anserrreeeeeeeerrrr. 6th and 9th one. answer it now I will mark it as brailist answer if crt
Answers
Answer:Efficiency of DC Generator
Efficiency is simply defined as the ratio of output power to the input power. Let R = total resistance of the armature circuit (including the brush contact resistance, at series winding resistance, inter-pole winding resistance and compensating winding resistance). The efficiency of DC generator is explained below in the line diagram.
efficiency-of-dc-machine
I is the output current
Ish is the current through the shunt field
Ia is the armature current = I + Ish
V is the terminal voltage.
Total copper loss in the armature circuit = Ia2Rat
Power loss in the shunt circuit = VIsh (this includes the loss in the shunt regulating resistance).
Mechanical losses = friction loss of bearings + friction loss at a commutator + windage loss.
Core losses = hysteresis loss + eddy current loss
Stray loss = mechanical loss + core loss
The sum of the shunt field copper loss and stray losses may be considered as a combined fixed (constant) loss that does not vary with the load current I.
Therefore, the constant losses (in shunt and compound generators) = stray loss + shunt field copper losses.
efficiency-of-dc-generator-eq-1
Generator efficiency is given by the equation shown below.
efficiency-of-dc-generator-eq-2
If Ish is small compared with Ir, then Ia = I
Therefore,
efficiency-of-dc-generator-eq-3
The efficiency ȠG will be a maximum when the denominator Dr is a minimum.
Where,
efficiency-of-dc-generator-eq-4
Dr is minimum when
efficiency-of-dc-generator-eq-5
Also,
efficiency-of-dc-generator-eq-6
Since d2Dr/dI2 is positive, the expression is given by the equation (1) is a condition for the maximum value of Dr and the condition for the maximum value of efficiency.
Equation (1) shows that the efficiency of a DC generator is maximum when those losses proportional to the square of the load current are equal to the constant losses of the DC generator. This relation applies equally well to all rotating machines, regardless of the type of machine.
This relationship is sometimes incorrectly stated as maximum efficiency occurs when the variable losses are equal to the constant losses.
Load Corresponding to Maximum Efficiency
Let,
Ifl be the full load current
IM is the current at maximum efficiency
efficiency-of-dc-generator-eq-7For maximum efficiency, Therefore, the current at maximum efficiency is given by the equation shown below.
iciency-of-dc-generator-eq-8
Mark me brainliest
Explanation:
1) Practical efficiency of a machine, obtained by dividing the available output of work or energy of a machine by the energy absorbed by the same machine. Thus in a dynamo part of the energy is usefully expended in exciting the field magnet, but this energy is not available for use in the outer circuit, is not a part of the output, and is not part of the dividend. If M represents the energy absorbed, and W the useful or available energy, the coefficient of commercial efficiency is equal to W/M. M is made up of available, unavailable and wasted (by Foucault currents, etc.,) energy. Calling available energy W, unavailable but utilized energy w, and wasted energy m, the expression for the coefficient of commercial efficiency becomes W / ( W + w + m ) when M = W + w + m Synonym--Net efficiency.
2) The commutator just mechanically changes the coils at the correct time so the output is always dc. Think of it as if you were doing the commutation yourself. You observe an ac waveform first rising from 0 volts to a peak, then decreasing back to zero and then negative voltages to a negative peak and so on. To keep the voltage always dc, you have a double pole, double throw switch connected to switch the output polarity-just throw the switch at the last second before the ac voltage would have gone negative. Thus the ac voltage is now a dc voltage from 0 volts to a peak dc voltage (dc voltage with lots of ripple). The commutator does the same thing automatically, since it is locked to the rotor shaft- it reverses the output at just the right time to output fluctuating dc only.
Hope helps