Substation Equipment Testing

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Choice is 50Hz

In India the electrical supply is based on 230 V Ac supply. Countries that now use the 50 Hz frequency tend to use 230 V, and those that now use 60 Hz tend to use 120 V. 

Unless specified by the manufacturer to operate on either 50 or 60 Hz, appliances may not operate efficiently or even safely if used on other than the intended supply frequency 

Reasons : Several factors influence the choice of frequency in an AC system. Lighting, motors, transformers, generators and transmission lines all have characteristics which depend on the power frequency. The first applications of commercial electric power were incandescent lighting and commutator-type electric motors. Both devices operate well on DC, but DC cannot be easily transmitted long distances at utilization voltage and also cannot be easily changed in voltage. With AC, transformers can be used to step down high transmission voltages to lower utilization voltage. Since, for a given power level, the dimensions of a transformer are roughly inversely proportional to frequency, a system with many transformers would be more economical at a higher frequency. 

If an incandescent lamp is operated off a low-frequency current, the filament cools on each half-cycle of the alternating current, leading to perceptible change in brightness and flicker of the lamps; the effect is more pronounced with arc lamps, and the later mercury-vapor and fluorescent lamps. 

Commutator-type motors do not operate well on high-frequency AC since the rapid changes of current are opposed by the inductance of the motor field; even today, although commutator-type universal motors are common in household appliances, they are universally of low ratings less than 1 kW. 

Once the induction motor had been developed, it was found to work well on frequencies around 50 to 60 Hz but with the materials available in the late 1800s would not work well at a frequency of, say, 133 Hz. There is a fixed relationship between the number of magnetic poles in the induction motor field, the frequency of the alternating current, and the rotation speed; so, a given standard speed limits the choice of frequency (and the reverse). 

Electric power transmission over long lines favors lower frequencies. The effects of the distributed capacitance and inductance of the line are less at low frequency. 

Generators operated by slow-speed engines will produce lower frequencies, for a given number of poles, than those operated by, for example, a high-speed steam turbine. For very slow prime mover speeds, it would be costly to build a generator with enough poles to provide a high AC frequency. As well, synchronizing two generators to the same speed was found to be easier at lower speeds. Generators can only be interconnected to operate in parallel if they are of the same frequency and wave-shape. By standardizing the frequency used, generators in a geographic area can be interconnected, providing reliability and cost savings. 

Direct-current power was not entirely displaced by alternating current and was useful in railway and electrochemical processes. Prior to the development of mercury arc valve rectifiers, rotary converters were used to produce DC power from AC. Like other commutator-type machines, these worked better with lower frequencies. 

All of these factors interact and make selection of a power frequency a matter of considerable importance. The best frequency is a compromise between contradictory requirements.

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ISOLATION of Electric Power from Ground

Electrical contacts with ground can cause injury when they complete a circuit that permits a large flow of current. One strategy for ensuring safety is to isolate all electrical power sources from ground, making it impossible for ground to be used as a path for injurious or damaging currents.Traditionally, implementation of this strategy in the operating room has been accomplished by means of isolation transformers, which usually take the form of large wall panels having outlets and meters. The term “isolation transformer” comes from the fact that power outputs are isolated from ground.Electrical power for an operating room comes from a primary hospital source that usually originates from a connection to an alternating-current (AC) station of the local power company. (Sometimes an emergency gasoline-powered electrical generator is the primary source.) After arriving at an operating room, electrical power is modulated, isolated, and dispensed to electrical outlets in the room by the secondary coils of one or more large isolation transformers. Connections in three-hole power outlets in operating rooms, therefore, are somewhat different from connections in standard outlets found elsewhere in the hospital. ¹²  In operating rooms, a circuit cannot be completed by connecting one of the two power contacts to the ground contact.

The panel of each isolation transformer is required to have a line isolation monitor (LIM), which is simply an electrical current meter that demonstrates the isolation of the transformer‘s output power from ground. The large isolation transformers seen in operating rooms are somewhat anachronistic because the NFPA requires their presence only for environments in which inflammable anesthetics are used. ¹⁴  This does not mean that basic notions of safety have changed with respect to the need to isolate circuits from ground. However, isolation of electrical power is now accomplished with advanced technology that was unavailable when large isolation transformers were initially required. In principle, manufacturers are capable of incorporating good electrical isolation into the design of each piece of electrical equipment used in the operating room. Indeed, it is possible to argue that the obsolescence of central isolation and LIMs has already been demonstrated by the absence of these items in the intensive care unit (ICU) and the postanesthesia care unit (PACU). All electrical instruments that are permitted in the operating room are also used in ICUs and PACUs, yet one does not see isolation transformers and LIMs in ICUs and PACUs. Should one then assume that isolation transformers and LIMs should be eliminated from operating rooms or not installed in new operating rooms? The answer is neither yes nor no, ^13,14  as suggested earlier. The issue of safety for surgical patients who are wet with fluids that conduct electricity is better understood after a review of some fundamentals of electrical isolation.Figure 83–1 A shows a schematic diagram of an isolation transformer. For each power outlet, two hot-wire contacts come from the secondary coil of the transformer. The primary circuit of the transformer is attached to ground, but the secondary circuit of the transformer is not. The third contact, which is at the end of the ground wire in the plug, is connected to the standard hospital ground and not to the isolation transformer. 

