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Plant Utility System (TKK-2210)14/15 Semester 4 Plant Utility System (TKK-2210) Instructor: Rama Oktavian Office Hr.: M-F 13-15
Electrical Equipment/Training Agenda: Electricity Future electricity scenario Generation & distribution Phase of electricity Active and reactive power Power factor correction Electrical load management Electrical billing mechanisms Transformers Electrical Equipment/ Electricity This is an important chapter because it explains the basics of electricity. You need to understand this basic information in order to understand the chapters on electrical equipment, namely, Fans, Pumps, Electric motors, Cooling towers, Air conditioning & refrigeration, Compressors, and Lighting The session starts with explaining the world’s electricity scenario, generation & distribution of electricity, active & reactive power, electrical load management, electrical billing mechanism, and transformers © UNEP 2006
Electrical Equipment/Electricity General Electricity Scenario Development can be measured by a nation’s electricity consumption Electricity usage is divided into: Industrial Commercial and residential Agriculture and irrigation Electricity important input for industry Electrical Equipment/ Electricity The 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. © UNEP 2006
Electrical Equipment/Electricity General Electricity Scenario International Energy Agency predicts for 2030: 78% of population in developing countries has access to electricity 1.4 billion people no access 665 billion US$ needed to overcome this Electrical Equipment/ Electricity In the existing scenario, electrification in developing countries reaches 78 per cent of the population in 2030, leaving 1.4 billion people without access to electricity. The electrification scenario projects an added investment of $665 billion in order to reach 100 per cent access by This would increase global electricity supply by 3per cent. © UNEP 2006
General Electricity ScenarioHow can electricity supply shortage be solved? Renovation and modernization of plants, transmission and distribution systems Demand side management with the utilization of energy efficiency technologies Awareness raising among energy users Electrical Systems/ Electricity (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 technology Demand side management: adoption and continuation of energy efficient technologies and usage practice Creating awareness amongst fellow energy users for adoption of energy saving measures and accepting new technologies when available. © UNEP 2006
Generation & DistributionElectricity Generation & Distribution Electricity generation: fossil fuels and uranium Renewable energy is growing Electrical Systems/ Electricity Renewable 21% Nuclear 16% Fossil fuels 63% World electricity generation by energy Electricity is mostly generated by power stations that use fossil fuels (coal, gas, oil) and nuclear facilities that use uranium. Due to environmental and safety concerns, and more recently energy security concerns as the oil supply is dependent on fewer and fewer countries, alternative sources of energy are being explored. Renewable energy provides 21 percent of the world energy needs, including hydropower (20 percent), solar, wind, geothermal, biomass, and tidal energy (approximately 1 percent but growing). As the renewable energy sector grows, the technologies used are become more efficient and less expensive. Therefore prices are becoming more comparative to electricity from non-renewable sources. (US Energy Information Administration, 2004) © UNEP 2006
Generation & DistributionElectricity Generation & Distribution Generator 10.6 KV GT 220 KV Step down transformer Distribution Power plant Transmission system Distribution system Electrical Systems/ Electricity This figure illustrates the generation, transmission and distribution of electricity © UNEP 2006
Generation & DistributionElectricity Generation & Distribution AC generators (“alternators”) generate electricity Electricity generated at 9-13 KV Power generated from 67.5 to 1000 MW Power stations: generating transformers (GTs) to increase voltage to KV Substations: step-down transformers to reduce voltage before distribution Electrical Systems/ Electricity Electricity 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. © UNEP 2006
Generation & DistributionElectricity Generation & Distribution Benefits of high voltage transmission Less voltage drop: good voltage regulation Less power loss: high transmission efficiency Smaller conductor: lower costs Electrical Systems/ Electricity Less 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 efficiency Smaller 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. © UNEP 2006
Electricity Phase of Electricity Electrical Systems/ ElectricitySingle phase AC circuit: Two wires connected to electricity source Direction of current changes many times per second Electrical Systems/ Electricity 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 circuits One neutral line 3 waveforms offset in time: cycles/second © UNEP 2006
Electricity Phase of Electricity Electrical Systems/ ElectricityStar connection Electrical Systems/ Electricity 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 © UNEP 2006
Active and Reactive PowerElectricity Active and Reactive Power Active power (kW): real power used Reactive power (kVAR): virtual power that determines load/demand Utility pays for total power (kVA) Electrical Systems/ Electricity 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)2 kVA = (KW)2 + (KVAR)2 Source: OIT © UNEP 2006
Power Factor CorrelationElectricity Power Factor Correlation Electrical Systems/ Electricity The 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 lower The 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. Figure: Power factor of electric circuit © UNEP 2006
PF Correction: CapacitorsElectricity PF Correction: Capacitors kVAR demand should be as low as possible for the same kW output Electrical Systems/ Electricity To 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 generator Figure: Capacitor as kVAR generator © UNEP 2006
PF Correction: CapacitorsElectricity PF Correction: Capacitors Act as reactive power generators Reduce reactive power Reduce total power generated by the utilities Electrical Systems/ Electricity The 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 © UNEP 2006
PF Correction: CapacitorsElectricity PF Correction: Capacitors Advantages for company: One off investment for capacitor Reduced electricity costs: Total demand reduced No penalty charges Reduced distribution losses Increased voltage level at load end, improved motor performance Electrical Systems/ Electricity The 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 costs Reduced 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 eliminated Reduced distribution losses (kWh) within the plant network Voltage level at the load end is increased resulting in improved performance of motors © UNEP 2006
