Đây là tài liệu chỉ dẫn tính toán lựa chọn chống sét cho tủ điện trung thế trong nhà Selection surge arresster for indoor medium voltage Switchgear. Step 1: Define technical parameters of system Maximum operation voltage of system Um = (1.05÷1.1Ur) In Vietnam, Um =1.1Ur Define earth fault factor:
GUIDE FOR SURGE ARRESTOR SELECTION History Records No Revision No Revised by Issued Date Descriptions A SINH.NH 2015.Sep.15 Issue for training B SINH.NH 2015.Oct.26 Issue for training ELECTRIC AND ESTIMATION TEAM Contents No Descriptions Scope Introduction Define condition service Calculating and selection for rated voltage Selection for normal discharge current Example ELECTRIC AND ESTIMATION TEAM Scope This document applies to non-linear metaloxide resistor type surge arrester without spark gaps designed to limit voltage surges on A.C power circuits ELECTRIC AND ESTIMATION TEAM Introduction This document will be pressent steps to select a SA as below: • • A Define condition service • B Calculating for rated voltage C Selection for normal discharge current ELECTRIC AND ESTIMATION TEAM A Define condition service - Indoor or outdoor Temperature of environment Atitude above sea level: this information is very important to calculating operating voltage Etc… ELECTRIC AND ESTIMATION TEAM B Calculating for rated voltage • Step 1: Define technical parameters of system - Maximum operation voltage of system Um = (1.05÷1.1Ur) In Vietnam, Um =1.1Ur - Define earth fault factor: - Define temporary over voltage: Utov = Ke * Um/ √3 Grounded method Ke wiring repeat grounded system 1.25~ 1.35 1.5 wiring cables wiring- Solidly-Grounded System 1.4 wiring- High impedance-Grounded System 1.73 wiring- - Delta-Grounded System 1.73 ELECTRIC AND ESTIMATION TEAM B Calculating for rated voltage • • - Step 2: Define continuously operation voltage: COV (MCOV) Uc ≥ Um/ √3 Step 3: Define overvoltage withstand capability Insulated neutral: t ≥ 2h Solidly grounded neutral: t = 10s ELECTRIC AND ESTIMATION TEAM C Selection for normal discharge current - We select normal discharge current following table of IEC 60099 standard ELECTRIC AND ESTIMATION TEAM C Selection for normal discharge current 10 ELECTRIC AND ESTIMATION TEAM EXAMPLE Example 1: Selection SA for system:22kV-25kAsolidly grounded (EVN project) Um = 1.1 * 22 = 24 (kV) - Utov = 1.4 * 24/ √3= 19.42kV - Uc ≥ 24/ √3 = 13.87 - Base on protective characteristics table, we select SA 18kV with Uc = 15.3kV 11 ELECTRIC AND ESTIMATION TEAM EXAMPLE - - Define time duration: T = Utov/Uc = 19.42/13.87 = 1.27 So, we easily to see in TOV curver the time duration is 1000s >10s It satisfy withstand condition requirement Following table 15 we will select the normal discharge current is 10kA Conclusion : SA-18kV-10kA 12 ELECTRIC AND ESTIMATION TEAM Example 2: Selection SA for system:10kV-50kA-3 wiring- High impedance-Grounded System (MONG DUONG project) - Um = 1.1 * 10 = 11 (kV) - Utov = 1.73 * 11/ √3= 11kV - Uc ≥ 11/√3 = 6.35kV - Base on protective characteristics table, we can select SA 9kV with Uc = 7.65 - Define time duration: T = Utov/Uc = 11/7.65 = 1.43 We see in TOV curve the time duration approximate 70s < 2h It does not satisfy withstand condition requirement So we will select SA 10 kV, Uc = 8.4 T = Utov/Uc = 11/8.4 = 1.3 We see in TOV curve the time duration approximate 1000s It satisfy Following table 15 we will select the normal discharge current is 10kA Conclusion : SA-10kV-10kA (So, in my opinion, we select SA 9kV for Mong Duong project is wrong.) 13 ELECTRIC AND ESTIMATION TEAM Example 3: Selection SA for system:6.6kV-25kA-3 wiring- High impedance-Grounded System (SAMSUNG project) - Um = 1.1 * 6.6 = 7.2 (kV) - Utov = 1.73 * 7.2/ √3= 7.2kV - Uc ≥ 7.2/√3 = 4.15kV - Base on protective characteristics table, we can select SA 6kV with Uc = 5.1 - Define time duration: T = Utov/Uc = 7.2/5.1 = 1.4 We see in TOV curve the time duration approximate 70s < 2h It does not satisfy withstand condition requirement So we will select SA kV, Uc = 7.65 T = Utov/Uc = 7.2/7.65 = 0.9 We see in TOV curve the time duration > 10000s It satisfy Following table 15 we will select the normal discharge current is 10kA Conclusion : SA-9kV-10kA (We bought SA 6kV for Sam Sung project is wrong Now, they are storing at inventory :D) 14 ELECTRIC AND ESTIMATION TEAM THANKS FOR WATHCHING 15 ELECTRIC AND ESTIMATION TEAM ... Issue for training B SINH.NH 2015.Oct.26 Issue for training ELECTRIC AND ESTIMATION TEAM Contents No Descriptions Scope Introduction Define condition service Calculating and selection for rated... ESTIMATION TEAM C Selection for normal discharge current - We select normal discharge current following table of IEC 60099 standard ELECTRIC AND ESTIMATION TEAM C Selection for normal discharge... pressent steps to select a SA as below: • • A Define condition service • B Calculating for rated voltage C Selection for normal discharge current ELECTRIC AND ESTIMATION TEAM A Define condition service