FIGURE 83–1 Schematic diagrams of (A) an isolation transformer and (B) electrical grounding for an ECG in the operating room (outlet to equipment).

When an ECG monitor is plugged into a power outlet in the operating room ( Fig. 83–1 B), neither of the two “hot wires” from the secondary coil of the transformer is connected to ground by the ECG circuitry. This demonstrates the general principle that electrical circuits within an apparatus need not be grounded, although the metal case that houses the circuits is always grounded. Indeed, for many circuits, proper functioning depends on good isolation. Thus the statement “all operating room equipment must be grounded” is always true regarding connections between ground and the external case but is not always true regarding powered circuits within the apparatus.In the example given in Figure 83–1 B, the ECG case is connected to the hospital‘s electrical ground, and the internal circuitry is connected to the output of the isolation transformer. This safe system is worthy of further discussion.Let us suppose that mechanical or electrical damage causes us to worry about the electrical safety of an ECG monitor. Could a failure occur inside the ECG monitor that would place the patient or the anesthesiologist in contact with the internal circuitry? If so, would electric current travel through the person from the ECG circuitry to ground, causing injury or distress? Thanks to isolation of the ECG circuitry, the answer is no.Figure 83–2 A shows how isolation provides safety. In Figure 83–2 A, a grounded person is touching the internal circuitry at point B. The isolation transformer supplies current to pathways that connect the two “hot” leads in the outlet, indicated by points A and D. However, the only way for electric current to get from point A to D is through impedance Z. Because each of the hot points in the wall outlet is not grounded, the person in Figure 83–2 A is safe from shock. 

FIGURE 83–2 Diagrams showing that (A) no electric shock occurs if an isolated power line is touched, (B) an electric shock does occur if a faulted secondary power line is touched, and (C) a line isolation monitor can watch for a fault.

Figure 83–2 B, however, shows that two inadvertent ground contacts could produce a dangerous situation, especially if one of those contacts is a human being. Suppose that a fault occurs near point D, causing the internal circuitry to come in contact with the external metal case. A dangerous shock would result from touching the circuit at point B. Because of the fault, current could complete a pathway through the person and ground (i.e., from point A to D). Thus, it is useful to isolate power lines from ground and to know when isolation is compromised by a fault.

As mentioned, every isolation transformer has a LIM that monitors the isolation of the transformer‘s two power output lines from ground. Figure 83–2 C shows how the LIM (an ammeter) replaces the smiling and frowning people in Figures 83–2 A and B. When very low amperage is indicated, the LIM verifies that the power output lines of the transformer are indeed isolated from ground, as in Figure 83–2 A. The reality of the LIM connections is actually different because either of the hot wires could become grounded accidentally. Therefore, the LIM is actually connected to both sides of the isolated power output (Fig. 83–3) and is set to sound an alarm when either side has an impedance to ground that is less than 25,000 ohms, or when the maximum current that a short circuit could cause exceeds 2 mA. Note that the LIM is insensitive to currents below 2 mA. As is discussed later, the LIM provides no protection against microamp currents and microshock. 

FIGURE 83–3 Schematic showing complete connections of the line isolation monitor (LIM). The alarm sounds that there is a “first fault” if either isolated power line has less than 25,000 ohms impedence, corresponding to 2 mA or more being drawn through the LIM.

One event that occurs commonly in the operating room could produce a short circuit between power and ground, causing the LIM to go off. This event is the dripping of saline, blood, or other conducting liquid into the receptacles of an electrical extension cord that is on the floor near the operating table. For this reason, electrical extension cords in operating rooms frequently have watertight covers that flip into place over unused outlets. If wet receptacles on an extension cord appear to set off an LIM, the extension cord should be changed. If, on the other hand, the LIM rings suddenly and unexpectedly or immediately after a new piece of equipment is plugged in, that equipment should be unplugged immediately. If plugging in a piece of equipment repeatedly causes the LIM to sound an alarm, the equipment should not be used until it is checked. Similarly, if use of a particular power outlet repeatedly causes an alarm, it, too, should not be used until it has been checked. When an LIM alarm indicates a “first fault,” that is, that one power line is grounded, large, potentially damaging currents may subsequently occur through ground connections if there is a second ground fault. The path of damage might include the anesthesiologist, the patient, or an essential piece of equipment. Thus, an alarming LIM warns that someone in the operating room might receive an electrical shock or burn when touching connections to electrical equipment.

As mentioned earlier, detection of a first fault in grounding is possible without the use of isolation transformers and LIMs. The direct-installation GFCI outlets provide protection against a first fault. However, it provides protection, as described earlier, by suddenly shutting off all power from the outlet. An advantage of the LIM is that one learns about a first fault without losing electrical power. A disadvantage of the LIM is its susceptibility to newly developed artifactual causes of alarm. Certain new devices used in operating rooms emit electrical radiation, intentionally or incidentally, that falsely cause LIMs to sound an alarm. These include instruments that generate ultrasonic sound waves for tumor disintegration and aspiration and stereotaxic monitors that use radio waves to track sensors attached to patients. 

