Primary & Backup Protection

Primary Protection

Primary protection, also known as main protection, serves as the first - line of defense. It is designed to rapidly and selectively clear faults within the boundaries of the specific circuit section or element it safeguards. Each section of an electrical installation is equipped with primary protection. This protection mechanism is engineered to respond promptly to abnormal conditions, ensuring that the affected area is isolated as quickly as possible to minimize damage and disruption to the overall electrical system.

Backup Protection

Backup protection functions as a safeguard for when the primary protection malfunctions or needs to be taken out of service for repairs. It is an essential component for the seamless operation of the electrical system, acting as the second line of defense. In the event that the primary protection fails to function correctly, the backup protection steps in to isolate the faulty section of the system. Failures of primary protection can occur due to issues such as a malfunction in the DC supply circuit, problems with the current or voltage supply to the relay circuit, failures within the relay protective circuit, or faults in the circuit breaker.

Backup protection can be implemented in two ways. It can be configured on the same circuit breaker that the primary protection would normally operate to open, or it can be installed in a different circuit breaker. Backup protection is particularly crucial in scenarios where the main protection of an adjacent circuit cannot effectively back up the main protection of a given circuit. In some cases, for the sake of simplicity, backup protection may have relatively low sensitivity and is designed to operate within a limited backup zone.

Example: Consider a scenario where remote backup protection is provided by a small time - graded relay, as depicted in the figure below. Suppose a fault F occurs on relay R4. Relay R4 then triggers the circuit breaker at point D to isolate the faulty section. However, if the circuit breaker at D fails to operate, the faulty section will be isolated by the activation of relay R3 at point C.

The application of backup protection hinges on both economic and technical considerations. Oftentimes, due to economic factors, backup protection does not operate as swiftly as primary protection.

Related Terms:

• Difference Between Primary and Secondary Memory: This pertains to the distinctions in characteristics, functions, and performance between the main memory that the computer's central processing unit can access directly (primary memory) and the storage that offers supplementary and long - term data retention (secondary memory).

• Bus - Bar Protection: Involves safeguarding the bus - bars, which are crucial conductors in an electrical system that distribute electrical power. Protection mechanisms are put in place to detect and isolate faults occurring on the bus - bars, preventing widespread power outages.

• Feeder Protection: Focuses on protecting the feeders, which are the electrical conductors that carry power from the source (such as a substation) to the consumers or other parts of the distribution network. Protective devices are installed to identify and deal with faults in the feeders.

• Differential Protection of a Transformer: A protection scheme for transformers that operates by comparing the input and output currents of the transformer. Any significant difference between these currents, which may indicate a fault within the transformer, will trigger the protection to isolate the transformer.

• Differential Protection of a Generator: Similar to transformer differential protection, this is a protective measure for generators. It monitors and compares the currents entering and leaving the generator. If there is an abnormal differential current, it implies a fault in the generator, and the protection acts to disconnect the generator from the system.