Engineering plant facilities 02 electricity fundamentals

ELECTRICITY

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Engineering-Book ENGINEERING FUNDAMENTALS AND HOW IT WORKS

September 2014

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Atom

An atom is the basic constituent of matter. An atom consists of a central nucleus which is surrounded by one or more electrons.

The nucleus contains protons, which are positively charged, and neutrons, which are electrically neutral.

Atom

Electricity Fundamentals

Electrons

Electrons

The electrons closest from the nucleus are strongly attracted. But those which revolve in orbits far from the nucleus, less attracted, can leave easily the atom and become free.

We say that the atom has become a positive ion.

But a free electron can also “hang up” to a neutral atom which will become a negative ion.


Voltage

Voltage

The force that wants the free electrons return to the positive ion is called Voltage. The unit for the voltage is the Volt (V) and the conventional symbol is U.


Electricity Current

These electrons travel through a conductor.

The movement of these electrons is known as Current. The unit for measuring this flow is the Ampere and the conventional symbol is I.

Current


Resistance

Resistance is the opposition to this movement. The unit measuring the resistance is the Ohm (Ω) and the conventional symbol is R. We have the following formula:

U = R.I

Resistance


Conductor

A conductor is a material which lets circulate the electric current. There are several different conductors:

Silver (one of the best conductors)Iron, copper, aluminum…

Water (especially salt water)Human body (composed mainly of water)

…

But there are also several materials which are not conductor:

WoodStoneRubberPaper sheet…

Conductor


Electric Power & Energy

Electric power is the multiplication of the voltage U by the current I. The unit is Watt (W) and the conventional symbol is P. We have the following formula:

P = U.I

The energy is the consumption of power during a certain period of time. Energy is the product of power, in Watts, and time, in hours. The unit is Kilowatt hour (kWh).

Electric power


Direct Current DC

We name the current Direct Current (DC) when the direction of current is flowing in one constant direction.

Direct Current


Alternating Current AC

When the direction of current flowing is constantly being reversed back and forth, the current is named Alternating Current (AC).

Alternating Current


Period & Frequency

The period is the time required for the same event occurs again. The unit is second (sec) and the conventional symbol is T.

The frequency is the number of times a repeating event occurs during 1 second. The unit is Hertz (Hz) and the conventional symbol is f.

f = 1/T

Period & Frequency


Series Circuit

In a series circuit, all of the components carry the same current.

Current: I

Voltage: UPN = UR1 + UR2

Resistance: Rtotal = R1 + R2

Series Circuit


Parallel Circuit

In a parallel circuit, the voltage is the same for all elements.

Current: I = I1 + I2

Voltage: U = U1 + U2

Resistance:

Parallel Circuit


Single-phase Electric Power

Single-phase electric power refers to the distribution of a single source of Alternating Current.

So we have one conductor for input, the phase, and neutral for output. Typically, a third conductor, called the ground, is used as a protection against electric shock.

Single phase is widely used in rural areas.

Single-phase


Three-phase Electric Power

Three-phase electric power refers to the distribution of three sources of Alternating Current.

So in a three-phase system, we have three circuit conductors, with the same frequency, which reach their instantaneous peak values at different times. We have also the neutral and a fifth conductor, the ground.

Three-phase


230 V / 400 V

A single-phase system usually frees a voltage, between the phase and the neutral, equals to 230 V.

In a three-phase system, if we measure the voltage between one phase and the neutral, we have 230 V.

The voltage between two phases is equal to 400 V.

We can notice the following formula:


Phasing reversed

What happens to a three-phase motor if the phasing of the power source is reversed?

If we reconnect the phases switching any two of the three phases, the motor will turn in the opposite direction. It is important to ensure proper connection of wires because the rotation of the motor can be important.

Tip: there is a color code to get it right.

US EuropePhase 1 Phase 2 Phase 3 Neutral Ground


Phase disconnected

What happens when a phase gets disconnected in a three-phase system?

When a phase gets disconnected, the motor will run until it is stopped, but it will not start again. In that case, the other 2 phases will increase in amps.


Safe Working Electricity Fundamentals

Electric Motor components and applications









Electricity FundamentalsElectric Motor components and applications

Electricity FundamentalsElectric Motor components and applications





Motor burned

Why a motor burns?

