the Electrical designs and determine loads in Building

 

The electrical design professional should determine a building’s electrical load characteristics early in preliminary design stage of the building to select proper power distribution system and equipment having adequate power capacity with proper voltage levels, and sufficient space and ventilation to maintain proper ambients. once power system is determined it is often difficult to make major changes because of the coordination required with other disciplines. Architects and mechanical and structural engineers will be developing their designs simultaneously and making space and ventilation allocations. It is imperative, therefore, from the start that the electric systems be correctly based on realistic load data or best possible typical load estimates, or both because all final, finite load data are not available during the preliminary design stage of the project. When using estimated data, it should be remembered that the typical data applies only to the condition from which the data was taken, and most likely an adjustment to the particular application will be required.

 

This involves a continuing exchange of information that starts as preliminary data and is upgraded to be increasingly accurate as the design progresses. Documentation and coordination throughout the design process is imperative.At the beginning of a project, the electrical design professional should review the utility’s rate structure and the classes (system types) of service available. Information pertaining to demand, energy, and power factor should be developed to aid in evaluating, selecting, and specifying the most advantageous utility connection. As energy resources become more costly and scarce, items such as energy efficiency, power demand minimization, and energy conservation should be closely considered to reduce both energy consumption and utility cost.

 

System power (i.e., energy) losses should be considered as part of the total load in sizing service mains and service equipment. ANSI/NFPA 70-2002, NEC recommends that the total voltage drop from the electrical service to the load terminals of the farthest piece of equipment served should not exceed 5 percent of the system voltage and, thus, the energy loss,I²R, will correspondingly be limited. Listed hereafter are typical load groups and examples of classes of electrical equipment that should be considered when estimating initial and future loads.

Lighting
Interior (general, task, exits, and stairwells), exterior (decorative, parking lot, security), normal, and emergency.

Appliances
Business and copying machines, receptacles for vending machines, and general use.

Space conditioning
Heating, cooling, cleaning, pumping, and air-handling units.

Plumbing and sanitation
Water pumps, hot water heaters, sump and sewage pumps, incinerators, and waste handling.

Fire protection
Fire detection, alarms, and pumps.

Transportation
Elevators, dumbwaiters, conveyors, escalators, and moving walkways.

Data processing
Desktop computers, central processing and peripheral equipment, and uninterruptible power supply (UPS) systems, including related cooling.

Food preparation
Cooling, cooking, special exhausts, dishwashing, disposing, and so forth.

Special loads
For equipment and facilities in mercantile buildings, restaurants, theaters, recreation and sports complexes, religious buildings, terminals and airports, health care facilities, laboratories, broad casting stations, and so forth.

Miscellaneous loads
Security; central control systems; communications; audio-visual, snow-melting, recreational, or fitness equipment; incinerators, shredding devices, waste compactors, shop and maintenance equipment, and so forth.

 

Reference: Electrical engineer’s handbook by Robert B. Hickey

 

Generator theory

Faraday Law
Any change in the magnetic environment of a coil of wire will cause a voltage (emf) to be “induced” in the coil. No matter how the change is produced, the voltage will be generated. The change could be produced by changing the magnetic field strength, moving a magnet toward or away from the coil, moving the coil into or out of the magnetic field, rotating the coil relative to the magnet, etc.

 

 

Faraday’s law is a fundamental relationship which comes from Maxwell’s equations. It serves as a succinct summary of the ways a voltage (or emf (electromotive force) may be generated by a changing magnetic environment. The induced emf in a coil is equal to the negative of the rate of change of magnetic flux times the number of turns in the coil. It involves the interaction of charge with magnetic field.

 

 

Lenz Law

When an emf (electromotive force) is generated by a change in magnetic flux according to Faraday’s Law, the polarity of the induced emf is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant. In the examples below, if the B field is increasing, the induced field acts in opposition to it. If it is decreasing, the induced field acts in the direction of the applied field to try to keep it constant.

 

 

Coil and Magnetic
When a magnet is moved into a coil of wire, changing the magnetic field and magnetic flux through the coil, a voltage will be generated in the coil according to Faraday’s Law. In the animation picture at the top page show, when the magnet is moved into the coil the galvanometer deflects to the left in response to the increasing field. When the magnet is pulled back out, the galvanometer deflects to the right in response to the decreasing field.

The polarity of the induced emf is such that it produces a current whose magnetic field opposes the change that produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant. This inherent behavior of generated magnetic fields is summarized in Lenz’s Law.

 

Resource  http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html

 

 

 

 

Introduction to circuit breaker.

