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Contactor AC contactor for pump application. In semiconductor testing, contactor can also refer to the specialised socket that connects the device under test. In process industries a contactor is a vessel where two streams interact, for example, air and liquid. A contactor is an electrically controlled switch (a relay) used for switching a power or control circuit.[1] A contactor is controlled by a circuit which has a much lower power level than the switched circuit. Contactors come in many forms with varying capacities and features. Unlike a circuit breaker a contactor is not intended to interrupt a short circuit current. Contactors range from those having a breaking current of several amps and 24 V DC to thousands of amps and many kilovolts. The physical size of contactors ranges from a device small enough to pick up with one hand, to large devices approximately a meter (yard) on a side. Contactors are used to control electric motors, lighting, heating, capacitor banks, and o...

Current transformer A current transformer is a device for measuring a current flowing through a power system and inputting the measured current to a protective relay system. Electrical power distribution systems may require the use of a variety of circuit condition monitoring devices to facilitate the detection and location of system malfunctions. Current transformers and current sensors are well known in the field of electronic circuit breakers , providing the general function of powering the electronics within the circuit breaker trip unit and sensing the circuit current within the protected circuit. Ground fault circuit breakers for alternating current distribution circuits are commonly used to protect people against dangerous shocks due to line-to-ground current flow through someone's body. Ground fault circuit breakers must be able to detect current flow between line conductors and ground at current levels. Upon detection of such a ground fault current, the contacts of th...

Voltage and current As was previously mentioned, we need more than just a continuous path (circuit) before a continuous flow of electrons will occur: we also need some means to push these electrons around the circuit. Just like marbles in a tube or water in a pipe, it takes some kind of influencing force to initiate flow. With electrons, this force is the same force at work in static electricity: the force produced by an imbalance of electric charge. If we take the examples of wax and wool which have been rubbed together, we find that the surplus of electrons in the wax (negative charge) and the deficit of electrons in the wool (positive charge) creates an imbalance of charge between them. This imbalance manifests itself as an attractive force between the two objects:   If a conductive wire is placed between the charged wax and wool, electrons will flow through it, as some of the excess electrons in the wax rush through the wire to get back to the wool, filling the deficien...

Static electricity It was discovered centuries ago that certain types of materials would mysteriously attract one another after being rubbed together. For example: after rubbing a piece of silk against a piece of glass, the silk and glass would tend to stick together. Indeed, there was an attractive force that could be demonstrated even when the two materials were separated: Glass and silk aren't the only materials known to behave like this. Anyone who has ever brushed up against a latex balloon only to find that it tries to stick to them has experienced this same phenomenon. Paraffin wax and wool cloth are another pair of materials early experimenters recognized as manifesting attractive forces after being rubbed together: This phenomenon became even more interesting when it was discovered that identical materials, after having been rubbed with their respective cloths, always repelled each other: It was also noted that when a piece of glass rubbed with silk was exposed to a ...

FOR E "http://ww.onesmartclick.com/engineering/basic-electrical-engineering.html" DOS & DON’TS FOR 210 MW TURBO GENERATORS & ITS AUXILIARIES BEFORE START UP & DURING OPERATION BEFORE STARTUP MAIN T.G. DOS 1. Check IR value & polarization index of stator winding w.r.t body as well as w.r.t other phases. Megger used is 1000 volts. 2. Check IR value rotor winding with 500 volt megger. 3. Check IR value of generator bearing pedestals on exciter side and that of the seal oil and lubricating oil pipelines. 4. Check up IR values of various RTD’s. 5. Check the lubricating oil is flowing through the generator bearing. 6. Check that oil is flowing through the shaft seals of the generator. 7. Check that inlet valves of TG gas coolers are fully open and water flow through gas coolers is regulated by outlet valves only. 8. Check the functioning of the various instruments connected with main TG. 9. Check the tension of brushes on T.G. slip rings. 10. Chec...