Distance relays characteristics may be Mho, Quadrilateral, Offset Mho, etc. In the case of the quadrilateral characteristic or long reaching mho characteristics, additional care may be required to remain secure during heavy load.In the case of parallel lines, the mutual coupling of these lines can cause distance relays to under reach and over reach. Distance protection, in its basic form, is a non-unit system of protection offering considerable economic and technical advantages.Unlike phase and neutral overcurrent protection, the key advantage of distance protection is that its fault coverage of the protected circuit is virtually independent of source impedance variations. Figure 1 – Advantages of distance over overcurrent protectionDistance protection is comparatively simple to apply and it can be fast in operation for faults located along most of a protected circuit. It can also provide both primary and remote back-up functions in a single scheme. It can easily be adapted to create a unit protection scheme when applied with a signalling channel.In this form it is eminently suitable for application with, for the protection of critical transmission lines. Such a relay is described as a distance relay and is designed to operate only for faults occurring between the relay location and the selected reach point, thus giving discrimination for faults that may occur in different.The basic principle of distance protection involves the division of the voltage at the relaying point by the measured current.
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The main objective of the project is to develop a model or models to implement V/f control of an induction motor. In order to do that, one must be familiar with the PWM Inverter which drives the induction motor. Hence, PWM signal generation, and Inverter topologies are also studied and simulated. LECTURENOTESON FUNDAMENTALSOFCOMBUSTION Joseph M. Powers Department of Aerospace and Mechanical Engineering University of Notre Dame Notre Dame, Indiana.
The apparent impedance so calculated is compared with the reach point impedance. If the measured impedance is less than the reach point impedance, it is assumed that a fault exists on the line between the relay and the reach point.The reach point of a relay is the point along the line impedance locus that is intersected by the boundary characteristic of the relay.Since this is dependent on the ratio of voltage and current and the phase angle between them, it may be plotted on an R/X diagram.
The loci of power system impedances as seen by the relay during faults, power swings and load variations may be plotted on the same diagram and in this manner the performance of the relay in the presence of system faults and disturbances may be studied.Relay performanceDistance relay performance is defined in terms of reach accuracy and operating time. Reach accuracy is a comparison of the actual ohmic reach of the relay under practical conditions with the relay setting value in ohms. Reach accuracy particularly depends on the level of voltage presented to the relay under fault conditions.The impedance measuring techniques employed in particular relay designs also have an impact. Operating times can vary with fault current, with fault position relative to the relay setting, and with the point on the voltage wave at which the fault occurs.Depending on the measuring techniques employed in a particular relay design, measuring signal transient errors, such as those produced by Capacitor Voltage Transformers or saturating CT’s, can also adversely delay relay operation for faults close to the reach point. It is usual for electromechanical and static distance relays to claim both maximum and minimum operating times.However, for modern digital or, the variation between these is small over a wide range of system operating conditions and fault positions.Distance Relay CharacteristicsSome numerical relays measure the absolute fault impedance and then determine whether operation is required according to impedance boundaries defined on the R/X diagram.Traditional distance relays and numerical relays that emulate the impedance elements of traditional relays do not measure absolute impedance.
They compare the measured fault voltage with a replica voltage derived from the fault current and the zone impedance setting to determine whether the fault is within zone or out-of-zone. Distance relay impedance comparators or algorithms which emulate traditional comparators are classified according to their polar characteristics, the number of signal inputs they have, and the method by which signal comparisons are made.The common types compare either the relative amplitude or phase of two input quantities to obtain operating characteristics that are either straight lines or circles when plotted on an R/X diagram.
1-2 Characteristics of GearsThe teeth are straight and parallel to the shaft axis. Transmits power and motion between rotating two parallel shafts.Features:. Easy to manufacture. There are no axial force.
Relatively easy to produce high-quality gears. The most common type of gearApplications:. Transmission componentsThe teeth are twisted oblique to the gear axis.Helix direction (helix hand):The hand of helix is designated as either left or rightRight-hand and left-hand helical gears mate as a set.
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