Earthing star point

An unrestricted earth fault relay that is connected in the star-point earth circuit of the equipment being protected. The characteristic is time dependent so that time coordination is achieved with the 50 N devices downstream. 

High voltage generators used in the oil industry are usually earthed by connecting an impedance, which is invariably a resistor, between its star point and the ground . Occasionally generators are... 

The star-point connection to earth is provided with a current transformer and a sensitive relay. The relay (51 G) is of a definite time delay or inverse time delay type so that it can be graded as back-up protection to earth fault relays at downstream feeders and consumers. 

Figure 12.10 is almost the same as Figure 12.9, the difference being that the star point of the secondary winding is solidly earthed, which is usually the case with low voltage secondary systems. 

Most power systems use the solidly earthed star points. High impedance earthing may be preferred for ships, occasionally for offshore platforms, and frequently for emergency and uninterruptible supplies in all locations. 

It is possible to design three-wire and four-wire systems that do not need to be solidly earthed. Instead a high impedance is inserted between the star point connection and earth, as shown in Figure 13.3. Alternatively an artificial star point is created and again a high resistance is connected to earth as shown in Figure 13.4. 

The first letter denotes the source of power from a star-connected winding. T denotes that the star point of the source is solidly connected to earth, which is usually at a location very near to the winding. 1 denotes that the star point and the winding are isolated from earth by their design and... 

The type TNS method shonld be nsed, TNG and TNCS are not recommended. The neutral conductor and the protective earth condnctor shall only be connected together at the star point of the source. A transition from TNS to TNG or from TNG to TNS shonld be avoided otherwise the design may become too complicated. 

This method is commonly used in the oil industry because of the predominance of steelwork in a typical installation. In this method the power system is earthed separately from the equipment frames and cnbicles. The star point at the sonrce is the only common earthing point. The lEG standard reqnires the circuit to be protected by a residual earth fault current device at the switchboard or motor control centre, where the consumer is located in a Zone 1 area. 

In any star-connected system currents flow along the lines (/O, through the load and return by the neutral conductor connected to the star point. In a balanced three-phase system all currents have the same value and when they are added up by phasor addition, we find the resultant current is zero. Therefore, no current flows in the neutral and the star point is at zero volts. The star point of the distribution transformer is earthed because earth is also at zero potential. 

SVLs are installed at SSJs in order to suppress short-term sheath overvoltages. Figure 3.18 shows the connection of SVLs when the sheath circuit is cross-bonded in a link box. SVLs are often arranged in a star formation with their neutral points earthed. If study results show that the sheath overvoltage exceeds the TOV rating of SVLs, the ECC can be installed as shown in... 

The H and He produced in the Big Bang served as "feed stock" from which all heavier elements were later created. Less than 1% of the H produced in the Big Bang has been consumed by subsequent element production and thus heavy elements are rare. Essentially all of the heavier elements now in the Earth were produced after the Big Bang inside stars. Following the Big Bang, the universe expanded to the point where instabilities formed galaxies, mass concentrations from which up to stars could develop. 

One of the projects planned for the next decade is Darwin, to be organised by ESA. Darwin will be a flotilla of four or five spacecraft that will search for Earth-like planets around other stars and analyse their atmospheres for the chemical signature of life. Three of the spacecraft will carry 3 1 m space telescopes , which will form the Infrared Space Interferometer IRSI they will be stationed 1.5 million kilometres from Earth, in the opposite direction from the Sun, at the Lagrangian Point L2 (a libration point at which the gravitational forces of the Earth and the sun cancel out). 

Taking a value of 107 for N would mean that in our galaxy (with its perhaps 100 billion stars), there could be several million planets with life forms capable of interstellar communication. However, if these were distributed statistically, the nearest would still be 200 light years away from Earth. One point is important the term probability used in the Drake equation is interpreted in the sense of subjective probability (a term from the nomenclature used by statisticians and probability theorists), as the numerical value of this probability is determined only by the experience of the scientist concerned (Casti, 1989). Casti also provides more information on the Drake factors (apart from the factor fs) in the chapter Where are they then In summary, we can say that the Drake equation is a first attempt to quantify the ETI problem in order to move from the area of science fiction and pure speculation to that of serious scientific debate. 

Promethium is a silvery-white, radioactive metal that is recovered as a by-product of uranium fission. Promethium-147 is the only isotope generally available for smdy. The spectral lines of promethium can be observed in the light from a distant star in the constellation Andromeda. Even so, it is not found naturally on Earth, and scientists consider it to be an artificial element. Its melting point is 1,042°C, its boiling point is estimated at 3,000°C, and its density is 7.3 g/cm. ... 

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