EE4503 Electrical Systems Design Protective Devices and Protective Devices Cooordination

Topics LV protective systems Protective Devices Protective Devices Coordination

Low Voltage Protective Systems Fully Rated Protective System Selective Protective System Cascade Protective System

Protective Systems Fully Rated Protective System All devices are able to withstand the maximum short circuit current. (Interrupting Capacity) Highest Cost No need to prioritize the devices

Protective Systems Fully Rated Protective System If short circuit at F2 is 30kA and F1 is 10kA A, B, C: 𝐼 𝑐𝑢 =30𝑘𝐴 D, E, F: 𝐼 𝑐𝑢 =10𝑘𝐴 Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

Protective Systems Selective Protective System All devices are able to withstand the maximum short circuit current. (Interrupting Capacity) Tripping Characteristic Curve of each devices are “selected” in the way that the device that is closer to the fault trips first.

Protective Systems Selective Protective System A, B, C: 𝐼 𝑐𝑢 =10𝑘𝐴 D, E, F: 𝐼 𝑐𝑢 =5𝑘𝐴 There are two kinds Fully Partially Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

Protective Systems Fully Selective Protective System The selectivity is on the full range of short current. A & B are selective more than 10𝑘𝐴 Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

Protective Systems Partially Selective Protective System The selectivity is only on a certain range of short current. A & B are selective up to 5𝑘𝐴 Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์

Protective Systems Cascade Protective System The upstream device has the faster tripping rate at the high current than the lower one. The upstream device is able to withstand the maximum short circuit current while the downstream is lower capacity. In case of high current short circuit the upstream handle the breaking function.

Protective Devices Coordination Overlay the plot of tripping curve of each protective devices In general, no crossing of tripping curve Lower current (downstream devices) branch will be tripped faster. Higher current (upstream devices) branch will be tripped slower.

Protective Devices Coordination http://www.poweranalytics.com/designbase/pdf/Protective_Device_Coordination.pdf

Reference Electrical Systems Design: ประสิทธิ์ พิทยพัฒน์ http://www.poweranalytics.com/designbase/pdf/Protective_ Device_Coordination.pdf Coordination of LV protection devices: Schneider Electric Depend on the area, end-user can connect to the “meter” of the authority in three ways.