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Wound Rotor Induction Generators (WRIGs): Steady State


Wound rotor induction generators (WRIGs) are provided with three phase windings on the rotor and on the stator. They may be supplied with energy at both rotor and stator terminals. This is why they are called doubly fed induction generators (DFIGs) or double output induction generators (DOIGs). Both motoring and generating operation modes are feasible, provided the power electronics converter that supplies the rotor circuits via slip-rings and brushes is capable of handling power in both directions. As a generator, the WRIG provides constant (or controlled) voltage Vs and frequency f1 power through the stator, while the rotor is supplied through a static power converter at variable voltage Vr and frequency f2.


The rotor circuit may absorb or deliver electric power. As the number of poles of both stator and rotor windings is the same, at steady state, according to the frequency theorem, the speed ωm is as follows:

{\omega _m} = {\omega _1} \pm {\omega _2};         {\omega _m} = {\Omega _R}.{p_1}               (1.1)
where
{p_1} is the number of pole pairs
{\Omega _R} is the mechanical rotor speed
Wound rotor induction generator (WRIG) main operation modes: (a) basic configuration, (b) subsynchronous generating (ωr < ω1), (c) supersynchronous generating (ωr > ω1), and (d) rotor output WRIG (brushless exciter).
FIGURE 1.1 Wound rotor induction generator (WRIG) main operation modes: (a) basic configuration, (b) subsynchronous generating (ωr < ω1), (c) supersynchronous generating (ωr > ω1), and (d) rotor output WRIG (brushless exciter).
The sign is positive (+) in Equation 1.1 when the phase sequence in the rotor is the same as in the stator and ωm < ω1, that is, subsynchronous operation. The negative (−) sign in Equation 1.1 corresponds to an inverse phase sequence in the rotor when ωm > ω1, that is, supersynchronous operation.
For constant frequency output, the rotor frequency ω2 has to be modified in step with the speed variation. This way, variable speed at constant frequency (and voltage) may be maintained by controlling the voltage, frequency, and phase sequence in the rotor circuit.
It may be argued that the WRIG works as a synchronous generator (SG) with three-phase alternating current (AC) excitation at slip (rotor) frequency ω2 = ω1 − ωm. However, as ω1 ≠ ωm, the stator induces voltages in the rotor circuits even at steady state, which is not the case in conventional SGs. Additional power components thus occur.
The main operational modes of WRIG are depicted in Figure 1.1a through Figure 1.1d (basic configuration shown in Figure 1.1a). The first two modes (Figure 1.1b and Figure 1.1c) refer to the already defined subsynchronous and supersynchronous generations. For motoring, the reverse is true for the rotor circuit; also, the stator absorbs active power for motoring. The slip S is defined as follows:
s = \frac{{{\omega _2}}}{{{\omega _1}}}   _{     < 0; \sup ersynchronous operation}^{     > 0; subsynchronous operation}
A WRIG works, in general, for ω2 ≠ 0 (S ≠ 0), the machine retains the characteristics of an induction machine. The main output active power is delivered through the stator, but in supersynchronous operation, a good part, about slip stator powers (SPs), is delivered through the rotor circuit. With limited speed variation range, say from Smax to −Smax, the rotor-side static converter rating — for zero reactive power capability on the rotor side — would be {P_{conv}} \approx |{S_{\max }}|{P_s} With Smax typically equal to ±0.2 to 0.25, the static power converter ratings and costs would correspond to 20 to 25% of the stator delivered output power.
At maximum speed, the WRIG will deliver increased electric power, Pmax:
{P_{\max }} = {P_s} + {P_{r\max }} = {P_s} + \left| {{S_{\max }}} \right|{P_s}                (1.3)
with the WRIG designed at Ps for ωm = ω1 speed. The increased power is delivered at higher than rated speed:
{\omega _{m\max }} = {\omega _1}\left( {1 + \left| {{S_{\max }}} \right|} \right)               (1.4)
Consequently, the WRIG is designed electrically for Ps at ωm = ω1, but mechanically at wmmax and Pmax. The capability of a WRIG to deliver power at variable speed but at constant voltage and frequency represents an asset in providing more flexibility in power conversion and also better stability in frequency and voltage control in the power systems to which such generators are connected.
The reactive power delivery by WRIG depends heavily on the capacity of the rotor-side converter to provide it. When the converter works at unity power delivered on the source side, the reactive power in the machine has to come from the rotor-side converter. However, such a capability is paid for by the increased ratings of the rotor-side converter. As this means increased converter costs, in general, the WRIG is adequate for working at unity power factor at full load on the stator side.
Large reactive power releases to the power system are still to be provided by existing SGs or from WRIGs working at synchronism (S = 0, ω2 = 0) with the back-to-back pulse-width modulated (PWM) voltage converters connected to the rotor controlled adequately for the scope.
Wind and small hydroenergy conversion in units of 1 megawatt (MW) and more per unit require variable speed to tap the maximum of energy reserves and to improve efficiency and stability limits. High-power units in pump-storage hydro- (400 MW [1]) and even thermopower plants with WRIGs provide for extra flexibility for the ever-more stressed distributed power systems of the near future. Even existing (old) SGs may be retrofitted into WRIGs by changing the rotor and its static power converter control.
The WRIGs may also be used to generate power solely on the rotor side for rectifier loads (Figure 1.1d). To control the direct voltage (or direct current [DC]) in the load, the stator voltage is controlled, at constant frequency ω1, by a low-cost alternating current (AC) three-phase voltage changer. As the speed increases, the stator voltage has to be reduced to keep constant the current in the DC load connected to the rotor (ω2 = ω1 + ωm). If the machine has a large number of poles (2p1 = 6,8,12), the stator AC excitation input power becomes rather low, as most of the output electric power comes from the shaft (through motion).
Such a configuration is adequate for brushless exciters needed for synchronous motors (SMs) or for generators, where field current is needed from zero speed, that is, when full-power converters are used in the stator of the respective SMs or SGs.
With 2p1 = 8, n = 1500 rpm, and f1 = 50 Hz, the frequency of the rotor output f2 = f1 + np1 = 50 + (1500/60) 4 = 150 Hz. Such a frequency is practical with standard iron core laminations and reduces the contents in harmonics of the output rectified load current.
In these series of articles, the following subjects related to WRIG steady state will be detailed:
  • Construction elements
  • Basic principles
  • Inductances
  • Steady-state model (equations, phasor diagram, equivalent circuits)