PF Correction: CapacitorsElectricity PF Correction: Capacitors Advantages for utility: Reduced reactive component of network Reduced total current in the system from the source end Reduced I2R power losses Reduced need to install additional distribution network capacity Electrical Systems/ Electricity The advantages of an improved power factor through the installation of a capacitor are: For the utility supplying electricity Reactive component of the network and the total current in the system from the source end are reduced I2R power losses are reduced in the system because of reduction in current Available capacity of the electricity distribution network is increased, reducing the need to install additional capacity © UNEP 2006
Electrical Load ManagementElectricity Electrical Load Management Goal: reduce maximum electricity demand to lower the electricity costs Load curve predicts patterns in demand Electrical Systems/ Electricity KVA Hours At a macro level, growing electricity consumption and congestion of electricity demand during certain times during the day has led to shortfalls in capacity to meet demand. As capacity addition is costly and can only be installed over a longer timeframe (especially if a new power plant must be built), better load management at the user end helps to minimize peak demands on the utility infrastructure and improve the utilization of power plant capacity. Some of the techniques for effective load management are given in Table 2. As the demand charges constitute a considerable portion of the electricity bill, from user angle too there is a need for integrated load management to effectively control the maximum demand. A presentation of the load demand of a consumer against time is known as a ‘Load Curve’. If load demand is plotted for the 24 hours of a single day, it is known as an ‘Hourly Load Curve’ and if daily demands plotted over a month, it is called ‘Daily Load Curve’. Load curves are useful in predicting patterns of high a low power demand for a plant section, and entire plant, a distribution network etc. Daily load curve of an engineering industry (National Productivity Council, India) © UNEP 2006
Electrical Load ManagementElectricity Electrical Load Management Strategies to manage peak load demand: Shift non-critical / non-continuous process loads to off-peak time Shed non-essential loads during peak time Operate in-house generation or diesel generator (dg) sets during peak time Operate AC units during off-peak times and utilize cool thermal storage Install power factor correction equipment Electrical Systems/ Electricity For more detailed description of each bullet, refer to Table 2 in the textbook chapter © UNEP 2006
Electricity Billing MechanismEnergy charges Actual charges based on active power Charge based on apparent power Maximum demand charges Based on maximum demand registered Penalty for peak load Electrical Systems/ Electricity Utilities 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. © UNEP 2006
Electricity Billing MechanismPower factor penalty or bonus Fuel costs Electricity duty charges Meter rentals Lighting & fan power consumption Time of Day (TOD) rates Electrical Systems/ Electricity Other 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 value Electricity duty charges: additional charges based on electricity units consumed Meter rentals: a monthly fixed charge for the installed energy meter Lighting and fan power consumption: charges that are higher than normal electricity rates, which can be levied on a slab basis or on actual metering basis Time Of Day (TOD) rates: different rates for peak and non-peak hours Penalty for exceeding contract demand © UNEP 2006
Electricity Billing MechanismUtility uses trivector meter for measurement during billing cycle (usually month): Maximum demand Active energy in kWh Reactive energy in kVArh Apparent energy in kVAh Electrical Systems/ Electricity The 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 cycle Active energy in kWh during billing cycle Reactive energy in kVArh during billing cycle and Apparent energy in kVAh during billing cycle © UNEP 2006
A Typical Demand Curve (National Productivity Council)Electricity Electricity Billing Mechanism Demand measured in time intervals Maximum demand is highest reading Customer charged on highest maximum demand value! Electrical Systems/ Electricity 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) © UNEP 2006
Electricity Transformer Electrical Systems/ ElectricityStatic electrical device that transforms electrical energy from one voltage level to another Two or more coils linked magnetically but electrically insulated Electrical Systems/ Electricity 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 voltages Transformers 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. Figure 12: A view of a transformer (Indiamart.com) Turns Ratio: turns on 2nd coil (connected to load) turns on 1st coil (connected to power source) © UNEP 2006
Electricity Transformer types Electrical Systems/ ElectricityTransformers are classified based on: Input voltage Operation Location Connection Electrical Systems/ Electricity 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. © UNEP 2006
Transformer Losses & EfficiencyElectricity Transformer Losses & Efficiency PTOTAL = PNO-LOAD+ (% Load/100)2 x PLOAD PTOTAL = PNO-LOAD+ (Load KVA/Rated KVA)2 x PLOAD Electrical Systems/ Electricity As there is no rotating part in a transformer, the efficiency remains in the range of 96 to 99 percent. Losses are mainly attributed to: Constant Loss: this is also called iron loss or core loss, which mainly depends upon the material of the core and magnetic circuit of the flux path. Hysteresis and Eddy current loss are two components of constant loss. Variable Loss: this is also called load loss or copper loss, which varies with the square of the load current. Note: The best efficiency of a transformer occurs at a load when constant loss and variable loss are equal. Typical transformer losses as a percentage of the load current are shown in Figure 14. Transformer manufacturers normally provide the no-load loss (PNO-LOAD) and full load loss (PLOAD). The following mathematical relations give the total loss (PTOTAL) at any load condition in a transformer. (Click once) The following mathematical relations give the total loss, PTOTAL, at any load condition in a transformer. P TOTAL = P NO-LOAD + ( % LOAD/100)2 x P LOAD Transformer loss versus percent loading (BEE, 2004) Transformer losses: constant and variable Best efficiency: load where constant loss = variable loss © UNEP 2006
Electricity Electricity Formulae Electrical Systems/ ElectricityResistance (Ohm) Voltage (Volts) Reactance Impedance Real power (Watt) Reactive power Apparent power Power factor Efficiency Transformer ratio Voltage drop in a line Star connection Delta connection Electrical Systems/ Electricity © UNEP 2006
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