At normal operating voltages, the SPDs are in a high-impedance state and do not affect the system. When a transient voltage occurs on the circuit, the SPD moves into a state of conduction or low impedance and diverts the surge current back to its source or ground. This limits or clamps the voltage to a safer level. After the transient is diverted, the SPD automatically resets back to its high-impedance state. The two main types of SPDs are voltage limiting and voltage switching components.
Voltage limiting components change in impedance as the voltages rise, resulting in clamping the transient voltage. Most systems today incorporate both component types together to aggregate the strengths and limit the weaknesses of each individual part. Voltage switching components include gas discharge tubes GDTs and spark gaps.
The response time of a given component simply means how quickly the component reacts when the surge threshold is surpassed. Voltage limiting components—TVS diodes, in particular—have faster response times than voltage switching components i. This occurrence is limited to voltage switching devices. This allows current to continue to flow through the device during normal operation.
This phenomenon is less of a concern in AC systems , as the zero crossing allows the component to turn-off and return to a high impedance state. We'll also find out what levels of protection are available and see why you might not have all the protection you need, even if you do use a quality surge protector.
The main job of a surge protector system is to protect electronic devices from "surges. A power surge, or transient voltage , is an increase in voltage significantly above the designated level in a flow of electricity. In normal household and office wiring in the United States, the standard voltage is volts. If the voltage rises above volts, there is a problem, and a surge protector helps to prevent that problem from destroying your computer. To understand the problem, it is helpful to understand something about voltage.
Voltage is a measure of a difference in electric potential energy. Electric current travels from point to point because there is a greater electric potential energy on one end of the wire than there is on the other end.
However, not all surge protectors have this built-in breaker, and space heaters can easily overwhelm a surge protector. To be on the safe side, avoid plugging high-power appliances like air conditioners and space heaters into a surge protector.
Instead, plug these devices directly into a wall. Now that you know what a surge protector is and how it works, make sure you know what to look for when buying a surge suppressor for your electronics.
You will also want to check the energy absorption rating and clamping voltage. The first refers to how much energy the surge protector can absorb before failing and should be a minimum of to joules.
Clamping voltage is the amount of voltage that triggers the MOV. Ideally, this should be volts or less. Want the ultimate protection against dangerous power surges? Call Brennan Electric today to learn about whole-house surge protection in Seattle and request a free estimate.
We can also help you with electrical repairs, installation, and maintenance as well as generator installation. How Do Surge Protectors Work? March 19, Categories: Surge Protection. Areas We Serve. MOVs are the most commonly used technology for the protection of AC power circuits. The surge current rating of an MOV is related to the cross-sectional area and its composition. In general, the larger the cross-sectional area, the higher the surge current rating of the device.
MOVs generally are of round or rectangular geometry but come in a plethora of standard dimensions ranging from 7 mm 0. The surge current ratings of these surge protective components vary widely and are dependent on the manufacturer.
As discussed earlier in this clause, by connecting the MOVs in a parallel array, a surge current value could be calculated by simply adding the surge current ratings of the individual MOVs together to obtain the surge current rating of the array. In doing so, consideration should be given to coordination of the operating characteristics of the MOVs selected. There are many hypotheses on what component, what topology, and the deployment of specific technology produces the best SPD for diverting surge current.
Instead of presenting all of the options, it is best that the discussion of surge current rating, Nominal Discharge Current Rating, or surge current capabilities revolve around performance test data. Regardless of the components used in the design, or the specific mechanical structure deployed, what matters is that the SPD has a surge current rating or Nominal Discharge Current Rating that is suitable for the application.
A more extensive description of these components follows. Typically, MOVs consist of a round or rectangular shaped body of sintered zinc oxide with suitable additives. Other types in use include tubular shapes and multilayer structures. Varistors have metal particle electrodes consisting of a silver alloy or other metal.
The electrodes may have been applied to the body by screening and sintering or by other processes depending on the metal used. Varistors also often have wire or tab leads or some other type of termination that may have been soldered to the electrode. The basic conduction mechanism of MOVs results from semiconductor junctions at the boundary of the zinc oxide grains formed during a sintering process.
The varistor may be considered a multi-junction device with many grains acting in series-parallel combination between the terminals. A schematic cross-sectional view of a typical varistor is shown in Figure 1.
Varistors have the property of maintaining a relatively small voltage change across their terminals while the surge current flowing through them varies over several decades of magnitude. This nonlinear action allows them to divert the current of a surge when connected in shunt across the line and limit the voltage across the line to values that protect the equipment connected to that line.
The P-N junction breakdown diode, in its basic form, is a single P-N junction consisting of an anode P and a cathode N. See Figure 2a. In DC circuit applications, the protector is reverse biased such that a positive potential is applied to the cathode N side of the device.
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