Relay settings and logic scheme stop the catastrophic effects of an electrical fault and act as a control switch to ensure that the electrical power system is in safely and efficiently operating. Electrical power systems sometimes deviate from nominal current and voltage values due to apparatus failure, lightning, strong winds, among others, resulting in an electrical fault. Subsequently, it could compromise the power system network and the safety of people and equipment.

What is Relay Logic?

Most electromagnetic and electronic relays are designed by qualified integration engineers to implement a set logic that delivers optimum safety.

Relay logic refers to the method of applying time-independent logic (combination logic) to the electrical control circuitry. It uses several electrical relays that are wired up in a particular configuration, depending on the logical switching application.

It is the implementation of instrumentation to a hard-wired control system, which may consist of relays, electric motors, contactors, timers, actuators, and switches. It typically requires mass wiring and several devices to achieve a specific task.

A relay logic control performs ON and OFF functions, in which the relay switches between Normally open (NO) or Normally close (NC) states through the introduction of a current. The logic applied to a relay causes a sequence of events that will get the electrical system to work or stop operating automatically.

What Are the Uses of Relay Logic?

A relay logic takes part in the protection, monitoring, and schematic control of power assets. It is implemented primarily for safety and automation purposes in various control operations.

The most common yet crucial application of relay logic is in maintaining the transmission line communication. It allows permissive tripping, intertripping, and block-tripping schemes to reduce or eliminate intentional time delays due to a fault in the protected line.

Relay logic is also used to control the directional movement of motors, routing, and signaling in railways, lighting control and is implemented on a three-way switch.

While the electromechanical relay logic is still used in many industries today, many power systems use a programmable logic controller (PLC) for more robust control, monitoring, and recording of events. It was introduced in the ‘60s and remained an essential functionality for electrical assets.
The programmable capabilities that can be introduced to relays include event recording, metering, remote and automatic control, enhanced communication, relay interlocking, monitoring, arc flash reduction, and continuous self-monitoring.

How to Apply Relay Logic

Relay to relay communication in massive electrical power assets relies on programmable logic to carry out tasks and operations. The process of the control system in relay logic involves wiring to a control panel. As it is typically hard-wired, a change in the system means re-wiring and re-configuring the interconnection of switches, counters, timers, etc.

Define the Control Process

Before implementing an actual relay logic scheme, there needs to be an identification of the specific operations that will be controlled by the relay. The purpose of the relay should be determined, whether it is for a manufacturing plant or an induction motor since the design will highly depend on how the relay would be used.

Description and Documentation

Regardless of the relay type, there should be documentation of the logic scheme. It should consider the circumstances under which the relay logic may or may not work. The description of the relay, including its purpose and function.

Sequence the Operation

Determining the sequence by which the components will operate is essential in starting a relay logic. It is done by listing all the steps and the entire process in great detail. There is no uniform way of writing the sequence—it can either be in sentence form or table form. What matters is the amount of detail that will later determine how the entire system is going to be configured.

Sketch the Logic Diagram

A logic control circuit design can be done by reusing logical blocks from previous operational plans. It shows in detail the components found in the system. There are basic things to consider, such as drawing the diagram vertically, with outputs on the right, and inputs on the left. Every rung is made of a single output.

When drawing the operation process, the familiarization of symbols used in the schematic diagram is necessary. Each symbol indicates the NO and NC contact, Push button (ON or OFF), the relay coil, and the Output device. Additional components will depend on the purpose of the logic system.
There are many ways to draw a circuit, which also applies standards and laws followed in the country it is used. Component symbols and circuit configuration can vary.

We Can Help You

Industries rely on relay setting and logic to ensure that their equipment, electrical circuits, and people are always safe and protected from any untoward accident. Designing a relay logic schematic diagram should be detail-oriented and inclusive of technologies to optimize operations and promote greater productivity and safety for any enterprise.

At NST, our expert engineers can help you design the schematic diagram and establish your relay settings. Message us today to learn how!