Circuit, Construction & Working principle Valve-type lightning arrestor

I think you probably came across the question "What are Valve-Type Lightning Arresters?"

Then read the content fully for more information.

First, understand What is lightning arrestor?

Lightning arrestor- (Protective device's) Function is to divert surge voltage into the earth. 

Now, the topic will become easier to understand.

The valve-type lightning arrester is also a protection device used to protect high-voltage rated equipment (above 33KV) against surge voltage, high transient voltage, and lightning strikes. High voltage equipment such as overhead power lines and the transformer needs efficient protection against electrical faults. 

The operating time of the valve-type lightning arrester is less than one second (1s). The impulse ratio of a valve type arrestor lies in the range of unity. Operating time also satisfies the fundamental requirement of a protective device.

The impulse ratio is defined as the spark voltage to the power frequency voltage.

Spark voltage - voltage produced due to breakdown voltage in the spark gap. 

Power frequency voltage: Voltage at the rated frequency with respect to time. 

Circuit of  valve type lightning arrestor

Construction of Valve type lightning arrester

The construction and installation of valve-type lightning arresters play an important role in the protection of high voltage equipment. Obviously, engineers should connect the valve-type lightning arrestor in such a way that can protect the high voltage equipment such as the transformer that is being connected to the transmission line or even to protect the transmission line. The factors such as height, size, the number of spark gaps, and the number of non-linear resistor discs are determined by the voltage rating.

There are five important components in a valve-type lightning arrestor.

1. Current terminals
2. Spark gap with grading resistor
3. Non-linear resistor
4. Porcelain housing.

Valve-type lightning arrestor embodies complete enclosure in a porcelain insulating material. This acts as insulating housing and provides mechanical strength. This protective system consists of the current terminal to which incoming and outgoing circuits are connected. 

Valve type lightning arresters are fitted with a spark gap stack with grading resistors consisting of various conducting electrodes which are held at a distance by an insulating medium such as air. These spark gaps are connected in series to the non-linear resistor discs.

Finally, the Outgoing current terminals are located at the end.  

Functions of Major parts

The four important components in valve-type lightning arresters can be classified into Interior Components and Exterior components.

Exterior components are outer parts of the lightning arrestor

• Porcelain Housing, and
• Current terminals

Interior components of valve type LA

The interior components of the valve type arrestor are sensitive to surge voltage. Let's look briefly at this topic.

Interior components are inner parts of the lightning arrestor

• Non-linear resistor, and
• Spark gap with grading resistor

Non-Linear Resistors Disc in valve type arrestor

Basically, there are two types of resistors Linear Resistor and Non-Linear resistor. Non-Linear resistors are extensively used in valve-type lightning arresters because of their operating characteristics.

Non-linear resistors are made up of semiconducting components such as silicon carbide (thyrite element, or metros element). Valve-type lightning arresters are also known as thyrite arresters or non-linear arresters.

Non-linear resistors do not depend upon Ohm's Law as well as it depends upon applied voltage and temperature. In simple Non-linear resistors is a voltage-dependent resistor.

Function

Non-linear resistors offer high reactance under normal operating voltage. That means the Lightning arrester does not divert the normal operating voltage.

In this case, the non-linear resistors offer very low resistance when break-down voltage flows. It means Valve-type arresters operate only at the time of the electrical fault.

Spark Gap in valve type arrester

The gap between two or more conducting electrodes is called a spark gap. 

The grading resistors are helpful in the process of linearizing the breakdown voltage. 

Function

Spark gaps are designed to produce a spark or arc in between the gap during the flow of break down voltage.

Exterior components of valve type LA

Exterior components are the outermost parts of the Valve type arrester. They are

Porcelain Housing for Valve type LA

The housing of valve type LA protects the interior components against abnormal conditions of the environment. The porcelain housing provides mechanical strength to the lightning arrester.

The housing of valve type LA is made up of insulating material named "porcelain".  The porcelain has the property of high resistivity, so it does not allow the high voltage to pass on the body of the device. 

Function

This increases the strength of the arrester and protects the interior parts against bad weather conditions. The enclosure will do not allow the breakdown voltage to come outside the atmosphere.

Current terminal for valve type LA

The current terminal is the primary part of valve type LA. The terminal of the lightning arresters is designed suitably to connect it with an equipment circuit that needs protection.

Current terminals are made up of highly conductive material such as copper, or aluminum.

Function

Current terminals are nothing but connectors. Current terminals are simply connectors. Surge voltage can pass through the incoming and outgoing current terminals.

How the Valve type arrester work?

Valve-type lightning diverts electrical faults caused by surge voltage, breakdown voltage, into the earth. But How? 

Keep in mind

At Normal operating voltage, the valve-type arrestor will not operate. Because spark gap and non-linear resistors offer very high reactance to the normal operating voltage.

But whenever surge voltage occurs, the incoming current terminals of valve type lightning arrester receive a surge voltage from the fault circuit and sent it to the spark gap. Once the surge voltage attains a break-down voltage, the spark gap produces a spark or arc in between the gaps. The grading resistors of the spark gap receive breakdown voltage and linearize the breakdown voltage to the non-linear resistor discs. 

Finally, Non-linear resistors offer very low resistance to this high voltage surge and efficiently diverts this surge voltage to the outgoing current terminals, where it picks up the high surge voltage and drains it to the earth.

As a result, a valve-type lightning arrester diverts the surge voltage into the earth thus preventing the failure of high voltage equipment such as power transformers, power lines, or an electrical motor.

Advantage of valve type lightning arrester

1. This lightning arrester operates only at the time of high surge voltage. This will not divert the normal operating voltage.
2. This has the ability to protect high-voltage-rated equipment (up to 220 Kv) in an efficient manner.
3. It always maintains the impulse ratio at unity
4. This valve-type arrester takes only less time to operate which is less than 1 sec.

Dis-advantage of Valve type lightning arrester

1. This type of lightning arrestor does not suitable for very steep fronted waveforms.
2. It can be used only in tight enclosures such as porcelain housing because it going to use spark gap constraints for operation.

Maintenance of valve type lightning arrestor

• Periodically check the value of earth resistance. It should be below 2 ohms.
• Clean the dust particles from the porcelain housing or enclosure.
• De-energize the transmission line while servicing.

Conclusion

A valve-type lightning arrester is the best protective device for protecting high voltage equipment from surge voltage.

This valve-type arrestor just going to divert the surge voltage into the earth. This arrestor is best suitable for a power station rated 220KV, as well as a substation, rated 66KV. 

With the unity impulse ratio and offers protection for high-voltage equipment, engineers can't afford to ignore it.

This lightning arrestor also meets the fundamental requirements of the protective device.

Did you found anything interesting in valve-type lightning arresters?

Is it advisable to use valve-type lightning arrester in homes?😅just fun

To know about various types of lightning arresters click here.