There are several reasons why a motor burns. We can retain the 4 following reasons:

All mechanical parts wear out eventually Insulation breaks down over time due to heat exposure Some motors are intended to be lubricated from time to time Anything that is powered by electricity will last longer in a cooler environment.


Short circuit

A short circuit is an abnormal low-resistance connection between two conductors supplying electrical power. This results in excessive current flow in the power source and may even cause the power source destroyed.

We saw before the following formula: U = R.I

If we have a short circuit, then R decreases sharply. With this formula, if U must remain constant then I have to increase strongly.

Short Circuit

Practical case:

Assume that U = 9 V. If we have a resistance R equals to 3 Ω then the current I must be equal to 3 A (3*3 = 9).

Now, U = 9 V but R is now equal to 0.03 Ω. The current I = 300 A.


Hot Terminals

Why terminals get hot ?

There are several causes for hot terminals; most of them are usually result of focal points of resistance. They often appear with higher temperature at the point of high-strength. Load imbalances appear just as hot at the stage or in the part of the circuit which is bad design or overloaded.

If the driver is hot, it might be is wrong sizing or overloaded.

Why it is important to detect it early?

The most common example of damage is a burned fuse. In the control circuit of a motor, this can produce a single-phase condition and, possibly, a costly damage to the engine.


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Content

Overview of electrical power system

Maintenance, Testing and Commissioning

● Regular test

● Maintenance activities

● Cable testing

● Capacitor testing

● Switchboard

● Circuit Breakers

● Contactors and Relays

● Electric Motors

Electrical safety


Overview of power distributionElectricity Fundamentals

Maintenance, Testing and Commissioning

Checking the insulation system, electrical properties, and other factors related to the overall operation of the distribution system.

Insulation testing

Relay and protective device testing

Circuit breaker time to trip

Earth grounding resistance

Infrared inspection testing

Power Quality

Regular test


Maintenance and Testing

A well-organized and implemented program minimizes accidents, reduces unplanned shutdowns, and lengthens the mean time between failures (MTBF) of electrical equipment:

Cable and cable Insulation

Capacitor Banks

Switchboards

Earth links and potential

Connections

Maintenance activities


Cable and Insulation TestingElectricity Fundamentals

Damage to electrical cables can cause them to not effectively transmit electricity. Even worse, these faults can cause electrical sparks which become a fire hazard.

Cable and Insulation Testing

Cable meggers detect cable faults through the use of a pulse echo, which helps electricians locate damage to a cable. Poor joints or impedance cause damage and resistance to the current flow.

Electric cables


Cable and Insulation Testing

Testers can find the location of the fault by tracking the amount of time that the pulse takes to reflect back to the cable megger.

Impendence is an opposition to alternating currents.

Testers send a pulse down a cable at a velocity determined by the insulation of the cable. Changes in the cable will cause the pulse to be reflected back.


Capacitor Bank Testing

Capacitor Banks

Capacitor Banks should be checked with an Infra-red scanner on a monthly basis.

Six monthly Capacitor test using a megger or Ohm meter, this is specialised work and should be undertaken only by Technicians skilled in this area.


Should be infra-red scanned every three months

Main Distribution Board Testing

Main Distribution Board


Contactor and Relay Testing

First look at the relay or contactor to find out what voltage it takes to pull in the coil. Check to make sure your getting power to it and the voltage is correct. If yes continue below tests the coil of the relay or contactor is probably open. Set meter to measure Ohms.

1. Each coil contains two terminals A1(positive)and A2 (negative or 0V). 2. Detach wires from A1 and A2 Touch one probe to each terminal. 3. The meter usually read around 80-200ohms. If its less than 20 ohms coil is

most likely shorted. If its above 500 ohms it is most likely open and should be replaced. If possible look for another solenoid to compare readings with.

4. If coil ohm resistance looks ok and correct voltage is at coil, replace the coil or contact.

5. If voltage is low check A1 to the common (0V) on a main terminal strip. If this is ok you have a loose connection or bad wire on the common side.

Contactor & Relay


http://en.wikipedia.org/wiki/File:ACcontactor.JPG

Circuit Breaker Tester: Clamping Ammeter

Circuit breakers that trip every time they're reset may be overloaded.

