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What is ac generator?
An AC or alternating current generator is a piece of machinery that produces AC electricity. Most commonly this machine is powered by steam.in simple terms it consists of a series of blades that are turned by steam.a magnetic field is excited on the rotor which then cuts through lines of magnetism that are present on the stator by the power grid. As more power is applied to the rotor, the turbine must spin harder,not faster, to push more power onto the grid. RPM of rotor is determined by the number of poles in the stator. Most commonly a turbine will spin at 3600rpm.... or, 60 times per second giving us the USA electrical grid a 60Hz frequency. This is scratching the paint on AC generation but its a start.
Why voltage have negative sign?
The strength of a electrical flow is measured in Voltage and Electrons are negative. Alternating current (AC) oscillates between positive and negative as the direction of flow periodically reverses direction. An alternating current of 60Hz therefore changes direction 60 times a second, and can be visualised as a sine wave that oscillates above and below the zero baseline, with a period (a complete cycle) of 1/60th of a second. Direct current (DC) infers constant polarity, meaning the direction of flow is unidirectional (one direction only). While DC can oscillate as a full-wave rectification or a half-wave rectification, it is always indicated as a positive voltage (the line or wave is always above the zero baseline). A voltage or current indicated with a negative symbol therefore implies alternating current although AC is more correctly indicated by the ± symbol. Direct current is generally indicated by a long horizontal bar above three short horizontal bars.
