Discover Surge Protectors and Their Types!

How familiar are you with surge protectors? In this article, we, the Electrosheil team, intend to discuss surge protectors and their various types with you. Stay with us for valuable insights.

First of all, let’s delve into the definition of a surge protector. Here, you can read about life-saving switches. What is a surge protector?

A surge protector is a safety device used to guide transient voltage waves to the ground and prevent them from entering power transmission and distribution stations. In the continuation of this educational article, we will acquaint ourselves with surge protectors and their types

This device is typically installed at the end of transmission lines and at the input of transformers. The breakdown voltage of a surge protector must be lower than the breakdown voltage of the insulation layer of the equipment installed in the substation.

Surge Protectors and Their Types

1) Rod Surge Protector

2) Air-Gap Surge Protector

3) Non-Linear Resistance Surge Protector

4) Non-Air-Gap Surge Protector

5) Capacitor Surge Protector

6) Fuse Surge Protector

Now, it’s time to explain each of these surge protectors for you.

Rod Surge Protector

Another type of surge protector and its various forms are rod surge protectors, which are among the simplest and most economical surge protectors and the first ones developed. Despite their age, these rod surge protectors still have many applications today.

This surge protector consists of two sharp-tip rods, one installed in the live part and the other installed under the insulator or the body, connecting to the ground. The distance between the two tips is adjustable according to the voltage, conditions, and time of applying voltage to the system.

Adjusting this distance in a way that maximizes system stability against the maximum voltage and only discharges electrically during high-voltage surges is crucial. However, the adjustment of surge protectors is far from ideal, and it can be said that it operates in a voltage band, and an accurate performance characteristic cannot be envisioned for it within that voltage range.            

Air-Gap Surge Protector

Another type of surge protector used in high-voltage substations is the branch-type surge protector. These surge protectors are known as spark gap (air-gap) surge protectors and have widespread applications in connecting the grounding grid to the conductors or around the bushings of distribution transformers.

As we know, surge protectors must behave like an open switch against the nominal voltage of the network and, like a closed switch, against voltages exceeding the nominal network voltage.

In air-gap surge protectors, as the voltage increases, an arc is established between the branches, and the surge energy is transferred to the ground. This action prevents the equipment from being damaged.

Applications of Air-Gap Surge Protectors

Currently, this type of surge protectors is only used in specific cases, including:

1) Above the bushings of transformers (to protect transformer windings)

2) In high-pressure transmission lines designed in a loop shape, playing the roles of both a surge protector and a corona ring.

Non-Linear Resistance Surge Protector

Among the various types of surge protectors, the present type is formed by one or more capacitors in series along with one or more non-linear resistors. These capacitors, primarily designed in the form of air gaps, prevent the flow of electric current into the surge protector under normal system conditions.

In the event of a voltage increase in the system due to certain reasons, the air gaps between the capacitors ionize, allowing electric current to pass through. The passage of current through the non-linear resistor determines the voltage drop and the voltage across the surge protector.

The air gaps in the surge protector must be designed to withstand the maximum operating voltage of the system. If the voltage increases and a short circuit occurs, after normal conditions are restored, the surge protector can interrupt the current flow, a task performed by non-linear resistors.

A combination of capacitors and non-linear resistors is placed inside an insulator made of insulating materials. The choice of multiple capacitors instead of a single capacitor is made to increase the surge protector’s resilience against reverse voltages.

To ensure a uniform voltage distribution across parallel capacitors, a series of capacitors and resistors are placed in parallel at both ends of the air gaps. This process is known as voltage grading.

Corona Phenomenon

As we know, the corona phenomenon refers to incomplete electrical discharge in a non-uniform field. This phenomenon is particularly observed in high-voltage substations, especially at the points where the conductor is connected to the equipment. Therefore, to remedy this flaw, it is necessary to make the field uniform in these areas to reduce the detrimental effects of corona.

The surge protectors used in substations today are of the ZNO type, where inside them, discs made of zinc oxide (ZNO) are placed, and the number of these discs varies depending on the network voltage level.

Another point is that these surge protectors must act as a non-linear resistor. That is, they should have a high impedance against the nominal voltage of the network and a low impedance against voltages higher than the nominal network voltage to discharge the corona.

Therefore, the zinc oxide discs used in modern surge protectors effectively play the role of a non-linear resistor and have very low leakage current (under normal network conditions). Thus, the voltage is divided across these discs.

Now, if the field is non-uniform, the voltage division across the discs will certainly not be uniform. In this case, one disc, especially the higher discs, tolerates higher voltages and is more prone to damage, leading to improper surge protector performance.

Therefore, if we can make the field uniform (or approach uniformity), the voltage distribution among the discs will take a more balanced form. This action undoubtedly increases the lifespan of the discs and enhances the performance of surge protectors. For this purpose, a device called “coronaguard” or “corona ring” is used; it essentially directs the field towards uniformity and brings the voltage distribution across the discs closer to a balanced state.

Discover Surge Protectors and Their Types!

Non-Air-Gap Surge Protector

A type of non-air-gap surge protector used today has its series capacitors made from zinc oxide components. These components are produced in the form of discs with various sizes and are placed alongside each other. These surge protectors are simpler in construction and have a smaller volume.

These surge protectors have the ability to operate at lower voltages. Therefore, the protective voltage level of the equipment can be reduced, resulting in cost savings. Additionally, the leakage current in these types of surge protectors is minimal or nearly zero.

Capacitor Surge Protector

For low-pressure voltages, a capacitor-type surge protector is used, which stores the energy generated from the voltage wave in the capacitor.

Fuse Surge Protector

This type of surge protector is designed to burn out in the face of overvoltage, which leads to the passage of a high current. The spark inside it is extinguished by gas or non-flammable materials inside it and is mostly used as secondary protection.

Installation Location of Surge Protectors

Surge protectors should be installed at the entrance of transformer substations before any equipment and as close to them as possible. In addition to the surge protector installed at the entrance of transformer substations, a separate surge protector is also installed before critical equipment such as power transformers. Usually, a discharge counter is placed in the path of the surge protector to the ground, which can record the number of discharges of transient voltage waves on the surge protector.

We appreciate your accompanying us until the end of the article on surge protectors and their types. To procure industrial electrical equipment, you can get in touch with our experts.

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