EC&M’s Electrical Calculations Handbook - Chapter 13

Circuits for Special Loads Mạch thiết kế cho tải điện khác nhau Các thủ tục bình thường được sử dụng để xác định kích thước mạch và đặc điểm cho tải điển hình là để xác định phương pháp hệ thống dây điện và dây dẫn cách điện và các loại được sử dụng từ việc cài đặt dữ liệu môi trường, giải quyết cho hiện tại mà sẽ được rút ra tải, chọn kích thước dây dẫn, và sau đó xác định kích thước Raceway. Sau khi tất cả điều này là hoàn thành, tính toán giảm điện. | Chapter 13 Circuits for Special Loads Designing Circuits for Various Electrical Loads The normal procedure used to determine circuit sizes and characteristics for typical loads is to determine the wiring method and conductor and insulation types to be used from the installation-site environmental data solve for the current that will be drawn by the load select the conductor size and then determine the raceway size. After all this is completed a calculation of the voltage drop in the system is normally done to determine that sufficient operating voltage is available at the terminals of the load for it to operate satisfactorily. A solution using this methodology is shown in Fig. 13-1. When the load can operate for 3 hours or longer it is considered to be a continuous-duty load and the circuit must be designed for continuous operation. Figure 13-2 is the solution method used for designing the electrical circuit to a continuous load. There are many types of electrical loads that exhibit special operational characteristics such as large inrush currents on initial energization. The electrical system must be designed to 33S Copyright 2001 by The McGraw-Hill Companies Inc. Click here for Terms of Use. 8 PROBLEM AN ELECTRICAL SKID THAT CAN OPERATE FOR ONLY 30 MINUTES AT ONE TIME. IT HAS A NAMEPLATE LOAD OF 82 kW AT 240 VOLTS 1-PHASE. SOLVE FOR THE MINIMUM SIZES OF BRANCH CIRCUIT ELEMENTS. SOLUTION STEP 1. DETERMINE THE LINE CURRENT DRAWN BY THE LOAD 82000W 240V AMPERES. STEP 2. DETERMINE WIRE AMPACITY 100 OF AMPERES AMPERES STEP 3. SELECT WIRE FOR THE LOAD AT LEAST AMPERE 75 DEGREE INSULATION SUCH AS THW 500 kCMIL COPPER. STEP 4. DETERMINE BREAKER RATING TO PROTECT THE CONDUCTOR NEXT STANDARD SIZE OVER AMPERES 350 AMPERES STEP 5. DETERMINE SIZE OF EQUIPMENT GROUNDING CONDUCTOR FOR 350 AMPERE OVERCURRENT DEVICE 3 AWG. STEP 6. DETERMINE SIZE OF CONDUIT FOR 2 - 500 KCMIL THW WIRES AND ONE 3 THW COPPER GROUND WIRE. 2 X 1 SQ. IN. .