A circuit breaker is protective device which is design to automatically open an electrical circuit thus preventing harm and damages to equipment and personal. The damages are due to overload, short circuits and sometimes earth faults. Circuit breakers are made in varying sizes, from small device which carry fractional amperes (e.g.  a 10 milli ampere residual circuit breaker) like that in a typical house up to extremely large ones like a generator circuit breaker which continuously few tens of thousands of amperes. An LV/MV system circuit breaker is similar to its fuse counterpart in its main function of fault interruptions. However, a circuit breaker differs from a fuse in its other functions which are breaking loads as well as normal opening with or without current in the circuit.

Further, it performs closing function and is non-destructive (except requiring periodic maintenance, replacement of current interrupting contact and in some forms becomes device of that needs a part of it to be replaced after specific numbers of operations) a fuse however, operated once and then has to be replaced, a circuit breaker can be reset (either manual or automatically) to resume normal operation.

There are two attributes to electricity which is quite apparent due to its obviousness to the real world which are the Current and the Voltage as well as some functional derivative of these two like Real power (Watt), Reactive power (VAR), Energy (kWH) etc. Performance of a circuit breaker in its main function relates with making, carrying and breaking currents in an Electrical circuit. To make or break a circuit there must be some component which connects and disconnects which is called Contacts/interrupters. While making a circuit the components (one or both or many has to move in an Electric field) and since the movement is to make a circuit, the field gets progressively increased as the components move and we can imagine a pre-arc (prestrike). While breaking, it is opposite thing and we imagine a restrike.  Voltage and currents are related same way as an Electric field (due to available static electric charge) with a Magnetic field (due to moving Electric charge). Some more parameters gets added since circuit breakers are often linked in some way with neighboring circuit components, or magnetic devices (like motors, welding etc) which introduces switching transients and atmosphere (lightning transients). These are actually are called impulses (surges) and have a characteristic front, peak and tail of a definite polarity (+ve or negative).  Some others may be oscillatory (decaying, steady, increasing) which can be for the sake of study and computation addressed as a function of the fundamental part (frequency 50Hz. 60Hz etc). Thus we added Impulse withstand requirement for a circuit breaker, reactive (capacitive/inductive) duty and harmonics performance.

Operation of a circuit breaker

All circuit breakers have common features in their operation, although details vary substantially depending on the voltage class, current rating and type of the circuit breaker. To breaking a fault, firstly a fault condition needs to be detected. For higher capacity CBs this function is delegated to external Protective devices due to size, proximity to High volatges, sophistication in detection of all types of faults accurately to specific requirement of time. In low-voltage circuit breakers this is usually done within the breaker enclosure. To perform in a small space with cost effective and efficient way against demanding forces and heat we can imagine special design is required to confine it to limited area within a CB. So we identified some interrupting means. Once a fault is detected, contacts within the circuit breaker must open to interrupt the circuit; some mechanically-stored energy (using something such as springs or compressed air) contained within the breaker is used to separate the contacts, although some of the energy required may be obtained from the fault current itself. Small circuit breakers may be manually operated; larger units have sophisticated to trip the mechanism, and electric motors to restore energy to the springs.

 

The circuit breaker contacts must carry the load current without excessive heating, and must also withstand the heat of the arc produced when interrupting the circuit. Contacts are made of copper or copper alloys, silver alloys, and other materials.

Service life of the contacts is limited by the erosion due to interrupting the arc. Miniature and molded case circuit breakers (MCB and MCCB) are usually discarded when the contacts are worn, but power circuit breakers and high voltage circuit breakers (HVCB) have replaceable contacts. When a current is interrupted, an arc is generated. This arc must be contained, cooled, and extinguished in a controlled way, so that the gap between the contacts can again withstand the voltage in the circuit. Different circuit breakers use vacuum, air, insulating gas, or oil as the medium in which the arc forms.

Finally, once the fault condition has been cleared, the contacts must again be closed to restore power to the interrupted circuit.

Resource: Circuit Breakers in Power Systems

Basic Principle

A significant proportion of industrial electricity is about single phase and three phase, transformers AC and DC machines for troubleshooting electrical equipment and control circuits, it is important to understanding basic principle on which the electrical equipment works. In each plant, the mechanical movement of different equipment is caused by an electric prime mover (motor). Electrical power is derived from either utilities or internal generators and is distributed through transformers to deliver usable voltage levels. Electricity is found in two common forms :

AC (Alternating current) and DC (Direct current)

Electrical equipments can run on either of the AC/DC forms of electrical energies. The selection of energies source for equipment depends on its applications requirements. Each energy source has its own merits and demerits. Industrial AC voltage levels are roughly defined as LV (low voltage) and HV (High voltage) with frequency of 50-60 HZ. An electrical circuit has the following three basic components irrespective of its electrical energy form :

1. Voltage (volt)
2. Ampere (amps)
3. Resistance (ohm)

Voltage is defined as the electrical potential difference that causes electrons to flow. Current is defined as the flow of electrons and is measured in amperes. Resistance is defined as the opposition to the flow of electrons and is measured in ohms. All three are bound together with Ohm law which gives the following relation between the three :

V = I x R

Where

V = Voltage.

