Surge protective device types | SPD type 1,type 2,type 3,type 4
Introduction: Surge Protective Devices (SPDs) are essential components in electrical systems because they play a crucial role in safeguarding equipment and devices from the damaging effects of electrical surges. These surges, often caused by lightning strikes, power grid switching, or other electrical disturbances, can result in a sudden and excessive increase in voltage. Without proper protection, these voltage spikes can lead to irreparable damage to sensitive electronic equipment, appliances, and electrical systems. SPDs act as a line of defense by diverting excess voltage away from the protected equipment, thereby preventing potential damage.
This page mentions different Surge protective device (SPD) types viz. type 1 surge protector, type 2, type 3 and type 4 surge protector. We will also understand functions of SPD types viz. GDT (Gas Discharge Tube), TSPD (Thyristor Surge Protection Devices), TVS(Transient Voltage Suppressor), MOV(Metal Oxide Varistor), PESD (Polymer device) etc. and explore difference between them.
What are surge protective devices (SPD) ?
Introduction:
• The devices used to prevent damage to electronic or electrial equipments from voltage spikes or
transients are known as surge protector or surge suppressor.
• It is inserted in AC utility line and/or telephone line.
• It is also called transient suppressor.
• Surge protectors provide protection by dissipating any excess power and preventing it
to reach connected equipments/devices. Electronic equipments such as desktop, laptop or hard drive are designed to
operate with certain power range. If too much voltage is passed to them, they will get permanent damage.
• It assists protection of equipments against transients originating from lightning and from other switching
sources.
The figure-1 depicts surge protective device in the network. As shown the device is connected in parallel on the power supply circuit of the loads which has to be protected. It diverts current waves to the earth and hence limit the amplitude of the overvoltage to a value which is not hazardous for electrical installation.
Type 1 Surge protector device (SPD)
• This SPD device is mounted on line side of main service entrance.
• Type-1 SPD is characterized by a 10/350 µs current wave and used for outdoor applications.
• It protects against external power surges which are caused by lightning or due to utility capacitor bank switching.
It is considered to be first line of defense of your home or office.
• Built-in alarm systems indicate when device needs to be replaced based on its life cycle.
It is also known as secondary surge arrester.
Type 2 Surge protector device (SPD)
• This SPD device is mounted on load side of main service entrance.
• Type-2 SPD is characterized by an 8/20 µs current wave.
• It is used to protect branch circuit or service entrance against residual lightning energy,
surges due to motor and other surges.
• Its main function is to limit transient voltage and protects sensitive electronics and
Mp/Mc based boards.
• It is used for commercial and industrial applications.
Type 3 Surge protector device (SPD)
• Type-3 SPD is characterized by a combination of voltage waves (1.2/50 µs) and
current waves (8/20 µs).
• Its main function is to limit low level surges which can damage sensitive electronic circuits in
TVs, PCs and electric appliances.
• It is considered to be last line defense in surge protective network.
• It is known as power strips.
Type 4 Surge protector device (SPD)
• It is known as surge protection module.
• It provides protection to servo motors, PLCs and other devices used in industrial applications.
• This surge protector device provides wired in surge protection.
Surge protective device types - GDT, TSPD, TVS, MOV, PESD
Following are over voltage protection devices. Let us understand construction and
functions of these surge protective device types.
Thyristors: They are crowbar devices used as surge protective devices.
They are based on pair of intertwined bipolar transistors created by four layer stack of
n and p doped silicon regions. Refer TVS diode >>,
TVS Thyristor selection guide >> for more information.
Transient voltage suppressors:They are based on avalanche diodes and zener diodes.
Diodes are made of semiconductors usually silicon, at a junction between n and p doped
regions. TVS devices provide protection with combination of forward bias and reverse bias
breakdown conduction. Refer ESD protection diode >>
MOV (Metal Oxide varistor) : Varistors are usually made of ceramic of zinc oxide grains
in a matrix of other oxides. The grains form diodes with surrounding matrix, creating
a complex array of parallel and anti-parallel diodes. At higher voltages, the individual diodes
begin to conduct and the resistance of the varistor drops dramatically.
Polymer ESD devices: Polymer devices are bidirectional crowbar devices.
They have very high turn on voltages, often over 200 Volts, but
they turn on quickly which limits exposure to high voltage. Polymer ESD devices consist of
a polymer embedded with conducting particles.
Gas Discharge Tubes: They are usually formed with ceramic body filled with
gas mixture containing neon and argon and two or more electrodes. When voltage across
the electrodes exceeds a specified value an arc occurs within the tube which provides
low current path.
Fuses: They are used as over current protection devices.
Following table mentions difference between surge protective device types.
High Power Surge Events - 8x20µs, 10x1000µs
| Type | Speed | Accuracy | Current capability | Size on board | Lowest crowbar trigger voltage | Wearout |
|---|---|---|---|---|---|---|
| Gas Discharge Tube (GDT) | Slow | Fair | High | Large | 75 V | Will fail after numerous stresses depending on severity. |
| Thyristor Surge Protection Devices (TSPD) | Fair | Good | Medium | Small | 80V | NO |
| Transient Voltage Suppressor (TVS) | Fast | Good | Low | Small | NA | NO |
| Metal Oxide Varistor (MOV) | Fair | Poor | Medium | Small | NA | Yes |
Very Fast Surge Events - ESD (IEC61000-4-2)
| Type | Speed | Accuracy | Current capability | Size on board | Lowest crowbar trigger voltage | Wearout |
|---|---|---|---|---|---|---|
| PESD (Polymer Device) | Fast | Poor | Low | Small | ~100V | Yes |
| MOV (Metal Oxide Varistor) | Fair | Poor | Medium | Small | NA | Yes |
| Silicon ESD suppressor (TVS) | Fast | Good | Medium | Small | NA | NO |
Conclusion : In summary, understanding the distinct roles and applications of various Surge Protective Device (SPD) types, including Type 1, Type 2, Type 3, and Type 4 surge protectors, is crucial for effective surge protection in diverse electrical systems. Each type serves a specific purpose, ranging from safeguarding against direct lightning strikes to protecting sensitive electronic equipment from transient voltage spikes.
Moreover the array of surge protection devices, including GDTs, TSPDs, TVS, MOVs and PESDs collectively contribute to the robust defense against transient voltage spikes in electrical systems. Each device type offers unique characteristics tailored to specific applications.