Clean electricity from Coal

Key Inventions and Selected patents of TESLA

1. AC MOTOR

Any electrical motor, from an idealized viewpoint, consists of two sets of magnets—one set stationary, one set free to move—placed in special geometric relation to one another.For most practical motors, electromagnets are employed: they don't weaken as permanent magnets do, but they must be energized with currents to have any magnetic force at all. These electromagnets are generally mounted in two rings, one set within the other, and connected up so that polarities will alternate north-south in each ring of pole projections. As to which set of magnets is to move (the rotor) and which to stand still (the stator), either will do. Though most familiar motors spin the inner array, some other designs rotate the entire outer circumference around a stationary center.Magnets, even electromagnets, have no natural need to keep moving. A rotor with 12 sets of poles mounted on a shaft so as to nearly contact 12 sets of surrounding stator windings would move itself just enough to tug attracting north-south pairs into closest alignment. And there the arrangement would sit, humming quietly, wasting electricity, and going nowhere.To become a motor, the useless device imagined above must constantly reverse the north-south polarity of its electromagnets. We'll suppose in a particular motor the rotor poles remain constant while the stator's switch constantly. Then, the rotor's unchanging poles cannot find a resting place. Each is pulled a little distance toward an opposite pole only to have it reverse just as the two poles reach alignment. The rotor pole is then repelled, sent in the direction of the next stator pole, which happens, moreover, to be rebuilding its field at the attractive polarity. It's an electrical con game, bait and switch, taking place many times each second that makes a motor turn.

AC and DC Motors

AC motors before Tesla were rare, laboratory devices—curiosities. They never ran smoothly, perhaps because a good design needed to anticipate and utilize the rather more complex, dynamic rules that govern currents and fields in AC circuits.Direct current was the name of the game prior to Tesla. Yet direct current motors have one obvious drawback: reversing current direction through magnet windings can happen only with some sort of switching that swaps current direction end for end. In practice, this is normally done by applying power through a pair of stubby contacts, called "brushes," that ride against the spinning rotor shaft, against a ring of contacts (the "commutator"); the commutator, thus, is always rotating its connections with the brushes, sending current through the rotor windings first in one direction and then the other.

Tesla's Invention

What Tesla conceived is essentially this: an alternating current fed to stator windings would create poles that reversed themselves without any mechanical aid. Though the stator remains motionless its fields are, in effect, whirling around its interior from one pole face to the next.He understood, as well, no physical power connection need be applied to the rotor. Rotor poles might be made to generate their currents by induction from the stator fields—a tricky proposition in 1888, for the conditions of voltage, current, and field must be choreographed very closely.AC motors proved both durable and adaptable. Within the space of two years Tesla had patented over twenty useful modifications of his new motors: to start up under heavy loads, to run at variable speed, or at constant speed, or with polyphase power supply, to mention a few. The great advantage of polyphase motors is, for a given number of poles, a smoother, more intense whirling field; such motors, in myriad forms, launched the electrical age of heavy industry. A somewhat more modest lineage of AC motors has powered most of the familiar appliances of twentieth-century life, from refrigerators to coffee grinders

2. TESLA COIL

To investigate the electrical realm of high-frequency and high-voltage, Tesla invented an apparatus that pushed the limits of electrical understanding. None of the circuit's typical components were unknown at the time, but its design and operation together achieved unique results—not the least because of Tesla's masterful refinements in construction of key elements, most particularly of a special transformer, or coil, which is at the heart of the circuit's performance.Such a device first appeared in Tesla's US patent No. 454,622 (1891), for use in new, more efficient lighting systems. In its basic form, the circuit calls for a power supply, a large capacitor, the coil (transformer) itself, and adjustable spark-gap electrodes. Why these components, and what do they accomplish?

Oscillators

Capacitors (or condensers) and inductors (or coils) are, electrically speaking, somewhat opposite in operation. Whereas current builds quickly in a capacitor as it charges up, voltage lags. In an inductor, voltage is felt immediately, while current is retarded as it works against the magnetic field its own passage builds in the coil. If a coil and condenser are sized and selected to act with exactly opposite timing—with voltage peaking in the coil just as it reaches a minimum in the capacitor—then the circuit may never reach an electrically quiet, stable state. A bit like the sloshing of water back and forth in a tub, current and voltage can be made to chase each other back and forth, from end to end of the circuit. (An oscillator of this kind is often called a tank circuit.)

Spark Gaps

To set his oscillator "ringing," Tesla employed sudden discharges, sparks, across an adjustable gap between two electrodes. Voltage on a capacitor builds until it reaches a level at which air in the gap breaks down as an insulator. (Precision screws set the gap clearance, so that a larger or smaller gap selects a larger or smaller breakdown voltage.)The initial impulse is very powerful—all the energy stored over several microseconds is released in a rush, and that impulse is itself transformed to a somewhat higher voltage in passing from the primary coil windings to those of its secondary. This, of course, completes but a single cycle in the circuit's operation. The air gap restores itself as an insulator, and the capacitor begins to charge until it reaches a breakdown value once again. The whole process can repeat itself many thousand times per second.

