ELECTRICAL POWER SYSTEM

PRINCIPLES OF ELECTRICITY 

INTRODUCTION: ELECTRIC SYSTEM

An electric power system is a network of electrical components deployed to supply, transfer, store, and use electric power. An example of an electric power system is the grid that provides power to an extended area.

Figure 1: Examples of Electrical Power System (Source: Wikipedia)

      ATOMIC THEORY

 Everything in the universe is made up of matter. Matter can exist as liquid, solid  or gas. Matter can be broken down into small particles, known as atoms.

Figure 2 : Athomic Theory (Source: Wikipedia)

ELECTRON FLOW

If an electromotive force(EMF) is applied across a conductor, or conductive circuit, e.g a length of wire, electrons from each atom can be forced out of their orbit. These electrons are then capable of moving to another atom. Electrons flow from the negative terminal of a power supply towards the positive terminal of the power supply through an electrical circuit.

                                              

Figure 3 : Electron flow (Source: Wikipedia)

CURRENT FLOW

In past current was assumed to flow through a conductor from positive to negative (+ >> -). Many rules were formulated based on this assumption and are still used today, even though it is known that electrons move in the opposite direction.

The two forms of electricity are:

·      Static electricity- charge builds up on the surface of an object.

·      Current electricity-electricity comes from a power source, such as a battery or generator.

Figure 4 :Current Flow (Source: Wikipedia)

ELECTRICITY

Current electricity refers to electricity that is flowing continuously through an electric circuit. That mean, path the current flows through is called an electric circuit.

CIRCUIT

There are two types of circuit;

•  Series-one path only 
• Parallel-more than one path    
• Series/parallel (Combination of both)

The following conditions can exist in any given circuit;

• Open-no current is flow
• Closed-current is flowing
• Shorted-current is flowing through a shorter path and the load in the circuit is bypassed.

Figure 5 Circuit Types (Sources: Wikipedia)              

CIRCUIT CONDITION

Short circuit    

A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or a very low electrical impedance.

                       

Figure 6: Short Circuit (Sources: Dummies.com)              

Closed circuit   

A circuit without interruption, providing a continuous path through which current can flows.

Open circuit

A discontinuous circuit through which no current can flow.

Figure 7 Open Circuit (Sources: Dummies.com)              

TERMINOLOGY OF ELECTRICITY

Current (A)

Current is the flow of electron in a circuit. The unit of measure for the flow of current is ampere and it is measured by using ammeter. Current is also referred to as electromotive force or electrical potential.

Voltage (v)

Voltage is electrical pressure that pushes a charged electrons to enable them to do work such as illuminating a light. Voltage is also the difference in a charge between two points and the unit of measure it is volt.

Resistance (Ω)

The constant of proportionality is called the resistance. Resistance is the opposition that a substance offers to the flow of electric current. The standard unit of resistance is the ohm which symbolized by the uppercase Greek letter omega (Ω).

ELECTRICAL BASICS- IVR, OHMS LAW

Based on the reading from German physicist, there is a relationship between Voltage, Current and Resistant in every electrical circuit.

Voltage is the potential difference between two points which include a resistance.

Ohm’s Law is given by: V= IR 

Figure 8.1  How IVR Works? (Sources: ElectronicsTutorials)

Based on Ohm’s law, if we increase the voltage of the circuit, the current will increase in direct proportion. In contrast, if we increase the resistance in a circuit, the current flow will decrease in a direct proportion.

By knowing any two values of Voltage, Current or Resistance quantities, we can use Ohms Law to find the third missing value.

 Figure 8.2: How IVR Works? (Sources: ElectronicsTutorials)

Therefore, to find the Voltage, (V)

V= I x R

To find the Current, (I)

I = V ÷ R

To find the Resistance, (R)

R= V÷ I

LAW OF CONSERVATION OF ENERGY

Law of Conservation of energy can define as the total energy of an isolated system remains constant. This law means that energy can neither be created nor destroyed. Basically, conservation of energy was distinct from conservation of mass and it can only be transformed from one form to another. For example, electrical energy can be transformed into thermal energy through the present of a closed circuit.

THREE MAJOR COMPONENTS

The electrical power system consists of three major components: generation, transmission and distribution system. 

A. Power Generation

Sources of power generation

Power generation is the process of generating electric power from sources of primary energy in the electric power industry. There is a lot of sources of energy that are in use for power generation. However, there are only six sources of voltage (electromotive force), which are pressure, magnetism, heat, light, chemical and friction.

Pressure

When pressure is applied, electrons leave one side of the material and accumulate on another side of it. A charge is produced as long as pressure remains. While the pressure is removed, the charge is again distributed, so no over-all charge exists. The voltage produced is small and must be amplified to be useful.

