Presentation on theme: "Mechanical and Electrical Systems [CIV 311]"— Presentation transcript:
1Mechanical and Electrical Systems [CIV 311] Comprehensive coverage of mechanical systems, electric al systems, plumbing, fire protection, security, vertical transportation, lighting, acoustics and communications. The course includes analysis techniques and design principles for each system. A comprehensive design project is required for a major building project.. Psychrometry and process of air. Cooling load estimation. Refrigeration cycles. Water chiller systems. Air handling system. Cooling towers. Equipment selection. Installation, operation and maintenance of air conditioning systems.Basic knowledge of data communication: data transmission technology, transmission media, signal interference, etc. Network topology: logical aspect and physical aspect. Local area network technology. Networking equipment: repeaters, signal transceivers converters, switches/hubs, connectors/interfacing equipment, etc.Principles of lighting, lighting design for buildings which includes artificial lighting, point, line and area light sources, types and properties of luminaries, polar curves, design methods and calculations, glare index, lighting design standard, luminaire heat recovery system and lighting energy management, hybrid lighting, daylighting of buildings, effect of climate on lighting
2PART ONE ELECTRICAL Chapter 1 Electrical fundamental
3Electricity General Electricity Development can be measured by a nation’s electricity consumptionElectricity usage is divided into:IndustrialCommercial and residentialAgriculture and irrigationElectricity important input for industryThe electricity consumption per capita is often used as an indicator of a country’s development. Because when people get richer they start using electrical appliances such as TVs, washing machines, ovens, telephones, vacuum cleaners etc.In developing countries, industry is the largest consumer of electricity and about 30 percent of people still has no access to electricity.(Click once) Electricity is used by industry; commercial and residential; and agriculture and irrigation.(Click once) Electricity is one of the most important inputs for the industrial sector, the development of the nation is generally compared by the per capita consumption of electricity.
4Electricity General Electricity How can electricity supply shortage be solved?Renovation and modernization of plants, transmission and distribution systemsDemand side management with the utilization of energy efficiency technologiesAwareness raising among energy users(Question to audience) With regard to the ever increasing gap of electricity supply and demand, how can this challenging task best be met? What are your views of the best way to solve this gap? (Wait for comments. Discussion) Is the right approach to maximize electricity production? Or is it to minimize electricity usage?The IEA recommends the following to assure universal access to electricity (IEA, 2004):Renovation and modernization of conventional power plants, and transmission and distribution system with new energy efficient technologyDemand side management: adoption and continuation of energy efficient technologies and usage practiceCreating awareness amongst fellow energy users for adoption of energy saving measures and accepting new technologies when available.
5Generation & Distribution ElectricityGeneration & DistributionGenerator10.6 KVGT220 KVStep down transformerDistributionPower plantTransmission systemDistribution system22 or 11 KV380/220 VThis figure illustrates the generation, transmission and distribution of electricity
6Generation & Distribution ElectricityGeneration & DistributionAC generators (“alternators”) generate electricityElectricity generated at 9-13 KVPower generated from 67.5 to 1000 MWPower stations: generating transformers (GTs) to increase voltage to KVSubstations: step-down transformers to reduce voltage before distributionElectricity is mostly generated by AC generators called “alternators” in thermal, hydro or nuclear power plants at 50 or 60 cycles per second.Electricity is typically generated at about 9 to 13 KV at the generator terminal. The power generated by one generator (also termed as UNIT) is in the range of 67.5 MW, 110 MW, 220 MW, and 500 MW, although 1000 MW generators also exist. Higher MW rating of generation capacity is preferred because of less auxiliary power consumption and other operation & maintenance cost.Electricity must be generated when it is needed since electricity cannot be stored. All power stations have generating transformers (GTs) that increase the voltage to extra high voltages (EHV, e.g. 132 KV, 220 KV, 400 KV) prior to transmission.Similarly, sub-stations have step-down transformers, which reduce the voltage for distribution to industrial, commercial and residential users through distribution lines.There is no difference between a transmission line and a distribution line except for the voltage level and power handling capability. Transmission lines operate at EHV and are usually capable of transmitting large quantities of electric energy over great distances. Distribution lines carry limited quantities of power at a lower voltage over shorter distances.
7Generation & Distribution ElectricityGeneration & DistributionBenefits of high voltage transmissionLess voltage drop: good voltage regulationLess power loss: high transmission efficiencySmaller conductor: lower costsLess voltage drop: Voltage drops in transmission/distribution lines are dependent on the resistance, reactance and length of the line, and the current drawn. For the same quantity of power handled, a higher voltage results in a lower current drawn and lower voltage drop. Benefit is good voltage regulation i.e. the difference between voltages sent and received at small.Less power loss: the power loss in lines is proportional to the resistance (R) and the square of the current (I), i.e. PLoss = I2R. A higher voltage results in lower currents and therefore lowers power losses. Benefit is high transmission efficiencySmaller conductor: a higher voltage results in lower currents and therefore a smaller conductor is needed to handle the current. Benefit is less capital and erection cost.