  • Steady-state characteristics at power grid
  • Steady-state characteristics for isolated loads
  • Losses and efficiency
Construction Elements
The WRIG topology contains the following main parts:
  • Stator laminated core with Ns uniformly distributed slots
  • Rotor laminated core with Nr uniformly distributed slots
  • Stator three-phase winding placed in insulated slots
  • Rotor shaft
  • Stator frame with bearings
  • Rotor copper slip-rings and stator (placed) brushes to transfer power to (from) rotor windings
  • Cooling system
Magnetic Cores
The stator and rotor cores are made of thin (typically 0.5 mm) nonoriented grain silicon steel lamination provided with uniform slots through stamping (Figure 1.2.a). To keep the airgap reasonably small, without incurring large core surface harmonics eddy current losses, only the slots on one side may be open. On the other side of the airgap, they should be half closed or half open (Figure 1.2b).
Though, in general, the use of radial-axial ventilation systems led to the presence of radial channels between 60 and 100 mm long elementary stacks, at least for powers up to 2 to 3 MW, axial ventilation with single lamination stacks is feasible (Figure 1.3a and Figure 1.3b). As the airgap is slightly increased in comparison with standard induction motors, the axial airflow through the airgap is further facilitated. The axial channels (Figure 1.3a) in the stator and rotor yokes (behind the slot region) play a key role in cooling the stator and the rotor, as do the radial channels (Figure 1.3b) for the radial-axial ventilation.
The radial channels, however, are less efficient, as they are “traveled” by the windings, and thus, additional phase resistance and leakage inductance are added by the winding zones in the radial channel contributions. In very large, or long, stack machines, radial-axial cooling may be inevitable, but, as explained before, below 3 MW, the axial cooling in unistack cores, already in industrial use for induction motors, seems to be the way of the future.
(a) Stator and (b) rotor slotted lamination FIGURE 1.2 (a) Stator and (b) rotor slotted lamination.
Stator and rotor stacks: (a) for axial cooling and (b) for radial-axial coolingFIGURE 1.3 Stator and rotor stacks: (a) for axial cooling and (b) for radial-axial cooling.
Windings and Their mmfs
The stator and rotor three-phase windings are similar in principle. Later in Synchronous Generators, their design is described in some detail. Here, only the basic issues are presented. The three-phase windings are built to provide for traveling magnetomotive forces (mmfs) capable of producing a traveling magnetic field in the uniform airgap (slot openings are neglected or considered through the Carter coefficient KC = 1.02 to 1.5):
{B_g}\left( {x,t} \right) = \frac{{{\mu _0}{F_{s,r}}\left( {x,t} \right)}}{{g{K_C}\left( {1 + {K_s}} \right)}}                (1.5)
where
{{F_{s,r}}\left( {x,t} \right)} is equal to the mmfs per pole produced by either stator or rotor windings g is the airgap
{{K_C}} is the Carter coefficient to account for airgap increase due to slot openings
{{K_s}} is the iron core contribution to equivalent magnetic reluctance of the main flux path (Figure 1.2a)
To produce a traveling airgap field, the stator and rotor mmfs, seen from the stator and from the rotor, respectively, have to be as follows:
{F_s}({\theta _s},t) = {F_{1s}}\cos \left( {{p_1}{\theta _s} - {\omega _1}t} \right)                (1.6)
{F_r}({\theta _r},t) = {F_{1r}}\cos \left( {{p_1}{\theta _r} \pm {\omega _2}t} \right)               (1.7)
where p1 is the number of electrical periods of the magnetic field wave in the airgap or of pole pairs. The rotor mmf is produced by currents of frequency ω2.
At constant speed, the rotor and stator geometrical angles are related by
{p_1}{\theta _r} = {p_1} - {\omega _r}t + \gamma ;   {\omega _r} = {\Omega _r}.{p_1};   {p_1}{\theta _s} = {\omega _1}t                (1.8)
where ωr is the rotor speed in electrical radians per second (rad/sec). Consequently, Frs, t) becomes
{F_r}({\theta _s},t) = {F_1}\cos \left[ {{p_1}{\theta _s} - \left( {{\omega _r} \pm {\omega _2}t} \right) + \gamma } \right]               (1.9)
The average electromagnetic torque and power per electric period is nonzero only if the two mmfs are at standstill with each other. That is,
{\omega _1} = {\omega _r} \pm {\omega _2};   S = {\omega _2}/{\omega _1}                 (1.10)
The positive sign (+) is used when ωr < ω1, and thus, the rotor and stator mmf waves rotate in a positive direction. The negative sign (−), used when ωr > ω1, refers to the case when the rotor mmf wave moves in the opposite direction to that of the stator. Also, the torque is nonzero when the angle γ ≠ 0, that is, when the two mmfs are phase shifted.
To produce a traveling mmf, three phases, space lagged by 120° (electrical), have to be supplied by AC currents with 120° (electrical) time-lag angles between them (see Chapter 4 in Synchronous Generators, on the SG).
So, all three phase windings for, say, maximum value of current, should independently produce a sinusoidal spatial mmf:
{\left( {{F_{sA,B,C}}\left( {{\theta _s},t} \right)} \right)_{t = 0}} = \frac{2}{3}{F_{1s}}\cos \left( {{p_1}{\theta _s} - \left( {i - 1} \right)\frac{{2\pi }}{3}} \right)               (1.11)
Each phase mmf has to produce 2p1 semiperiods along a mechanical period. With only one coil per pole per phase, there would be 2p1 coils per phase and 2p1 slots per phase if each coil occupies half of the slot (Figure 1.4a).
From the rectangular distribution of phase mmf (Figure 1.3a and Figure 13.b), a fundamental is extracted:
{F_{_{sA}}}\left( {{p_1},{\theta _s}} \right) = \frac{4}{\pi }{n_c}I\sqrt 2 \cos {p_1},{\theta _s};   {n_s} - turns/coil               (1.12)
The harmonics content of the phase mmf in Figure 1.4b is hardly acceptable, but more steps in its distribution (more slots) and chorded coil would drastically reduce these space harmonics (Figure 1.5).
For the two-pole 24-slot winding with chorded coils (coil span/pole pitch = 10/12), the number of steps in the phase mmf is larger, and thus, the harmonics are reduced (Figure 1.5). For the fundamental component (based on Figure 1.5b), we obtain the expression of the mmf per pole and phase:
Elementary three-phase winding with 2p1 = 4 poles and Ns = 12 slots: (a) coils of phase A in series and (b) phase A magnetomotive force (mmf ) for maximum phase current
FIGURE 1.4 Elementary three-phase winding with 2p1 = 4 poles and Ns = 12 slots: (a) coils of phase A in series and (b) phase A magnetomotive force (mmf ) for maximum phase current.
Two-pole (2p1 = 2), Ns = 24 slots three-phase winding, with two layers in slot, coil span y/τ = 10/12: (a) slot-to-phase allocation for layer 1 and coils of phase A and (b) phase A magnetomotive force (mmf) for maximum current.
FIGURE 1.5 Two-pole (2p1 = 2), Ns = 24 slots three-phase winding, with two layers in slot, coil span y/τ = 10/12: (a) slot-to-phase allocation for layer 1 and coils of phase A and (b) phase A magnetomotive force (mmf) for maximum current.