The transformer's secondary is rather special, too, designed by Tesla to react quickly to a sudden energy spike and, most importantly, to concentrate voltage at one end as astanding wave. Its length is calculated so that wave crests, as they reach the end and are reflected back, meet and exactly reinforce the waves behind them. The net effect is a wave, a voltage peak, that appears to stand still.
1 http://www.hvtesla.com/
1 http://www.extremeelectronics.co.uk/tccct/
2 http://www.physics.ucla.edu/demoweb/demomanual/electricity_and_magnetism/electrodynamics/tesla_coils.html

A spectacular demonstration with the small Tesla coil is to hold a fluorescent bulb in one hand and a metal rod in the other. When you draw an arc with the metal rod from the Tesla coil, the current passes through your body and lights the bulb. The voltage is over 1 million volts; why doesn't it shock or kill you? There are a number of hypotheses on this: a. The skin effect -- the current travels in the outer dead layer of skin. b. Human nerve circuits do not respond to high frequencies like 1 MHz, perhaps because of the reason mentioned above; there isn't time for the sodium and potassium ions to move far in the nerve cells. c. The impedance of the Tesla coil is very high, and it therefore induces only very small currents in humans.A skin depth calculation using the conductivity of sea water, sigma = 4 mhos/m, gives a depth of 0.25cm, so this effect would not play a large role in protecting you, at least from pain stimulation on the skin surface. The answer is probably a combination of effects b and c from above. The current through the body is too small to generate enough heat to injure the person, and the high frequency does not stimulate pain nerves, or induce muscle contraction.Our giant Tesla coil does sting you if you get into its circuit path to the ground. Tesla coil builders claim that the "gentleness" of the particular Tesla coil depends on the cleanness of the separation of 60 Hz and the high frequency at the spark gap.

Applications

If, as happened in practice, Tesla made an antenna of the high-voltage end of his secondary, it became a powerful radio transmitter. In fact, in the early decades of radio, most practicable radios utilized Tesla coils in their transmission antennas. Tesla himself used larger or smaller versions of his invention to investigate fluorescence, x-rays, radio, wireless power, biological effects, and even the electromagnetic nature of the earth and its atmosphere.

Today, high-voltage labs often operate such devices, and amateur enthusiasts around the world build smaller ones to create arcing, streaming electrical displays—it is not difficult to reach a quarter million volts. (One of the very first particle accelerator designs, by Rolf Wideroe in 1928, generated its high voltage in a Tesla coil.) The coil has become a commonplace in electronics, used to supply high voltage to the front of television picture tubes, in a form known as the flyback transformer

Q: How does a Tesla coil work?

ANS-1: Stripped down to it’s most essential parts, a Tesla coil is a wire sticking out of the ground. To get sparks to fly out of the top the rest of the machine “sloshes” electrons up and down the wire.The picture you should have in your head is a long bathtub, open to the ocean on one end.  The machinery of the Tesla coil is like some dude in the bathtub sliding back and forth, splashing water (electrons) out of the closed end, while the tub is refilled from the ocean (ground).The electricity in the primary coil is what’s doing the pushing, and the electricity in the secondary coil is what’s being pushed.  To understand how the driving mechanism works requires a new metaphor and some answer gravy.

Aside from inspiring fear, Tesla coils are useless. Truly, Tesla was a genius. The strange shape is an attempt to avoid arching from the torus to the primary coil, which is bad.

To get sparks to really fly you need very high voltage (up to several million volts) at a fairly exact frequency.  The current that flows up and down the secondary coil, and sloshes out the top, has a high resonant frequency (~MHz, unless the coil is ridiculously huge) that you really can’t do much about.  But the current coming out of the wall has a frequency of only 60 Hz (50 Hz for our Old World readers).

One possible circuit configuration for a Tesla coil.

So how do you change frequencies?  The answer is you “pluck” the primary coil.  For example: If you pick a guitar string once a second you have a frequency of 1 Hz, but the string vibrates on its own at whatever frequency it’s made for (~10 kHz).The AC mains have a low frequency (60 Hz) while the secondary coil needs to be driven at a high frequency (~1,000,000 Hz).  That means that the secondary will slosh back and forth thousands of times every time the current from the wall turns over just once.  Since the fast part of the circuit is so much faster than the slow part, you can just pretend that the current from the transformer is DC (direct current = 0 Hz).The secret to plucking is to change the circuit’s “shape” using a spark gap.  Spark gaps have some pretty slick properties.  They have an essentially infinite resistance until a high enough voltage is applied across them, at which point they spark (hence the name).  The spark you see is the air being pulled apart and ionized.  Now ionized gas is a really good conductor, so a spark is like instantly closing a switch.Also, spark gaps are the cheapest circuit element evar.  Can you cut a wire?  Now you got a gap!Also, adding spark gaps to a device is one of the quickest ways to bridge the divide between regular and mad science.

The transformer on the left forces charge to build up in the capacitor on the top. But the voltage across a capacitor is proportional to the amount of charge it's holding, so eventually the voltage is high enough to trip the spark gap.

The only job that the slow part of the circuit has is to charge the capacitor (pull back the string).  When the spark gap sparks (pluck!) the fast part of the circuit takes over, and the slow part is essentially ignored until all the energy is exhausted by exciting the secondary coil (string vibrates and slows).

With the spark gap active the charge can flow out of the capacitor and swing back and forth many times, very fast (thousands to millions of times per second). The current through the primary coil then drives current up and down the secondary, causing electrons to "overflow" from the top of the Tesla coil. The "overflow" is a delight to children of all ages.

