Electrical4U 
A generator needs protection because insulation stress, mechanical force and temperature rise can destroy the machine. Those forces act on every alternator in service. A machine that stays within rating still sees brief overloads. Protection must still clear a fault before that overload becomes a winding or rotor failure. Relays and mechanical trips limit overload … Read more
Electrolyte of Lead Acid Battery Care of a flooded lead acid battery cell means keeping electrolyte strength, cell voltage and water level within the maker’s limits so the plates stay as lead dioxide and sponge lead. The electrolyte is sulfuric acid in distilled water. Concentrated sulfuric acid has a specific gravity of about 1.84. Stationary … Read more
To derive power conditions for alternators and synchronous motors, first consider two sinusoidal sources separated by a series impedance. The circuit contains a voltage source E1, a second source E2 and a branch with one resistor in series with an inductor. Let source E1 lead source E2 by load angle δ, with current defined from … Read more
What is a Block Diagram in a Control System? A block diagram shows each element of a control system as a box that holds that element’s transfer function. Read the diagram by following the signal from the reference input through those boxes to the output. The overall transfer function of that diagram is C(s)/R(s): the … Read more
A signal flow graph of a control system is a directed graph of the same linear relations as a block diagram. Nodes stand for signals. Branches replace blocks, summing points and take-off points.The gain of a branch is called transmittance in a signal flow graph. The equation y = Kx is one gain drawn as … Read more
Routine tests are the factory checks run on every circuit breaker before it leaves the works. IEC 62271-100 and IEC 62271-1 group them as follows Each test below confirms one part of that standard routine-test set. Type tests such as lightning-impulse and switching-impulse dielectric tests are not repeated on every unit. Power Frequency Over Voltage … Read more
The time response of a second-order control system is the output c(t) after a known input, most often a unit step. The order itself is the highest power of ‘s’ in the denominator of its transfer function. A control system is second order when that highest power of s is 2. Its unit-step shape is … Read more
After installation of power transformer, commissioning is the set of site tests and instrument checks that prove the unit matches the factory report and can be energised. Those checks must finish before the transformer is put into service. Common Pre-commissioning Tests of Transformer Measure insulation resistance of each winding with the transformer isolated from lines … Read more
Differential protection trips for an internal fault in the stator winding of a generator or alternator. It compares current at each end of the winding.That differential protection is applied with a longitudinal differential relay.instantaneous attracted armature type relays are used because they operate with little intentional delay. They still need matching CTs and restraint or … Read more
In power system protection a differential relay is the usual unit scheme for protecting transformers and generators from faults inside a defined zone.Differential relays trip when the difference between two or more similar currents or voltages exceeds a set value. They stay stable for a fault outside that zone. An over current relay trips when … Read more