to be continued ……….

Free Energy with the Use of Tesla Generator

With the value of electricity escalating, many people are trying to find more affordable choices for sources of energy. The most popular alternatives however, cost excessive for any average Joe to afford. Solar power systems and wind generators or windmills, which are effective alternatives for the conventional electric sources, could cost thousands.
An alternative source of energy is helpful not only in your case and also for the environment as well. However, regardless if using alternative sources like solar and wind energy, it only cuts a small percentage of the common electric bill.
Scientists continue to look for methods to generate free electricity if you use inexpensive materials, but to no avail. In contrast to what many individuals believe, however, it has been a century since a relatively inexpensive and natural power source was invented. The Tesla generator was a controversial invention by a man named Nikola Tesla. He developed an equipment that draws power from the air and in the radiation from the sun. Since it is powered by radiation, it does not need the light of the sun like solar panels do. Although Tesla was considered a "mad scientist" in his time, he clearly had one of several brightest minds in history. He was the genius who discovered electromagnetic power (AC), unlike what folks are aware that it was Thomas Edison who did.
The Tesla generator utilizes a fuel-less generator that generates power with little cost. It had been referred to as "zero point technology", which people doubted initially. During Tesla's last days, he documented his invention to be able to come up with the design, and after that patented them.
The advantage of the Tesla generator is its simplicity. Composed of a rotor, simple wiring and situated magnets, the generator can make free natural electricity that you can use in your house. If you want to trim your expenses, the Tesla generator will help you trim your electricity bill by half or more.
The earth has depended a great deal on fossil fuels along with other similar sources that slowly destroy environmental surroundings. Although consequences are not clearly seen today, the future generation will obviously suffer. The Tesla generator will slow up the usage of environmental sources for the creation of electricity. It is best for the environment and to humanity, and that's why people should begin to use the free energy that it generates.

