国外电气专业PPT教学讲义.ppt

1、Schedule,Introduction,Load Estimation,Terminology,Basic Equipment,Codes and Standards,Power Distribution & Final Circuit,Protection & Cable Wiring,Earthing,Design of Electricity Distribution,Standby Generator and Power Supplies,Introduction and Load Assessment,Date : 23 October 2008 Module Code :,Ir

2、. KF Cheung,Objectives,To understand the roles and duties of building services engineers To enable students to design simple power distribution systems To appreciate various power distribution design,Question,Power requirements of HVAC system By HVAC engineer? By Electrical engineer?,1Definition 2Lo

3、ad Assessment 2.1 Code of Practice (CoP) 2.2 Practice At Early Stage Detailed Design Stage,1. DefinitionA) Active Power (Useful Power) - 1,Active Power = Real Power Time average of instantaneous power when the average is taken over a complete cycle of an A/C waveform. Expressed in Watt (W),1. Defini

4、tionA) Active Power (Useful Power) - 2,For Single Phase P = V I cos For Balanced Three-Phase P = 3 Vph-ph I cos ,1. DefinitionB) Apparent Power,For Single Phase AP = VI For Three Phase AP = 3 V(ph-ph) I,* Expressed in Volt-ampere (VA),1. DefinitionC) Connected Load,The Sum of all the loads connected

5、 to the electrical system. This is usually expressed in watts.,1. DefinitionD) Demand Factor,This is the factor applied to the connected load of an installation to assess the maximum demand value. Demand Factor = Maximum demand Connected load,1. Definition(E) Load Factor,Load Factor is the ratio of

6、the average demand to the maximum demand over a defined interval. In most commercial building, for example between the hours of 9:00 to 18:00 the load factor is usually close to unity.,1. Definition(E) Load Factor,Typical Load Profile for an Office Building,1. Definition(F) Power Factor,Power Factor

7、 is defined as the ratio of the apparent power in a circuit (V.A) to the useful power (W) if the voltage and current are sinusoidal Power Factor = kW/ kV.A,Example - 1,Calculate the current demand of a residential flat (single phase 220V)with: 6 nos. of 100W light bulbs and 4 nos. of 40W fluorescent

8、 lights 1 no. of 1.5HP and 2 nos. of 1HP Air conditioners 1 no. of 3000W Electric Power 2 set of 30A Ring Circuits for 13A Socket Outlets,Example 1Answer,Total Connected Load =,2. Load Assessment,Fundamental to electric design Feasibility of a project Cost,2. Load Assessment,How to assess Electrical

9、 Load? COP for the Electricity (Wiring) Regulation Practice,2.1 Load Assessment Current Demand,The Current rating of a circuit should not be less than the current demand of the circuit,2.1 Load Assessment Determination of Current Demand,General The information and value given in this CoP for determi

10、nation of current demand are intended for general guidance only as it impossible to specify the appropriate allowances for diversity for every type of electrical installations,2.1 Load Assessment Determination of Current Demand,For circuit supplying non- simultaneous or cyclic loads For a circuit ha

11、ving non- simultaneous or cyclic loads such that only one of these loads can be in use at any one time, the greatest of these loads should be used in calculating the current demand of the circuit.,2.1 Load Assessment Determination of Current Demand,For final circuit According with CoP Code 6, curren

12、t demand of the circuit concerned should be the same as the rating of overcurrent protective device of the circuit,2.1 Load Assessment Determination of Current Demand,For final circuit Each socket outlet in a radial final circuit should be assumed to demand its rated current rating Lighting outlets

13、should be assumed to demand the connected lad with a minimum of 100W per lampholder Current using equipment of a rating not greater than 5VA may be neglected Discharge lighting should assumed to have a demand in volt-amperes of the rated lamp wattage multiplied by not less than 1.8. All other fixed

14、equipment should be assumed to demand the rated or normal current,2.1 Load Assessment Determination of Current Demand,Allowance for Diversity - 1 This table is applicable to installation having a current demand not exceeding 400A in each phase.,2.1 Load Assessment Determination of Current Demand,All

15、owance for Diversity -2,2.1 Load Assessment Determination of Current Demand,Allowance for Diversity -3,2.1 Load Assessment Determination of Current Demand,Allowance for Diversity - 4,Example 2Applying Diversity Factor,Total Current Demand =,Example - 3,Calculate the load demand of the shop (3 phase

16、380V) with: 40 nos. of 100W Light Bulbs 24 nos. of 60W Fluorescent Lights 2 set of 12kW 3 phase machines with 0.87 power factor and 90% efficiency 3 nos. of 18kW 3 phase electric heaters 3 set of 30A ring circuits for 13A socket outlet,Example 3Answer,Total Current Demand = 132.3A,2.2 Load Assessmen

17、t - Practice At Early Stage,At Early Stage Statistic Historical Data/ Experience Type of Buildings,2.2 Load Assessment - Practice At Early Stage,Residential Building What are the key parameters?,2.2 Load Assessment - Practice At Early Stage,Commercial Building What are the key parameters?,2.2 Load A

18、ssessment - Practice At Early Stage,Industrial Building What are the key parameters?,2.2 Load Assessment - Practice At Early Stage,Purpose Built Plant What are the key parameters?,2.2 Load Assessment - Practice At Early Stage,Minimum design load capacities for lighting and small power equipment for

19、various types of building,Measured total maximum demand loads for representative sample of large office buildings,2.2 Load Assessment - Practice At Early Stage - Example,Calculate the load of a Residential Tower 2-bedroom flats (93 nos.) (UFA less than 50m2) 3-bedroom flats (51 nos.) (UFA less than

20、50-80m2) 3-bedroom flats (UFA more than 80m2) (4 nos.) Lifts (4 nos.) General Lighting & Power (1 lot) Plumbing & Drainage System (1 lot),2.2 Load Assessment - Practice At Early Stage - Example,Calculate the load of a Commercial Tower Carpark Lighting & Power (13500m2) Arcade Lighting (1000m2) Escal

21、ator (12 nos.) Lifts (4 nos.) Podium Lighting & Power (excluding arcade lighting) (1 lot) Plumbing & Drainage System (1 lot),2.3 Load Assessment Practice B) At Detailed Design Stage,The electrical load within most commercial buildings can be arranged into the following broad categories: Lighting Sma

22、ll power and special user equipment HVAC equipment Lifts and escalators,2.3 Load Assessment - PracticeB) At Detailed Design Stage,Lighting Lighting Load between 8 and 18 W/m2 for maintained illuminance levels of 350-500lux For large office building, lighting load between 12-20 W/m2 is reasonable In

23、some area of a building special-purpose lighting is likely to result in higher electrical loads greater than this.,2.3 Load Assessment Practice B) At Detailed Design Stage,What is Special-Purpose Lighting?,2.3 Load Assessment Practice B) At Detailed Design Stage,Small Power and Special User Equipment Small Power and user equipment generally consists of items which are plugged into socket outlets or permanently c