Digital Protection

In a large interconnected power system, having large sizes of alternators and higher capacity transmission lines, the protective relays and circuit breakers should operate as fast as possible to improve the transient stability of the system. The transients consist of a large number of harmonic currents and voltages with the addition of doing. component,

Both Fundamental components of current and voltage are with inherent large time delays required. For protective relaying purpose applications. Earlier, analog filters were used. The digital filters extract the fundamental components from the transient in about half a cycle.

The reasons for using digital protection relaying schemes in place of analog protection offer many advantages over analog protection. As minicomputers, microprocessors, and microcontrollers are developing protective relaying schemes have been developed on these devices. These devices offer low burden, filter in operation, low maintenance, and are not affected by external causes such as mechanical shocks and vibrations.

Digital protection Advantages

(a) Functional flexibility: A variety of protection functions such as distance relay characteristics (mho, ohm, quadrilateral, parabolic, etc.) can be obtained with a slight change in hardware and software.

(b) Low cost: The cost of equipment in digital protection is low.

(c) Self-checking functions: By using proper software, the hardware faults can be easily diagnosed.

(d) Easy communication: Using a microprocessor-based relay, an easy interface with digital communication equipment is possible.

(e) System integration and digital environment: The system of the digital relay can be easily integrated with other devices.

(f) Longer life: The performance of digital protection equipment does not change because of the aging of components.

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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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