In order to diagnose a circuit breaker overload you can test the circuit breaker by using a clamping ammeter. This circuit breaker tester is used to check overloads and shorts that are in progress and determine whether the electric current is running through the circuit.

Circuit Breaker Testing

The clamping ammeter should be clamped to a single wire not the cable in order to accurately test the circuit breaker.


Electric Motor Testing

Testing and troubleshooting electric motors can save you a trip to a repair shop, but it does require caution.

If they're completely beyond repair, most electric motors will have an acrid smell that indicates burnt windings; if yours doesn't, troubleshooting may lead you to a solution.

Maintenance of electric motor


Maintenance of electric motor

Put on safety glasses. Any time you are repairing an electrical device, safety glasses should be your No. 1 tool. Shut off all electric power to the motor, whether by turning off a circuit breaker or removing fuses from the disconnect switch.

Electric Motor TestingElectricity Fundamentals

Read the motor's nameplate data to confirm whether it's a low-voltage a 230-volt motor or a three-phase high-voltage 440-volt motor. This will determine the number of power leads the motor has.

All single-phase 230-volt motors have two wire leads that connect to the power supply.All three-phase 440-volt motors have three wire leads that connect to the three-phase power supply.

Electric Motor TestingElectricity Fundamentals

Remove the plastic wire connectors that connect to the power supply.

You may have to identify the power leads to the wires on the motor if it is a three-phase motor. This will ensure the rotation will be correct when you re-terminate the motor.


Turn your volt-amper meter to the ohm setting. The meter should read OL (open lead) or zero ohms.



Touch one lead to the case of the motor, and test each motor lead. The ohm meter should read OL, or zero ohms.

If a reading of any ohms is observed, you may have a direct short in the motor windings; the motor may be bad.

Some motors, especially the three-phase type, may have a large resistance reading--in the 20 mega ohms range or larger. This may be fine, or this may be a sign that the bearings are going bad, as the motor may have deteriorating windings due to excessive heat.


Remove the capacitor from its housing if you are testing a single-phase motor that has a capacitor. Be careful not to touch the exposed leads.

The capacitor is like a battery and stores a high-voltage charge. Turn your volt ohm meter to volts and carefully touch to the bare leads of the capacitor.


If voltage is read, the capacitor still contains a charge. Holding the leads of the meter to the capacitor should show it discharging.



Continue until zero voltage is observed on the meter.

Most modern volt ohm meters have a capacitor-testing switch, making it easy to determine the status of the capacitor.

In most cases, the capacitor only needs to be replaced on these types of single-phase motors.


Deaths

Electrocutions rank fourth (9%) in causes of industrial fatalities (behind traffic, violence and construction). The National Safety council estimates 600 people die every year of electrical causes. Most of these accidents involve low voltage (600 volts or less).

Effects on your body

A small night-light with a 6-watt bulb draws 0.5 ampere, and even that small amount of current can be fatal. Here are some effects of current (in milli amps) passing through a 150 pound body (note that perception is only .5 to 1.5 milli amps):

Shock you painfully Damage sensitive equipment Ignite combustible materials Can be fatal

Electrical Safety

Why Worry About Electricity?


This training module will cover some basic safety rules you should follow in regards to electrical safety.

Electrical SafetyElectricity Fundamentals

What are the leading causes of electrical accidents?

The leading cause is Unsafe Acts.

Electrical Safety

There are 2 reasons for unsafe acts: 1. We know better but intentionally do

something unsafe. 2. We don't know better.


Procedure to avoid the following unsafe acts

1. Failure to de-energize, lockout & tag out hazards during maintenance, repair or inspections.

2. Use of defective and unsafe tools. 3. Use of tools or equipment too close to energized parts. 4. Not draining off stored energy in capacitors. 5. Using 3-wire cord with a 2-wire plug. 6. Removing the third prong (ground pin) to make a 3-prong plug fit a 2-

prong outlet. 7. Overloading outlets with too many appliances. 8. Using the attached electrical cord to raise or lower equipment. 9. Not verifying power is off when making repair (drilling into a 110 Volt

AC line can kill). 10. Working in an elevated position near overhead lines.


