What is Transition or Contact Resistance? Example

In electrical contact theory, the term 'Transition Resistance' is a very important factor. Transition Resistance is also known as electrical contact resistance(ECR). In this article, we are going to discuss the basic concept of transition resistance. Also, we will discuss the cause and effects of transition resistance, how it forms, and how can we minimize it. To increase the reliability of the electrical and electronic conduction, transformation, and conversion we should increase the efficiency of electrical or electronic contacts where contact resistance or transition resistance is a very important factor.

What is Transition Resistance?

When two electrical conductors are connected temporarily or permanently then resistance is formed at the transition point between the two conductors. When two conductors are joined, that jointing point does not act as an ideal conductor, there must be some resistance. This not only indicates the contact between two conductors, but it may also be the contact between two metals carrying electricity.

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Causes of Transition Resistance Formation

The main reason for forming transition resistance is the limited areas of true contact at an interface and the presence of a resistive surface or oxide layers. It depends upon various factors such as Contact Size, type of conductor, or metal, contact area, thermal abstract, chemical phenomena, etc. Other reasons for the forming of contact or transition resistance are contaminated contacts, loose connections, Tension on the joint area, corrosion, etc.

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Effects of Contact Resistance

Transition or contact resistance affects the current conduction and distortion. It is also an important reason for voltage drop. 

Important Factors Transition Resistance Depends

There are some important factors that must be considered in which transition resistance or contact resistance depends.

1. Contact Size

Transition resistance is also called electrical contact resistance so it must depend upon the size of the contacts. Naturally, when the size of the contacts is big transition resistance will be more but electrical conduction also is more, so when the contact size is big transition resistance can be assumed as low with respect to the contact point and conduction.

2. Chemical Phenomena

Any chemical reaction or layer in the contact area can affect the proper contact or electricity conduction. The effect of chemicals with contact resistance can be observed in SF6, oil circuit breakers.

3. Dust in the Contact Area

Dust particles in the contact area also can increase the transition or contact resistance.

4. Electrical Quantities

Electrical quantities such as current, voltage, and frequency also can affect the transition or contact resistance.

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Transition Resistance Example

Now let's go to know where we can see transition resistance. As we know transition resistance forms in electrical contacts. Some examples are autotransformers, Tap Changer on Transformer, Pantograph in traction systems, electrical plugs and sockets, circuit breakers, relays, contactors, etc.

If you see the nameplate of the On Load Tap Changer(OLTC) then you can see there is mentioned about the value of transition resistance. Transition resistance in OLTC is a very important factor because it affects the voltage and current conduction.

Another example of transition resistance is electric spot welding. In electric spot welding, we can see the effects of transition or contact resistance.

Everywhere we can see transition resistance where electrical contact is available but in some cases, we need to test and minimize it. 

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Transition or Contact Resistance Test

Nowadays, in every industry, company, and power system electrical contact resistance test is performed. It is performed because, from the contact resistance test, we can easily identify any loose connection, voltage drop, and the efficiency of the electrical panels, circuit breakers, busbar, etc.

Contact resistance tests must be performed periodically to find out any leakage or loose contacts in electrical panels, conductors, and connections that may cause the sparking or even fire.

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