Simulink Getting Started

       

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Definition of Nonlinear Loads

Nonlinear Load

This type of load is very much in demand all over the world, regardless whether they

are industrial, commercial, or domestic users. Computers, air conditioners, and televisions are examples of this type of load and it is understandably impossible to eliminate them away, even their impact to power system is already well documented. Nonlinear load, is define as,

“ A class of load that, when subjected to sinusoidal voltage source, would draw

 non-sinusoidal current into the system.”

	TYPE OF USER	TYPE OF LOADS	ELECTRICAL CHARACTERISTICS
	DOMESTIC COMMERCIAL INDUSTRIAL	Incandecent Lamps, Water heaters Computers, Flourocent Lamps, Water heaters. Motors, ASDs Furnances, Pumps	Resistive            Resistive            Resistive            Resistive            Nonlinear            Inductive

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Characteristics of different earthing systems:

TN system neutral-connected exposed conductive part

•    Letter T depicts that

            The neutral is directly earthed.

  

•     Letter N depicts that

            The exposed conductive parts of the loads are connected to the neutral conductor.

There are two types of systems, possibly depending on whether the neutral

conductor and protective conductor (PE) are combined or not:

 Case 1: When neutral and protective conductors are joined in a single conductor in this case it is known as PEN. This type system is identified by a third letter C and is called TNC system. PEN conductor eliminates potential rises in the exposed conductive parts if a fault occurs.

(Reference: IEC 60364-5, section 546-2) 

 Case 2: In this case the neutral conductor and protective conductor are different. These type of systems are recognized by a third letter S and is said as TNS.

Characteristics of different earthing systems:

IT system: Specific characteristics:

•     Switching upon occurrence of a double fault is usually generated by phase-to phase fault protective devices (circuit-breakers, fuses, etc.).

•     If the short-circuit current is not sufficient to activate protection against phase-2-phase faults, In        case if the loads are far away, protection should be done by residual current devices (RCD).                               

           

TT system:

Specific characteristics:

•    The installation of RCDs is compulsory.

•     All exposed conductive parts protected by the same protective device should be connected to the same earth.

•     The neutral earth and the exposed conductive part earth may or may not be Interconnected or combined.

•  The neutral may or may not be distributed.

Specific characteristics of TNS and TNC systems:

•  Fault switching is obtained by devices providing protection against phase2 phase faults (circuit-breakers, fuses, etc.).

• both TNS and TNC systems can be used in the same installation. The TNC system (4 wires), however, must never be downstream of the TNS system (5wires).

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MATLAB FOR BEGGINERS

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PROTECTION OF THE GENERATOR DUE TO UNBALANCE LOADING

Because of fault there is a unbalance condition in the three phase stator currents and because of these unbalance currents dual frequency currents starts flowing in rotor core. these dual frequency currents heats up rotor and harms rotor. due to same unbalance currents damage of stator also takes place.

 Negative arrangement channel furnished with the over current relay is utilized for the insurance against unbalance loading. From the hypothesis of the symmetrical components, we realize that unbalanced three phase currents contains the negative sequence part. This negative sequence current reasons warming of the stator.The negative warming accompanies the resistance law so it is corresponding to the square of the current. The warming time consistent normally rely on the cooling framework utilized and is equivalent to I²t=k where I is the negative succession current and t is the time of flow in seconds and k is the constant generally lies between 3 and 20. Its general practice to utilize negative current transfers which matches with the above warming aspects of the generator. In this sort of assurance three Cts are joined with three stages and the yield from the secondaries of the Cts is sustained to the curl of over current transfer through negative succession channel. Negative succession circuit comprises of the resistors and capacitors and these are joined in such way that negative succession currents moves through the transfer loop. The hand-off might be set to work at any specific quality of the unbalance currents or the negative succession part current.

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Earthing standard and Terminology (Part-1)

Earthing systems are governed by standard IEC 60364-3. There are three types of systems: IT, TT and TN.

The first letter defines the neutral point in relation to earth:

•     T stands for directly earthed neutral.

•     I stand for unearthed or high impedance-earthed neutral (e.g. 2200 Ω).

 

The second letter defines the exposed conductive parts of the electrical  Installation in relation to earth:

• T stands for directly earthed exposed conductive parts.

•    N stands for exposed conductive parts directly connected to the neutral conductor.

 

IT system unearthed or impedance-earthed neutral (see Figure-1)

Letter I depicts that

The neutral is unearthed or connected to earth by a high impedance (an Impedance of 1600 Ω is often used).

Letter T depicts that

The exposed conductive parts of the loads are interconnected and earthed. A group of loads can be individually earthed if it is situated far away from the Other loads.

TT system directly earthed neutral 

 First letter T depicts that

The neutral is directly earthed.

Second letter T depicts that

The exposed conductive parts of the loads are interconnected either altogether or by a group of loads. Each interconnected group is earthed. One exposed conductive part can be individually earthed if it is far away from the others.

