Surge protection device
What is a surge protection device?
The terms surge protection device (SPD) and transient voltage surge suppressor (TVSS) are used to describe electrical devices typically installed in power distribution panels, process control systems, communications systems, and other heavy-duty industrial systems, for the purpose of protecting against electrical ...
Where do you put a surge protective device?
In an electrical systems, surge protection devices (SPDs) are usually installed in tap-off configuration (in parallel) between the live conductors and the earth. The operating principle of SPD can be similar to that of a circuit breaker.
How does surge protection work?
How Does a Surge Protector Work? A typical surge protector passes the electrical current along the outlet to number of the devices plugged into the power strip. If the voltage happens to rise above the acceptable level, the protector will divert the extra electricity into the outlets grounding wire.
Is it worth getting surge protection?
Without a surge protector, a power spike or power surge could shorten the life of your computer, wipe out all of your data, or even completely destroy your system. In fact, you should use a surge protector with any high-end electronic device
What is the difference between Type 1 and Type 2 surge protection?
Type 1 devices are installed before the main device in the loadcenter, whereas Type 2 are installed following the main devices in the loadcenters. ... Type 1 devices are dual-rated for Type 2 applications as well, providing the highest ratings available for installation at the service entrance.
Surge Protection Devices (SPD) are used for electric power supply networks[1], telephone networks, and communication and automatic control buses.
The Surge Protection Device (SPD) is a component of the electrical installation protection system.
This device is connected in parallel on the power supply circuit of the loads that it has to protect (see Fig. J17). It can also be used at all levels of the power supply network.
This is the most commonly used and most efficient type of overvoltage protection.
SPD connected in parallel has a high impedance. Once the transient overvoltage appears in the system, the impedance of the device decreases so surge current is driven through the SPD, bypassing the sensitive equipment.
Principle
SPD is designed to limit transient overvoltages of atmospheric origin and divert current waves to earth, so as to limit the amplitude of this overvoltage to a value that is not hazardous for the electrical installation and electric switchgear and controlgear.
SPD eliminates overvoltages
- in common mode, between phase and neutral or earth;
- in differential mode, between phase and neutral.
In the event of an overvoltage exceeding the operating threshold, the SPD
- conducts the energy to earth, in common mode;
- distributes the energy to the other live conductors, in differential mode.
The three types of SPD
Type 1 SPD
The Type 1 SPD is recommended in the specific case of service-sector and industrial buildings, protected by a lightning protection system or a meshed cage.
It protects electrical installations against direct lightning strokes. It can discharge the back-current from lightning spreading from the earth conductor to the network conductors.
Type 1 SPD is characterized by a 10/350 µs current wave.
Type 2 SPD
The Type 2 SPD is the main protection system for all low voltage electrical installations. Installed in each electrical switchboard, it prevents the spread of overvoltages in the electrical installations and protects the loads.
Type 2 SPD is characterized by an 8/20 µs current wave.
Type 3 SPD
These SPDs have a low discharge capacity. They must therefore mandatorily be installed as a supplement to Type 2 SPD and in the vicinity of sensitive loads.
Type 3 SPD is characterized by a combination of voltage waves (1.2/50 μs) and current waves (8/20 μs).
SPD normative definition
| Direct lightning stroke | Indirect lightning stroke | ||
|---|---|---|---|
| IEC 61643-1 | Class I test | Class II test | Class III test |
| IEC 61643-11/2011 | Type 1 :  | Type 2 :  | Type 3 :  |
| EN/IEC 61643-11 | Type 1 | Type 2 | Type 3 |
| Former VDE 0675v | B | C | D |
| Type of test wave | 10/350 | 8/20 | 1.2/50 + 8/20 |
- Note 1: There exist
+ 
SPD (or Type 1 + 2 SPD) combining protection of loads against direct and indirect lightning strokes. - Note 2: some SPD can also be declared as
.
Characteristics of SPD
International standard IEC 61643-11 Edition 1.0 (03/2011) defines the characteristics and tests for SPD connected to low voltage distribution systems (see Fig. J19).
Common characteristics
- Uc: Maximum continuous operating voltage
- This is the A.C. or D.C. voltage above which the SPD becomes active. This value is chosen according to the rated voltage and the system earthing arrangement.
- Up: Voltage protection level (at In)
- This is the maximum voltage across the terminals of the SPD when it is active. This voltage is reached when the current flowing in the SPD is equal to In. The voltage protection level chosen must be below the overvoltage withstand capability of the loads. In the event of lightning strokes, the voltage across the terminals of the SPD generally remains less than Up.
- In: Nominal discharge current
- This is the peak value of a current of 8/20 µs waveform that the SPD is capable of discharging minimum 19 times[2].
Why is In important?
In corresponds to a nominal discharge current that a SPD can withstand at least 19 times[2]: a higher value of In means a longer life for the SPD, so it is strongly recommended to chose higher values than the minimum imposed value of 5 kA.
Type 1 SPD
- Iimp: Impulse current
- This is the peak value of a current of 10/350 µs waveform that the SPD is capable of discharging of discharging at least one time[3].
Why is Iimp important?
IEC 62305 standard requires a maximum impulse current value of 25 kA per pole for three-phase system. This means that for a 3P+N network the SPD should be able to withstand a total maximum impulse current of 100kA coming from the earth bonding.
- Ifi: Autoextinguish follow current
- Applicable only to the spark gap technology. This is the current (50 Hz) that the SPD is capable of interrupting by itself after flashover. This current must always be greater than the prospective short-circuit current at the point of installation.
Type 2 SPD
- Imax: Maximum discharge current
- This is the peak value of a current of 8/20 µs waveform that the SPD is capable of discharging once.
Why is Imax important?
If you compare 2 SPDs with the same In, but with different Imax: the SPD with higher Imax value has a higher "safety margin" and can withstand higher surge current without being damaged.
Type 3 SPD
- Uoc: Open-circuit voltage applied during class III (Type 3) tests.
Main applications
- Low Voltage SPD
- Very different devices, from both a technological and usage viewpoint, are designated by this term. Low voltage SPDs are modular to be easily installed inside LV switchboards.
- There are also SPDs adaptable to power sockets, but these devices have a low discharge capacity.
- SPD for communication networks
- These devices protect telephone networks, switched networks and automatic control networks (bus) against overvoltages coming from outside (lightning) and those internal to the power supply network (polluting equipment, switchgear operation, etc.).
- Such SPDs are also installed in RJ11, RJ45, ... connectors or integrated into loads.
Notes
- ^ find out more in application examples such as SPD for EV charging application, SPD for photovoltaic applications and SPD application example in Supermarket
- ^ 1 2 Test sequence according to standard IEC 61643-11 for SPD based on MOV (varistor). A total of 19 impulses at In:
- One positive impulse
- One negative impulse
- 15 impulses synchronised at every 30°on the 50 Hz voltage
- One positive impulse
- One negative impulse
- ^ for type 1 SPD, after the 15 impulses at In (see previous note):
- One impulse at 0.1 x Imp
- One impulse at 0.25 x Imp
- One impulse at 0.5 x Imp
- One impulse at 0.75 x Imp
- One impulse at Imp