Dry Type and Liquid-Filled Transformers: A Quick Comparison

Transformers under load generate heat due to winding (copper) and core losses occurring during operation. There is an 'acceptable' temperature rise for transformers used in power applications, and this can even limit their size. This acceptable temperature rise is directly related to the limitations of the transformer materials; safety regulations; or component parts in close proximity that may have high-temperature reliability problems.
High temperatures can damage the winding insulation; the heat generated from core and winding losses must thus be dissipated. This dissipation can be achieved with a combination of radiation and convection from the exposed surfaces of the transformer. Dry type power transformers up to several hundred kVA can usually be cooled by convection or even by fans. Power transformers can also be immersed in coolant liquids - which can range from mineral oils to silicone-based oils or ester-based vegetable oils.
Based on the type of cooling used, transformers are thus classified into 'dry type' and 'liquid-filled'.
Liquid-Filled Transformers
  1. Oil-filled Transformers
    Oil-filled transformers primarily use mineral-based oil and cellulose paper (Kraft or Aramid) in their insulation systems. This proven combination exhibits outstanding thermal and dielectric properties at a relatively low cost. So popular and effective are these units, that all other transformer designs are judged in relation to them. They are still unparalleled in terms of purchase cost, among all the options available. The inherent weakness of a mineral oil-filled transformer, of course, is flammability; which is why oil-filled transformers are usually restricted to outdoor installations, or indoor installations that have elaborate means of fire protection.
    Typical Applications:
    Oil-filled transformers, thanks to their lower purchase costs, find applications in literally every sort of power distribution. Of late, the awareness of the fire risks associated with mineral oil-filled transformers has created a movement towards safer alternatives that use non-flammable, biodegradable liquids, or even dry-type transformers.
  2. Non-Flammable Liquid-Filled Transformers
    Polychlorinated biphenyl (PCBs) were produced in large quantities starting as early as the 1930s, in response to the electrical industry's need for a less flammable substitute for mineral oil as a cooling/insulating fluid for transformers. Several industrial incidents, however, brought the toxicity of PCBs to the fore. As confirmed organic pollutants, PCBs were banned by the late 1970s. A number of alternatives have since surfaced - major ones being silicone, perchloroethylene, high temperature hydrocarbons, and mixtures of oil with perchloroethylene. The first high molecular-weight hydrocarbon-based fluid (HMWH),  was introduced in 1975. This fluids possesses similar dielectric properties as mineral oil, provide remarkable levels of fire-resistance, and do not have undesirable environmental fallouts.
    Typical Applications:
    Non-flammable liquid-filled transformers can be installed indoors and outdoors, close to buildings, walkways and rooftops. Usually, no additional infrastructure is required to address issues like fire safety.
  1. Biodegradable Fluid Liquid-Filled Transformers
    Animal fats and vegetable oils offer substitutes that are significantly less harmful to the environment than petroleum oils. However, vegetable oils were not used in transformers for a long time; a fluid which could be stable in the transformer environment and available in the required quantities was simply not available.
  1. Transformer manufacturers have since worked on transformer designs that utilize vegetable oil-based dielectric fluids. Comparable in size and electrical performance to conventional liquid-filled units, these transformers are filled with the less flammable dielectric fluids mentioned above. The immediate advantages of biodegradable fluids are clear: higher fire and flash points, thus reducing flammability concerns. The other, and perhaps more long-term advantage, is the fluid's biodegradability: it has demonstrated high environmental assimilation (over 95% in less than a month) - and it has the virtue of coming from a toxin-free resource.
    Typical Applications:
    Biodegradable fluid liquid-filled transformers find application in wind turbines, and other indoor and outdoor areas of heightened environmental and safety sensitivity.
Dry Type Transformers
  1. Vacuum Pressure Impregnated (VPI) Conventional Dry Types
    Dry type transformer construction uses high-temperature insulation that exceeds the ratings of cellulose or 'O' and 'K' class fluids. Modern conventional dry type transformers feature insulation systems comprising carefully coordinated high-temperature (220'C) materials coated with a high-temperature, moisture-resistant polyester sealant. On better quality premium units, the polyester sealant is typically applied with a vacuum pressure impregnation (VPI) process. Units built in this fashion have exhibited high resistance to most chemical contaminants. Dry type transformers are generally rated up to 30MVA; performance under overload is demonstrably limited, but the addition of cooling fans can usually help augment this.
    Typical Applications:
