What is Protection system?

A system that protects electrical systems from faults by isolating the problematic part from the remainder of the system, preventing power from being cut from healthy elements, improving system dependability and efficiency is the protection system. Protection devices are the equipment that are utilized to implement the protection system.

Protection devices serve their purpose by isolating or breaking the circuit in which the faults have occurred from the rest of the system, allowing it to function without interruption. The purpose of a protection system is not only to avoid faults but also the protective devices are used to do maintenance of the main electrical machines when needed.

Purpose of Protection System

• The entire system electrical system may be vulnerable to catastrophic damage and degeneration, putting people, property, and other equipment in jeopardy. Protection devices are used to reduce the likelihood of failure-related damage.
• Protection devices limit the failure to the defective equipment or location, reducing the likelihood of an electrical outage and by using various sensing equipment like relays.
• Different protection techniques were created to continuously monitor the system and maintain it secure by just disconnecting the components that were faulty and keeping as much of the grid as operational.

Protection Zone

A protection zone is a defined area that is protected by each protection scheme. Each part of electricity equipment is surrounded by a protection zone. Only the circuit breaker in that zone trips when a fault occurs in any of the zones. As a result, only the problematic component is unplugged, leaving the remainder of the system unaffected.

The six types of protection zones listed below can be implemented in a system.

• Lines (transmission, sub-transmission, and distribution)
• Utilization equipment (motors, static loads, or other)
• Capacitor or reactor banks (when separately protected)
• Generators and generator–transformer units
• Transformers
• Buses

Protection Devices and Equipment

There are various types of Protection devices used in protection System as following.

• Relay
• Circuit Breaker
• Fuse
• Instrument Transformer
• Surge protection device etc.

Types of Protection System

• Overcurrent Protection System
• Differential Protection System
• Distance Protection System
• Directional Protection System

Overcurrent Protection System

The figure shows the schematic arrangement of overcurrent Protection System. A fault effect can be defined as a sudden increase in current. Because the amount of the current can be used as a signal for the presence of a problem, over-current protection can be considered the most evident concept of protection. However, the amplitude of the fault current is determined by the fault type and source impedance.

The source impedance varies depending on the number of producing units in use at any one time and changes over time. As a result, the set point for distinguishing fault current magnitude from normal current, as well as the over-current protection operating period, varies from fault to fault and over the time.

There are Three types of Overcurrent Relay:

1. Instantaneous Overcurrent Relay- There is no deliberate temporal delay when the term "instantaneous" is used. An instantaneous relay's operating time is measured in milliseconds. This type of relay simply has a pick-up setting and no time setting.
2. Definite Time Overcurrent Relay- A definite time overcurrent relay is an adjustable relay in which the trip can be adjusted so that the relay trips just after some intentional time delay as soon as it picks up. Thus, both the time and the pickup can be adjusted.
3. Inverse Time Overcurrent Relay- The necessity that the more severe a problem is, the faster it should be cleared to avoid damage to the apparatus is reflected in the inverse time characteristic. Inverse time features have been standardized as follows:

• OC relay with inverse definite minimum time (IDMT).
• OC relay with a very inverted time.
• OC relay with extreme inverse time.

Differential Protection System

Figure shows the schematic arrangement of Differential Protection of Transformer. Another well-known and appealing concept is differential protection. It is based on the assumption that the current leaving and entering a protected section must be equal. A fault is indicated by any discrepancy between the two endpoints of a single segment. As a result, compare the phase or magnitude of the two currents, or both.

If both ends of an instrument are physically close to each other, this type of fault detection is quite popular. It should stay constant if there is an exterior or through-fault outside of its protection zone, and only trip if the fault is internal. The ability of this protection to discern between internal and exterior defects define its stability. However, applying this approach to a transmission line is impractical due to the enormous distance between the ends and the inability to equalize information.

Distance Protection System

Figure shows the basic principle of Distance Protection System. The voltage and current at the same end are linked in a distance protection scheme. The impedance between the protection site and the fault spot is calculated using this approach. It then compares it to a pre-determined value before making a trip decision.

Due to the simple series model, the impedance of a transmission line can be directly proportional to the distance of a defect in a line, which aids in fault site identification. Distance protection, sometimes known as under-impedance protection, is a sort of protection. In practice, the term "under" is no longer used, and it is now simply referred to as "impedance protection."

Directional Protection System

In a double-ended feed system, parallel lines, or a ring main system, as the fault occurs it is supplied from the both the sides. It is important for the protection that it must be sensitive to the fault power flow direction in order to be selective. This is an attribute of a directional protection strategy.

Other circumstances may necessitate the employment of a directed scheme to supervise overcurrent schemes. Because directional protection units are more expensive and require the use of power transformers, they should only be utilized when absolutely necessary.

Advantages of Protection System

• Improves the stability and safety of the power system.
• Enhances the quality of power.
• Extends the life of power system assets by reducing wear.
• Reduces the likelihood of internal transformer and generator malfunctions.
• Improves the safety of public and utility workers.
• Lower the risk of property damage.
• It Provides the most precise fault location in real time and is unaffected by the issues that plague impedance-based fault location methods.
• Allows real-time adaptive auto reclosing cancel logic based on fault location.

Context and Applications

This topic has applications in different places such as:

• Protection of Generators and generator–transformer units.
• Protection of Transformers.
• Protection of Buses.
• Protection of Lines transmission, sub-transmission, and distribution.
• Protection of motors, static loads, or other.
• Protection of Capacitor or reactor banks.

In each of the expert exams for undergraduate and graduate publications, this topic is huge and is mainly taught in:

• Bachelor of Technology in Electrical Engineering.
• Master of Technology in Electrical Engineering.

Related Concepts

• Protection Devices
• Electrical Power Protection System
• Fire Protection System
• Protective Relays

Common Mistakes

• Not carrying proper gloves while working.
• Not wearing personal protective equipment.
• Trusting an unskilled person for safety.
• Not paying attention to the safety training.
• Using defective test equipment to troubleshoot.
• Not carrying out the equipment service at time..
• Working on energized systems or equipment.

Practice Problems

1. What are the protective devices are used in Protection system?

A. Relay

B. Circuit Breaker

C. Fuse

D. Instrument Transformer

E. All of the Above

Answer: E

Explanation: The protective devices used in Protection system are relay, circuit breaker, fuse, instrument transformer, sdurge protection device etc.

2. What are types of Protection System?

A. Overcurrent Protection System

B. Differential Protection System

C. Distance Protection System

D. Directional Protection System

E. All of the above

Answer: E

Explanation: Types of Protection System are Overcurrent Protection System, Differential Protection System, Distance Protection System and Directional Protection System.

3. What are the types of Overcurrent Protection Relay?

A. Instantaneous Overcurrent Relay

B. Definite Time Overcurrent Relay

C. Inverse Time Overcurrent Relay

D. All of the above

Answer: D

Explanation: The types of Overcurrent Protection Relay are Instantaneous Overcurrent Relay, Definite Time Overcurrent Relay and Inverse Time Overcurrent Relay.

4. What are the features of Inverse Time Overcurrent Relay?

A. OC relay with inverse definite minimum time (IDMT).

B. OC relay with a very inverted time.

C. OC relay with extreme inverse time.

D. All of the above

Answer: D

Explanation: The features of Inverse Time Overcurrent Relay are OC relay with inverse definite minimum time (IDMT), OC relay with a very inverted time, OC relay with extreme inverse time.

5. Distance protection is also known as.............

A. Overcurrent Protection System

B. Differential Protection System

C. Impedance Protection System

D. Directional Protection System

Answer: C

Explanation: Distance protection is also known as Impedance Protection System.