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.

Scientists have carried out important studies on the characteristics and effects of lightning strikes for years, and have developed technological products accordingly. Today, tests of these products can also be carried out by simulating a lightning strike in this context.

Lightning Strike Wave Types:

The lightning strike can be studied in two different wavelengths.

1. Direct Lightning Strike 10 / 350μs:

Impulse currents in a waveform of 10/350 μs occur in direct lightning strikes. This pulse rapid voltage increase releases great power with a large current pulse.

Today, External Lightning Protection System materials and Type 1 / Class I type Surge Arrester circuit elements are tested according to these criteria according to the standards.

2. Lightning Strike and Switching Voltages on a Remote Area 8 / 20μs:

Lightning strikes at a distant location and impulse currents with switching voltages 8/20 μs waveform occur.

The energy content of this pulse is significantly lower than the lightning test current's pulse current wave of 10/350 μs. Type 2 / Class II and Type 3 / Class III type Surge Protector (Surge Arrester) circuit elements are tested according to these criteria according to the standards.

Standards

Some frequently listed standards include:

• IEC 61643-11 Low-voltage surge protective devices - Part 11: Surge protective devices connected to low-voltage power systems - Requirements and test methods (replaces IEC 61643-1)
• IEC 61643-21 Low voltage surge protective devices - Part 21: Surge protective devices connected to telecommunications and signalling networks - Performance requirements and testing methods
• IEC 61643-22 Low-voltage surge protective devices - Part 22: Surge protective devices connected to telecommunications and signalling networks - Selection and application principles
• EN 61643-11, 61643-21 and 61643-22
• Telcordia Technologies Technical Reference TR-NWT-001011
• ANSI/IEEE C62.xx
• Underwriters Laboratories (UL) 1449.
• AS/NZS 1768

Each standard defines different protector characteristics, test vectors, or operational purpose.

EN 62305 and ANSI/IEEE C62.xx define what spikes a protector might be expected to divert. EN 61643-11 and 61643-21 specify both the product's performance and safety requirements. In contrast, the IEC only writes standards and does not certify any particular product as meeting those standards. IEC Standards are used by members of the CB Scheme of international agreements to test and certify products for safety compliance.

In addition, the following standards are not standards for standalone surge protectors, but are instead meant for testing surge immunity in electrical and electronic equipment as a whole. Thus, they're frequently used in the design and test of surge protection circuitry.

• IEC 61000-4-2 Electrostatic discharge immunity test
• IEC 61000-4-4 Electrical fast transient/burst immunity test
• IEC 61000-4-5 Surge immunity test

Principle

SPD is designed to limit transient overvoltage 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 control gear.

SPD eliminates overvoltage

• 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 overvoltage 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

Fig. J18 – SPD standard definition

According to this;

First Stage: Type 1 / Class 1 / Class B lightning protection surge arrester are the front protection units of the facility / structure. They are circuit elements capable of absorbing and damping direct lightning strikes that may come from power lines.

It must be installed in the main distribution / transformer panel inside and / or outside the building.

It should have been tested in 10/350 µSec waveform. It must be able to discharge a load of at least 50kA between Phase-Neutral, and at least 100kA between Phases, Neutral-Earth.

Second Stage: Type 2 / Class 2 / C Class Surge Protection Devices (Surge Arresters) are circuit elements used in the secondary and / or lower secondary panels of the facility / building. Compared to Type 1 / Class II surge arresters, their strength is lower but their sensitivity is better.

It should have been tested in an 8/20 µSec waveform. It must be able to discharge a load of at least 10kA between Phase-Neutral, and at least 25kA between Phases, Neutral-Earth.

Type 1 + 2 / Class 1 + 2 / B + C Class compact protection elements have been used as second level protection in recent years.

It should have been tested in 10/350 µSec waveform. It must be able to discharge a load of at least 40kA between Phase-Neutral, and at least 100kA between Phases, Neutral-Earth.

It is used in the electrical panel of the uninterruptible power supply and / or in the secondary panels positioned like a main panel.

Third Stage: Type 3 / Class 3 / D Class sudden overvoltage protection surge arresters are circuit elements used in its lines to protect sensitive electronic devices.

The product range is quite wide as it can be connected to different devices with different connection protocols / sockets / ports.

Below are some of the Type 3 / Class 3 / D Class surge arresters for different circuits / devices.