High-resistance short circuits

Electrical applications represent the primary use of IR thermography in facilities and utilities. They also represent the most straightforward application of the equipment. The most common electrical findings are caused by high electrical resistance, short circuits, open circuits, inductive currents, and energized grounds. 

The basic difference between the circuit breaker and the GFI is the amount of current to which each is designed to respond. Basically, the GFI is an extremely rapidly acting device sensitive to very low current—approximately 5 to 20 milliamperes. The GFI is used where a live conductor may develop a high-resistance short to a direct earth ground for example, where faulty insulation may develop in wet areas or a spill becomes electrically hot. Conventional breakers ordinarily will not respond to current leakage in such cases. In the U.S., electrical codes require that all outlets that are newly installed in bathrooms, kitchens near sinks, and outdoors be protected by GFI devices. Their purpose is to protect... 

There are several methods to determine and compare the resistance to partial discharges. Some tests are done on finished cables, such as the U-bend test, and others are done on laboratory samples molded from the insulation, that are subjected to partial discharges created by sharp objects, such as needles under high voltages. The tests compare either the energy required or the length of time required to erode or fail (short circuit) samples of similar thickness. 

Spontaneous low resistance internal short circuits can develop in silver—zinc and nickel—cadmium batteries. In high capacity cells heat generated by such short circuits can result in electrolyte boiling, cell case melting, and cell fires. Therefore cells that exhibit high resistance internal short circuits should not continue to be used. Excessive overcharge that can lead to dry out and short circuits should be avoided. 

If it is very high, so that its power loss Vf/Rj is low then it may be left permanently in the circuit. Otherwise it should be introduced into the circuit only during interruption through the switching device) (wired across the N(D contact of the switching contactor). This will provide the resistance across the capacitor banks when being interrupted and short-circuit it when closed. 

Underwriters Laboratories (UL) requires that consumer batteries pass a number of safety tests [3]. UL requires that a battery withstand a short circuit without fire or explosion. A positive temperature coefficient (PTC) device [4] is used for external short-circuit protection. The resistance of a PTC placed in series with the cell increases by orders of magnitude at high currents and resulting high temperatures. However, in the case of an internal short, e.g., if the positive tab comes lose and contacts the interior of the negative metal can, the separator could act as a fuse. That is, the impedance of the separator increases by two to three orders of magnitude due to an increase in cell temperature. 

Separators in lithium ion batteries must separate positive electrodes and negative electrodes to prevent short circuits, and must allow passage of electrolytes or ions. Porous films and nonwoven fabrics of resins are known separators. The lithium ion battery separators are also required to exhibit stable properties at high temperatures such as in charging, and therefore high heat resistance is desired (21). 

Alkaline batteries are capable of high current discharges and accidental short circuits should be avoided. Spontaneous low resistance internal short circuits can develop in silver-zinc and nickel-cadmium batteries. 

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