As current flows through the primary it creates a voltage across the secondary that’s so high that electricity actually flies out of the top of the coil, despite having nowhere in particular to go.  It generally takes at least several hundred thousand volts to make that happen.The loop in the picture above forms an RLC circuit with a high resonant frequency (that matches the frequency dictated by the secondary).  As the energy in this system runs out the voltage needed to maintain the spark gap (which is much less than the voltage needed to start it) is lost, and the whole thing returns to the slow, charging phase.Since the power supply oscillates at 60 Hz, the whole system briefly turns off 120 times every second (the voltage is +, 0, -, 0, +, 0, …).  For this reason Tesla coils have a very loud 120 Hz hum that sounds “staticy” and ominous, as opposed to Jacob’s ladders which are continuous, and tend to sound more like “tearing”
ANS-2

The principles behind the Tesla coil are relatively simple. Just keep in mind that electrical current is the flow of electrons, while the difference in electric potential (voltage) between two places is what pushes that current. Current is like water, and voltage is like a hill. A large voltage is a steep hill, down which a stream of electrons will flow. A small voltage is like a near-flat plain with almost no water flow.The power of the Tesla coil lies in a process called electromagnetic induction, i.e., a changing magnetic field creates an electric potential that compels current to flow. Conversely, flowing electric current generates a magnetic field. When electricity flows through a wound up coil of wire, it generates a magnetic field that fills the area around the coil in a particular pattern, shown with lines below:

Photo modified from Los Alamos National Lab.

Similarly, if a magnetic field flows through the center of a coiled wire, a voltage is generated in the wire, which causes an electrical current to flow.The electric potential (“hill”) generated in a coil of wire by a magnetic field through its center increases with the number of turns of wire. A changing magnetic field within a coil of 50 turns will generate ten times the voltage of a coil of just five turns. (However, less current can actually flow through the higher potential, to conserve energy.)This is exactly how a common alternating current (AC) electrical transformer, found in every home, works. The constantly fluctuating electric current flowing in from the power grid is wound through a series of turns around an iron ring to generate a magnetic field. Iron is magnetically permeable, so the magnetic field is almost entirely contained in the iron. The ring guides the magnetic field (in green below) around and through the center of the opposite coil of wire.

Photo: Wikimedia

The ratio of coils on one side to the other determines the change in voltage. To go from 120 V household wall voltage to, say, 20 V for use in a laptop power adapter, the output side of the coil will have 6 times fewer turns to cut the voltage to one sixth its original level.Tesla coils do the same thing, but with a much more dramatic change in voltage. First, they employ a pre-made high voltage iron core transformer to go from 120 V wall current to roughly 10,000 V. The wire with 10,000 volts is wrapped into one very large (primary) coil with only a handful of turns. The secondary coil contains thousands of turns of thin wire. This steps up the voltage to between 100,000 and one million volts. This potential is so strong that the iron core of a normal transformer cannot contain it. Instead, there is only air between the coils, which can be seen in a Tesla coil below:

The large (primary) coil with few turns is on the bottom. The secondary coil with thousands of turns is the cylinder standing up vertically, separated from the lower coil by air. (Photo:Wikimedia)

The Tesla coil requires one more thing: a capacitor to store charge and fire it all in one huge spark. The circuit of the coil contains a capacitor and a small hole called a spark gap. When the coil is turned on, electricity flows through the circuit and fills the capacitor with electrons, like a battery. This charge creates its own electric potential in the circuit, which tries to bridge across the spark gap. This can only happen when a very large amount of charge has built up in the capacitor.Eventually so much charge has accumulated that it breaks down the electrical neutrality of the air in the middle of the spark gap. The circuit closes for a fleeting second and a huge amount of current blasts out of the capacitor and through the coils. This produces a very strong magnetic field in the primary coil.

The secondary wire coil uses electromagnetic induction to convert this magnetic field to an electric potential so high that it can easily break apart the air molecules at its ends and push their electrons in wild arcs, producing enormous purple sparks. The dome on the top of the device acts to make the secondary coil of wires receive energy more fully from the first coil. With some careful mathematical calculations, the amount of electrical energy transferred can be maximized.Flying blue streamers of electrons flow off the coil and through the hot air searching for a conductive landing place. They heat the air and break it into a plasma of glowing ion filaments before dissipating into the air or surging into a nearby conductor.

A tremendous light show is generated, as well as a loud buzzing, crackling sound, which can be used to play music. The electrical theatrics are so stunning that Tesla was known to use his device to scare and mesmerize visitors to his lab.

ANS-3

A classic Tesla coil consists of two inductive-capacitive (LC) oscillators, loosely coupled to one another. An LC oscillator has two main components, an inductor (which has inductance, L measured in Henrys) and a capacitor (with capacitance C measured in Farads). An inductor converts an electrical current (symbol I, measured in Amperes) into a magnetic field (symbol B, measured in Tesla [yes, named in honor of Nikola Tesla]), or a magnetic field into a current. Inductors are formed from electrical conductors wound into coils. Capacitors consist of two or more conductors separated by an insulator. A capacitor converts current into an electric field (symbol V, measured in Volts) or an electric field into current. Both magnetic fields and electric fields are forms of stored energy (symbol U, measured in Joules). When a charged capacitor (U=CV²/2) is connected to an inductor an electric current will flow from the capacitor through the inductor creating a magnetic field (U=LI²/2). When the electric field in the capacitor is exhausted the current stops and the magnetic field collapses. As the magnetic field collapses, it induces a current to flow in the inductor in the opposite direction to the original current. This new current charges the capacitor, creating a new electric field, equal but opposite to the original field. As long as the inductor and capacitor are connected the energy in the system will oscillate between the magnetic field and the electric field as the current constantly reverses. The rate (symbol [Greek nu], cycles per second or Hertz) at which the system oscillates is given by (the square root of 1/LC)/2pi. One full cycle of oscillation is shown in the drawing below. In the real world the oscillation will eventually damp out due to resistive losses in the conductors (the energy will be dissipated as heat).

