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DictionarySeegaitThree-Phase Circuit three-phase circuit[′thrē ¦fāz ′sər·kət] (electricity) A circuit energized by alternating-current voltages that differ in phase by one-third of a cycle or 120°. Three-Phase Circuit (or three-phase system), a combination of three single-phase AC circuits—the phases—in which there are three alternating voltages of identical frequency that  Figure 1. Three-phase circuits: (a), (b), and (c) with star-connected generator windings, (d) and (e) with delta-connected generator windings, (a), (b), and (d) with star-connected phase loads, (c) and (e) with delta-connected phase loads, (a) with neutral conductor, (b) without neutral conductor; (A), (B), and (C) line wires, (N) neutral conductor, (G) generator, (L) load, (Ul) and (Up) line and phase voltages, (ll) and (lp) line and phase currents
are shifted in phase with respect to one another. The three-phase circuit is a special case of a multiphase system. Balanced three-phase systems, whose voltages are sinusoidal and of equal magnitude and have a phase shift of 120°, are the most common. Each phase of a three-phase system may constitute an independent electric circuit, or the phases may be electrically interconnected. Electrically interconnected systems are usually used in practice. In the simplest case, such systems consist of the phase windings of a three-phase generator, three power receivers (phase loads), and connecting line wires (see Figure 1). If the phase windings of the generators and the phase loads are star-connected, the circuit may also include a neutral conductor, which connects the neutral points of the generator and load. The neutral conductor reduces the influence of each phase’s operation on the other phases and makes possible the connection of single-phase loads to three-phase circuits. The voltages between the line wires are called line voltages, and the currents flowing through the conductors are called line currents. Currents flowing through the phase windings of the generator and through the phase loads are called phase currents, and the voltages across the windings and loads are called phase voltages. Generally speaking, the line currents and voltages differ from the phase currents and voltages. The three-phase system has become the most widely used system in power engineering. It was first proposed in 1891 by M. O. Dolivo-Dobrovol’skii, who developed all the basic components of the system, including generators, transformers, transmission lines, and three-phase electric motors. A three-phase circuit is more economical than a single-phase AC circuit, and it provides a substantial reduction in ripple of the rectified current. The use of three-phase circuits simplifies the generation of a rotating magnetic field in AC electric motors. REFERENCESObshchaia elektrotekhnika. Edited by V. S. Pantiushin. Moscow, 1970.
Teoreticheskie osnovy elektrotekhniki, vol. 1. Moscow, 1972.M. A. MARICHEV three-point gait
gait [gāt] the manner or style of walking.gait analysis evaluation of the manner or style of walking, usually done by observing the individual walking naturally in a straight line. The normal forward step consists of two phases: the stance phase, during which one leg and foot are bearing most or all of the body weight, and the swing phase, during which the foot is not touching the walking surface and the body weight is borne by the other leg and foot. In a complete two-step cycle both feet are in contact with the floor at the same time for about 25 per cent of the time. This part of the cycle is called the double-support phase.
An analysis of each component of the three phases of ambulation is an essential part of the diagnosis of various neurologic disorders and the assessment of patient progress during rehabilitation and recovery from the effects of a neurologic disease, a musculoskeletal injury or disease process, or amputation of a lower limb.antalgic gait a limp adopted so as to avoid pain on weight-bearing structures, characterized by a very short stance phase.ataxic gait an unsteady, uncoordinated walk, with a wide base and the feet thrown out, coming down first on the heel and then on the toes with a double tap.double-step gait a gait in which there is a noticeable difference in the length or timing of alternate steps.drag-to gait a gait in which the feet are dragged (rather than lifted) toward the crutches.equine gait a walk accomplished mainly by flexing the hip joint; seen in palsy" >crossed leg palsy.festinating gait one in which the patient involuntarily moves with short, accelerating steps, often on tiptoe, with the trunk flexed forward and the legs flexed stiffly at the hips and knees. It is seen in parkinson's disease" >parkinson's disease and other neurologic conditions that affect the ganglia" >basal ganglia. Called also festination.four-point gait a gait in forward motion using crutches: first one crutch is advanced, then the opposite leg, then the second crutch, then the second leg, and so on.  Four-point gait. From Elkin et al., 2000.gluteal gait the gait characteristic of paralysis of the gluteus medius muscle, marked by a listing of the trunk toward the affected side at each step.helicopod gait a gait in which the feet describe half circles, as in some conversion disorders.hemiplegic gait a gait involving flexion of the hip because of footdrop and circumduction of the leg.intermittent double-step gait a hemiplegic gait in which there is a pause after the short step of the normal foot, or in some cases after the step of the affected foot.Oppenheim's gait a gait marked by irregular oscillation of the head, limbs, and body; seen in some cases of multiple sclerosis.scissors gait a crossing of the legs while advancing with slow, small steps.spastic gait a walk in which the legs are held together and move in a stiff manner, the toes seeming to drag and catch.steppage gait the gait in footdrop" >footdrop in which the advancing leg is lifted high in order that the toes may clear the ground. It is due to paralysis of the anterior tibial and fibular muscles, and is seen in lesions of the lower motor neuron, such as multiple neuritis, lesions of the anterior motor horn cells, and lesions of the cauda equina.stuttering gait a walking disorder characterized by hesitancy that resembles stuttering; seen in some hysterical or schizophrenic patients as well as in patients with neurologic damage.swing-through gait that in which the crutches are advanced and then the legs are swung past them.swing-to gait that in which the crutches are advanced and the legs are swung to the same point.tabetic gait an ataxic gait in which the feet slap the ground; in daylight the patient can avoid some unsteadiness by watching his feet.three-point gait that in which both crutches and the affected leg are advanced together and then the normal leg is moved forward. See illustration at crutches.two-point gait that in which the right foot and left crutch or cane are advanced together, and then the left foot and right crutch. See illustration at crutches.waddling gait exaggerated alternation of lateral trunk movements with an exaggerated elevation of the hip, suggesting the gait of a duck; characteristic of muscular dystrophy" >muscular dystrophy.three-point gaitA gait in which the crutches and the affected leg are advanced first, then the other leg.See also: gait |