Electrical Safety

• Loose connections

• Faulty insulation

• Improper grounding (removal of 3rd prong)

• Use of "homemade" extension cords

• Defective parts

• Unguarded live parts--for example:

• Bare conductors or exposed terminals • Metal parts of equipment may become energized when connected by cord or plug. Capacitance may cause up to 55% of line voltage to be stored on the casing of metal tools.

Some common causes of unsafe equipment


Hazardous Environments

Use special precautions when working in potentially hazardous environments and situations. Even an accidental static discharge can cause a fire or explosion in areas where the following are present: •Flammable vapors, liquids and gasses •Combustible dusts •Corrosive atmospheres •Explosive environments •Poor housekeeping: blocked electrical boxes, flammable materials stored in equipment rooms, lack of proper hazard signs, excess clutter.

Electrical Safety

Special care is also need in wet or damp locations - water and electricity are a bad combination. If the wire is frayed or damaged, a fatal electrical shock can result.


What can you do to help protect yourself ?

Basics of Electricity:

•Electrical current will not flow unless it has a complete path (circuit) that returns to its source (battery, transformer). •Current flows through you and other conductors, such as metals, earth and concrete. •Current can harm you when it flows through your body (electric shock). •Insulators resist the flow of electricity. Insulating materials are used to coat copper conducting wires and are used to make electrical work gloves. Insulators help to protect humans from coming into contact with electricity flowing through conductors. •Just as there is pressure in a water pipe, even with no water flowing, there is voltage at a receptacle, even if current is not flowing. Another word for voltage is "Potential."

Electrical Safety

You have to know about electricity and how it can harm you and your colleagues.


How electricity can harm you ?

Current passing through your body can cause electric shock, resulting in 3 types of potential injuries:

Burns (arcs burn with heat & radiation) Physical injuries (broken bones, falls, & muscle damage)

At 10 mA, the muscles clamp on to whatever the person is holding.

Nervous system effects (stop breathing at 30 to 75 mA alternating current at 60Hz, fibrillation at 75 to 100 mA at 60Hz)

Fibrillation = heart is "twitching" and there is no blood flow to the body.

The heart can be damaged because it is in the path of the most common routes electricity will take through the body:

• Hand-to-hand• Hand-to-foot


Electrical Safety

Minimize your exposure to static shocks

Never clean the glass face of your computer monitor while the computer is on.

You can be injured by the reaction to the shock even though such shocks in themselves are not hazardous.

During normal operation, the glass surface of a monitor's CRT accumulates an electrostatic charge. When you touch the screen with a finger, the charge is from the portion of the screen you touched and it discharges through your finger with a tiny spark. Electric current does not normally flow through glass, so only the part of the screen that your finger touches is discharged.

However, when you clean a monitor the entire glass is wet and the charge on the entire screen will discharge to your finger or hand, causing a much more painful shock.


Control hazards though safe work practices

• Plan your work and plan for safety • Avoid wet working conditions and other dangers

• Use Ground Fault Circuit Interrupters. GFCI's are electrical devices that are designed to detect ground faults (when current is "leaking" somewhere outside its intended pathway). If your body provides the path to ground for the leaking current, you could receive a shock or be electrocuted. GFCI's should be used in all wet locations and on outside outlets.

• Avoid overhead power lines: Position yourself so that the longest conductive object you are using (saws, poles, tools, brooms, etc.) cannot come closer than at least 10 feet to any unguarded, energized overhead line.

• Use proper wiring and connectors • Use extension cords properly and temporarily: • Cords must be UL listed and have 3 prongs • Power bars must have a fuse or breaker • Do not use 2-prong, ungrounded cords in a lab • Do not run cords through walls, doors, under rugs, or across aisles • Do not repair cords--buy new ones



Follow the Administrative Controls

Safe work procedures Lockout and Tag out Proscribed work practices Signs warning of electrical hazards

Electrical Safety

Use safe equipment Do not use equipment that has been damaged or improperly modified. Always use equipment according to the manufacturer's specifications. "Live" parts (greater than 50 volts) must be guarded by one or more of the following: An enclosure that requires a tool for access. A locked enclosure. An interlocked access door. A substantial insulating guard to prevent contact. Check cords--they should: Be completely free of damage and deterioration.


Electrical Emergencies: How to Respond ?


