# How to Work Motor

You can find DC motors in many portable home appliances Automobiles and types of industrial equipment In this site, we will logically understand the operation and construction of commercials DC motors

Let, first start with the simplest DC motor possible looks like this. The stator provides a constant magnetic field and the armature, which is the rotating part, is a simple coil armature is connected to a DC power source through a pair of commutator rings when the current flows through the coil, an electromagnetic force is induced on it according to the Lorentz law the coil will start to rotate. notice that as the coil rotates, the commutator rings connected with the power source of opposite polarities its results on the left side of the coil the electricity will always flow And on the right side electricity will always flow.

This ensures that the torque action is also in the same direction throughout the motion the coil will continue rotatingBut, if you observe the torque acting on the coil closely will notice that when the coil is nearly perpendicular to the magnetic flux the torque action nears zeroes a result there will be an irregular motion of the rotor you run such a DC motor here is the trick to overcoming this problem: Add one more loop to the rotor, with a separate commutator pair for in this arrangement when the first loop is in the vertical position the second loop will be connected to the power source.

so the motor force is always present in the system moreover, the more such loops, the smoother will be the motor rotation a practical motor the armature loops are fitted inside slots with highly permeable steel layers this will enhance magnetic flux interaction spring-loaded commutator brushes help to maintain contact with the power source permanent magnetic stator pole is used only for very small DC motors most often, an electromagnetic is used the field coil of the electromagnetic is powered from the same DC source field coils can be connected to the rotor windings in two different waysParallel or seriesThe result is two different kinds of DC motor constructions shunt and a series motors.

The series-wound motor has good starting torque, but the speed drops drastically with the loa date shunt motor has a low starting torque but it is able to run almost at a constant speed irrespective of the load acting on the motor unlike the other electrical machines, DC motors exhibit a unique characteristic: The production of BACK EMFA rotating loop in a magnetic field will produce an EMF according to the principle of the electric magnetic induction case of the rotating armature loops is also the same internal EMF will be induced that opposes to the applied input voltage BACK EMF reduces armature current by a large amount back EMF is proportional to the speed of the rotor the starting of the motor BACK EMF is too low, thus the armature current becomes too high leading to the burnout of the rotor.

Thus a proper starting mechanism that controls the applied input voltage is necessary for large DC motors one of the interesting variations of the DC motor is a universal motor that is capable to run under both AC and DC.

### Limitations of Terzaghi Theory

Limitations of Terzaghi Theory The value of the coefficient of consolidation has been assumed to be constant.  The distance d of the drainage path cannot be measured accurately in the field. The thickness of the deposit is generally variable, and an average value has to be estimated.  There is sometimes difficulty 1n locating the drainage face, sometimes thin previous seams that can act as good drainage face are missed in the boring operations. The equation is based on the assumption that the consolidation is one-dimensional. In the field, the consolidation is generally 3-dimensional. The lateral drainage may have a significant effect on the time rate of consolidation. The initial consolidation and secondary consolidation have been neglected. Sometimes these form an important part of the total consolidation. In actual practice, the pressure distribution may be far from linear or uniform. Read More Muller-Breslau principle

### Price Guard Wire Method

Price Guard Wire Method Some form of  Price Guard Wire Method  is generally used to eliminate the errors caused by leakage currents over insulation. Fig. 3.14 illustrates the operation of This Method. In fig 3.14(a), a high resistance mounted on a piece of insulating material is measured by the ammeter voltmeter method. The micro-ammeter measures the sum of the current through the resistor (IR) and the current through the leakage path around the resistor. The measured value of resistance computed from the readings indicated on the voltmeter and the microammeter, will not be a true value but will be in error.   Figure 3.14 Application of  guard  circuit for measurement of high resistance In fig, 3.14 (b), the  guard  terminal has been added to the resistance terminal block. The  guard  terminal surrounds the resistance terminal entirely and is connected to the battery side of the micro-ammeter. The leakage current IL now bypasses t

### Negative Booster

Negative booster A negative booster is employed to conform to the regulation that the potential difference between any two points of the rail return shall not exceed 7 V. Two boosters, positive and negative, are used which are mechanically coupled together and driven by a DC motor. The positive booster is connected to the trolley wire (near the generating station) and the negative booster (separately excited) is connected to the track rail.  The 'positive booster' adds voltage to the line while the 'negative booster lowers the potential of the point it is connected to. As we go along the trolley wire away from the generating station/sub-station, the potential drop increases, and the voltage of the trolley wire falls. Since the current returns via the track rail points away from the generating station acquire high potentials. This potential is brought down by the negative boost provided by the negative booster. When the load is sufficiently far away from the generating stati