8Electricity Phase of Electricity Single phase AC circuit: Two wires connected to electricity sourceDirection of current changes many times per second A single-phase AC circuit has two wires connected to the source of electricity. However, unlike the DC circuit in which the direction of the electric current does not change, the direction of the current changes many times per second in the AC circuit depending upon the frequency of the supply. The 240 volt (V) electricity supplied to our homes is single-phase AC electricity and has two wires: 'active' and 'neutral'.Three lines carry electricity from three electrical circuits, and they share a common neutral line (i.e. three active lines and one common neutral line). Three-phase systems have 3 waveforms (usually carrying power) that are 2/3 π radians (120 degrees,1/3 of a cycle) offset in time.The figure shows one cycle of a three-phase system, from 0 to 360 degrees (2 π radians), along the time axis. The plotted line represents the variation of instantaneous voltage (or current) in time. This cycle will repeat 50 or 60 times per second depending on the power system frequency. The colors of the lines represent the American color code for three-phase systems: black=VL1 red=VL2 blue=VL3.3-phases of an electric system(Wikipedia contributors, 2005)Three phase systems:3 lines with electricity from 3 circuitsOne neutral line3 waveforms offset in time: cycles/second
9Electricity Phase of Electricity Star connection Delta connection The three-phase supply system is further represented by star and delta connection as shown in the figure. But as part of this training we will not explain these in detail.Delta connection
10Active and Reactive Power ElectricityActive and Reactive PowerActive power (kW): real power usedReactive power (kVAR): virtual power that determines load/demandUtility pays for total power (kVA)Active power, measured in kilowatt (kW), is the real power (shaft power, true power) used by a load to perform a certain task. However, there are certain loads like motors, which require another form of power called reactive power (kVAR) to establish the magnetic field. Although reactive power is virtual, it actually determines the load (demand) on an electrical system. The utility has to pay for total power (or demand)The vector sum of the active power and reactive power is the total (or apparent) power, measured in kVA (kilo Volts-Amperes). This is the power sent by the power company to customers.Here the different powers are represented of a power triangle where the vector sum of the active power and reactive power make up the total power used. This is the power sent by the power utility companies for the user to perform a given amount of work. Total power, also known as apparent power is measured in kilo Volts-Amperes.You can see from the figure that the active power, and the reactive power required are 90 degrees apart vectorically in a pure inductive circuit. In other words reactive power kVAr lagging the active kW. The apparent power, kVA, is the vector sum of active and reactive power. Mathematically it may be represented with the following formula (Click once): kVA = (KW)2 + (KVAR)2kVA = (KW)2 + (KVAR)2Source: OIT
11Power Factor Correlation ElectricityPower Factor CorrelationThe power factor is the ratio between active power (kW) and total power (kVA), or the cosine of the angle between active and total power. A high reactive power, will increase this angle and as a result the power factor will be lowerThe power factor is always less than or equal to one. Theoretically, if all loads of the power supplied by electricity companies have a power factor of one, the maximum power transferred equals the distribution system capacity. However, as the loads are inductive and if power factors range from 0.2 to 0.3, the electrical distribution network’s capacity is stressed.Hence, the reactive power (kVAR) should be as low as possible for the same kW output in order to minimize the total power (kVA) demand.
