ELECTRICAL CIRCUITS

Electrical symbols are quicker and easier to draw than realistic pictures of the components.

circuit diagramsIn circuit diagrams components are represented by the following symbols;cellbatteryswitchlampmotorammetervoltmeterbuzzerresistorvariable resistor

Series Circuits

Parallel Circuits

types of circuitThere are two types of electrical circuits;SERIES CIRCUITSPARALLEL CIRCUITS

The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round.SERIES CIRCUITSIf one bulb blows it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITSThe current has a choice of routes.The components are connected side by side. If one bulb blows there is still be a complete circuit to the other bulb so it stays alight.

measuring current & voltagecopy the following circuits on the next two slides.complete the missing current and voltage readings.remember the rules for current and voltage in series and parallel circuits.

measuring current & voltageVV6V4AAAa)

measuring current & voltageVV6V4AAAAb)

answers3V3V6V4A4A6V6V6V4A4A2A2A4Aa)b)

ELECTRICAL MACHINES INVERVIEW QUESTIONS

Principle of operation of a generator?An electric generator is a machine that converts mechanical energy into electrical energy. An electric generator is based on the principle that whenever flux is cut by a conductor, an e.m.f. is inducedThe direction of induced e.m.f. (and hence current) is given by Flemings right hand rule.

Role of a Commutatorto facilitate the collection of current from armature conductors.To convert alternating current induce in the armature conductors into unidirectional current

function of brushessimply to lead current from the rotating loop or winding to the external stationary load.

Different types of generators(i) Separately excited d.c. generators(ii) Self-excited d.c. generatorsA d.c. generator whose field magnet winding is supplied from an independent external d.c. source (e.g., a battery etc.) is called a separately excited generator. A d.c. generator whose field magnet winding is supplied current from the output of the generator itself is called a self-excited generator.

Series generator the field winding is connected in series with armature windingShunt generator the field winding is connected in parallel with armature winding Compound generator there are two sets of field windings on each pole Short Shunt in which only shunt field winding is in parallel with the armature winding Long Shunt in which shunt field winding is in parallel with both series field and armature winding

losses in DC MachinesCopper losses: Iron or core losses: Types 1.Hysteresis loss 2. Eddy current lossMechanical lossesconstant losses: Iron losses, Mechanical losses, Shunt field lossesVariable losses: Copper loss.