Energized grounds

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. 

Similar to overhead line projects, switching transients such as cable energization, ground fault, and fault clearing are also studied for EHV AC cable projects as standard work. However, severe overvoltages related to these switching transients on cable systems have not been reported in the literature. 

This check may be carried out both at the works, after final assembly, and at the site after the installation before conducting routine tests or energizing the assembly. The ehecks can be carried out at a lower voltage to detect any shorting links or spanners left inadvertently on live terminals, weak insulation or insufficient clearance or creepage distances between the phases or phase to ground conduetors. In the ease of a defect the same must be rectified immediately. 

Shock occurs when tlie body becomes a part of tlic circuit, i.e. the current enters the body at one point and leaves at another. Shock normally occurs in one of tliree ways. The person must come in contact witli both wires of the electrical circuit with one wire of an energized circuit and the ground or w ith a metallic part that has become "hot by being in contact w ith an energized w ire while the person is also in contact with the ground. 

The electrodes face each other with a differential potential between the two sets, one set grounded and the other energized [91]. 

When the liquid makes contact with any of the electrodes, an electric current will flow between the electrode and ground. The current energizes a relay which causes the relay contacts to open or close depending on the state of the process involved. The relay in turn will actuate an alarm, a pump, a control valve, or all three. A typical system has three probes a low level probe, a high level probe, and a high level alarm probe. 

Secondary unimolecular reactions in these systems usually result either from production of hot energized species by chemical reaction or from conventional thermal activation. In a few systems, residual excitation from the original photochemical process may be of importance. An interesting and potentially valuable example, due to Srinivasan, is the production of highly vibrationally excited, ground electronic state diene molecules by internal conversion which follows photoexcitation. 

Sonic examples of how these rules apply are showai in Table l.l. Hydrogen, for instance, has only one electron, which must occupy the lovvest-energ - orbital. Thus, hydrogen has a l.s ground-state configuration. Carbon has six electrons and the ground-state configuration Is 2s 2p. nd so forth. Note that a super-script is UbCd tn represent the number of electrons in a jiarticular orbital. 

In contrast with j rotic solvents, w hich decrease the rates of S j2 reactions by lowering the ground-state energy of the nucleophile, X)lar aprotic solvents increase the rates of S]sj2 reactions by raising the ground-state energ) of the nucleophile. Acetonitrile (CH CN), dimethylformamide f(CH3)2NCHO,... 

Equipment failure is another cause of electrical shock. Some examples include leakage in washing machines, electrical irons, water pumps, broken energized power lines, grinding, and drilling machines. The equipment must he grounded with three wire cables. 

In this reaction, triplet methylene inserts in the ethene molecule to produce an energized cyclopropane molecule, which may then either isomerize to propene or may be collisionally deactivated to give cyclopropane. Molecules may also be activated photochemically. Although most photochemical processes involve more than one electronic state of the molecule, it is possible in some cases to produce molecules in their electronic ground states with high vibrational excitation, and these may subsequently isomerize or dissociate. A typical example is the photoexcitation of cycloheptatriene followed by its isomerization to toluene. 

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