Once upon a time, people thought that, if he owned a magical power he could control something. At last, this thought has been fruitful with the blessings of modern science and technology. It gifts us a controlling device named switch. We can control a load or machine by switching actions. There are many kinds of switches in various structures for various purposes. Ground switch is one of them. Today, let’s discuss the ground switch.
What is ground switch?
We all hear about transformers. It’s a very familiar device in the electrical engineering field. Suppose, a transformer is connected to a three-phase system. Electrical faults may occur in a three-phase power system. A ground fault is more vital of them. The switch which protects the transformer from a three-phase ground fault is called a ground switch. Its name is assigned as “ground switch” for this kind of action.
Clear Conception about ground fault
Now. I want to express a clear conception of the ground fault. As electrical engineers, we all know there are three-phase lines in the three-phase system without any neutral. The system will be balanced if :
- There is same voltage magnitude in three phase lines
- There is 120° phase difference among three phase lines
If these conditions will not be satisfied then the system is called an unbalanced system. When an electrical fault occurs in the power system then three phases become unbalanced.
Types of electrical faults
Now, let’s come to the main point. There are two types of electrical fault. They are:
- Symmetrical faults
- Asymmetrical faults
A ground fault is one kind of asymmetrical fault. This fault may happen single line to ground or double line to ground. single line to ground fault occurs in 70-80% of cases.
Applications of ground switch
The ground switch not only protects the transformer from ground fault but also protects the three-phase induction motor from excessive bus voltage. This switch can isolate the motor or transformer body from the power system.
Voltage, breaking current and fault clearing time
- Operating voltage of this switch is 115kV-230kV
- Breaking Current is 120kA
- Fault clearing time 3 seconds
Why we use this ground switch in spite of having buchholz relay?
Confusion may arise in your mind that, why we use this switch in spite of having Buchholz relay? Actually, this switch can’t directly trip the circuit. It helps to trip the power by activating the Buchholz relay. So, it takes a few minutes to trip the power. This time is fault clearing time. If the fault clearing time will be delayed for any reason then the transformer may be damaged. So, fault clearing time is a crucial fact here.
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