than a suppressor that has a let building would experience, and Underwriters Laboratories (UL) through Voltage of 400 volts when that it's harshest interior surge 1449 is the listing a surge tested with a category B3.

4 Environment is one that would suppressor receives when it is waveform. This is because the experience 100 surges of 6,000 tested with the ANSI/IEEE category B3 waveform has a volts, 3,000 amps in one year's waveforms, and it refers to the current value 2 times larger time . Medical facilities certainly Let-Through Voltage . The ratings than the category A3 waveform. fall into this category. Given the range from 330 volts to 6,000 When the Voltage and/or current magnitude of the problem, a volts. are increased on the testing standard on how to test surge waveform, the Let-Through Voltage suppressors was put into place. Extreme care must be given when also increases.

5 The American National Standards comparing the Let-Through Institute (ANSI) standard voltages of different suppressors. Transient Voltage Protection for Medical Imaging & Treatment Typical medical OEM equipment this limit, it is also important to lower. As stated earlier, power specifications limit the maximum address surge voltages and conditioners and shielded isolation transient Voltage allowed to 1,500 transients that range from nominal transformers are often used with volts peak. Transient voltages to the clip point of 1,500 volts. To TVSS to provide a more complete must be kept below this level to create an optimal power quality solution. The TVSS clips the top avoid damaging OEM equipment.

6 Environment, transient Let-Through part of the transient Voltage and While it is important not to exceed voltages should be limited even the shielded transformer attenuates the remaining part of eliminates the concern of surge or disrupting critical imaging and the transient close to nominal voltages and transient damaging treatment equipment. source Voltage . This virtually Harsh Environment = 100 Surges of 6,000 Volt & 3,000 Amp per Year 6,000 Vti Facility Transformer Medical Equipment Does Not Ensure surge levels stay < 1,500Vp, a defined requirement by medical equipment manufacturers. 6,000 Vti Facility Transformer Ultra K/M 700F/M Medical Equipment OR.

7 Ensures Maximum let through Voltage of 330Vp (on 208V) when exposed to a 6,000V / 3,000A waveform The Controlled Power Company Solution Some surge suppression standard is a guideline for testing approach virtually eliminates the manufacturers claim their device and does not mandate results. concern of surge voltages and protects equipment from surges of transient damaging or disrupting up to 6,000 volts as described in In sharp contrast, the SureImage critical imaging and treatment ANSI/IEEE , but they do not Ultra-K/M Power Conditioning equipment. tell you the Voltage waveform and Transformer and Model 700F/M. current with which their device was Voltage Regulator with Power When using the SureImage tested, or its Let-Through Voltage .

8 Conditioning attenuate a category product for electrical noise Likewise, specifications may B3 waveform (6,000 volts / 3,000 attenuation, you can be assured indicate that a device meets or amps) to a Let-Through Voltage of that your critical medical exceeds ANSI/IEEE , but less than 330 volts. Attenuation is equipment will be protected from this claim has no relative meaning achieved via the integral triple- dangerous Voltage spikes, and to the amount of spike attenuation shielded isolation transformer and meet the medical OEM's maximum it provides. The ANSI/IEEE output filter with TVSS. This transient Voltage limits.