Electrical Shock

A small night-light with a 6-watt bulb draws .05 ampere, and even that small amount of current can be fatal.

Protect yourself Don't touch the person. That person might be energized, so take time to protect yourself. Don't try to use a conductive tool to free the person. Don't touch anyone who has become grounded.

Electrical Safety

Call for help, if the person:

is obviously injured (loss of consciousness, significant trauma, etc.) has an altered mental status (confusion, slow/slurred speech, etc.) has other obvious injury (laceration, burn, etc.)


First things to do when there is an electrical accident

Keep others from being harmed Shut off the power (fuse or circuit-breaker or pull the plug; this might

be difficult because there might be secondary sources; if you are not sure, get help)

Move the victim to safety only when power is OFF and no neck or spine injuries are possible

Give necessary first aid (keep CPR training up-to-date). Report accident to supervisor (even minor shocks and close calls must be

reported) Secure area Collect data for an investigation and to prevent reoccurrence.


Electrical Safety

In Summary


Safe Working

Learning objectives

By the end of this program participants will be able to demonstrate their understanding of the control measures to be followed , as detailed in the safe working procedure, when working with fixed and portable electrical systems and equipment.


Safe Working

Operational Analysis and Control (OAC)Model

Analyse the Operation

Manage the Operation

Effectiveness Review

What can cause harm?What are you doing about it?Is it enough?

What has to be done?What resources do you need?When does the operation need reviewed?

Has the operation progressed as planned?Detail the changes needed?List the improvement actions?


Safe Working

Set your work objectives to include

“...tasks/ activities are to be completed on time and in a manner that does not cause harm to the employees, customers, other non-employees, or the company/ organisation.”

Three key questions to start with are… • What can cause harm?• What are you doing about it?• Is it enough?

Remember the process is simple but it is NOT to be considered simplistic.


Safe Working

Know where the harm is:

Identify the key hazards & outcomes of exposure to electricity

Source of hazards (non-exhaustive list)

BatteriesDamage items, e.g. light bulbs

Fixed electrical installationsFlammable and explosive environments

Fuses, circuits and other devicesOverhead lines

Portable electrical appliancesSockets and plugs

Static electricitySwitches and conduits

Trailing cables and leadsUnderground cables

Outcomes of exposure (non-exhaustive list)

ShockBurnsArcing

FireExplosion


Short circuit

If it is a battery that is shorted, the battery will be discharged very quickly.

Short circuit can produce very high temperatures due to the high power dissipation. Electric arc is a common example due to short circuit.

Short Circuit


Safe Working

Controlling the Hazard - Options

In priority order:

Eliminate where possible, Use control measures,

Protect all those exposed to the hazard


Safe Working

Systems and Equipment

Proper design, construction and maintenance.

Employ competent staff.

Maintain competence.

Inspections and tests.

Pre-use visual checks.


Safe Working

Preventative Action

Inspect all electrical equipment,

Check suitable circuit protection equipment is installed,

Test equipment for circuit protection,

Regularly inspect equipment,

Avoid work near live conductors,

Use proper systems,

Use safe working methods,

Ensure competence.


Safe Working

When equipment faults occur or are identified…

Isolate from the power source,

Put a warning label on,

Report the fault, and

Have the equipment repair or replaced.


Safe Working

Construct & protect equipment from…

Mechanical damage,

Effects of weather, temperature and pressure

Effects of any other natural hazards,

Effects of wet, dirty, dusty or corrosive conditions, or

Any flammable or explosive substances.

REMEMBER Electrical systems and equipment for use in potentially flammable or explosive atmospheres are to be appropriately Certificated as being intrinsically safe.


Safe Working

Business Activity Managers

Safety Managers

Managing Director

Employees

Duty Holders

Ensuring compliance.

Providing professional safety advice.

Complying with the requirements.

Responsible for…

Co-operating with the requirements.


Safe Working

Documentation

Schedule of inspections and tests.

Maintenance log.

Statutory certifications.

Company Specific Statutory documents


Thank You

L | C | LOGISTICS PLANT MANUFACTURING AND BUILDING FACILITIES EQUIPMENT

Engineering-Book

ENGINEERING FUNDAMENTALS AND HOW IT WORKS

ELECTRICITY