In a Tesla coil, the two inductors share the same axis and are located close to one another. In this manner the magnetic field produced by one inductor can generate a current in the other. The schematic below shows the basic components of a Tesla coil. The primary oscillator consists of a flat spiral inductor with only a few turns, a capacitor, a voltage source to charge the capacitor and a switch to connect the capacitor to the inductor. The secondary oscillator contains a large, tightly wound inductor with many turns and a capacitor formed by the earth on one end (the base) and an output terminal (usually a sphere or toroid) on the other.

While the switch is open, a low current (limited by the source) flows through the primary inductor, charging the capacitor. When the switch is closed a much higher current flows from the capacitor through the primary inductor. The resulting magnetic field induces a corresponding current in the secondary. Because the secondary contains many more turns than the primary a very high electric field is established in the secondary capacitor. The output of a Tesla coil is maximized when two conditions are met. First, both the primary and secondary must oscillate at the same frequency. And secondly, the total length of conductor in the secondary must be equal to one quarter of the oscillator's wave length. Wave length (Greek lambda, in meters) is equal to the speed of light (300,000,000 meters per second) divided by the frequency of the oscillator.
Tesla coils differ in the type of switch used, the physical size of the components and the input voltage. Automotive ignition coils typically have a twelve volt input and are switched by a distributor, with moving contacts. They provide an output of 15-20,000 volts. Television fly-back transformers produce lower outputs but usually have 120 volt inputs and are switched by transistors or, in very old sets, vacuum tubes. The classic Tesla coil is switched by a spark gap. In this case, the primary circuit is known as a tank circuit. In its simplest form, the spark gap switch has two conductors separated by an air gap. When the electric field stored in the capacitor reaches a level sufficient to ionize the air within the gap a highly conductive plasma is formed, effectively closing the switch. Spark gap switched coils operate with inputs of about 5-20,000 volts and produce outputs of 100,000 to several million volts. For the spark gap to be effective, it must be able to open rapidly after the primary oscillation has damped out, in order that the capacitor may recharge. This is achieved by several methods, all of which amount to ways of cooling and dissipating the hot plasma formed during conduction. The simple gap can switch a few hundred watts of input power. Forced air cooling of the gap and, or using a number of gaps in series can increase power handling to several thousand watts. Higher power levels usually require a rotary gap, which mechanically moves gap electrodes rapidly into and out of conduction range. I should note here that even at input power levels of a thousand watts, the instantaneous power levels during gap firing can reach a million watts or more.

3. RADIO

Fundamentals of Radio

In the usual sense, radio refers to equipment used to send or receive electromagnetic waves in the range of frequencies lying, more or less, between one hertz and a few gigahertz.

Electromagnetic radiation occurs in wave form, that is, in a train of regularly rising and falling strengths. Distance from one crest to the next makes up one wavelength. In an ordinary AM broadcast signal, say 1000 kHz on your AM dial, wave crests are spaced at about 969 feet apart. The number of crests going by in one second is called thefrequency of the wave. Thus, if the speed of a wave is known (it's light speed, of course, for radio waves) then wavelength and frequency may be calculated one from the other according to the formula: v = fw, where v stands for velocity,f for frequency, and w for wavelength.

The height of a wave is its amplitude—usually that's expressed in volts for a radio wave. Common sense suggests that for waves of the same amplitude, those of higher frequency, more of them arriving in each second, are more intense, more powerful. Indeed, this is the case. A single gamma ray (extremely high in frequency) packs a concentrated wallop, while a wave of energy spread out in time, across longer wavelengths, doesn't knock things apart.

Early Radio Concepts and Equipment

Radio communication requires, at the very least, a transmitter that produces, amplifies, and radiates power at a useful radio frequency, while at the same time incorporating some kind of information into its signal; and a receiver that can detect the selected frequency, separate the signal's information content, and present it to a recipient.

Once physics had advanced far enough to understand and describe electromagnetic waves, the biggest hurdle for practical use lay in achieving sufficiently high frequencies and voltages for radio transmission. Tesla obtained both with his versatile resonant and "magnifier" coils (Tesla coils). Getting information into and out of a radio wave remained, however, a rather clumsy process until the development of electronic vacuum tubes, most notably Lee De Forest's triode in 1906.

For a decade or two after radio had become an accomplished fact, signals worked more or less like Morse dots and dashes, either on or off. A train of pulses separated by intervals made up the message. To know whether a signal was present or not, early receivers often relied on devices called coherers—in effect, just switches that turned on when a pulse excited an antenna, and had to reset themselves before the next pulse arrived. No one ever invented a coherer that was really satisfactory, Tesla included, but in his visionary way he solved another problem in communications whose implications reach right through modern computing and encryption techniques.

Tesla's Individualization

Tesla understood immediately, from the construction of the first radio transmitter, that a confusing welter of signals would soon cover the world. With this in mind he invented circuits that would respond only when a preselected set of frequencies were detected at the same time or in a specific sequence. A sender, thereby, could feel assured that messages would be received only at their intended destinations and would remain identifiable against a noisy background of unrelated radio traffic.

