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Difference between Primary Protection and Backup Protection
The main difference between primary protection and backup protection is in their functionality. Primary Protection is provided to quickly detect the fault and isolate the faulty section from the healthy part, while Backup Protection is provided to isolate the faulty and healthy parts if the primary protection fails.
In this article, we will discuss in detail about the primary and backup protections used in power systems along with the major differences between them. So, let’s begin with a basic introduction of primary and secondary protections.
What is Primary Protection?
Primary protection is defined as the initial layer of protection provided in a power system to isolate the faulty elements, if the fault occurs in the zone of relay. It is also known as main protection.
The relay used to provide primary protection is referred to as a primary relay. The primary protection has ability to detect the faults or abnormal conditions rapidly. So that it can protect the power system equipment from damages.
The following are some main characteristics of the primary protection -
- Primary protection has high speed and sensitivity.
- Primary protection is provided closer to the equipment to be protected.
- Specially designed high-speed relays, fuses, and circuit breakers are used as the main elements of primary protection.
What is Backup Protection?
Backup protection is another type of protection used in power system to safeguard the equipment. It is also known as secondary protection.
It can be defined as a type of protection which employed to detect and clear the faults when the primary protection fails to operate due to any reason. The relay used to provide backup or secondary protection is known as backup relay.
The most significant characteristic of the backup protection is that it is independent of the factors that might cause primary relays to fail.
The other main characteristics of the backup protection are listed below -
- Backup protection activates only if the primary protection fails to operate.
- The operating speed of backup protection is slower than that of the primary protection.
Types of Backup Protection
The backup protection can be classified into the following three main types -
- Remote backup protection
- Relay backup protection
- Breaker backup protection
Let us discuss about each of these types of backup protections in detail.
Remote Backup Protection
In the remote backup protection, the backup relays are located at a neighboring station. In this type of backup protection, the backup relays provide protection to the entire protection scheme, including the relay, circuit breaker, potential transformer, current transformer, and many other components.
The remote backup protection is the most widely used type of backup protection for transmission lines. It is the cheapest and simplest form of the backup protection.
Also, this type of protection does not fail due to the factors causing the failure of the primary protection, this feature makes it a most desirable form of protection.
Relay Backup Protection
This is a local backup which is provided by placing an addition protection relay. In the relay backup protection, the backup relay trips the same circuit breaker if the primary relay fails. Also, the operation of this backup relay takes place without delay.
The relay backup protection is a very costly backup protection scheme and it is mainly used in places where a remote backup protection is not possible. It is important to note that the relay backup protection devices are supplied from separate current and potential transformer.
Breaker Backup Protection
The breaker backup protection is also a type of local backup protection. This type of backup protection is mainly used for a busbar system where a number of circuit breakers are connected to it.
When a protective relay operates in response to a fault and the circuit breaker fails to trip, then the fault is considered a bus bar fault.
In case if the desired circuit breaker does not trip withing a specified time, then after a certain delay, the main relay triggers a backup relay which then trips all the circuit breakers connected to the busbar system.
This is all about the basics of primary and backup protection. Let us now understand the major differences between them using a comparison table.
Difference between Primary and Backup Protection
The following table highlights all the major differences between the primary and backup protection in power system -
| Parameter | Primary Protection | Backup Protection |
|---|---|---|
| Main function | The primary protection is meant for provide the first layer of protection against faults and abnormal conditions in the power system. | The main function of the backup protection is to provide protection against faults when the primary protection fails. |
| Also known as | Primary protection is also known as main protection. | Backup protection is also known as secondary protection. |
| Operations speed | Primary protection scheme has high speed devices to quickly detect and isolate the fault. | The protective devices used in the backup protection have relatively slower speed than that are used in primary protection. |
| Operates when | Primary protection operates when a fault or any abnormal condition occurs in the system. | Backup protection operates only when the primary protection fails to operate, otherwise it does not operate. |
| Sensitivity | Primary protection has more sensitive in terms of detecting and responding to abnormal or fault conditions. | Backup protection is made to be less sensitive than primary protection. So that it does not cause any unwanted tripping. |
| Installation location | Primary protection is installed close to the equipment to be protected. | Backup protection is generally installed at a remote location from the primary protection. |
| Protection scope | Primary protection has a narrower scope of protection as it is intended to protect a certain section of the system. | The scope of protection of backup protection is wider than primary protection. Thus, it can protect a larger section of the system. |
| Priority | Primary protection has high priority in detecting and clearing faults. | Backup protection has lower priority than primary protection. Thus, it acts as secondary layer of protection. |
| Cost | The cost of primary protection scheme is higher due to high sensitive, accuracy, and speed. | Backup protection scheme is relatively less costly than primary protection. |
Conclusion
From the above discussion, we can conclude that the primary protection acts as the main protective layer in the power system while the backup protection acts as the secondary layer of protection.
The backup protection is so designed that it operates only when the primary protection fails to operate.
FAQs Related to Primary and Backup Protection
The following section of the article is meant for answering some commonly asked questions related to primary and backup protection.
1. What is a primary protection device?
A protective equipment used in power system to sense and clear a fault or abnormal condition by acting as a first layer of protection is referred to as a primary protection device. A primary protection device has high sensitivity, high speed of operation, and high accuracy.
2. What is primary and secondary backup protection?
Primary protection is defined as a type of power system protection that detects any fault or abnormal condition in the system very firstly. Whereas, the secondary or backup protection is defined as a type of protection that protects the system when the primary protection fails to operate.
3. What is the difference between primary and secondary protection?
Primary protection quickly responds when a fault occurs in the power system while the secondary protection operates only when the primary protection fails to operate.
4. What are the methods of backup protection?
As we know, backup protection is the secondary layer of protection that operates when primary protection fails to operate. The following are the most widely used methods of backup protection in power systems :
- Remote backup protection
- Relay backup protection
- Breaker backup protection
These backup protection methods are explained above in detail.
5. What is an example of secondary protection?
In electrical power systems, the backup distance protection is a common example of backup protection. In the backup distance protection, a distance relay is installed in the protection system remotely and provides the secondary protection in case when the primary protection scheme fails to operate.
6. What is backup relay?
A protection relay which has less sensitivity and used to protect an electrical system when the main relay fails to detect the fault is referred to as a backup relay.
7. Where is backup protection used?
Backup protection is commonly used in power systems to provide protection against faults when the main protection scheme fails to operate.
Backup protection is generally used to safeguard transmission lines, distribution feeders, electrical transformers, alternators, busbars, and other sensitive equipment.
Backup protection is mainly used where ensured and reliable safety against protection is essential.
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