GUIDE FOR LIGHTING ARRESTER SELECTION

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

ELECTRIC AND ESTIMATION TEAM

2

1 Scope

2 Introduction

3 Define condition service

4 Calculating and selection for rated voltage

5 Selection for normal discharge current

6 Example

3 ELECTRIC AND ESTIMATION TEAM

1 Scope

This document applies to non-linear

metal-oxide resistor type surge arrester without

spark gaps designed to limit voltage

surges on A.C power circuits

ELECTRIC AND ESTIMATION TEAM

4

• A Define condition service • B Calculating for rated voltage

ELECTRIC AND ESTIMATION TEAM

5 This document will be pressent 3 steps to select a SA as below:

• C Selection for normal discharge current

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

6

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:

ELECTRIC AND ESTIMATION TEAM

7

4 wiring repeat grounded system 1.25~

1.35

3 wiring- Solidly-Grounded System 1.4

3 wiring- High impedance-Grounded System 1.73

3 wiring- - Delta-Grounded System 1.73

- Define temporary over voltage:

Utov = Ke * Um/ √3

B Calculating for rated voltage

• Step 2: Define continuously operation

voltage: COV (MCOV)

- Uc ≥ Um/ √3

ELECTRIC AND ESTIMATION TEAM

8

• Step 3: Define overvoltage withstand

capability

- Insulated neutral: t ≥ 2h

- Solidly grounded neutral: t = 10s

C Selection for normal discharge current

- We select normal discharge current

following 2 table of IEC 60099 standard

ELECTRIC AND ESTIMATION TEAM

9

C Selection for normal discharge current

ELECTRIC AND ESTIMATION TEAM

10

Example 1: Selection SA for

system:22kV-25kA-solidly 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

ELECTRIC AND ESTIMATION TEAM

11

- 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

ELECTRIC AND ESTIMATION TEAM

12

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.)

ELECTRIC AND ESTIMATION TEAM

13

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 9 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)

ELECTRIC AND ESTIMATION TEAM

14

THANKS FOR WATHCHING

ELECTRIC AND ESTIMATION TEAM

15