Electrical4U 
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
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
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
An inter-turn stator fault shorts two turns of the same phase in one slot. Longitudinal differential and stator earth fault protection often miss it until the puncture reaches another phase or earth. A dedicated scheme is used on machines with many conductors of different potential in the same slot. The fault often becomes an earth … Read more
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
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