12PF Correction: Capacitors ElectricityPF Correction: CapacitorskVAR demand should be as low as possible for the same kW outputTo reduce kVAR, partial kVAR has to be supplied by some other source which, as a result, will reduce burden of kVAR on the supply system. Capacitors are such devices that supply the reactive power required by inductive loads. You can see this in the figure illustrating capacitor as kVAR generatorFigure: Capacitor as kVAR generator
13PF Correction: Capacitors ElectricityPF Correction: CapacitorsAct as reactive power generatorsReduce reactive powerReduce total power generated by the utilitiesElectrical Systems/ElectricityThe power factor can be improved by installing power factor correction capacitors (see Figure 8 and 9) to the plant’s power distribution system. They act as reactive power generators and therefore reduce the amount of reactive power, and thus total power, generated by the utilities.It should be noted that you only have to pay for the capacitor. As the utility doesn’t supply the kVAR, you don’t pay for it.Figure: Fixed capacitor banks Source: Ecatalog
14PF Correction: Capacitors ElectricityPF Correction: CapacitorsAdvantages for company:One off investment for capacitorReduced electricity costs:Total demand reducedNo penalty chargesReduced distribution lossesIncreased voltage level at load end, improved motor performanceThe advantages of an improved power factor through the installation of a capacitor are:For the company:A one-off investment in purchasing and installing the capacitor is needed but there are no ongoing costsReduced electricity costs for the company because (a) the reactive power (kVAR) is no longer supplied by the utility company and therefore the total demand (kVA) is reduced and (b) penalty charges imposed when operating with a low power factor are eliminatedReduced distribution losses (kWh) within the plant networkVoltage level at the load end is increased resulting in improved performance of motors
15PF Correction: Capacitors ElectricityPF Correction: CapacitorsAdvantages for utility:Reduced reactive component of networkReduced total current in the system from the source endReduced I2R power lossesReduced need to install additional distribution network capacityThe advantages of an improved power factor through the installation of a capacitor are:For the utility supplying electricityReactive component of the network and the total current in the system from the source end are reducedI2R power losses are reduced in the system because of reduction in currentAvailable capacity of the electricity distribution network is increased, reducing the need to install additional capacity
17Electrical Load Management ElectricityElectrical Load ManagementStrategies to manage peak load demand:Shift non-critical / non-continuous process loads to off-peak timeShed non-essential loads during peak timeOperate in-house generation or diesel generator (dg) sets during peak timeOperate AC units during off-peak times and utilize cool thermal storageInstall power factor correction equipmentFor more detailed description of each bullet, refer to Table 2 in the textbook chapter
18Electricity Billing Mechanism Energy chargesActual charges based on active powerCharge based on apparent powerMaximum demand chargesBased on maximum demand registeredPenalty for peak loadUtilities often apply a two-part tariff structure in their electricity bills for medium and large enterprises:Energy Charges - These charges relate to the actual energy or active power (kilowatt hours or kWh) consumed during a month / billing period. Some utilities now charge on the basis of apparent energy (kVAh), which is a vector sum of kWh and kVArh.Maximum Demand Charges - These charges relate to maximum demand registered during a month / billing period and corresponding rate of utility. The purpose of charging a penalty for the peak load is to encourage end users to reduce the peak load. Companies that manage their peak load (e.g. by reducing the power factor) therefore reduce the monthly electricity bill, without necessarily using less electricity.
19Electricity Billing Mechanism Power factor penalty or bonusFuel costsElectricity duty chargesMeter rentalsLighting & fan power consumptionTime of Day (TOD) ratesOther components of electricity bills may include:Power factor penalty or bonus rates, as levied by most utilities, are to contain reactive power drawn from the grid.Fuel cost: adjustment charges as levied by some utilities are to adjust the increasing fuel expenses over a base reference valueElectricity duty charges: additional charges based on electricity units consumedMeter rentals: a monthly fixed charge for the installed energy meterLighting and fan power consumption: charges that are higher than normal electricity rates, which can be levied on a slab basis or on actual metering basisTime Of Day (TOD) rates: different rates for peak and non-peak hoursPenalty for exceeding contract demand
20Electricity Billing Mechanism Utility uses trivector meter for measurement during billing cycle (usually month):Maximum demandActive energy in kWhReactive energy in kVArhApparent energy in kVAhThe utility employs an electromagnetic or electronic trivector meter for billing purposes, which measures the following:Maximum demand registered during the month, which is measured in set time intervals (e.g. 30 minutes) and this is reset at the end of every billing cycleActive energy in kWh during billing cycleReactive energy in kVArh during billing cycle andApparent energy in kVAh during billing cycle
21A Typical Demand Curve (National Productivity Council) ElectricityElectricity Billing MechanismDemand measured in time intervalsMaximum demand is highest readingCustomer charged on highest maximum demand value!A typical demand curve is shown in the Figure.The demand is measured over predetermined time intervals and averaged out for that interval as shown by the horizontal dotted line.The maximum demand will be the highest of the demand values recorded in the billing month.The meter registers only if the value exceeds the previous maximum demand value and thus even if average maximum demand is low, the industry/facility is charged based on the highest maximum demand value measured.A Typical Demand Curve (National Productivity Council)
22Electricity Transformer Static electrical device that transforms electrical energy from one voltage level to anotherTwo or more coils linked magnetically but electrically insulatedFigure 12: A view of a transformer(Indiamart.com)A transformer is a static electrical device, which transforms electrical energy from one voltage level to another voltage level. This permits electrical energy to be generated at relatively low voltages and transmitted at high voltages and low currents, thus reducing line losses, and to be used at safe voltagesTransformers consist of two or more coils that are electrically insulated, but magnetically linked. The primary coil is connected to the power source and the secondary coil is connected to the load.Features of transformers are:Turn’s ratio: the ratio between the number of turns on the secondary coil and the number of turns on the primary coil (see Figure 13).Secondary voltage: the primary voltage times the turn’s ratio.Ampere-turns: calculated by multiplying the current in the coil times the number of turns. Primary ampere-turns are equal to secondary ampere-turns.Voltage regulation of a transformer: the percentage increase in voltage from full load to no load.Turns Ratio: turns on 2nd coil (connected to load)turns on 1st coil (connected to power source)
23Electricity Transformer types Transformers are classified based on: Input voltageOperationLocationConnectionFor more details refer to Table 3 in the textbook chapter. But some examples for different transformer classes are:Step up and step down transformers are based on input voltage.Power, distribution and instrument transformer are based on operation.Outdoor and indoor transformers are based on location.Three phase and single phase transformers are based on connection.
