Also known as a disconnector or isolator, an electrical isolator is a certain type of equipment that is commonly used in power systems and electric devices. Its major function is to isolate two distinct parts of an instrument. Isolation is defined as the process of completely separating different parts of an instrument. The separation can be done either electrically, physically, or both.

Isolators are very important since their main purpose is safety. In case a fault happens in one part of a power supply or a circuit, then an electrical isolator will act as a switch to isolate that part from other parts of the system so that repair work can be done.

Similarly, isolators can also guarantee the safety of workers who are doing service and maintenance to the power system. Isolators are responsible for separating a particular circuit from the electricity mains and releasing any residual current to the ground.

What are Electrical Isolators?

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Isolators, commonly referred to as disconnect switches, function under no-load conditions. They are not produced either for breaking or creating current capacity. They do not include an arc quenching system inside it. Essentially, it is primarily used in the electrical system for disconnecting a certain part after experiencing a current interruption from that specific part.

They can guarantee that there is no current that exists in the circuit until everything is fine. Electrical isolators are usually placed on every side of the circuit breaker to provide separation. Ultimately, the preferred choice is an automatic type.

What is an Isolator Switch?

Generally, these switches are used for replacing or repairing circuit breakers. It serves as a switch that isolates the essential part from the circuit where the repair will be made.

Compared to CB, they do not have any current ratings since they are operated while having zero current in the circuit. Consequently, these switches can only be opened if the CB is open. Also, you cannot close the CB if the isolator is not closed.

How Does the Electrical Isolator Work?

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The way an isolator works is quite simple and there are different ways that it can be operated, such as semi-automatic, fully automatic, or manually operated.

Sometimes isolators are also used as switches which can either be opened or closed depending on its requirement. But most of the time, isolators are utilized permanently in an established position to provide isolation, for instance, in transformers, electrical transmission lines, as well as grid stations.

In transmission lines, isolators act as insulators to separate transmission towers from the conductor. In this situation, isolators are very helpful in getting rid of grounding loops, for instance, reducing the risk of unexpected paths for electric current to run towards the ground.

Particularly, isolator switches are mostly used in substations and power grids to accurately separate extremely high voltage instruments such as circuit-breakers and transformers when they are scheduled for maintenance.

Typically used isolators are not designed to halt current when a fault occurs to get rid of high voltage arcs, which are caused by the disturbance in electric conductors. When it comes to high-voltage power systems, these electrical isolators are used in combination with circuit breakers so that there is an extra layer of safety.

The first circuit breaker will be opened and will separate the circuit, afterward, the isolator will be opened. If the process is done in the reverse, then it will be done by closing the first isolator, then the circuit breaker will be closed and finally, the circuit will be reconnected.

What Are the Different Types of Electrical Isolators?

There are different kinds of isolators that you can find in the market right now. When it comes to choosing electrical isolators, it will likely depend on the application, requirement, as well as on placement in the system. Isolators that depend on their application have four types. These are the Double Break Isolator, Single Break Isolator, MCB Isolator, and Pantograph Isolator.

There is only one terminal that connects and disconnects in a single break isolator, while both terminals on every side are connected and disconnected in a double break isolator since the central terminal is flexible.

On the other hand, the pantograph isolator will connect and disconnect on both terminals at each side due to the forces of tension or stress, and typically it does not have any locking mechanism. This is popularly used in electric trains to acquire electricity directly from overhead transmission lines.

According to its name, the Miniature Circuit Breaker (MCB) is intended for low power requirements, for instance, in offices and homes. They are placed in small compact cases so they can be useful in domestic-scale wiring systems. Substations usually use horizontal double-break isolators.

Different Types of Isolators Based on their Position

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Based on the placement in the power system, there are three types of isolators. These are the transfer bus side isolator, bus side isolator, and lineside isolator. As the name suggests, the transfer bus side isolator is efficiently connected to the transfer bus. While the bus side isolator is accurately connected to the main bus. And finally, the lineside isolator is usually found at the line side of the feeder.

In an electrical system, Transfer Bus Side Isolators are used to achieve reliability. If the main bus side isolator cannot be used because of maintenance or some fault, then the transfer bus isolator will be utilized. These are used in combination with a circuit breaker.

The Bus Side Isolators are linked to the main buses through the substation. In case the bus requires repair or replacement, it must be operated. While the Lineside Isolators are linked between the line and any feeder. Feeders refer to the line that brings power from the Substation toward the distribution system.

Usually, isolators are utilized on both sides of the circuit breaker. This is done just to make sure that there is additional safety measure and protection. Take note that in a power system, there can be several sources of power in incoming and outgoing lines.

And most often, it is not sufficient to disconnect one side. Hence, having isolators on the two sides of the circuit breaker permits maintenance, repair, and replacement to be done safely.

Different Types of Isolators Based on the Line Voltage

There are three types of isolators depending on the line voltage. These are the low voltage, medium voltage, and high voltage. Low voltage isolators are intended to endure a voltage of up to 11KV. Medium voltage isolators are designed for voltages between 11KV to 66KV. While high voltage isolators work for voltages between 66KV to 330KV, additionally, they come with a high withstanding capacity.

What is the Difference Between a Circuit Breaker and an Electrical Isolator?

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You might be wondering why an isolator is utilized on both sides of the circuit breaker. Since an isolator is intended to be used when there is no load connected, it is also referred to as an off-loading device. On the other hand, a circuit breaker is recognized as an on-load device.

However, both devices have a common goal which is to disconnect a particular portion of the circuit from the remaining parts of the system. A circuit breaker is a certain type of electronic device that is comprised of solid-state components such as BJTs and MOSFETs. While an isolator is a certain type of mechanical equipment that can also be used as a switch.

So, what is the use of an isolator if it can’t even work under load, while a circuit-breaker trips instantly under fault? Well, when a circuit breaker trips because of a particular fault then there is no guarantee whether a faulty section is entirely isolated since most often circuit breakers are installed remotely. To ensure that a system is entirely isolated, an on-site mechanical and physical isolation system is utilized. Isolators have a lower capacity of withstanding voltage and current corresponding to the circuit breakers.

SEI offers RF and microwave products such as isolators, connectors, antennas, etc. For more details, just contact us at (408) 374-1031.