    Dry type transformers have been used effectively in diverse commercial and industrial environments for decades; at ratings exceeding 15 kVA. Appropriately designed and installed, VPI units can even be an exceptionally economical choice in medium voltage distribution (15 kVA, 10 MVA ratings), even with the inclusion of installation costs. Because of reduced fire risks, these transformers have been used successfully in special applications where the public are in close proximity, such as underground tunnels, residential apartments, oil rigs and more.
  2. Gas-Filled Dry Types
    Gas-filled dry type transformers are designed for applications where low flammability is a vital consideration. N2, C2F6, and SF6 gases are the ones used in these designs, providing a dielectric medium that is external to the windings. Apart from being the dielectric medium, these gases also act as the thermal medium to transfer heat from windings to tank walls. Gas-filled transformers are an alternative to dry-type construction with fewer fire and contamination risks. 
    Typical Applications:
    Gas media have somewhat limited thermal capabilities; and gas-filled dry type transformers usually do not exceed 3750 kVA (C2F6) or even 2000 kVA (N2). Their design also makes them considerably larger than oil-filled units - anywhere from 20% to 30% bigger. Properly designed and installed gas-filled transformers can operate in any environment and remain truly non-flammable. They are commonly installed in dry-docks to provide local power for shipbuilding. Dry-docks (including transformers) are eventually flooded to float the ship away from the construction site.
  3. Vacuum Pressure Encapsulated (VPE) Dry Types
    Military shipboard use is an exacting requirement, and VPE dry type transformers were developed to meet these needs. VPE transformers are similar to VPI transformers, but employ a resin made of silicone instead of polyester. The VPE method includes several dip processes to encapsulate the coil assembly; the coatings are then cured in an oven. The resin coating in the VPE design is also typically thicker, sometimes by as much as a factor of four; as can be expected, the thermal classification of the insulation system is markedly different for the military than for commercial applications. VPE transformers are more resistant to harsh and wet environments than VPI type counterparts.
    Typical Applications:
    VPE dry type transformers typically find applications in very harsh indoor and outdoor environments. VPE technology allows the transformer to be highly resistant to humid and caustic environments, but carefully designed enclosures are still a must.
  4. Epoxy Coated Dry Types
    Epoxy coated, or 'epoxy shielded' dry type units offer the benefits of better environmental protection, minimal noise, high basic impulse levels and better short circuit strength than cast coil types. Epoxy shielded transformers are also usually less expensive, flexible, smaller and lighter. There are typically two variants of epoxy coated transformers - in one, a VPI dry-type is given an overcoat of epoxy varnish; in the other, the epoxy varnish is used as a complete replacement for the polyester sealant.
    Typical Applications:
    Epoxy coated transformers can be ideally suited for environments that may be polluted with acids, alkalis and chlorides. They are also resistant to the effects of salt water and high humidity, thus finding numerous applications in areas which concentrations of these problems.
  1. RESIBLOC Epoxy Cast Dry Types
    Unlike conventional VPI dry type designs, RESIBLOC  Epoxy Cast dry type transformers do not use insulation papers in the windings. Instead, pure epoxy resin reinforced with glass fiber rovings are wound directly with the wire. Winding processes controlled by advanced electronics also ensure even distribution and high levels of precision. Aluminum/copper foils are used for the low voltage winding; and circular (or rectangular) copper conductors with glass-fiber reinforced epoxy resin insulation are used for the high voltage windings. The completed winding block is then 'cured' in a specially designed oven under rotation. This process enables cast winding production without molds or vacuum. As in most cast epoxy units, the dielectric material on the interior winding is the epoxy itself. RESIBLOC transformers are reliable, environmentally safe, offer extreme fire resistance, have high short circuit withstands, and can be exposed to extreme conditions with minimal maintenance.
    Typical Applications:
    RESIBLOC? transformers often find applications in energization, ovens, or traction; they are commonly found in the railways, marine propulsion and distribution, in the nuclear energy and windmill power sectors, and in the mining industry.
  1. Epoxy Cast Dry Types The primary and secondary coils in epoxy cast dry type transformers are usually wound with copper conductors, pre-heated and placed in a mold which will then be filled with de-gassed and mixed epoxy under vacuum. The molds are then cured in special ovens to allow sound, void-free casting. The result is a winding design that is void-free, hermetically sealed, and with a smooth exterior finish.
    Typical Applications:
    Epoxy cast dry type transformers are used inside buildings and tunnels, on ships, offshore platforms and cranes, food-processing plants, and more. They are often combined with primary and secondary switchgear and distribution boards, to form compact substations.
Read more: http://www.articlesbase.com/industrial--articles/dry-type-and-liquidfilled-transformers-a-quick-comparison-1285152.html#ixzz1Y7wfv5ty
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Extensive Use Of Photoelectric Sensor Due To Compact And Rugged Circuitry