His designs for "individualization" (Tesla's term) operate in the same way—indeed they introduced the principle—as logic gates in computer circuitry. And the idea of breaking up signals, moving them around in frequency or time, lies at the heart of present-day communications security.

4. IMPROVED LIGHTNING

Early Lighting

The various inventors of early electric lights knew essentially of two ways to produce illumination: by running currents through wires or fibers until they glowed, or discharging arcs between electrodes. Arcs have never been suitable for general lighting purposes, though they are intense sources. As to filaments, most materials don't behave well when heated near their melting points. They will oxidize, unless surrounded by vacuum or inert gas, and they destroy themselves through internal stress.
Discovering durable filaments, however, does not solve a deeper problem in the physics of incandescent bodies, which is to say they radiate a broad spectrum of energies, or frequencies. In the case of a common 60-watt bulb, no more than a few percent of the total radiated energy is in the light-frequency range; most of the remainder is lost as heat. It would be far more efficient to excite electrons (which are responsible for all the emissions) more selectively, instead of heating everything up until there's enough brightness to read by.
It had occurred to many early investigators of electricity, when its properties and nature were still quite puzzling, to run currents through or into substances just to see what happened. As improved vacuum pumps, better glass manufacture, and higher-frequency sources were invented, the search moved away from brute incandescent effects. Alexandre-Edmond Becquerel was perhaps first to collide a tiny stream of electrons (inside an evacuated tube) with a fluorescent coating, resulting in a relatively cold glow (1859). Fluorescent substances emit light immediately when excited by high voltage or ultraviolet energy.

Tesla's Inventions & Innovations

Credit for the first practical phosphorescent lamp belongs to Tesla—phosphorescent substances are slower to emit light than fluorescent ones, and they continue to glow for some time after the power is turned off.Tesla's earliest lighting inventions had operated as conventional filament or arc devices, but with high-frequency currents supplying power. As he quickly discovered, such currents could be made to bring diffuse gases to incandescence, or cause light emission in various solid materials. His innovations in this field, though influential and disclosed in a series of celebrated lectures, were seldom patented.
Inasmuch as Tesla created for himself more powerful apparatus, to operate at higher frequency and voltage than was available to anyone else, he was capable by 1890 of generating fields that would light up, without any wires, phosphorescent tubes across his laboratory. (His assistants recall these lamps strewn casually around the lab and working by their eerie green glow.) The energy is just long wavelength radio—from Tesla's high-frequency generators—though in this case the signal is very strong, strong enough to be useful as power, rather than as a means of communication.
His first demonstrations of wireless power—presented always with superb showmanship—left the electrical profession agog. And the general public, exposed to these mysteries at Tesla's lighting exhibit in the Columbian Exposition of 1893, came away with the impression that an age of scientific miracles was dawning.

Further Lighting Developments

It's easy to understand the fascination pioneers such as Becquerel, Tesla, Wilhelm Roentgen, P.A. Lenard, and J.J. Thompson felt in their personal work with electromagnetism inside curiously shaped glass worlds. New lighting was only the first result. Thompson, in 1897, identified the streaming "cathode rays" responsible for so many diverse effects as electrons. At ever-higher energies, where electrons occasionally run into nuclei, Roentgen and Tesla found electrons were jettisoning very powerful photons indeed, called x-rays. And John Fleming discovered a useful way of controlling electric currents inside a vacuum tube (the first electronic diode; 1904), inaugurating modern electronics

5. REMOTE CONTROL

A Revolutionary Demonstration

In Madison Square Garden, at the Electrical Exhibition of 1898, Tesla staged a scientific tour de force, a demonstration completely beyond the generally accepted limits of technology. His invention, covered in patent No. 613,809 (1898), took the form of a radio-controlled boat, a heavy, low-lying, steel craft about four feet long. Inasmuch as radio hadn't been officially patented yet (Tesla's basic radio patent was filed in September 1897, but granted in March 1900), examiners from the US Patent Office were reluctant to recognize improbable claims made in the application "Method of and Apparatus for Controlling Mechanism of Moving Vessels or Vehicles." Confronted with a working model, however, examiners quickly issued approval.In fact, Tesla had been walking around New York City since 1895 picking up radio signals generated in various high-frequency experiments; he had received them as far as thirty miles away, at West Point. With the invention or improvement of several more control elements, he was able in short time to put them to use.

                                                                   The Boat

Tesla's tublike craft powered itself; there were several large batteries on board. Radio signals controlled switches, which energized the boat's propeller, rudder, and scaled-down running lights—simple enough in concept, but quite difficult to accomplish with existing devices. Even registering the arrival of a radio signal pulse taxed the rudimentary technology. Tesla invented a new kind of coherer (a radio-activated switch) for this purpose, essentially a canister with a little metal oxide powder in it. The powder orients itself in the presence of an electromagnetic field, like radio waves, and becomes conductive. If the canister is flipped over, after the pulse's passage, the powder is restored to a random, nonconductive state.Tesla contrived for a number of things to happen when the coherer conducted, most importantly for a disk bearing several differently organized sets of contacts to advance itself one step. Thus, if the contacts had previously connected the combination "right rudder/propeller forward full/light off," the next step might combine "rudder center/propeller stop/lights on." And with the aid of a few levers, gears, springs, and motors all would be accomplished, including a final step, flipping the coherer over so that it was ready to receive the next instruction.