Figure 2-3: directly earthed neutral (TT system) in low voltage

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Earthing and it’s Importance

In low voltage three-phase system there are three single Phases measured between each phase and a common 

point called the “Neutral point”. In actual fact, the neutral is the common point of three Star-connected windings

where all three phases meet.

Meaning of Unearthed and Earthed System:

When there is an open circuit between the neutral point and earth, we say that theNeutral is Unearthed.

On the other hand if there is a connection between earth And neutral in this case system is called Earthed.

A directly earthed neutral strongly limits over voltages but it causes very high fault currents, whereas an

unearthed neutral limits fault currents to very low values But encourages the occurrence of high over 

voltages.

In any installation, service continuity in the event of an insulation fault is also Directly related to the earthing system. An unearthed neutral permits service Continuity during an insulation fault. Contrary to this, a directly earthed neutral, or Low impedance-earthed neutral, causes tripping as soon as the first insulation fault

Occurs.

However, in an unearthed or high impedance-earthed network, the damage is Reduced, but the equipment 

must have an insulation level compatible with the level of over voltages able to cope in this type of network. The choice of earthing system in both low voltage and medium voltage networks depends on the type of

installation as well as the type of network. It is also influenced by the type of loads  and service continuity required.

From above discussion it is clear that we have to choose a compromise between The two, supply continuity and insulation protection.

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SOME IMPERATIVE SENTENCES FOR DAILY USE

There are some sentences which are very common in use with common mistakes.

        RIGHT                                                            WRONG

1.) READ OUT                                                       READ

2.) SPEAK OUT                                                     SPEAK

3.)  SHUT THE DOOR                                           CLOSE DOOR

4.) BOLT THE DOOR                                            LOCK THE DOOR

5.) MY NAME IS MIKE                                         MYSELF MIKE

6.) PLEASE SHIFT A BIT                                       PLEASE LET ME SIT

7.) SORRY                                                               WHAT

8.) I AM PURSUING MBA                                      I AM DOING MBA

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Yes it is Telephonic Talk

Ransach: Hello.


Kat : Hello. Is mike there?

Ransach: I'm sorry. He's not here right now.

 Kat: What time will he be back?

 Ransach : Around Two thirty.

 Kat: This afternoon?

Ransach : Yes. May I ask who's calling?


 Kat: This is his friend, pappu.

 Ransach: Okay. I'll tell him you called.

Kat : Thanks.

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Harmonics: Enemy of true sinusoidal wave

Harmonics: Enemy of true sinusoidal wave

In a perfect power system, the voltage supplied to user, and the supplied load current are exactly sine waves. In practice, notwithstanding, conditions are never perfect, so these waveform are sometimes distorted. This deviation from ideal sinusoidal waveform is  expressed as harmonic distortion of voltage and current waveform.

Harmonic signals are integer multiple of fundamental frequency of original signal. for example a signal of fundamental frequency 50 Hz will have its harmonic components of 3rd and fifth order with frequencies of 150 hz and 250 hz respectively.

Bad Effects of  Harmonics:

• Effects on the power system itself 

Causes over heating and thermal loss of life great challenge for motors and transformers.

•  Effects on consumer load 

Causes thyristor firing errors in inverter and SVC installations. performance of consumer devices and machines is adversely affected.

• Effects on communication circuits 

Distortion in communication signals may result in distorted demodulated signal.

•  Effects on revenue billing 

Harmonic voltage distortion can impact charging by bringing mistake into kilowatt  hour metering frameworks that depend upon correct acumen of the voltage zero. Also, of  course harmonic current wholes with central current requested by facility loads to  straightforwardly expand net billable kilowatt request and kilowatt hour utilization charges

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What Actually Power Factor Is?

 Power Factor is a measure of how productively electrical energy is utilized. The perfect Power Factor is
solidarity, or one. Anything less than one, (or 100% productivity),  implies that additional force is instructed to attain the true  errand nearby. This additional power is regarded as Reactive Power, which  tragically is important to give a magnetizing impact  needed by machines and other inductive loads to perform  their coveted capacities. Be that as it may, Reactive Power can likewise  be translated as watt-less, magnetizing or squandered power what's more an additional load on the power supply.

     It is measured as cosine of angle between voltage and current as depicted in the below figure.

It is clear from above example that due to inductive and capacitive loads power factor lags and leads respectively. reactive power comes into existence due to power factor. in capacitive loads reactive power is supplied to source and in inductive load reactive power is absorbed by load means supplied by source.

Above image shows best analogy of active and reactive power. Actually reactive power causes losses in system. In above figure fane (kvar) is reactive power liquid in cup can be considered as active power (kw) and KVA is apparent power.


Benefits of Power Factor Correction

1.  Power consumption reduced
2.  Electricity bills reduced
3.  Electrical energy efficiency improved
4.  Extra kVA availability from the existing supply
5.  Transformer & distribution equipment  losses are reduced
6.  Minimised voltage drop in long cables

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Principle of DOL starter:

A Direct-On-Line (DOL) starter is an electronic 3-phase  control framework which offers delicate begins in DELTA conneection. DOL starters are presently replacing the utilization of manual or semi automatic "star-delta" starters. In the  beginning of a 3-Phase Induction motor, full line voltages are connected to the motor through contactors. The DOL is these days the most widely recognized sort of 3-Phase starter utilized.