Sensors are of many sorts that may rely on the materials used and their applications. One of the most efficient and widely used sensors in the modern times is the photoelectric sensor which is affordable and adjusting in nature. You may define this sensor as the device which responds on the amount of light received. In fact, the sensor of this class is mainly used to detect the presence or absence of objects applying the concept of light transmission using an advanced transmitter, infrared and a receiver on the end.
Since it's photoelectric in nature and working, you will be happy to know they are very energy and cost effective both at the similar time. Almost all of the industries and factories have a dense and complicated network of sensors, also known as as photo eye because they act as the ears and eyes of the multiple installments. This sensor is principally utilized in safety relay for the management of industrial risks a lot of the time.
This class of sensor uses the concept of measuring the intensity of light from the object to be traced and thus, its mechanism of measurement may change depending on the working module and the instruments used inside the circuit of photoelectric sensor. Depending on the working, it could be classified as opposed arrangement, proximity sensing, diffused beam and light-dark operate. Each of the sensing modes has its own advantage and demerits. This is to be noted here that the photoelectric type sensor offers you numerous advantages over the other classified and extensively used sensors like the capacitive, magnetic, ultrasonic and inductive types. This is due to the fact that they provide great flexibility and easiness for the use, compact and light manufacturing, rugged circuitry and the option for the easy installation anywhere inside the home or in the industrial applications like security relay.
You may be surprised to note it down that conventional sensors in the same class have low feedback amount and thus, its proximity level may be undermined at most of the stages of application. But, within the recent times some of the smart and more advanced photoelectric sensor is in vogue. You will see that these sensors will have an in-built microprocessor and intelligent chips which are enough to monitor every step of working module. LED modules and LCD charts are there to assist display the wanted levels or intensity of light received by the sensor and thus, it becomes quite easy for the industries to use the sensor in safety relay where workforce gets acquainted by the inherent risks. Due to this merit, the operator will find it easier to tune the sensitivity level exactly between the light and dark levels.
When talking concerning the complexities of the photoelectric sensor, you will arrive at some new terms like hysteresis which greatly affect the switching stability of the sensor. In some modern applications like a safety relay, automatic selection and adjustment of the hysteresis level is available for the operator. Enhanced flexibility and durability of this sensor has made it more popular.

PILC Power Cables and Advancements

Paper Insulated, Lead Covered (PILC) cables were very common in the 1920s, 30s and 40s for the transmission of medium-voltage power. It is still used today in some parts of the world for underground reticulation, main distribution systems, sub-station wiring, and in mining.
PILC power cables have specific operational ranges where they function at their best. The functioning range depends on a number of factors, but due to the extensive use of these cables in the past, these factors are well known and widely documented.
One company makes 3 Core PILC cables. These come in two belted and one screened style. They can be ordered with Single Wire Armour (SWA) or a Double Steel Tape Armour (DSTA).
Armoured cable will reduce the loss from electromagnetic bleed if using Aluminum Wire Armoured (AWA) cable, but these single core power cables are available unarmoured as well. Available in sizes ranging from 25mm to 300mm, cables will have the following characteristics depending on the finished size
The following cables range in size from 25mm to 300 mm. These are the three most popular types.
3 Core PILC Belted 11/11KV power cables have the same size range but are not rated for as high an amp rating, but the impedance for these power cables is exactly the same as those listed above. 3 Core PILC Screened 6.35/11KV cables, being more resistant than the cables listed earlier, are the opposite of the belted cables being more resistant than the first cables listed.
Used in both dry and wet applications, PILC cables continue to be very popular where utility service is required for underground electrical distribution systems.
Replacement products have also been designed for old PILC cables currently in use today. Due to technological advancements these replacement products are available at significantly reduced costs with the added benefits that the production methods are less injurious to the environment as well. Offering up to an 8-10% reduction in cable diameter as compared to the older style PILC power cables, one can generate the same level of electrical transmission in a significantly smaller footprint.
If you are thinking of replacing an existing electrical network that currently uses PILC power cables, it would be wise to take a look at the newer cable designs and capacities available on the market today. Being able to move to a smaller cable diameter may just be in your best interest.