                                                                 Applications

The world of 1898 had little understanding or use for Tesla's brilliant idea. Though he rather darkly imagined a military clamor for such things as radio-guided torpedoes, government interest did not materialize. (In one of history's curious footnotes, Tesla's good friend Mark Twain wrote immediately to say he was anxious to represent Tesla in the sale of this "destructive terror which you have been inventing" to England and Germany.) The navy did finance some trials in 1916, but the money went to one of Tesla's competitors. He remarked bitterly he could find no listeners until his patent had expired.Tesla's fears (and Twain's business hopes) were misplaced. The world's military establishments discovered many destructive terrors, but radio-controlled devices didn't number among them in any significant way until late in the twentieth century, with refinements in rocketry and guided bombs. Radio control remained a novelty, an exciting field for experimentalists and specialists, until the launching of the Space Age and the orbiting of myriad commercial and military satellites, all under remote control

http://www.pbs.org/tesla/res/res_pats.html

Neutral vs Earthing

What is Load angle/Power angle/Torque angle? Why it exists?

1. There are three terms used in this context: Load angle, Power angle and Torque angle.

The load angle primarily used for synchronous generator and torque angle is the same thing for synchronous motor. Power angle is also same in context of synchronous machines but it is more generic – also used in power transmission line.

Let me explain what they are:

Load angle (or Torque angle): For a synchronous generator, the magnetic field rotates at synchronous speed and the rotating magnetic field is created in the stator. These two fields are not fully aligned. The stator field lags the rotating field. This lagging expressed in angle is called load angle. The power developed by the generator is directly proportional to sine of this angle. This angle plays an important role for the stability of the generator. If the angle goes beyond 90º, the generator becomes unstable. This may happen when sudden change of large load occurs or fault sustains longer time. The generator instability is one of reason for massive blackout in case of major fault occurs in transmission line.

For the case of synchronous motor, the angle is called torque angle and the rotating field lags the stator field in this case.

Power angle: For a generator, the power angle is the difference between the generator induced voltage and the generator terminal voltage. The value of the power angle is same as the load angle. So, in context of generator, power angle and load angle mean same thing.

For the case of transmission line the power angle is the angle between the angles of the voltages at two different points (bus). The transfer of power between the two points of power system is proportional to the sine of this angle.

Though there is a distinct difference between these three terms, they are used synonymously in many cases in power system.

See the links below for additional help:

http://www.eolss.net/ebooks/Sample%20Chapters/C05/E6-39A-05-03.pdf

http://services.eng.uts.edu.au/cempe/subjects_JGZ/eet/eet_ch6.pdf

http://media.wiley.com/product_data/excerpt/75/04716144/0471614475.pdf

http://cr4.globalspec.com/thread/47295/Synchronous-Machine-Load-Angle

2. Power transfer is 

P = [(E1 x E2) sin (a)]/X 

where 

E1 and E2 are the sending and receiving end voltages 

a is the angle between E1 and E2 

X is the reactance of the circuit

This expression says that will voltages constant, the power transfer through a circuit is a function of a. If a is zero, there is no power transfer. Maximum power transfer occurs when the a is 90 degrees. Because power transfer is a function of a, a is also known as the 'load angle'. 

If you have an array of generators on a system, the fact that the system operates at a single frequency means that the generators must all be rotating at the same speed. (Well - almost. All two-pole generators will be at one speed, while all four-pole generators will be at exactly have that rotational speed, etc.). But there will be a small difference in the physical position of the rotors of those generators - the rotors of generators that are more heavily loaded (in per unit of their individual rating) will lag the rotors of the more lightly loaded machines. These angular differences are the load angles of the individual machines and can be calculated from the power transfer expression above

3. In synchronous system while generator generates rated power and load increase in system, Than frequency start goes to down respectively same as rpm of the all generator start reduce but the speed of the rotating magnetic field is same, So the angle created between rotating magnetic field and generator rotor, This angle are known as load angle of generator.

4. Torque is the rotating force, right?? 

eg: you can pull 50 kg of load to a distance 100m in 1 min by appling 100 newton energy ( your torque) 

60 kG to 100 m in 1 min by 150 N 

if 60 kg is your full load and 150 N is your max torque then 

100 kg to 100 m in 3 min by 150 N

Similarly this torque angle is the angle between stator pole and rotor pole.According to design in a 4 pole motor the stator and rotor pole exactly matches. Since there is a rotating stator mag field and stationary rotor magnetic field, the rotor poles will get locked to the stator poles and rotates in a speed equl to stator mag field called sync speed. ok 

If there's a extra load on the rotor shaft. although the rotor wont loose its mag lock with the stator poles and slightly lags in its pole matching. we term this unmatched displacemnt of rotor from stator pole match in terms of angle called torque angle. even with the created torque angle, rotor runs at sync speed.

This torque angle is because that the motor need more power to drive the increased load. i.e field should be strengthened. so in order to decrease the load torque sync motor creates a torque called sync reactance torque to exactly match the poles ( nothing but decreasing the load angle).

You can further decrease the torque angle by strengthening the field but it is limited by the maximum load that the machine can take.