The boundary between each grain and its neighbor forms a diode junction, which allows current to flow in only one direction. When a small or moderate voltage is applied across the electrodes, only tiny current flows caused by reverse leakage through the diode junctions. When a large voltage is applied, the diode junction breaks down due to a combination of thermionic emission and electron tunneling, and large current flows.
Varistor can absorb part of a surge. The effect depends on the equipment and details of the selected Varistor. If a transient pulse is too high, the device may melt, burn, vaporize, or otherwise be damaged or destroyed. This set up can be arranged in the existing switch board from which the appliance gets power. The basic idea is be to delay the switching time of the relays which are electromagnetic switches to power on the electronic devices.
This simple circuit solves the problem. It gives power to the device only after a delay of two minutes when switched on or power resumes after a power failure.
During this interval, the mains voltage will stabilize. Basically the switching of the relay is controlled by the SCR, whose switching is in turn controlled by the rate of charging and discharging of the capacitor. The circuit works like the delay circuit in stabilizers. It uses only a few components and can be assembled easily. It works on the principle of charging and discharging of the capacitor.
A high value capacitor C1 is used to get the required time delay. At power on, C1 charges slowly through R1. When it gets fully charged, the SCR triggers and the relay switches on. So when the relay triggers, the device will switches on. The SCR has the latching property. That is, it triggers and the current flows from its Anode to Cathode when the gate gets a positive pulse.
The SCR continues to conduct, even if its gate voltage is removed. The SCR switches off only if its anode current is removed by switching off the circuit. An LED indicator is provided to indicate the activation of the relay. How to Set. Setting of the circuit is easy. The most important action is to remove yourself from danger. Crouching or getting low to the ground can reduce your chances of being struck, but does not remove you from danger.
If you are caught outside with no safe shelter nearby, the following actions may reduce your risk:. Indoor Safety Tips. Avoid electronic equipment Do NOT use your computers, laptops, game systems, washers, dryers, stoves, or anything connected to an electrical outlet. Lightning can travel through electrical systems, radio and television reception systems, and any metal wires or bars in concrete walls or flooring.
Equip your home with whole-house surge protectors to protect your appliances. Avoid corded phones Corded phones are NOT safe to use during a thunderstorm. Do NOT use them. However, it is safe to use cordless or cellular phones during a storm. Avoid windows, doors, porches, and concrete Do NOT lie on concrete floors during a thunderstorm. When lightning strikes that object, an arm of electricity, also referred to as a step leader, may branch off from the main bolt as the current jumps from object to human.
Conduction strikes occur when, as their name implies, conductive materials are involved. Think of these as the disembodied arms of a flash of lightning. When the lead bolt discharges, a streamer can appear nearby. And if you form a conductive bridge between one of these streamers and the ground, you can be struck. When you are struck by lightning, a few things happen. First, the electricity from the bolt moves over the surface of your skin, potentially causing burns—this is called a flashover.
Second, the current runs through your cardiovascular and nervous system, which is what causes the most damage. Because lightning is so hot five times hotter than the surface of the sun , burn damage is also a possibility, but may not be evident until necrosis or muscle damage sets in.
Your circulatory system can be clogged, kidneys damaged, and seizures and muscle contractions may ensue. The type of damage depends on the severity of the strike, but you may experience an irregular heartbeat, optical disturbances, memory issues, and ruptured ear drums.
According to Miguel Pineda, ER doctor and wilderness medicine fellow at UC San Diego, the extreme electric charge and pressure change caused by a strike can even paralyze the lungs and heart, leading to respiratory and cardiac arrest.
What is unique to lightning strikes, Pineda says, is that the paralysis of these affected organs will resolve after several minutes, similar to a computer rebooting. Lightning kills around 20 people each year and injures hundreds more.
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