Shanghai Chenzhu Instrument CO., LTD.
Shanghai Chenzhu Instrument CO., LTD.

Installation of Power Supply SPD

Jan 01 , 2024

Wiring of SPD


SPDs at various levels of the power supply line should be installed at the front end of the protected device's power supply line. The connecting terminals of each SPD should be connected to the corresponding terminals inside the distribution box. The grounding terminal of the SPD should be connected to the grounding terminal board of the distribution box's protective grounding line (PE), and the distribution box's grounding terminal board should be connected to the equipotential grounding terminal board of the lightning protection zone. To minimize residual voltage entering the protected equipment, the connection wires for SPD installation should be straight, and their length should be as short as possible, with a minimum cross-sectional area complying with the requirements of IEC 61643-12. In general, the total length of connections (a+b+c) should be less than 0.5m. If on-site conditions make this impractical, the Kelvin wiring method (V-shaped wiring) should be used. The distance between the SPD and the protected equipment should be less than 10m, and the grounding terminal of the protected device's outer shell should be grounded through the SPD grounding terminal.


chenzhuisolator-20221104-13.jpg


SPD cable minimum cross-sectional area:


SPD级数

SPD的类型

导线截面积 ( mm² )

SPD连接相线铜导线

SPD接地端连接铜导线

第一级

开关型或限压型

6

10

第二级

限压型

4

6

第三级

限压型

2.5

4

第四级

限压型

2.5

4



Insulated multi-strand copper core cables or wires should be used for connection.


Configuration of Pre-Current Protection Device for Power SPD


The configuration of the pre-current protection device for the power SPD can be selected based on the test correction values in the table below. For example, if the SPD's In (8/20us) (test correction value) is 10kA, it should be matched with a rated 40A gG fuse; if In=40kA, it should be matched with a rated 125A gG fuse; Iimp (10/350) =15kA, it should be matched with a rated 200A gG fuse.


Recommended Fuse Values Matching SPD Discharge Capability (IEC 61643-12):


8/20us

10/350us

熔断器额定电流 ( A )圆柱形gG

计算值 ( kA )

测试修正值 ( kA )

计算值 ( kA )

测试修正值 ( kA )

7.6

5



25

9.6

7



32

13.4

10



40

17.3

15



50

23.1

17



63

32.2

25



80

41.4

30

8.8

5

100

53.4

40

11.3

7

125



15.3

10

160



19.75

15

200



27.93

20

250



34.21

25

315



When the power supply SPD is running, for example, the SPD is subjected to lightning current that exceeds its tolerance capacity, or the power grid fails to overvoltage, etc., which may cause the SPD short-circuit fault. In this case, the overcurrent protection device is required to cut the SPD from the line.


chenzhuisolator-20221104-14.jpg


The configuration of the F2 pre-current protection device should simultaneously meet the following requirements:


  • Requirement 1: Match the discharge capability of the SPD and remain inactive during lightning surge impacts.

  • Requirement 2: Promptly and reliably operate when a short circuit fault occurs in the SPD.

  • Requirement 3: Operate F2 when a short circuit fault occurs in the SPD, while F1 remains inactive.


In general, circuit breakers cannot simultaneously meet these requirements. In practical applications, it is recommended to use fuses.


The rated current of F2 should neither be too small (Requirement 1) nor too large (Requirement 3). If situations arise where both requirements cannot be met simultaneously, the selection should be based on the actual circumstances. If the losses incurred due to shutdown are significant, priority should be given to coordinating F2 with F1. If the loss due to power outage is relatively small, priority should be given to ensuring the coordination of F2 with the discharge capability of the SPD. Assuming the recommended backup fuse value for the SPD is A, the selection of F1 and F2 is as follows (see the table below):


F1与A大小关系

保证供电连续性

保证SPD保护连续性

F1≥1.6A

F2=A

F2=A

A≤F1<1.6A

F2=F1/1.6

F2=A

F1<A

F2=F1/1.6

不需要F2



Additionally, F2 should promptly fuse when a short circuit fault occurs in the SPD (Requirement 2). From this requirement, its rated current should not be too large; otherwise, its operation time would be too long, potentially causing protection blind spots. For the SPD, the higher its own short-circuit withstand level, the more effectively it can cover the protection blind spots that may occur with the fuse. This enhances the safety of the SPD.

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