24Electricity Electricity is the flow of electrons in a conductor. The electrons must have a path to and from its source.This path is called a circuit.For more details refer to Table 3 in the textbook chapter. But some examples for different transformer classes are:Step up and step down transformers are based on input voltage.Power, distribution and instrument transformer are based on operation.Outdoor and indoor transformers are based on location.Three phase and single phase transformers are based on connection.
25Normal, Open and Short Circuits Normal CircuitWhen normal current is flowing through the circuitOpen CircuitWhen the current flow is interrupted by switch or fuseCircuit break presents an extremely high resistance.Short CircuitWhen the current flowing through the circuit is following a “shorter” low resistance path between the power source terminals.Allows high current to flow in the circuit
26ElectricityVarious electrical devices are used as a part of the circuit.These devices are used for a variety of activities, such as turning the electricity off and on, providing electricity to various lights or appliances, etc.
27Types of Electrical Currents Electrical current comes in two forms:Direct current (DC)Flows in only one direction.It is usually generated by battery-base electrical systems and used in the electrical systems of internal combustion engines or flashlight batteries.Alternating current (AC)Reverses the direction of flow of current many times each second.AC is the type used in homes, factories, etc.
28Electrical ServiceService is provided to homes, businesses and other small users of electricity by three wires from a utility pole.Two of the wires are “hot,” each carrying 220 volts.The other wire is “neutral,” and provides the return path for electricity.
29Electrical Service (cont.) These wires are connected to a service entrance, which is where the electricity enters a building.A meter is used in the service entrance to measure the amount of electricity being used.
30Electrical Service (cont.) The service entrance is grounded with a wire connected to a ground rod driven several feet into the ground.It is needed to provide a return path to the ground and to carry away stray electrical current out of the system.
31Service Panel Follows the meter. It houses the circuit breakers for the system and is used to distribute the power to individual circuits throughout the system.
32OvercurrentWhen a circuit uses too much electricity, an overcurrent causes a circuit breaker to trip, shutting down the power to that circuit.The excessive heat caused by an overcurrent condition may burn or damage a conductor’s insulation and cause a fire.A circuit breaker is a heat-sensitive switch, which automatically trips when electricity demand is too great which causes the temperature in the conductor to get too hot.
33Amps Volts Watts The following relationship exists between Amps, Volts and Watts. Amperes are a measure of the rate of flow of electricity in a conductor.Volts are a measure of electrical pressure.Watts are a measure of the amount of energy or work that can be done by amperes and volts.
34Amps Volts Watts (cont.) Thus, the following relationship exists. Work = Pressure x Flow Or Watts = Volts x Amperes
35Amps Volts Watts (cont.) This formula is commonly referred to as the West Virginia FormulaW=VAWhen we know any two variables of the formula, we can calculate the other.
37Calculating Amperage Amps = 100 Watts / 220 Volts If we have a 100 watt lamp plugged into a 120 volt receptacle, we can determine the rate of flow or the amperes for that circuit.Amps = 100 Watts / 220 Volts100 / 220 =.4545 Amps
38Calculating Watts Watts = 220 Volts x 20 Amps 4800 Watts =220V x 20A If a water heater operates at 20 amps on a 240 volt circuit, what is the wattage of the appliance?Watts = 220 Volts x 20 Amps4800 Watts =220V x 20AWatts=4400
39Calculating Volts Volts = 2640 Watts / 12 Amps 2640 / 12 = 240 Volts If an electric motor operates at 2880 watts and 12 amps, what would be the voltage requirement for that motor?Volts = 2640 Watts / 12 Amps2640 / 12 = 240 Volts
40Maximum Minimum Average Find the max and min load of the following domestics daily curveHour68912141618202424Kw10
43Example Design High rising building consists of 12 level Each level 4 flats (4 bed room, reception and two bath room)If each flat has the following equipmentThe main building has the following3 lefts 15 hp 0.8 pf3 water pump 12hp 0.7 pfOutdoor light 10kw 1 pfCalculateTotal power design the electrical installation of the buildingMain cable and branch cable cross sectionSwitchboard main and sub switchboard flat switchboardNo of transformerNumbe rpowerPower factorDishwasher12.5 KW0.7Air condition35 hp0.6Water heater4 KWWasher6 KW0.8Lighttotal7 KW