What are the types of surge protection devices and how are they tested?

In order for all SPD manufacturers to follow the same rules when testing their products, a standard EN 61643-11 was created. It describes requirements and test methods for surge protections devices and surge arresters. This standard works with normalised voltage and current curves that have a clearly defined waveform. These are test waves (pulses) that simulate different types of surges, which were explained in the previous article What is a surge and how to protect against it. They are defined by the peak value (the maximum value of a voltage or current that the test pulse reaches during its duration), duration T1 (the time it takes the pulse to reach 90% of its peak) and duration T2 (the time it takes for the pulse to drop down to 50% of that peak). These durations are written in the format (T1/T2) and are usually in microseconds.

Pic. Test lightning pulse 10/350 µs (left) and switching pulse 8/20 µs (right)

Lightning current arresters – SPD type T1

There are three basic types of SPDs. The first type is the so-called lightning current arrester referred to as T1, previously referred to as class B arrester. This is a robust protection, designed to divert/limit atmospheric effects, i.e. impulse currents arising from a direct lightning strike, either into the building (cause of damage due to a lightning strike S1 according to the standard EN 62305-1), or to the electrical system connected to the building (cause S3). Impulse currents reach values ​​of up to 200 kA. Their effect is simulated by class I tests, i.e. by an impulse discharge current I imp with a test waveform of 10/350 µs. Type T1 SPDs are installed at the beginning of the electrical installation, as close as possible to the entrance of the power line to the building - in main switchboards.

Surge arresters – SPD type T2

The second type is the so-called surge arrester referred to as T2, previously marked as class C. This type is intended to limit switching surges and the effects of indirect lightning strikes either near the building (cause S2) or near the electrical system connected to the building (cause S4). Their effect is simulated by class II tests, i.e. nominal discharge current I _n and maximum discharge current I _max with a waveform of 8/20 µs. Type T2 SPDs are installed further in the electrical installation in secondary switchboards.

Surge arresters – SPD type T3

The last basic type is the surge arrester referred to as T3, formerly class D. This is the finest protection intended for end devices and sensitive electronics, as it further eliminates residual surges beyond the upstream T2 arresters. These types are tested with a voltage pulse of 1.2/50 µs. They are installed as close as possible to the end devices so that there is not any unwanted induction and the occurrence of surge behind them that would endanger the end device.

Especially in industrial applications, this type is often combined with a high frequency (EMI/RFI) filter. It is installed in series with the protected deviceand is intendedfor single-phase or three-phase supply systems with rated currents from 10 A to 400 A. It effectively filters out industrial interference in the frequency range from 150 kHz to 30 MHz.

Combined arresters

There are also combined surge arresters of the type T1+T2, or T2+T3 or T1+T2+T3. Their advantage is the combination of several types of SPDs in one product, but it is vital to pay attention to the effective protective distance. Another advantage is their integrated coordination, which the user does not have to deal with. You will learn more about these terms in our other articles in Hakel Advices soon.

Multi-level protection

In the terminology of surge arresters, we can also encounter the term multi-level protection. This is the coordination of individual or combined types of SPDs connected in one circuit so that the surge energy gets gradually absorbed from coarse to fine protection and the required voltage protection level for the given device is reached. This principle is needed mainly because of the effective protective distance of SPDs, which is often impossible to maintain.

Tab. Types of surge arresters