Electrical4U Rotor earth-fault protection watches the field winding of an alternator for a connection to earth. One earth fault on an otherwise isolated field does not circulate current. A second earth fault shorts part of the winding, unbalances the air-gap magnetic field and can damage the bearings. Find the first field earth fault and take the … Read more
Mobility of a charge carrier is the ratio of drift velocity to the applied electric field in a conductor. Drift velocity is set by that field and by the metal’s mobility of charge carriers. Different metals therefore have different drift speeds in the same field.In a metal the valence band is not completely filled, so … Read more
This test measures insulation and sheath thickness on electric power cables. IS 10810-6 is the Indian method. A power cable needs enough wall to stand the rated voltage and the pull of laying. The product standard then compares the measured average and the measured minimum with its own limits. Apparatus required to test for thickness … Read more
The tensile test measures breaking strength of aluminium wires used in electric power cables. IS 10810-2 pulls a specimen to fracture so the conductor grade can be checked against IS 8130. The metal must survive pulling during stranding and laying. Soft copper uses the annealing (elongation) test instead. Apparatus required for Tensile Test Method of … Read more
The annealing test measures elongation at break of annealed copper wires, aluminium welding-cable wires and solid conductors of electric power cables. A current-carrying core of a power cable is twisted and bent during laying, so the metal must stretch without cracking. IS 10810-1 pulls a marked length to fracture and IS 8130 requires that elongation … Read more
High Voltage Test (Water Immersion Test) :Type, acceptance and routine tests are the three factory groups. For the water-immersion type test, IS 1554-1 takes about 3 m of core from the finished cable or cord. The core sits in a water bath with the ends at least 200 mm above the water. General-purpose PVC uses … Read more
A power cable is sized and rated for voltage, continuous current, short-circuit current and voltage drop. Overhead lines or buried circuits can both carry the same load. Power cables are the sheathed assemblies used for power transmission and distribution. Each core is one or more individually insulated electrical conductors, usually held together with an overall … Read more
In an electrical or electronic plant an Annunciator is a panel that announces a fault or an unusual process state so the operator can see which point has gone abnormal. What is Alarm Annunciator? An alarm annunciator is an audio-visual warning. A window flashes and a horn sounds when a field contact changes state. The … Read more
Loss of field or excitation means the field supply has failed. On a large machine that supply is often a separate auxiliary source or a separately driven DC generator. If that auxiliary supply or its driving motor fails, the machine loses field. After loss of excitation it runs above synchronous speed.The generator or alternator then … Read more
Stator earth-fault protection limits earth current when a stator winding of an alternator goes to earth. The stator star point is earthed through an impedance so the current is small enough to limit burning of the core and winding. If that impedance is high, earth current can sit below rated current. Phase differential relays then … Read more