Magnetism

Magnetism is one of the common method of producing electrical energy. If a wire is passed through a magnetic field, voltage is produced as long as there is motion between the magnetic field and the conductor. Magnetism is classified through the flow of the electrons as well. When the current flow in only one direction, the current is called direct current (DC). When electrons flow in both direction, the current is called alternating current (AC). There is schematic symbol for DC generator and AC generator.

Alternating Current Generator

Figure 9: AC Generator (Sources: ElectricalSymbols&ElectronicSymbols)

Direct Current Generator

Figure 10: DC Generator (Sources: Electrical-symbols.com)

Heat

Heat can be converted directly to electricity with a device called thermocouple. A thermocouple consists of two dissimilar metal wires twisted together. One wire is copper wire and the other wire is zinc or iron. When heat is applied to the twisted connection, the copper wire readily gives up free electrons, which are transferred to the other wire.

Figure 11: Thermocouple (Sources: IndiaMART)

Light

Light energy can be converted directly to electrical energy by light striking a photosensitive substance in a solar cell. A solar cell consists of photosensitive materials mounted between metal contacts. A single cell can produce small voltage (one watt 0.5 volt). Therefore, we have to linked many cells together to produce a usable current. When many cells are put together to create a module which is used to create a panel, it is known as an array.

Chemical

When two dissimilar metals were placed in a chemical that acted upon them, there was a built up of electrical potential energy, known as electromotive force.

Friction

Friction is another known method of producing electricity. A glass rod can become charged when rubbed with a piece of fur or silk. A Van de Graf generator is a device that operates using the same principles as a glass rod and is capable of producing millions of volts.

Figure 12: Van de Graaf Generator (Sources: Wikipedia)

B. Transmission system 

Transmission system is the dissemination of electrical energy from power plants (generators) to the high-voltage station via transmission lines @ power lines. Transmission lines are used to transport electricity from place to place. This electricity is in the form of alternating current and begins at step-up transformer, in which will increase the voltage level. The types of lines are classified according to the amount of its transmission voltage. In Malaysia, we have 500kV (the single largest transmission system in Malaysia, as backbone in West Malaysia), 275kV (for large transmission system), 132kV (for medium transmission system) and 33kV (for small transmission system). More than 420 transmission substations in West Malaysia are linked together by these transmission lines of a total distance of approximately 11000km. National Grid is the electrical power transmission network in West Malaysia, operated by Tenaga Nasional Berhad (TNB); there are two other grids in Sarawak and Sabah operated by Sarawak Energy Berhad (SEB) and Sabah Electricty Sdn Bhd (SESB) respectively.

Figure 13 : A 500kV transmission line passing through North-South Expressway near Taiping (Source: Wikipedia)

Figure 14 : A 132 kV transmission line in Tanjung Kling Power Station in Malacca. (Source: Wikipedia)

 C. Distribution System

Distribution system refers to the distribution of electrical energy from the high-voltage station to consumer fit-out source. This is the final stage in the delivery of electrical power.

C.1. Power Distribution in Small Buildings

Small commercial or residential buildings have a very simple power distribution system. The utility normally will own the transformer, which will sit on a pad outside of the building or to be attached with a utility pole. This transformer will reduce the high voltage of 13.8kV further down to 120/240 or 120/208 volts and then passes the electricity to a meter, which is owned by the utility and keeps a record of power consumption.

Figure 15: Power distributions in small buildings (Source: Archtoolbox)

C.2. Power Distributions in Larger Buildings

Large buildings have a much higher electrical load than small buildings; therefore, the electrical equipment must be larger and more robust. Building owners will purchase, provide, and maintain their own step-down transformer, which lowers the voltage to usable level. This transformer can be mounted on a pad outside the building or in a transformer room inside the building.

Figure 16: Power distributions in large buildings (Source: Archtoolbox)

TYPES OF POWER SUPPLY

       A.   Single Phase System

Single phase electricity is generated by rotating a single turn coil through a magnetic field. The shape of the waveform produced by a generator is in the form of sine wave, thus it peaks in voltage at 90° and 270°, with a complete cycle at 360°. With these peaks and dips in voltage, power supply is not constant. The wires used in single phase are live conductor (yellow), neutral conductor (blue) and earth conductor (green).

Figure 17: Waveform produced by Single phase electricity (Source: AEGIS Power Systems)

In fact, single phase electrical system is like a bicycle where one leg (phase) is pushing on one pedal rotating around a crankshaft axis (neutral). Mechanically, power is calculated as leg pressure (foot pounds) times speed (rotating speed). Electrically, power is calculated as leg force (voltage) times flow of electrons in it (current).

