8) This describes the essential skills and knowledge and their level, required for this unit. Evidence shall show that knowledge has been acquired of safe working practices and developing engineering solutions for d.c. machine problems. All knowledge and skills detailed in this unit should be contextualised to current industry practices and technologies. KS01-EG144A Direct current machine diagnostics Evidence shall show an understanding of developing engineering solutions for d.c. machine problems to an extent indicated by the following aspects: T1 Basic d.c. machine construction and operation encompassing: General principles of operation Applications of d.c. machines Construction of d.c. machines d.c. machine configurations; series, shunt, compound long shunt and compound short shunt Armature and field currents Insulation Ratings Cooling paths Bearings General maintenance of d.c. machines T2 Construction and use of lap and wave windings encompassing: coils and elements generated voltage equation for generator generated voltage equation for motors application of lap and wave windings T3 Commutation process encompassing: use of interpoles loading of machines brush shifting brush selection classes of brush grades Note: Examples include: natural graphite, hard carbon, electrographite, metal-graphite, metal-carbon, “treated” grades carbon brush contact characteristics Note: Examples include: specific resistance, thermal conductivity, density and porosity, elastic properties, contact properties carbon brush factors Note: Examples are: pressure, current, polarity, speed brush construction Note: Examples are: dimensions, tolerances, preferred sizes, surfaces, edges, bevels, flexible shunts, connection of flexible shunt to brush, insulation of flexible connections brush holders Note: Examples are: types, brush angles, trailing holders, reaction holders, top bevel angles, reversible rotation, cantilever holders, effective arc of contact, construction of brush holders, pressure mechanism mounting of brush holders and brushes Note: Examples are: clearances, brush angle, brush arm spacing, alignment, staggering, brush bedding, brush pressure brush operation Note: Examples are: temperature rise, number and size of brushes, current distribution etween brushes, slotting brushes, polarity effects, arc of contact, materials for commutators, mica selection of brush grades Note: Examples are: machine data, current density, commutator peripheral speed, brush arc, pitch of segments, number of segments covered by brush, cooling surface T4 Armature reaction in d.c. machines encompassing: effect of armature reaction on d.c. machine characteristics use of compensating winding T5 d.c. generators encompassing: relative advantages and disadvantages of the various dc generator configurations and their performance under various load conditions voltage regulation as a percentage or per unit value operation in parallel T6 d.c. motors encompassing: relative advantages and disadvantages of the various dc motor configurations and their performance under various load conditions shape of motor speed/torque curves reversal of rotation T7 Starting and protection of d.c. motors encompassing: types of d.c. motor starters in use d.c. motor protection T8 Speed regulation and speed control of d.c. motors encompassing: methods in use effect on motor design and operation caused by the use of SCR speed control equipment T9 Braking of d.c. motors encompassing: Plugging Dynamic Regenerative Mechanical T10 Losses, heating and efficiency encompassing: Copper losses Iron losses Mechanical losses Efficiency T11 Acceleration of d.c. motors and loads encompassing: characteristics of typical loads matching a suitable motor to a given load heating of windings derating of motors T12 Special d.c. motors construction, operation and applications encompassing: permanent-magnet motors brushless motors (e.c. motors) coreless and moving coil motors linear motors printed circuit motor stepping motors voice-coil motors T13 Maintenance of d.c. machines encompassing: routine maintenance breakdown repairs T14 types of faults encompassing: brushes/brush gear problems Note: Examples are: sparking, excessive heating, excessive wear of brushes, commutator or slip rings, bad surface conditions, excessive maintenance, flexible burning, flexible corrosion, separation or grooving, blackening, copper picking, copper dragging, brush noise T15 adjustment of machines encompassing: correct brush position machining and finishing of commutators |