3 Basic Clearance Guidelines You Need to Consider for Air Core Reactors

Dry type air core reactors are the devices that are usually installed at both transmission and distribution systems. Their installation for these systems is done for several reasons, such as fault current limiting, power flow control, reactive compensation, and reducing harmonics. Their size can vary from small devices with weight of tens or hundreds of pounds with power ratings less than 100kvar to very large devices with weight of 100,000 lbs or more with power ratings in the range of 600 Mvar.

Though these devices have been in existence for decades around the world, there is still a lot of confusion and misunderstanding when it comes to dealing with the effects of stray magnetic fields. 

To attain the much-needed clarity, here, you will learn the different clearance guidelines required to follow while installing air core reactors. 

Before directly plunging on to these clearances, it is better to be well familiar with the concept of magnetic fields of air core reactors. 

As the name implies, air core reactors don’t have a magnetic core to preserve the magnetic field. Consequently, the magnetic field strays in and around the reactor. 

The strength of this stray field is based on the power rating of the reactor. The general rule of thumb is the higher the rating, the higher the strength of the stray field. 

The stray field advances to not only the reactor components, such as windings and corona electrodes but also to the adjacent parts, such as terminals, bus supports, and connectors. In certain conditions, this stray field induces eddy currents and associated losses in electrically conductive parts that fall within its range. 

There are three basic installation clearance guidelines for air core reactors. 

• Electrical

• Ventilation

• Magnetic

Since air core reactors have exposed live parts at its outer surface, the installer should follow electrical clearance from the surface of the reactor to the nearby ground surfaces, to the surface of other reactors, and/or other live parts in adjacent circuits or phases. 

The air core reactors that are mounted in a way that the cooling ducts are oriented in a vertical fashion, proper provisions should be made for the unimpeded entry and exit of cooling air at the top and bottom of the cooling ducts. Most of the time, ventilation clearance are fewer than the magnetic clearance requirements and therefore, it is usually not a decisive factor in the installation arrangement. 

Magnetic clearance requirements are needed to follow because of the interaction of stray magnetic fields with nearby conductive parts and the resulting current that might be induced in them. There are two types of induced currents:

• Eddy currents: induced in nearby conductive components that give rise to minimum clearance required for metallic parts that don’t form closed loops. These clearances are typically known as MC1 Clearance.

• Circulating currents: caused by the coil flux that gives rise to a closed electrically conducting loops formed by concrete reinforcement rebar, nearby fencing, etc. These clearances are referred to as MC2 Clearance. 

When you procure air core reactors from one of the recognized or biggest air core reactors manufacturers, you will also be provided with a manual that contains manufacturer’s instructions for installation and precautions. It is also highly recommended to consider this manual to ensure proper installation.

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