It has an "closing circuit" and an "opening circuit". The closing circuit is for applying the supply lines to the motor and the opening -or "tripping" -circuit secures the motor by cutting-off (or "tripping") power to the motor from the administration lines if there is any over-load condition, single phasing fault etc.

DOL starting is sometimes used to start small  water pumps, compressor , fans and Conveyor belts. In the case of an asynchronous motor, such as the 3-phase, the motor will draw a high starting current until it has run up to full speed. This starting current is typically 6-7 times greater than the full load current. To reduce the inrush current, larger motors will have reduced-voltage starters or variablespeed drives in order to minimise voltage dips to the power supply.


 DOL starters are now and then used to start minor water pumps, compressor , fans and Conveyor cinchs For  induction motors, for example the 3-phase induction motor will draw a high beginning current until it has run up to full speed. This beginning current is regularly 6-7 times more stupendous than the full load current. To lessen the inrush current, bigger motors will have decreased voltage starters or variablespeed drives so as to minimise voltage dips to the force supply.

Connection Diagram of D.O.L starter:

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Starters for Three Phase Induction Motors

Starters for Three Phase Induction Motors:
There are  many types of starters used for starting three phase induction motors depending upon size of motor and the work for which motor is used. Starter selection also depend upon construction of the motor. due to advancement in electronic control, electronic starters are also very famous now a days. process type and working conditions are also considered in starter selection.

There are basically two types of Induction Motors:
1.) Squirrel cage Induction Motor.
2.) Wound rotor Induction Motor.


1. Starters for Squirrel Cage Induction Motors:

• Electromechanical starters.
• Electronic starters.
  

2. Starters for wound rotor Induction Motor:

• Rotor resistance starter.

Above two types can further be Classified as depicted in following diagram

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PROTECTION OF THE GENERATOR DUE TO UNBALANCE LOADING:

PROTECTION OF THE GENERATOR DUE TO UNBALANCE LOADING:

Because of fault there is an imbalance in the three phase stator currents and because of these irregularity flows, twofold frequency currents are impelled in the rotor center. This reasons the over warming of the rotor and therefore the rotor harm. Uneven stator currents likewise harm the stator. Negative sequence relay furnished with the over current relay is utilized for the assurance against unbalance stacking. From the hypothesis of the symmetrical parts, we realize that an unequal three phase currents hold the negative succession segment. This negative stage grouping current reasons warming of the stator. The negative warming takes after the safety law so it is corresponding to the square of the current. The warming time steady normally rely on the cooling framework utilized and is equivalent to I²t=k where I is the negative succession current and t is the present length of time in seconds and k is the steady normally lies between 3 and 20. Its general practice to utilize negative current transfers which matches with the above warming aspects of the generator. In this sort of insurance three Cts are joined with three stages and the yield from the secondaries of the Cts is bolstered to the loop of over current transfer through negative sequence relay. Negative sequence relay comprises of the resistors and capacitors and these are joined in such way that negative arrangement momentums courses through the hand-off curl. The transfer might be set to work at any specific quality of the unbalance ebbs and flows or the negative arrangement segment current

References:
1. Generator protection
http://www.cooperpower.com/Library/pdf/99066.pdf
2. Power system and protection
http://books.google.com/books?id=e0kdmbuWB0gC&pg=PA1&dq=generator+protectio
n&ei=I40fSLqaLKaiiwGIv_CKBg&sig=f8YRFoOQNFeheKHNB9u13v0ucSY#PPP1,M
1
3. Protective theory relaying and application by Walter A. Elmore
4. Voltage regulators
http://en.wikipedia.org/wiki/Voltage_regulator
5 power engineering
http://en.wikipedia.org/wiki/Power_engineering
6. Google books of power system stability and control by Leonard L. Grigsby

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Over/Under voltage Protection:

 Over voltage Protection:

 Over voltage happens in light of the increment in the speed of the prime mover because of sudden loss in the burden on the generator. Generator over voltage does not happen in the turbo generator in light of the fact that the control governors of the turbo generators are extremely touchy to the speed variety. Anyway the over voltage insurance is needed for the hydro generator or gas turbine generators. The over voltage assurance is furnished by two over voltage transfers have two units – one is the immediate transfers which is situated to get at 130 to 150% of the evaluated voltage and an alternate unit is IDMT which is situated to get at 110% of evaluated voltage. Over voltage might happen because of the inadequate voltage controller and additionally because of manual control errors

Under voltage security:

If more than one generators supply the burden and because of some excuse for why one generator is abruptly outing , then an alternate generators attempt to supply the load. Each of these generators will experience a sudden build in current and subsequently diminishes the terminal voltage. Immediate voltage controller joined with the framework attempt to restore the voltage. What's more under voltage relay type-27 is likewise utilized for the under voltage insurance.

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