Concept of Productivity & Productivity Management

Definition of Productivity
  1. The definition of Productivity appeared in different decades based on the social and economic changes subjects to the utility of the human civilization.
  2. 1766: The concept of productivity appeared first time in the world.
  3. 1979: Ratio of tangible output to tangible inputs over a period of time.
  4. 1990: Productivity is the ration of output over inputs.
  5. 1997: Productivity: (Output × Quality with Customer Satisfaction) / (Inputs × Commitment at all levels)
  6. 1998: Productivity: (Output with pollution-free products) / (Inputs with pollution-free managed)
  7. Recent Development of Productivity concept: Productivity is creating wealth through generation and application of knowledge management.
  8. To make products available and service that meet the need of the users and are consistent with social, environmental and economic goals of the society.
  9. Human mind is the main source of productivity improvement.
Philosophy of Productivity
  1. Productivity means attitude of mind.
  2. Productivity means team work.
  3. It is a conviction that one can better today than yesterday, and that tomorrow shall be better than yesterday.
  4. Productivity is a never-ending process.
Productivity Measurement
  1. Productivity = Output/Input = 10,000/ (50 × 8 × 25) = 1 calculator per man hour.
  2. Suppose this company is 2004 increased production to 12,000 calculator by hiring 10 additional workers at 8 hour per day for 25 days. Then,
    -Productivity = Output/Input = 12,000/ (60 × 8 ×25) = 1 calculator per man hour.
    -It is clear that production of calculator has gone up in 2004 by 20 percent, but productivity remains unchanged.
Basic difference between Production & Productivity
Production Productivity
How Much How Well
Quantity Produced/ Service Rendered Quantity, Quality, Minimization of Cost & Efficient use of all Inputs.
Only Efficiency Concept Combination of both Efficiency & Effectiveness.
Profit Oriented. Both Employers, Workers, Government, Consumers Equally Benefited.
Value Creation of Just –in- Time (JIT)
  1. To realize the value of One Year - Ask a student who has failed in a final year.
  2. To realize value of One Month - Ask the Editor of weekly newspaper.
  3. To ask value of One Hour - Ask the lovers who are waiting to meet.
  4. To ask value of One Minute - Ask the person who missed the train, bus, or plane.
  5. To realize value of One Second - Ask the person who survived an accident.
  6. To realize value of One Millie Second - Ask the person who has own a gold medal of the Olympic.
  7. Time waits for No One - Treasure every moment you have and share it someone special.
5-Steps of Productivity Management
  1. Create a productivity oriented plant/corporate culture and values.
  2. Constantly evaluate and redesign goods and service and their production process.
  3. Change the structure.
  4. Improve individual and group relation.
  5. Managing productivity.
Step-1:
Create a productivity oriented plant/corporate culture and values;
Action-1:
Develop a Plan/Corporate culture that everybody will say Productivity is Important.
Action-2:
Everybody will say that Productivity is a question of Survival.
Action-3:
Everybody will say that Productivity is a question of Changing Mindset.
Action-4:
Make a network with the people who are Productive.
Step-2:
Constantly evaluate and redesign goods and service and their production process.
Action-1:
Customer satisfaction.
Action-2:
Increase the listening to the product/ service personnel.
Step-3: Changes the structure
Action-1:
Minimize the formalities.
Action-2:
Reduce the process of centralization.
Action-4:
Reduce complexity.
Action-5:
Review the personal set.
Step-4:
Improve Individual and Group Relation
Action-1:
Motivation.
Action-2:
Build Productivity expectation.
Action-3:
Change behavior patterns.
Action-4:
Build a culture that productivity is a status of system.
Step-5:
Managing Productivity
Action-1:
Build productivity improvement plan.
Action-2:
Organize people for productively Improvement.
Action-3:
Develop people and system.
Action-4:
Develop productivity norm.
The 3 Different Types of Workplaces
  1. A 3rd class workplace: With people throwing rubbish around but none to clean up.
  2. A 2nd class workplace: With people throwing rubbish around and another group of people cleaning up.
  3. A 1st class workplace: Without anybody throwing any rubbish around, and yet everybody is cleaning up.
Some popular Tools for Productivity
Improvement and Management
Productivity through 5S
Japanese Meaning of 5S:
popular Tools for Productivity
popular Tools for Productivity
image
popular Tools for Productivity
popular Tools for Productivity

Principles for Creating Awareness to the Establishments of Linking Wages with Productivity
  1. High Wages with Low Productivity is Charity.
  2. Low wages with High productivity is Exploitation.
  3. Low wages with Low Productivity is Suicide.
  4. High Wages with High Productivity is Progress and Prosperity.
My name is Machine X
  1. I love you because you care for me, Master.
  2. Please wash my body and joints regularly before I become dirty and feel itchy.
  3. I will whisper to you when I feel uncomfortable. So please listen to me carefully and fix me before I become seriously ill.
  4. I like to work hard for you, Master. I also like to live a long life.
  5. Master, please understand me a bit more, so that I can enjoy working with you.
  6. Thank you for your kind considerations, master.
Importance of 5S
  1. A clean workplace is high in Productivity.
  2. A clean workplace has high Quality.
  3. A clean workplace keeps Cost down.
  4. A clean workplace ensures Delivery on time.
  5. A clean workplace is Safe for people t work.
  6. A clean workplace is high in  Morale.

Design & Implementation of Color Sensor

Presentation on Design & Implementation of Color Sensor.

