Relay control and protection guides

Protection Relays

The relay is a well known and widely used component. Applications range from classic panel built control systems to modern interfaces between control microprocessors and their power circuits or any application where reliable galvanic separation is required between different circuits. Altough considered to be a relatively simple component, the electromechanical relay and its technology is complex and often misunderstood.

History of relay

The earliest electrical relays were developed in the 1830s, as people began to recognize that such switches could be extremely useful. Historically, electrical relays were often made with electromagnets, which continue to be used today, although for some applications solid state relays are preferred. They key difference between electromagnetic and solid state options is that electromagnetic relays have moving parts, and solid state relays do not.

Electromagnets also conserve more energy than their solid state counterparts do.

Usage of relay

One of the reasons an electrical relay is such a popular tool for electricians and engineers is that it can control electrical output which is higher than the electrical input it receives. In the example discussed above, if the ignition connected directly to the battery, heavy duty insulated wiring would be needed to connect the steering column to the battery, and the ignition switch would also need to be much more robust.

A variety of circuits can be connected to an electrical relays. Relays can be used as amplifiers for electrical energy, as in the car example, and they can also connect to things like alarm switches, activating when a circuit is broken to trigger an alarm.

Many electrical failsafe systems utilize electrical relays which turn on or off in response to things like a current overload, irregular current, and other issues which may arise. These electrical relays trip to shut the system down until the problem can be addressed.

Browse guides and papers

Note that not all documents in this section are free to download. Navigate through sub-pages to discover all documents.

Better protection system for distribution networks with distributed energy resources

Existing distribution feeders and their integrated protection systems are not designed for high penetration of renewable energy (RE) based distributed energy resources (DERs). The overcurrent protection systems are designed considering… Read more

Nov 08, 2021

Applying directional overcurrent relays in ground fault protection of transmission lines

The term “ground source”, as it is commonly used, implies a source for zero sequence current from a grounded neutral connection during faults or other system unbalance conditions. The term… Read more

Nov 04, 2020

Fault event reconstruction using data pulled from intelligent electronic devices (IEDs)

In this report, the Working Group examined the meaning of synchronization and the means to achieve it. They tackled the question of how accurate time synchronization needs to be and… Read more

Oct 21, 2020

Cold load pickup and inrush problems in protection of distribution feeder circuits

Usually when a distribution circuit is restored after an extended outage, the demand is greater than before the outage. Attempting to pick up this load can be problematic because the… Read more

Oct 12, 2020

Trip and control circuit schemes of signaling between relays and circuit breakers

Modern microprocessor relay has a power supply that transforms the station voltage into a suitable processor and controls voltages for the relay’s internal electronics. The power supplies generally draw only… Read more

Oct 05, 2020

Why and where Rogowski Coil current sensors are favorable when compared to CTs

Rogowski Coils can easily replace conventional current transformers in protection, metering, and control applications. They can be applied at all voltage levels (low, medium, and high voltage). However, unlike CTs… Read more

Sep 28, 2020

Advanced protection scheme for power transformers based on IEC 61850 standard

Power transformers of medium and large sizes are very critical and vital components for power systems. Due to its significance and cost, its protection needs to be appropriately addressed. Transformer… Read more

Sep 16, 2020

Fast fault detection study for power distribution systems

Two case studies have been performed in order to investigate the performance of algorithms for fault detection and current limiting concepts on a model of a real power system. The… Read more

Sep 02, 2020

Best protection practice for microgrid distribution networks

Islanding detection is one of the critical issue to design an effective protection system. That’s why microgrid protection is analyzed by considering two aspects: islanding detection and fault current protection… Read more

Jul 08, 2020

New digital relay design to detect, classify, and localize faults in transmission lines

Electrical Power System (EPS) is divided into several parts and each part classified as a system. Transmission line considered one of the main parts of the EPS networks. However, Overhead… Read more

Jun 29, 2020

Lecture notes in power system protection

Protection is the art or science of continuously monitoring the power system, detecting the presence of a fault and initiating the correct tripping of the circuit breaker. The objectives of… Read more

Jun 22, 2020

Design of protection schemes in networks with future electric energy delivery

Future Renewable Electric Energy delivery and Management (FREEDM) system was developed as a smart grid system with a motivation to include renewable sources into the existing power grid. FREEDM system… Read more

Jun 17, 2020

Earth fault protection functions for long cable feeders in compensated networks

There are two types of faults in the network. First, we have symmetrical faults. These faults are easy to calculate because network can be translated to a simple single-phase equivalent… Read more

Jun 03, 2020

Study of new methods for protection of power cables used in both AC and DC grids

The challenge of having a good location of ground faults in power distribution networks drives the protection systems to use different methods and algorithms. The knowledge of the ground fault… Read more

Jun 01, 2020

Overcurrent protection study for power network (solving relay setting miss-coordination)

The basic function of electrical protection is to detect system faults and to clear them as soon as possible. For any one particular application, there are many ways to do… Read more

Apr 08, 2020