EE4503 Electrical Systems Design Branch circuit and Feeder (Motor)

Topics Motor Branch Circuit Protection & Controller Feeder

Motor Branch Circuit http://www.cooperindustries.com/content/dam/public/bussmann/Electrical/Resources/Solution%20Center/technical_library/BUS_Ele_Tech_Lib_Motor_Circuit_Notes.pdf

Motor Branch Circuit Motor Branch Circuit Conductors Motor Branch Circuit Short Circuit Protection Overload Protection Motor Controller Motor Disconnect Motor Control Circuits

Motor Branch Circuit Conductor Disconnect Short Circuit Protection Overload Protection Controller & Control Circuit http://www.1on1tutoringlive.com/files/ocp2.htm

Motor Branch Circuit Type of Motor Induction Motor 1 phase and 3 phase Synchronous Motor (only 3 phase) Armature & Field (DC) DC Motor Armature & Field

Motor Branch Circuit Ratings of Motor Power: HP or kW # of phase Voltage Current ( 𝑃𝑜𝑤𝑒𝑟 𝑉𝑜𝑙𝑡𝑎𝑔𝑒 /𝐸𝑓𝑓𝑖𝑐𝑖𝑒𝑛𝑐𝑦) Check Manufacturer for Data

Motor Branch Circuit Ratings of Motor http://www.stmaustralia.com.au/images/TecoLVTEFC.pdf

Motor Branch Circuit Current (cable) Calculation Normal Operation: 𝐼 𝑐 ≥1.25 𝐼 𝑛 Multi-speed Motor: maximum current On-Off Operation: 𝐼 𝑐 ≥ 𝐾 1 𝐼 𝑛 when 𝐾 1 is the multiplier

Motor Branch Circuit Current (CB) Calculation Motor Type Fuse (Fast Blown) (Slow Blown) CB (instantaneous) (invert time) Induction (DOL) 3.0 1.75 7.0 2.5 Induction (Auto Transformer) 2.0 Wound Rotor 1.5 DC

Motor Branch Circuit Current Calculation Ground Cable 115% of the rated current 𝐼 𝑝𝑒 =1.15 𝐼 𝑛

Short Circuit Protection Able to handle the starting current Fuse Non Time-Delay Fuse Time-Delay Fuse Circuit Breaker Inverse Time Circuit Breaker (normal) Instantaneous Circuit Breaker

Short Circuit Protection Circuit Breaker

Overload Protection To protect overheat of the motor Circuit Breaker cannot function well for overload because of the starting current Three methods of detecting temperature Bimetal Thermal Overload Relay Electronic Overload Relay Thermistor Protective Relay

Motor Controller Starter Inverter DOL: usually less than 7.5kW Reduced Voltage Starter Inverter

Motor Controller Reduced Voltage Starter Star-Delta Starting Autotransformer Starting Resistant Starting Part-Winding Starting Elecronics Starting

Motor Controller Contactor Turn on-off the motor The rating of Contactor needs to be higher than the rating of Motor Utilization Category AC2: handle 2-5 times the nominal current AC3: handle 5-7 times, but stop at nominal AC4: handle high amount of on-off operation

Motor Controller Reduced Voltage Starter Star-Delta Starting Autotransformer Starting Resistant Starting Part-Winding Starting Elecronics Starting

Motor Controller components Power Circuit Usually 3 phase power circuit Control Circuit Single phase or DC circuit

Motor Controller Direct On Line Starting http://www.scslow.co.uk/WEG%20MANUAL%20STARTERS.htm

Motor Controller Star-Delta Starting http://myelectrical.com/notes/entryid/83/motor-starting-star-delta

Disconnecting Means Disconnect when circuit is live Design for inductive load Install “within sight” and less than 15m Rating is higher than 115% of motor rating

Feeder Cable All motor: 𝐼 𝐹 ≥1.25 𝐼 𝑛,𝑚𝑎𝑥 + 𝐼 𝑛 Combination of Motor and other loads: 𝐼 𝐹 ≥1.25 𝐼 𝑛,𝑚𝑎𝑥 + 𝐼 𝑛 +1.25 𝐼 𝐿 𝐼 𝐿 is continuous load Neutral can be a lot smaller but not smaller than Ground

Feeder CB All motor: 𝐼 𝐹 ≥ 𝐼 𝐶𝐵,𝑚𝑎𝑥 + 𝐼 𝑛 Combination of Motor and other loads: 𝐼 𝐹 ≥ 𝐼 𝐶𝐵,𝑚𝑎𝑥 + 𝐼 𝑛 +1.25 𝐼 𝐿 𝐼 𝐿 is continuous load Neutral can be a lot smaller but not smaller than Ground

Reference Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์ Depend on the area, end-user can connect to the “meter” of the authority in three ways.