In this topic, we are going to learn about a topic called “What is Directional Relay?“, and about its construction, working principles, advantages, and applications as well. Welcome to Poly Notes Hub, a leading destination for diploma engineering notes for polytechnic students.
Author Name: Arun Paul.
What is Directional Relay?
A Directional Relay in electrical engineering is a protective device used in power systems to identify the direction of fault currents and isolate the damaged segment of the system while keeping the remainder of the network functional.
These relays are critical for guaranteeing the safety and reliability of electrical systems because they immediately identify and isolate issues. They function by constantly monitoring the flow of current in the system and activating when it exceeds predetermined thresholds or flows in the opposite direction of normal functioning.
Construction of Directional Relay
Below shows the Directional Relay Diagram and explain each and every section or ports of it:
- Potential Transformer (PT) Section: This portion includes a potential transformer, which reduces the voltage of the power system to a level that the relay can process. The potential transformer sends a proportionate voltage signal to the relay dependent on the voltage in the power system.
- Current Transformer (CT) Section: This part has one or more current transformers that reduce the current flowing through the power supply to a level suitable for the relay to manage. The current transformers send a proportional current signal to the relay based on the current flow in the system.
- Potential Coil: The potential coil, also called the voltage coil, is a winding inside the relay that receives the voltage signal from the potential transformer. It is normally linked in parallel with the system and serves as a reference for determining the direction of power flow.
- Current Coil: The current coil, also known as the directional coil, receives current signals from the current transformers. It is normally connected in series with the system, generating a magnetic field proportionate to the current running through it.
- To Trip Circuit Section: This section describes the mechanism for tripping the circuit breaker when a fault is identified. The directional relay identifies whether the fault is in the forward or backward direction by comparing the voltage and current signals received from the potential and current coils. If a failure is identified in the forward direction, the relay transmits a trip signal to the circuit breaker, which isolates the faulty component of the system.
Directional Relay Working Principle
The relay constantly monitors the current and voltage signals from the CTs and PTs, respectively. These transformers reduce the current and voltage levels to reasonable amounts for the relay to handle. The relay compares the phase angle of the current and voltage signals. By examining the phase connection between current and voltage, the relay can determine the direction of power flow in the electrical circuit.
Based on specified parameters and logic, the relay determines whether the current flow is in the intended (ahead) or opposing (reverse) direction. If the current flows in the forward direction according to the established values, it indicates normal operation. However, if the current flows in the opposite direction or exceeds predefined thresholds, signaling a failure, the relay takes preventative action.
When the directional relay detects a fault or abnormal state, it sends a trip signal to the circuit breaker connected with the faulty component of the system. This step separates the problematic portion from the remainder of the system, preventing equipment damage while also ensuring the electrical network’s stability and safety.
Advantages of Directional Relay
Below we listed some merits of directional relay –
- Timely disconnecting from abnormal currents prevents equipment damage.
- The decreased likelihood of electrical mishaps and fires improves overall safety.
- Reduced unnecessary tripping of circuit breakers improves system efficiency.
- Adjustable settings enable customisation to meet unique system needs.
Applications of Directional Relay
Below we listed some important uses of directional relay –
- Installed to protect transformers, circuit breakers, and other substation equipment from faults, hence ensuring transmission system reliability.
- Used to protect electrical equipment and humans in mines where electrical risks are common.
- Employed to protect important machinery and equipment from electrical problems, reducing downtime and production losses.