I = Current.

R = Resistance.

Power

In DC circuits, power (watts) is simply a product of voltage and current.

P = V x I

For AC circuits, the formula holds true purely resistive circuits; however, for the following types of AC circuits, power is not just a product of voltage and currents. Apparent power is the product voltage and ampere, i.e., VA or KVA is known as apparent power. Apparent power is total supplied to a circuit inclusive of the true and reactive power. Real power or true power is the power that can be converted into work and is measured in watts. Reactive power if the circuit is of an inductive or capacitive type then the reactive component consumes power and cannot be converted into work. This is known as reactive power and is denoted by VAR.

 

Relationship between powers.

Apparent power (VA) = V x A

True powers (watts) = VA x cos q

Reactive power (VAR) = VA x sin q

 

Power factor

Power factor is defined as the ratio of real power to apparent power. The maximum value it can carry is either 1 or 100 (%), which would be obtained in a purely resistive circuit.

 Power factor = True power / Apparent power

  = Watts / kVA

 

Electrical Energy.

This is calculated as the amount of electrical energy used in an hour and is expressed as follows :

Kilowatt hour = kW x H

Where

kW = kilowatt

H = hour

 

Type of circuits.

There are only two types of electrical circuits, series and parallel. a series circuit is defined as a circuit which the elements in a series carry the same current, while voltage drop across each maybe different.  A parallel circuit is defined as a circuit in which the elements in parallel have the same voltage, but the current maybe different.

 

 

How Motor works ?

The basic working of a motor is based on the fact that when a current carrying conductor is placed in a magnetic field it experiences a force. if you take a simple DC motor, it has a current – carrying   coil supported in between two permanent magnets (opposite pole facing) so that the coil can rotated free inside. When the coil ends are connected to a DC source then the current will flow through it  and it behaves like a bar magnet as shown in figure 1. as the current starts flowing, the magnetic flux line of the coil will interact with the flux line in the permanent magnet.  This will cause of a movement of the coil (Figures a, b, c, d) due to the force of attraction and repulsion between two fields. The Coil will rotate until it achieves 180° position. Because now the opposite poles will be in front of each other (figure 1e) and the force of attraction or repulsion will not exist.

Figure 1

The role of the commutator the commutator brushes just reverse the polarity of DC supply connected to the coil. This will cause a change in the direction of the current of the magnetic field and starting the coil by another 180° position (figure 1f). The brushes will move on like this to achieve continuous coil rotation of the motor. Similarly the AC motor also function on the above principle, except here the commutator contacts remains stationary, because AC current direction continually change during each half – cycle (every 180°)

Resources ;Practical Troubleshooting of Electrical Equipment and control circuits – M.Brown

NEMA Motor Data and Calculator

Three phase and Single phase motor

NEMA Motor data calculator is based on the NEC 2011

For three phase according to inputs ( Voltage and Horse power ) following data is calculated :

1. Full load ampere. (FLA)
2. Wire size.
3. Powerpact Breaker.
4. PowerPact Breaker Cat No.
5. HD Switch, Nema 1 Enclosed.
6. Dual Elem Time Delay Fuse Amps.
7. NEMA Starter Catalogue Number.
8. Melting Alloy Thermal unit.
9. NEMA Size starter.

 

For single phase input is Horse Power and following information is calculated for both voltages 115V and 230V :

1. Full Load Amps. (FLA)
2. Wire size.
3. PowerPact Breaker size.
4. PowerPact Breaker Cat No.
5. HD switch, NEMA 1 Enclosed.
6. Dual Elem Time Delay Fuse Amps.
7. Fractional HP N1 Starter class 2510.
8. Thermal Unit.
9. Integral Starter N1 Enc 2510.
10. One melting Alloy thermal unit.
11. NEMA Enclosed Starter Class 8536.
12. Thermal Unit.

NOTES

Fuse and Circuit Breakers shown are for short-circuit ground fault protection only. This data applies to normal service applications of switches, Starter or Breakers shown.

Do not use for Heavy service applications as defined in the latest catalogue digest.