Figure 18: Single Phase Illustration (Source: OEM Panels)

      B.   Three Phase System

In a three phase system there are three power wires, each 120⁰ out of phase with each other. Delta and wye are the two types of circuits use to maintain equal load across a three phase system, each resulting in different wire configurations. In the delta configuration, no neutral wire is used. The wye configuration uses both a neutral and a ground wire. (Note: In high voltage systems, the neutral wire is not usually present for a three phase system.)

          

Figure 19: Wye (Y) and Delta (∆) Circuits (Source: Wikipedia)

All three phases of power have entered the cycle by 120⁰. By the time a complete cycle of 360⁰ has completed, three phases of power have each peaked in voltage twice (see chart below.)With a three phase power supply, a steady steam of power is delivered at a constant rate, making it possible to carry more load. 

Figure 20: Waveform produced by Three phase electricity (Source: AEGIS Power Systems)

As for three phase electrical system, it is like a three- cylinder engine where the three pistons (phases) located (120° out of phase with one another) push rotating around a crankshaft axis (neutral). Electrically, power is calculated as cylinder force (voltage) times flow (current) times 1.732 (square root of 3).

Figure 21: Three Phase Illustration (Source: OEM Panels)

Three phase power supplies offer a superior carrying capacity for high load systems, including data centres, mobile towers, power grid, shipboard and aircraft, unmanned systems and any other electronic with a load greater than 1000 watts.

      C.   Compare and Contrast

SINGLE PHASE SYSTEM	THREE PHASE SYSTEM
Both supplies electricity
Typical domestic users	Commercial users
Less power	More power
Has one 100mp fuse	Has three 100mp fuses
Less complex design thus fewer design costs	More complex design thus high design costs
Higher labour handling costs	Lower labour handling costs

SEQUENCE CONTROL CIRCUIT

Devices for the purposes of controlling and protecting consumer are arranged in sequence in a circuit. This sequence is further divided into two parts, namely the supply part and consumer part.

      A.   Supply part

A.1. Service Fuse

It serves as the consumers’ back up protection. This is a property of Tenaga Nasional Berhad (TNB). Besides backing up protection to the fuse in the distribution board (DB) and Earth Leakage Circuit Breaker (ELCB), it also cuts off electrical supply to the consumers when required.

Figure 22: Service fuse example- indicated as in the green box; Digital energy meter reader example on the right (Source: Lowyat Forum)

A.2. Energy Meter Reader

Energy meter reader is used to monitor and record the total amount of electrical energy being consumed for the purpose of charging consumers through the issuance of electricity bills. It is the property of TNB too. There are two types of meters available, the digital one and the analog one.

Figure 23: Analog energy meter reader example (Source: syamzubir.blogspot)

      B.   Consumer part

B.1. Consumer’s Main Switch

It is located at the main incoming supply of the consumer’s Distribution Board. The purpose is to cut all the power supply to the consumer in the event that any maintenance work needs to be carried out. It is responsible to connect, cut off, and control the current if there is any excess current. It is a two- terminal one-way switch that contains fuse.

B.2. Distribution Board

This is where the distribution of electrical energy to various connected load take place inside the consumer premises. It also distributes the path for the earthing and neutral wire, and acts as a means of flowing leakage and return current respectively.

B.3. Earth Leakage Circuit Breaker (ELCB)

ELCB is a security device that used in an electrical system with high Earth impedance to avoid shock. It notices small stray voltages on the metal fields of electrical gear and interrupt the circuit if an unsafe voltage is detected. The main principle of the Earth leakage protectors is to stop injury to humans and nature due to the electric shock.

B.4. Miniature Circuit Breaker (MCB)

MCB is an electromechanical device which guards an electrical circuit from an over current, that may affect and cause short circuit, overload or imperfect design. This is a better option to a fuse since it doesn’t require alternate once an overload is identified. Its rated current is not more than 100 Amperes. Normally, trip characteristics are not adjustable.

COST OF ELECTRICAL USAGE

Tariff is based on the quantity of energy used. Energy measured in KWH. 1KWH is equivalent to 1 unit of energy.

Figure 24: Latest Malaysian domestic electricity tariff rate (Updated 1 Jan 2014) (Source: Tenaga Nasional Berhad)

SCHEMATIC SYMBOLS

Figure 25: Schematic symbols examples (Source:Nova Drawings)

RELEVANT SMM CLAUSE

The relevant clauses applicable to the piping works are:

• Section A: General rules
• Section B: Preliminaries
• Section D: Excavation work
• Section F: Concrete work
• Section R: Electrical installations

ELECTRICAL FITTINGS IN CASE BUILDING -PKU

Figure 26: Insulated electrical wiring (Source: PKU UTM)

Figure 27: Miniature Circuit Breaker (MCB) (Source: PKU UTM)

Figure 28: Distribution Board (DB) (Source: PKU, UTM)

THAT'S ALL FOR ELECTRICAL CAL SYSTEM! STAY TUNED TO NEXT WEEK TOPIC!