Do you know how the surge protection device (DPS) works? The fast cutting effect that DPS provides ensures protection for electrical and electronic equipment. In this article, the World of Electrical explains what a DPS is and how the DPS is inside, in addition to showing how it works in practice.
DPS – Surge Protection Device
Many electricians do not know how a DPS really works, how DPS is inside and why it manages to drain a surge of electrical voltage to the ground, that is what we are going to show now.
To demonstrate what a DPS looks like inside and how the DPS actually works, we will use a DPS model that can be separated from the fixing base, as if it were a cartridge. This greatly facilitates the exchange and maintenance of DPS in switchboards.
To remove the cartridge, just pull it out of the fixing base, as it is in this cartridge that the DPS is basically located.
Now that we have removed the cartridge from the fixing base, let’s open the cartridge. Inside the cartridge we have only one electrical component, which is the varistor, the blue part that occupies practically all the space inside the DPS.
Varistors can be classified in a category of “special resistors”. The varistor is actually a VDR (voltage-dependent resistor), that is, the varistor is a voltage-dependent resistor. Explaining its operation in a very simple way, the varistor is a resistor that has a resistance modified by the voltage.
Varistors have an extremely high resistance under “normal” conditions, (practically infinite). However, this resistance drops sharply to values close to zero ohms in less than 25 nanoseconds, when subjected to a higher voltage peak than specified for each varistor.
Knowing what a varistor is made it easier to understand how DPS works. The in the switchboard in parallel with the electrical installation. The DPS must always be installed before all other partial components and after a protective device, which can be the general circuit breaker. One of the terminals or poles of the DPS is connected to the phases or neutral of the installation, and the output terminals of the DPS are connected to the grounding system.
Under normal operating conditions of the installation and the electrical network, the voltage is always close to the electrical voltage specified for the varistor, the resistance of the DPS is extremely high and is able to block the flow of electrical current to the ground.
When a voltage surge occurs at the installation, the DPS resistance goes to near zero, providing a safe path for this surge to be diverted to ground. The outbreak may be a lightning strike in the electrical network, a voltage spike caused by the connection of a large load as a motor, or due to anomalies in the electrical network
The other part of the DPS is a mechanical mechanism that notifies you when the varistor inside the DPS is burned out. One of the terminals of the varistor is connected to the pole by a copper filament and a special solder that works as a fuse.
When the varistor burns, its temperature increases and the solder melts. The red part that is held by the weld and pressurized by a spring is loose, at this moment the spring pushes the red part upwards.
There is a hole in the body of the DPS and after the spring pushes the red part, the part is out of the hole, indicating that the DPS is no longer working.
DPS’s are designed to protect against specific maximum currents from electrical surges. These currents are selected according to the characteristics of the circuit in which the DPS will be installed and the location of the installation.
For example, what is the average amount of lightning that falls in the region of the installation per year. Whether or not the installation has a surge arrestor system and other characteristics. As it is a safety and protection device, the DPS must meet the standards, such as the IEC 61643-1 standard and the EN 61643-11 standard.