APPENDIX G THE LOAD ALLOCATED TO EACH LOAD CATEGORY CLOAD MODELS

Transcription

1 APPENDIX G THE LOAD ALLOCATED TO EACH LOAD CATEGORY CLOAD MODELS This Appendix obtains the percentage load allocated to each load category CLOAD models. To obtain these percentages the load class mix is determined e.g. the percentage of industrial, commercial, residential, etc. load present in the network. After obtaining the load class mix the composition of each load class is obtained e.g. the load class considered is made up of lighting, air conditioning, water heating, etc. Figure G.1 and figure G.2 show load class mix and load class composition are dependent on the load being represented for a particular instant in time - i.e. hour, day, month, year [49, p7-6]. FIGURE G.1 Sample load class mix for a busbar [49, p7-12] 226

2 FIGURE G.2 Sample residential energy usage for typical winter days [49, p7-27] The hourly demand data per load class, e.g. figure G.1, and the load class composition, e.g. figure G.2, are not readily available for the network south of Tutuka, Atlas and Grootvlei. This dissertation assumes the load class mix and load composition data published in the EPRI report Load Modelling for Power Flow and Transient Stability Studies [49] represent typical utility figures. The load class mix and load composition data listed in the above EPRI report are based on energy usage patterns observed in the United States. The EPRI report expresses load class mix data in terms of end user energy usage. A better approach would be to expresses load class mix data in terms of demand. The composition of most of the load classes is expressed in terms of demand data. 227

3 G.1 LOAD CLASS MIX According to 1982 energy usage the network load in the United States can be divided into the load classes listed in table G.1. Table G.1 Load class energy usage in the United States in 1982 [49, p4-5] LOAD CLASS PERCENTAGE OF ENERGY USE [%] Residential Commercial Industrial Other 3. 4 G.2 RESIDENTIAL LOAD CLASS Table G.2 lists the bulk contributors to residential peak demand. Table G.2 Bulk contributors to residential peak demand [49, p7-29] LOAD COMPONENT PERCENTAGE OF PEAK DEMAND [%] Space Heating Cooling 0 Water Heating Appliances Lighting 7. 8 Entertainment 4. 3 Miscellaneous

4 G.2.1 Space Heating Two types of space heating exist. The types are resistance space heaters and motor driven heat pumps. The resistors used in resistance space heaters are non-linear in nature but have a linear characteristic over the normal operating range. Hence, the load model is constant resistance and is given by: V P = P 0 V0 2 (G.1) The inertia constant, H, of the motors driving heat pumps is typically [49, 7-53 and 7-54]. Hence, these motors are small motors. For the years 1980 to 1985 the KWh/year usage of resistance heating in the United States was and the KWh/year usage of heat pump heating was 6350 [49, p7-20]. Based on these figures this dissertation assumes resistance heating makes up 60 % and heat pump heating makes up 40 % of space heating load. Space heating represents 24.9% of residential peak demand. The residential load class makes up 35.4% of network energy usage. Hence, the percentage constant resistence load present in the network load due to space heating is: ( ) % CR 1 5.3% (G.2-a) The percentage small motor load present in the network load due to space heating is: 229

5 ( ) % SM 1 3.5% (G.2-b) G.2.2 Water Heating Water heating is a thermostat controlled load [49, p7-56]. In first swing studies thermostat controlled load should be given a constant resistance characteristic [50, p478]. Water heating represents 21.4% of residential peak load. The residential load class makes up 35.4% of network energy usage. Hence, the percentage constant resistence load present in the network load due to water heating is: ( ) % CR 2 7.6% (G.3) G.2.3 Appliances The appliance use per customer, expressed as percentage of KW connected customer, is listed in table G.3. The residential electric range is a constant resistance load [49, 7-57] and represents 45 % of residential appliance demand. Hence, the percentage constant resistence load present in the network load due to the electric range is: ( ) % CR 3 = % (G.4) 230

6 Table G.3 Appliance use per customer [49, p7-26] APPLIANCE PERCENTAGE Electric Range 45 [%] Manual Defrost Refrigerator Frostless Refrigerator Freezer 5 Dishwasher 7. 2 Clothes Washer 3 Clothes Dryer The inertia constant, H, of motors driving manual defrost refrigerators, frostless refrigerators and freezers are typically [49, 7-58]. Hence, these motors are small motors. Residential refrigeration represents 32.8% ( ( )% ) of residential appliance demand. Hence, the percentage small motor load present in the network load due to residential refrigeration is: [ ] % SM 2 = % (G.5) The dishwasher is typically 1000 Watts. 750 Watt is water heating, i.e. constant resistance, and 250 Watts is motor load. The inertia constant, H, of the motors driving dishwashers are typically [49, 7-59]. Hence, these motors are small motors. The residential clothes washer operates similarly to a dishwasher except less energy is required. The inertia constant, H, of the motors driving clothes washers are typically [49, 7-59]. Hence, these motors are small motors. 231

7 The residential clothes dryer is typically 5. 5 KW. Clothes dryers have a resistive element, a blower (fan) and a motor to turn the tumble [49, p7-60]. The inertia constant, H, of the motors driving residential clothes dryers is typically [49, 7-60]. Hence, these motors are small motors. This dissertation assumes 75% of residential clothes dryer load is resistive load and 25 % of residential clothes dryer load is motor load. Residential dishwashers, clothes washers and clothes dryers represent 21.5% ( ( )% ) of residential appliance demand. Hence, the percentage constant resistence load present in the network load due to dishwashers, clothes washers and clothes dryers is: ( ) % CR 4 = % (G.6-a) The percentage small motor load present in the network load due to dishwashers, clothes washers and clothes dryers is: ( ) % SM 3 = % (G.6-b) G.2.4 Lighting This dissertation assumes all residential lighting is incandescent lighting. Incandescent lamps are often assumed to have a constant resistance characteristic. However, due to the large temperature swing that occurs in the filament the resistance changes with temperature. The results is active power that varies to the 1.55 power of the voltage [50, p477]. This dissertation assumes incandescent lamps are constant resistence loads. 232

