Terms with respect to d.c machine, Electrical Engineering

Q. Define coil pitch, Back pitch, front pitch, pole pitch, commutator pitch, resultant pitch, Multiplex winding and degree of Re-entrant of a winding, with respect to a D.C. machine.

Sol. Coil - span or coil pitch (Ys) :    It is the distance, measured in terms of armature slots (or armature conductors) between two sides of coil. It is, in fact, the periphery of the armature spanned by the two sides of the coil.


If the pole span or coil pitch is equal to the pole pitch (as in the case of coil A, coil wher coil - pitch of 4 has been assumed), then winding is called full - pitched. It means that coil span is 180 electrical degrees. In this case, the coil sides lie under opposite poles, hence the induced e.m.fs in them are additive. Therefore, maximum e.m.f. is induced in the coil as a whole, it being the sum of the e.m.f.s induced in the two coil sides. For ex, if there are 36 slots and 4 poles, then coil span is 36/4 = 9 slots. If no. of slots is 35, then Ys = 35/4 = 8 because it is customary to drop fractions.


If the coil span is less than the pole pitch (as in coil B where coil pitch is 3/4th of the pole pitch), then the winding is fractional - pitched coil. In this case, there is a phase difference b/w the e.m.fs. in the two sides of the coil. Hence, the total e.m.f. round the coil which is the vector sum of e.m.fs. in the two coil sides, is less in this case as compared to that in the first case.


Back Pitch (YB)


The distance, measured in terms of the armature conductors, which a coil advances on the back of the armature is called back pitch and is denoted by YB.


Front Pitch (YF)


The no. of armature conductors or elements spanned by a coil on the front (or commutator end of an armature) is called the front pitch and is denoted by YF.


Alternatively, the front pitch may be defined as the distance (in terms of armature conductors) b/w the second conductor of one coil and the first conductor of the next coil which are connected together at the front i.e. commutator end of the armature. Both front and back pitches for lap and wave - winding.


Resultant Pitch (YR) :  It is the distance b/w the beginning of one coil and the beginning of the next coil to which it is connected.


Pole Pitch :   It may be variously defined as ;

(i) The periphery of the armature divided by the no. of poles of the generator i.e. the distance b/w two adjacent poles.


(ii) It is equal the no. of armature conductors (or armature slots) per pole. If there are 48 conductor and 4 poles, the pole pitch is 48/4 = 12


Commutator Pitch (YC)


It is the distance (measured in terms of commutator bars or segments) b/w the segment to which the two ends of a coil are connected. It is clear that for lap winding, YC is the difference of YB and YF whereas for wave winding it is the sum of YB and YF.Obviously, commutator pitch is equal to the no. of bars b/w coil leads. In general, YC equals the 'plex' of the lap - wound armature. Hence, it is equal to 1, 2, 3, 4 etc. for simplex, duplex, triplex and quadruplex etc. lap - winding.


Degree of Re - entrancy of an armature winding


A winding is said to be single re - entrant, if on tracing through it once, all armature conductors are included on returing to the starting point. It is double re - entrant if only half the conductor are included in tracing through the winding once and so on.


Multiplex Winding


In such windings, there are several sets of completely closed and independent windings. If there is only one set of closed winding, it is called simplex wave windings. If there are two such windings on the same armature, it is called duplex winding and so on. The multiplicity affects a no .of parallel paths in the armature. For a given no. of armature slots and coils, as the multiplicity increases, the no. of parallel path in the armature increases thereby increasing the current rating but decreasing the voltage rating.

Posted Date: 7/23/2012 1:49:31 AM | Location : United States

Related Discussions:- Terms with respect to d.c machine, Assignment Help, Ask Question on Terms with respect to d.c machine, Get Answer, Expert's Help, Terms with respect to d.c machine Discussions

Write discussion on Terms with respect to d.c machine
Your posts are moderated
Related Questions
What is the purpose of carry (c) flag and zero (z) flag? Carry flag conatins the carry after addition or borrow after subtraction. This carry flag also shows error conditions,

Q. A paraboloidal antenna has an aperture ef?ciency of 0.6 and a diameter D = 100λ at 6 GHz. Illumination by the feed is such that the beamwidths of the principal-plane secondary p

Bus Organisation Set of  communication lines in microprocessor  which  carry  bits from microprocessor to  peripherals  ( memory  inputs ports  output  ports  and other chips

Torque-Speed Characteristics of 3-Phase Induction Motors Because the torque-slip characteristic is one of themost important aspects of the inductionmotor, we will now develop a

Derive Lame's equation for a thick cylinder subjected to internal pressure with clean diagrams. Evaluate the maximum and minimum hoop stresses across the section of a pipe of400

Q. Let the coil of the solenoid of have a resistance R and be excited by a voltage v = Vm sin ωt. Consider a plunger displacement of g = g 0 . (a) Obtain the expression for the

its defination and mathematical expression if any

Aggregate Technical and Commercial Loss It is unfortunate in that addition to T&D losses, there is also a loss in revenue because of non-realisation of billed demand which lea

Q. A voltmeter with a full scale of 100 V has a probable error of 0.1% of full scale. When this meter is employed to measure 100 V, find the percent of probable error that can exis

Power Diode A power diode is a two terminal, anode a and cathode K and  two layer P  and  N  junction devices. A PN  junction normally  formed  by allowing  diffusion and epita