Direct Current Motors

Motors are used in many equipment, such as fan, blender, pump, etc. How motors work?

Motor is the equipment which convent from electricity to rotation. Before discuss about motor, let us review relation between current, magnetic field and force. See figure 1, Force can be generated by current and magnetic field. If current flow at a wire and it is in the magnetic field, then they are generated some force to the wire. We can see the direction of magnetic field is from North (N) to south (S). By right hand rules, direction of current is showed by I, direction of magnetic field is showed by B, and force is showed by F. Then they are generated force at wire to down direction. We can determine their direction by right hand rule. 

Figure 1. (a)Force, current, and magnetic field; (b) Right hand rule of direction; (c) simple construction DC motor

Now, let us consider the construction of simple direct current motor. The current flows from positive along the wire to negative, the magnetic field direction is from North (N) to South (S). Based on the right hand rules, loop will make rotation like the arrow direction (clock wise).

Brushes are static, but commutators  move (make rotation movements). Commutators will connect to the different pole of electricity (battery) alternately . Then, when the current flows, there will be a force to down direction at the right part of loop and force to up direction at the left part of loop. The construction of simple DC motor make a rotation at one direction (clock wise or counter clock wise) depend on the current flows.

Source of figure: Halliday, Resnick, Walker: Fundamentals of Physics; 
Douglas Giancoly: PHYSICS PRINCIPLES WITH APPLICATIONS

How to produce electricity

Electricity can be generated by several ways. One of them is by using faraday law which explained relation between electromotive force and magnetic flux.  Electromotive force (electrical voltage) will occur if there are changes of magnetic flux.

Magnetic flux is magnetic field which through perpendicular on some area.  If the area is parallel with magnetic field direction, the flux magnetic will be zero. If the area is perpendicular it will be maximum. See figure 1.

Figure 1. Generate the electromotive voltage.

We can see at the figure 1, magnet have magnetic field which have direction from north to south pole of magnet. Magnetic field through the circle of wire (it is magnetic flux). If we move the magnet, thus there are changes of magnetic flux at the circle of wire. Based on faraday law the electromotive force will occur.  So, as we can see the electrical voltages are detected at galvanometer. If we move the magnet by the opposite direction, electromotive force also have the opposite value. For example at the figure we move the magnet into the circle of wire, then galvanometer show the positive voltage. if we move the magnet away from circle of wire, then galvanometer will show the negative voltage.

Besides that, the changes of magnetic flux also can occur if the circle of wire is moved. Based on this principle, electrical generator can be built. There are several types of generator, but generally generators are divided in two types: Alternate current generator and direct current generator.


Source of figure: Halliday, Resnick, Walker: Fundamentals of Physics

GENERATOR Alternate Current (AC)

Generator is equipment which can converts from mechanical energy (kinetic energy) into electricity. Generally, generator can be divided into two types: AC Generator and DC Generator. Generator can produce electricity based on the faraday which law which said that change of flux magnetic will produce electromotive force (electrical voltage).

Based on faraday law, to build generator we need magnetic field.  Flux magnetic is magnetic field which through at surface area.  We can get the change of flux magnetic by rotate/drive the surface. Figure 1. Is construction of Simple Generator

Figure 1. (a) construction simple generator. (b) its electrical voltage

There are two kinds of poles magnet: N and S, so there will be magnetic field from N to S direction. Field magnetic which is through the loop area, it is called flux magnetic.  Loop is wire which is made like a loop.  Flux magnetic will be maximum when loop is vertical and will be zero when loop horizontal. By rotate the loop, we can get the changes of magnetic flux and it will produce electromotive force/emf (Electrical voltage). greater number of loops will produce greater voltage. Loops is connected by wire to slip rings. Slip rings are driven as external rotator rotation. Slip rings are  also connected to brushes which is static (not rotate as slip rings). These brushes are made from conductor which can transfer electricity that we use it.

We can connect external rotator to turbine, thus we can simplify above:
Rotation of external rotator --> Rotation of loop --> changes of flux magnetic --> electromotive force (emf)

loop is connected to slip rings by wire, so electrical voltage can move from loop to slip rings and we can use it to our need.

Source of figure: Halliday, Resnick, Walker: Fundamentals of Physics

STEAM POWER PLANT (PART 2: RANKINE CYCLE TURBINE)

Rankine cycle is one of the thermodynamic cycles which convert from heat into power (kinetic energy). We say it is a cycle because the process in this cycle always repeat and repeat again. To convert from heat energy into kinetic energy, it has several processes  and needs several components to support those processes. Those are: Boiling, expansion, condensation, and pumping. Figure 1. Is schema of those processes.

               Figure 1. Schema Rankine Cycle

At figure 1 there are two kinds of lines, ref and blue. Red is sign for high pressure and blue is sign for low pressure. Processes from 1 to 4 will be repeated again and again, so the rotor of turbine will be rotated continuously.

1 to 2, pumping  the water into boiler. At point 1 the pressure of water is low and at point 2 the pressure is high. The phase at point 1 and 2 is water (liquid).

2 to 3, Boiling. This Process needs energy especially heat energy, it can be from kerosene, coal, etc. Water will be boiled and water phase changes from water (liquid) into steam (gas). This steam (at point 3) has high pressure and temperature, so it has high energy (enthalpy).

3 to 4, Turbine Expansion. In this process occur the conversion into work (kinetic energy).  The high energy whose steam at point 3 is used to produce work (kinetic energy). This process causes drop pressure and temperature of steam (steam at point 4).

4 to 1, Condensation. To change phase from steam (gas) into water (liquid) need remove heat or in other word it has to be cooled. This process usually need heat exchanger, so that it can remove heat then the steam phase will change.

Those processes from 1 to 4 will be repeated again and again, so the rotor of turbine will be rotated continuously.