8 Lighting represents 7.8% of residential appliance demand. Hence, the percentage constant resistence load present in the network load due to residential lighting is: ( ) % CR 5 2.7% (G.7) G.2.5 Entertainment and Miscellaneous Television makes up the entertainment component of the residential load class and base load appliance makes up the miscellaneous component of the residential load class [49, p7-26]. Base load appliance include coffee maker, frying pan, toaster, trash compactor, hand iron, bed covering, dehumidifier, attic fan, window fan, hair dryer, radio, radio/ record player, clock and vacuum cleaner [49, p7-21]. Except television, the mentioned appliances are either heating, i.e. constant resistence, or small induction motor load. This dissertation assumes 50 % of the entertainment and miscellaneous load class is heating load and 50 % is small induction motor load. The entertainment and miscellaneous load component represents 8.2% ( ( )% ) of residential appliance demand. Hence, the percentage constant resistence load present in the network load due to entertainment and miscellaneous load is: ( ) % CR 6 1.5% (G.8-a) 233

9 The percentage small motor load present in the network load due to entertainment and miscellaneous load is: ( ) % SM 4 1.5% (G.8-b) G.3 COMMERCIAL LOAD CLASS Table G.4 shows the composition of commercial load in the United States. The percentages listed are based on the end user usage in Btu. Table G.4 Composition of the commercial load class [49, p7-37] LOAD COMPONENT PERCENTAGE OF Btu NEEDS [%] Lighting Cooling Fans and Pumps Space Heating 7. 3 G.3.1 Lighting load This dissertation assumes all commercial lighting is discharge lighting. Commercial lighting makes up 41.5% of commercial energy usage. Commercial energy usage makes up 25.2% of network energy usage. Hence, the percentage commercial discharge lighting present in the network load is: ( ) % DL % (G.9) 234

10 G.3.2 Cooling load Commercial cooling is made up of heat pump, central air conditioning and room air conditioning [49, p7-40]. The inertia constant, H, of the motors driving commercial cooling is typically [49, p7-55 and p7-56]. Hence, these motors are small motors. Commercial cooling makes up 36.2% of commercial energy usage. Hence, the percentage small motor load present in the network load due to commercial cooling is: ( ) % SM 5 9.1% (G.10) G.3.3 Fans, pumps and space heating load The inertia constant, H, of motors driving commercial fans and pumps is 0. 7 [49, p7-67]. Hence, these motors are small motors. Commercial space heating is achieved using heat pumps [49, p7-40]. The inertia constant, H, of motors driving commercial heat pumps is [49, p7-53 and p7-54]. Hence, these motors are small motors. Commercial fans, pumps and space heating make up 22.3% ( ( )% ) of commercial energy usage. Hence, the percentage small motor load present in the network load due to commercial fans, commercial pumps and commercial space heating is: [ 0.252] % SM 6 = % (G.11) 235

11 G.4 INDUSTRIAL LOAD CLASS Three industrial load classes can be identified when looking at industries that require large amounts of energy. These classes are listed in table G.5. Table G.5 The industrial load classes with associated components [49, p7-42] LOAD CLASS ASSOCIATED COMPONENTS PERCENTAGE OF ENERGY USAGE [%] Primary Aluminium Industry Electrolysis 100 Steel Mills Arc Furnace 25 Electric Drives 75 (Large and small) Other Heavy Industry Electric Drives (Large and small) 100 The industries situated south of Tutuka, Atlas and Grootvlei belongs to the Other Heavy Industry category. Hence, electric drives (large and small) make up 100 % of the industrial energy needs (table G.5). Many industrial motors fall into the large motor category [48, p1]. Hence, this dissertation assumes 20 % of industrial motors are large motors and 80 % of industrial motors are small motors. Industrial energy usage makes up 36.0% of network energy usage. Hence, the percentage large motor load present in the network load due to industry is: ( ) % LM 1 7.2% (G.12-a) 236

12 The percentage small motor load present in the network load due to industry is: ( ) % SM % (G.12-b) G.5 OTHER LOAD CLASS This dissertation assumes street and highway lighting and irrigation make up the other load class. Irrigation load is a large motor load [49, p7-6] and street and highway lighting are discharge lighting load. We assume 50 % of the other load class is irrigation and 50 % is street and highway lighting. The other load class makes up 3.4% of network energy usage. Hence, the percentage discharge lighting load present in the network load due to street and highway lighting is: % DL 2 ( ) 1.7% (G.13-a) The percentage large motor load present in the network load due to irrigation is: % LM 2 ( ) 1.7% (G.13-b) 237

13 G.6 LOAD PERCENTAGES The percentage network load that is large motor load is: ( LM ) % LM = + LM 1 2 = ( )% = 8.9% (G.14-a) The percentage network load that is small motor load is: ( SM + SM + SM + SM + SM + SM ) % SM = + SM = ( )% = 53.6% (G.14-b) The total motor load is 62.5%. This is an acceptable value since motor load makes up 60 % to 70 % of the network load in most networks [1, p274]. The percentage network load that is discharge lighting load is: ( DL ) % DL = + DL 1 2 = ( )% = 12.2% (G.14-c) 238

14 The percentage network load that is constant resistence load is: ( CR + CR + CR + CR + CR ) % CR = + CR = ( )% = 25.3% (G.14-d) 239