Trapped Charge Effect

Trapped charges occur on the transmission lines in three-pole out closure operations. The contact-making of three poles of a circuit breaker is non-simultaneous. Consider breakers at the sending end and receiving ends of a line and a transient ground fault, which needs to be cleared by an auto closure operation. The opening of two breakers is nonsimultaneous and the one which opens later must clear two-line phases at no load. These two phrases can, therefore remain charged at the peak of the power frequency voltage, which is still present when the closure takes place. After the dead time, one breaker has to close with two phases still charged.

If the closing instant happens to be such that the trapped charge and power frequency voltage are of opposite polarity, maximum transient overvoltage will occur. And these overvoltages will result in the over-current m transmission line.

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Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant. The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated. There is sometimes difficulty 1n locating the drainage face, and sometimes thin previous seams that can act as good drainage faces are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform.

Types Of Current Collector

Current Collector A current collector is a device used to collect electrical current from a moving conductor, such as a train or a trolley. It is typically used in electric vehicles, such as trains and trams, to transfer power from an overhead power source to the vehicle's electric motor. The current collector consists of a sliding contact, which is often made of carbon or copper, that makes contact with an overhead power source, such as an overhead catenary wire or a third rail. The sliding contact is mounted on the vehicle and is typically in the form of a pantograph or a trolley pole. The pantograph is a device with a metal frame and a spring-loaded arm that presses against the overhead power source. It is raised and lowered by the operator of the vehicle, and as it moves along the overhead power source it maintains contact and collects the electrical current. The trolley pole is a vertical pole that is mounted on the roof of the vehicle and has a horizontal arm that extends out

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