Electrical4U What is an Ohmmeter? An ohmmeter, also written as ohm meter, measures electrical resistance. The instrument applies a known test stimulus and measures the response produced by electric current. Micro-ohmmeters and milliohmmeters are designed for very low values, while Megohmmeters, including instruments made by Megger, use higher test voltages to measure insulation resistance. A measured … Read more
Armature windings on a DC machine come in two families: lap windings and wave windings. This page is about lap windings, including simplex and duplex lap. Simplex lap has one set of paths (m = 1). Duplex lap has two (m = 2). What is a Lap Winding? Successive coils in a lap winding overlap. … Read more
Boiler feed water treatment strips dissolved salts, silica, suspended solids and dissolved gases from make-up so tubes do not scale or corrode. Natural sources all carry some of those loads; how much depends on the catchment.Why it is necessary to treat the raw water?Untreated raw water will deposit hardness salts on the boiler.Because- That is … Read more
Prospective short-circuit current is set by the source and the impedance up to the fault, not by the circuit breaker (CB). While that current still flows through a closed CB, the poles take thermal I2t heating and electrodynamic force. The formulas below estimate those stresses from a known short-circuit current. If the conducting parts are … Read more
Vacuum switchgear interrupts in a sealed vacuum bottle rather than in gas or oil. In medium voltage switchgear the usual voltage window is 3 to 36 kV. On that band vacuum now outsells air, SF6 and oil for new indoor boards, because a vacuum circuit breaker copes with frequent fault and load switching with little … Read more
A 3 kV to 36 kV switchgear system is classed here as medium voltage switchgear or MV switchgear. IEC practice can run MV from 1 kV to 52 kV, so this band is a common indoor and outdoor range rather than the only definition. These switchgears come as metal enclosed indoor type switchgear, metal-enclosed outdoor … Read more
Armature reaction is the armature mmf acting on the main field. At no load the magnetic neutral axis sits on the geometrical neutral axis, so the brushes sit there too. On load the armature flux lies along the interpolar axis and looks roughly triangular. That brush-axis mmf cross-magnetizes the main field. Flux crowds at the … Read more
On this page, high voltage switchgear means gear that handles voltage above 36 kV. IEC lists other HV steps (often 52 kV and up), so 36 kV is a common site cut-off rather than the only one. Switching at these levels draws a long, hot arc, so the poles and tanks have to be designed … Read more
Arc interruption theory is how a breaker kills the plasma after the contacts part. The insulating material (gas, oil, vacuum or air) in a circuit breaker has to do two jobs: On a fault the relay trips the breaker. As the poles part, an arc is drawn in the ionized gap. The insulator and the … Read more
A magnetic circuit is a closed path that magnetic flux follows, the magnetic analogue of an electric circuit. An iron-cored solenoid carrying DC sets up flux that leaves the N pole, crosses air to the S pole, then returns in the iron. A path that uses both air and iron is a composite magnetic circuit. … Read more