How Do Relays Function in Industrial Power Distribution Systems?


Courtesy of Larson Electronics LLC

How Do Relays Function in Industrial Power Distribution Systems?

Power distribution systems that manage large currents come with components that protect the system from abnormal conditions, which can damage the unit. One of these components is a relay, which is used to isolate, limit or control electrical loads.

Relays, or simple switches that are set off or activated via an electrical current, can decrease risks associated with overheating and trips – ensuring the system remains operational with minimal disruption.

Primary Functions and Roles

Relays can operate both electrically or mechanically, making them electro-mechanical switches. In power distribution systems that handle high voltage, the unit’s main role is to decrease electrical arcing and current discharge. In the presence of an abnormal condition, the relay will automatically close its contacts, preventing damage to the system. For low voltage applications, the units can be applied to reduce overall noise in circuits.

In a basic relay model, the current from one circuit triggers the opening or closing of another circuit. When an electric current or voltage surpasses a specific threshold value, it energizes the electromagnet and generates a magnetic field. This causes the contact arm to be attracted to the lower arm (energized relay), which would result in the closing of the contacts or pins. In a de-energized (off) relay, the energized coil is stopped and the contacts return to their original, opened position. The force that causes the return of the moveable armatures are almost equivalent to half the strength of the magnetic force. This abrupt movement is supported by the spring and gravity.

One of the most common types of relays is the electromechanical relay (General Purpose Relay, Machine Control Relay, Reed Relay and etc.), which functions as described above. Its main parts include the following: contacts, springs, magnetic core (wrapped in a wire coil) and a moveable armature (with an attached iron yoke). Electromechanical relays are versatile, in a sense that they can manage a handful of voltages and circuits reliably without issues.

Like all mechanical components, electromechanical relays will eventually fail when continuously used and exposed to high-power electrical currents. In most cases, the coil is most susceptible to damage, as well as contacts. A drawback with using this type of relay is the possibility of producing electrical arcs during operation (although such units are equipped with features to control sudden discharges). This can disrupt nearby components, causing the applicable machine to malfunction or fail, such as sensitive electronics that are prone to malfunction when radio frequency interference is present.

Industrial Power Distribution

In power distribution systems, protective relays mitigate the damaging effects of short circuits, overcurrents and other electrical-related abnormal conditions. The units are activated when the electrical current exceeds normal operating standards and settings. Overcurrents can be caused by a wide range of abnormal conditions, such as overloading, ground faults and short circuits. In an overload scenario, a heavy current is present that is above the rating capacity or threshold of the system. Ground faults occur when an electrical path is created between a power source and a surface that is grounded.

When a relay is activated due to an exceedance of the set limit (and the relay contacts have been triggered), the operator may exercise the following options: (1) remove power to prevent damage to the system, or (2) turn on an alarm indication to alert other workers about the abnormal condition. The latter option may also help workers quickly identify the root of the issue before it is cleared from fault.

The pitfalls of traditional relays have ushered in the use of digital protective relays. Such components are underpinned by algorithms that monitor, detect and manage electrical faults. The use of such mechanisms can make power distribution more reliable. Maintenance and testing are streamlined and protective functionalities are more accurate. Since digital protective relays are data-driven, operators must monitor data closely or setup notifications that alarm workers when abnormal conditions are present.

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