 

Nema Motor Data Calculator

 

 

 

My Interpretation

Method of operation

There are two 2 unit motors to operated this Boiler. motor  1 has using as a booster pump from water tank to Boiler and another one used to Blow air and couple to the fuel pump. Motor 2 would not operated till motor 1 run.

Motor 1

Actuation of pushbutton On and positioning selector switch Manual or auto energize the coil of contactor C1. The contactor switches ON the motor and maintains itself via it’s own auxiliary contact C1/13-14. Contactor is de-energized  in the normal course of events by actuation pushbutton Off or break by level switch LS1 when selector switch in the position Auto. In the event of an overload, it is de-energized via normally contact 95-96 on the thermal overload relay TOR. The coil current is interrupted and switches the motor Off.

Motor 2

Pushbutton ON is energized trough over the Limit switch LS2, pressure switch HP and LP and temperature limit switch and then timing relay TR 1, the normally open contact TR1/17-18 (instantaneous contact)  Which applies voltage to star contactor C4. C4 closes and applies voltage to main contactor C2 via normally open contact C4/14-13. C2 and C3 maintain themselves via normally open contact C2/14-13. C2 applies voltage to motor in Star connection. When the set change over time has elapsed, TR/17-18 open the circuit of C4 and after 50 seconds closes the circuit via TR/17-28 of C3. Star contactor drops out, Delta contactor C3 closes and switches Motor 2 to full main voltage. At the same time normally close contact C3/22-21 interrupt the circuit of C4, thus interlocking against renewed switching on while the motor is running. The motor cannot start up again unless it has previously been disconnected by pushbutton Off, shut down by HP pressure switch, TS temperature switch and LS2 level switch or in the event of an overload by the normally closed contact 95-96 of the TOR (thermal overload relay). After the motor run transformer will energize ignition at the same time solenoid valve open the fuel. An ignition will be closes when warm touch photocells sensor.

Thanks

Quotation

 

Scientist study the world as it is, engineers create the world that never has been.

Theodore von karman.

If A is success in life, then A equals X plus Y plus Z, work is X, Y is play and Z is keeping your mouth shut.

Albert Einstein.

The important thing about a problem is not it’s solutions, but the strength we gain in finding the solutions.

Anonymous.

I often say that when you can measure what you are speaking about, and express it in numbers, you know something about it; but when you can not express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge but you have scarcely, in your thoughts, advance to the stage of science whatever the matter maybe.

Lord Kevin

 

 

” Engineering is not learning a profession, it is also learning a profession, one whose practitioners first become and then remain students throughout of their active careers ”

William L Everitt.

The desire to understand the world and desire to reform it are the two great engines to progress.

Betrand Russell.

An expert problem solver must be endowed two compatible quantities, a restless imagination and patient pertinacity.

Howard W. Eves

An engineers unordinary person who can do for one dollar what any ordinary person can do for two dollars.

Anonymous.

Society is never prepared to receive any invention. every new thing is resisted, and it take years for the inventor to get people to listen to him and years more before it can be introduced.

Thomas Alva Edison.

One machine can do the work of fifty ordinary man, No machine can do the work of extraordinary man.

Elbert G. Hubbard.

God has created the world, and  the Engineers that changes it

Henry Siregar

Interlocking of three phase motor

 

Method of operation.

Actuation pushbutton ON energize the coil of contactor. The contactor switches ON the motor and maintain its self  after the button is enables via its own auxiliary contact/ 13-14. Contactor is de-energized course of events by actuation pushbutton OFF. in the event of an overload, it is de-energized via the normally closed contact 95-96 on the overload relay. the coil current is interrupted and contactor switch the motor OFF.

 

 

Star – Delta switching of three phase motor

Method of Operation ;

Push Button (PB) ON’ energize Time relay, the normally open (NO’) contact time delay/1-4 ( Instantaneous contact ) Which applies voltages to star contactor C3. C3 close and applies voltage to mains contactor C1 via normally open contact C3/ 14-13. C1 and C3 maintain themselves via the normally open contacts C1/ 14-13. C1 applies voltage to motor in STAR connection.  When the set changeover time has elapsed, time delay /1-4 open the circuit of C3 and after 50 seconds close the circuit via time delay /1-3 of C2. Star contactor drop out. DELTA contactor closes and switches motor to full mains voltage. at the same time, normally close contact C2/22-21 interrupts the circuit of C3, thus INTERLOCKING against renew switching ON while the motor is running. The motor cannot star up again unless it has previously disconnected by PB OFF’, or in the event of an overload by the normally closed contact 95-95 of the Thermal Overload Relay (TOR) or Circuit Breaker.