Introduction
Light is a physical phenomenon.When the components of light are absorbed or transmitted in different proportions by an object, color occurs. The color of an object is apparent only when light strikes the object. For color to be perceived, the viewer must have blue, green, and red receptors. Depending upon its chemical make-up, matter has the ability to absorb, reflect or transmit visible light.
When all the components of visible light are absorbed by matter, the object is said to be black.On the other hand, if all the components of visible light are reflected or transmitted by the object, the object is considered white or clear. The visible light spectrum is a small part of the electro-magnetic spectrum. The visible spectrum has a wavelength range of about 380 to 740 nm. Human eye can perceived only the visible light.
Wavelength & frequency interval of different colors

Color Name
Wavelength Interval
nm
Frequency Interval
THz
Violet
380-450
668-789
Blue
450-495
606-668
Green
495-570
526-606
Yellow
570-590
508-526
Orange
590-620
484-508
Red
620-750
400-484
Objectives

The main objective of our project is to detect the color of an object. Our target is to detect ten colors.The target colors are Black, Green, Red, Blue, Yellow, Magenta, Yellow-lemon,Pink,
Gray, White.
To relate color system wherein color purity and mixings is identified perfectly and is independent of human observations or subjective judgments.
Possible Outcome

To detect the color of an object with high precision even under varying environment conditions, such as fluctuations in the ambient temperature or variations of incidence light on the object to be measured.
Experimental Design

A color sensor includes a light receiving element for receiving the light from an object(target) illuminated by the lights from the light emitting sources and a circuit arrangement for producing output signals representing the color of the object.
Experimental Design

Design & Implementation of Color Sensor
Op-amp

The op-amp is basically a differential amplifier having a large voltage gain, very high input impedance and low output impedance. Most of the time operational amplifiers are used to compare voltages of unequal magnitudes. They are called ``operational'' amplifiers, because they can be used to perform arithmetic operations (addition, subtraction, multiplication) with signals.
Op-amp Circuit Notation

Op-amp
V + : non-inverting input
V- : inverting input
Vout : output
Vs+: positive power supply
Vs-: negative power supply
Pin Connection of LM741

Pin Connection of LM741
Analog-to-digital converter (ADC)

An analog-to-digital converter (A/D) takes an analog voltage or current and after a certain amount of time it produces a digital output code that represents the analog input.
Simply, an analog-to-digital converter is a device which converts continuous signals to discrete digital numbers.

General Block Diagram (ADC)

General Block Diagram (ADC)

Pin diagram & free running connection

Pin diagram & free running connection
Pin diagram of ADC0804

Pin diagram of ADC0804
Free running connection

Microcontroller

Microcontroller is a programmable integrated circuit which contains Processor, memory and input/output functions in a single chip. It is a microprocessor emphasizing high integration. In contrast to a general-purpose microprocessor, the microcontroller integrates additional elements such as read write memory for data storage, read-only memory for program storage, EEPROM for permanent data storage, peripheral devices, and input/output interfaces.
Pin diagram (PIC16F84A)

Pin diagram (PIC16F84A)
Pin function

Pin diagram (PIC16F84A)
Circuit Diagram

Color Sensor circuit diagram

Color Sensor circuit diagram
Program

TRISA = 0
TRISB = 255
Dim a As Byte
PORTA = 0
WaitMs 10
main:
PORTA = 0
a = PORTB
If a < 11 Then PORTA = 1 '//Black
If a > 6 Then
If a < 27 Then PORTA = 2 '//Blue
Endif
If a > 26 Then
If a < 31 Then PORTA = 3 '//green
Endif
If a > 39 Then
If a < 44 Then PORTA = 4 ''// Pink
Endif
If a > 44 Then
If a < 50 Then PORTA = 5 '//Red
Endif
If a > 49 Then
If a < 57 Then PORTA = 6 '//Megenta
Endif
If a > 56 Then
If a < 63 Then PORTA = 7 '// White
Endif
If a > 64 Then
If a < 73 Then PORTA = 8 '//Yellow
Endif
If a > 89 Then
If a < 93 Then PORTA = 9 '//Gray
Endif
If a > 92 Then
If a < 96 Then PORTA = 10 '//Yel+lem
WaitMs 200
Goto main
Result

Our project is designed for detection of ten colors. But we have detected eight colors successfully. The detected eight colors are red, green, yellow, yellow-lemon, pink, gray, black & white.
Error

We can’t detect two colors. The colors are blue & magenta. This two colors are overlapped with green & red.
Limitation
  1. The major limitation of our project is that it can’t detect the object which contains number of colors.
  2. One limitation of this project is that it can’t display the color name. But it is possible to display the color name with the help of LCD display by proper programming.
  3. Our blue sensor can’t work properly. So we can’t detect the blue color as well as other color.
  4. We can’t filter the color perfectly.

Future study & improvement

  1. To display the detected color name.
  2. To increase the number of detected color.
  3. To detect number of colors even exist as a narrow strip within the object.
  4. Sort objects by color
Reference
  1. “Digital Systems Principles and Applications” By, Ronald J. Tocci, Neal S. Widmer & Gregory L. Moss
  2. “Digital Logic and Computer Design” By, M. Morris Mano
  3. “Operational Amplifiers and Linear Integrated Circuits” , Sixth edition By, Robert F. Coughlin and Frederick F. Driscoll
Submitted By Anup Kumar Das and Prashanta Kumer Sarker