Electrical4U 
Enthalpy, entropy and the second law sit on top of the first-law energy balance. Enthalpy is u + pv. Entropy change along a reversible path is dq_rev / T. The second law says the entropy of an isolated system does not fall. This page then covers internal energy, cyclic and arbitrary processes and reversibility. Internal … Read more
Industrial automation uses PCs, PLCs and PACs to run plant machines and process units with far less hands-on work than a mechanized line. A mechanized machine still needs an operator at the controls. Plants specify programmable control when a process needs tighter accuracy, repeatable quality and measured cycle time.Automation sits beyond mechanization: those controllers run … Read more
A motor protection relay for a high-voltage induction motors feeder trips the breaker when current, stall or earth-fault measurements show a winding or driven-load fault. IEEE Std C37.96 is the usual AC motor protection guide. Plants often choose high voltage for ratings above about 250 HP so operating current and cable size stay lower. That … Read more
A motor protection circuit breaker (MPCB) is a compact electrical protection device for electric motors. It is a disconnect with a thermal overload trip plus a magnetic short-circuit trip, often built to IEC 60947-2 and IEC 60947-4-1. Motors drive fans, pumps and machines, so they need that combined protection. MPCBs are common on these commercial … Read more
A three-phase AC system uses three voltages 120° apart. Utilities use it for power generation, power transmission, distribution and electric motors because a balanced three-phase circuit carries more power for a given conductor mass and gives nearly constant instantaneous power. Many homes still take a single-phase service from that network. A Three phase system has … Read more
A cyclotron is a compact ion accelerator. Its working principle of a cyclotron is that ions spiral in a uniform magnetic field while a radio-frequency voltage across two Dees adds kinetic energy at each gap crossing. The orbit period is independent of speed in the non-relativistic limit, so a fixed radio frequency stays in step. … Read more
Engineering thermodynamics studies energy, heat and work in plant and equipment. That heat-power branch of engineering is used to rate machines and processes. Plant performance is judged by product output, feed or fuel use, production cost and environmental load. Engineers apply thermodynamics to equipment meant for safety and comfort. Classical engineering thermodynamics grew through the … Read more
The conductor resistance test measures the DC resistance of copper or aluminium conductors. IS 10810-5 reports that value in ohms per kilometre at 20°C. For a given voltage, higher resistance means less current. Conductor size, construction, temperature and resistivity all change the reading. Cable standards compare the corrected value with a maximum in ohms per … Read more
The wrapping test checks whether aluminium wire used in power cables can wrap and unwrap around its own diameter without breaking. IS 10810-3 (1984) is the Indian cable method for that ductility check. A conductor that passes can take the torsion of stranding and installation without snapping. The pass rule in that method is simple: … Read more
The Substitution theorem says you may replace one branch by an equivalent source without changing the voltages and currents in the rest of a uniquely solved network. The usual replacements are a voltage source equal to that branch voltage, or a current source equal to that branch current. The same idea is used to prove … Read more