This section provides an overview for protective relays as well as their applications and principles. Also, please take a look at the list of 29 protective relay manufacturers and their company rankings.
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A protective relay is a device that instantly detects sudden changes in current and voltage occurring in power system equipment and sends a control signal to the circuit breaker to isolate the faulty point.
By quickly disconnecting the faulty part in the event of an accident in the power system, the protective relay not only prevents the spread of damage caused by overcurrents, but also minimizes the duration of power outages and ensure a stable supply of electric power.
For this purpose, equipment fault elimination relays to isolate faulty equipment and accident spread prevention relays to prevent the spread of the effects of accidents are dispersed throughout the power system. A reclosing device for quick recovery from an accident is also treated as a type of protective relay.
Protective relays are used to prevent the effects of accidents such as lightning strikes from spreading throughout the power system and to ensure a stable supply of electricity. Protective relays are installed in various places in facilities that make up power systems, such as power plants, substations, and power transmission and distribution lines managed by power companies.
Private power generation facilities that are connected to the power company's power system are also required to install protective relays at the receiving points to protect the power system in the event of a failure of the private power generation facilities and to protect the private power generation facilities in the event of an accident on the power system.
In addition to power generation facilities, protective relays are also used to protect power receiving and transforming facilities in buildings, factories, hospitals, railroads, and other power demand facilities.
The principle of operation of protective relays depends on the type of protective relays.
Over Current Relay (OCR): Operates when the current value at the location where the protective relays are installed exceeds the set value. There are two types of elements that trigger the overcurrent protective relays: dimensional elements and instantaneous elements. The dimensional element operates when it detects that an overcurrent has flowed for a long period of time due to an overload, and the higher the current value, the sooner the normal system is protected. The instantaneous element detects the instantaneous flow of a large current far in excess of the rated current due to a short circuit and protects the normal system.
Over Voltage Relay (OVR: Over Voltage Relay): Operates when the voltage at the location where the protective relays are installed exceeds the set value. Detects overvoltage on the power system side due to a generator or other failure and protects the system and equipment on the load side.
Under Voltage Relay (UVR): Operates when the voltage at the location where the protective relays are installed drops below a set value. Detects a drop in power due to a power failure or short-circuit failure, and protects the load-side system and equipment.
Ground Fault Protective Relays (GR: Ground Relay): Operates by detecting ground faults caused by cables contacting the earth. Ground protective relays use a zero-phase alternator (ZCT) to detect unbalanced current due to an imbalance in the three-phase circuit in the event of a ground fault. At this time, since a ground fault is detected only by the magnitude of the current, it is not possible to distinguish between an accident current in the power system and an accident current on the self circuit side, which may result in false detection.
Directional Ground Relay (DGR): Operates by detecting a ground fault using the zero-phase current and zero-phase voltage between the line and the ground. It can detect only the fault current of its own line in the direction of the phase difference between the current and voltage.
Differential protective relays (DFR: Differential Relay): Operates when the differential current proportional to the vector (current value and phase) difference between the input and output currents in the protective section exceeds a certain value. Only when a short circuit occurs in the protective section, a difference is generated in the secondary current of the alternator (CT) and a differential current flows to the operating coil. With this method, the differential current does not reach zero during normal operation due to the characteristic difference of the CT, etc., and may malfunction.
Ratio Differential Relay (RDFR): To prevent malfunction of the differential protective relays, differential protective relays have a structure with an additional suppression coil that generates a suppression force when a current passes through it. When a large current due to an external accident passes through the relay, a large suppression force is applied to prevent malfunction.
Other types of protective relay systems include power protective relays, overfrequency protective relays, underfrequency protective relays, short-circuit protective relays, and short-circuit direction protective relays.
*Including some distributors, etc.
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Wisconsin Oven Corporation has operated since 1973 and is located in East Troy, Wisconsin. Wisconsin Oven designs, engineers, and manufactures industrial ovens and other heating equipment for numerous applications including heat treating, powder coating, paper pulp drying, finishing, drying, and curing in the aerospace, automotive, composite, energy, finishing, foundry, heat treating, annealing, military, and pharmaceutical industries. Types of ovens and equipment include custom and standard batch ovens, conveyor ovens, pollution control equipment, and walk-in ovens.
NOARK is based in Pomona, California, and is a global manufacturer of low-voltage electrical components for industrial applications. NOARK specializes in motor controls and protection for original equipment and manufacturers with products covered by five-year limited warranties. NOARK parts are used in numerous solutions such as HVAC and refrigeration, industrial food equipment, panel builders, digital storage, and engine generators. NOARK’s main product lines include low-voltage power circuit breakers, molded case circuit breakers, miniature circuit breakers, overload relays, and circuit control devices.
ABB E-mobility provides electric vehicle charging solutions for customers around the globe. ABB E-mobility offers DC fast chargers as well as AC chargers with focus on reliability and uptime. Since 2010, ABB E-mobility has sold over 50,000 DC fast chargers and over 1 million total AC chargers. ABB E-mobility offers home single and multi-charge units, retail, workplace, and hospitality charge units, electric vehicle fleet sales, as well as public transportation. Additionally, numerous digital solutions and software services are available.
WIN SOURCE is a customer-focused online store serving a wide variety of markets industries ranging from consumer to automotive to medical, industrial, and aerospace. WS specializes on size and speed, offering a catalog of over 1 million SKUS that can be shipped within 24 hours around the world. Offerings include an extensive array of semiconductor components, audio products, cable assemblies, racks, and battery products. WIN SOURCE is AS9120B, ISO9001, ISO14001, and ISO45001 certified and is a member of the anti-counterfeiting organization, ERAI.
Industrial Electric Machinery, also known as IEM, was originally founded in 1988 as Northwest Motor Service. IEM serves industrial customers with products and services including motors, relays, transformers, UPS batteries, and more. IEM offers 4 primary product categories: Controls such as low voltage VFDs and transformers, gearboxes & couplings, motors, and power distribution including MCCs and automatic transfer switches. IEM also offers field service including 24/7 availability for troubleshooting, analysis, calibration, field testing, and repairs. Additional services such as training courses and warehousing of spare equipment is also available.
Hybrid Electronics is a global distribution specialist of electronic components, with access to over 50 million unique components. Among the markets HE serves are the aerospace, automotive, communications, defense, industrial, medical, national security, and test & measurement industries. In addition to components, HE also provides quality and compliance testing, counterfeit detection, upscreening, and other forms of quality control. Examples of component subtypes that HE offers include ICs, batteries, capacitors, semiconductor products, sensors, circuit protection, interconnectors, filters, optoelectronics, relays, switches, power supplies, and cables and cable assemblies.
AutomationDirect.com was founded in 1994 to provide solutions for the industrial automation market and has been growing its list of offerings ever since. AutomationDirects’ extensive catalog includes individual components such as cables, various controls, I/O devices, relays, gauges, fittings, and sensors to complete systems. Many parts and devices, especially PLC units are customizable. AutomationDirect.com also provides support via video instructions, online manuals, a learning library, an active community forum to further assist customers.
Siemens began in 1847 and is headquartered in Munich, Germany. Siemens focuses in automation and digitalization technology and operates globally. Siemens’s 5 operating segments are digital industries, smart infrastructure, mobility, Siemens Healthineers, and Siemens Financial Services. Siemens Financial Services provides debt and equity investment as well as financing solutions. Siemens Healthineers is a medical devices company that provides products and consulting. Mobility includes passenger and freight transportation. Smart infrastructure includes full solutions for electrification. Digital industries offer both software and hardware for industries and production efficiency.
Toshiba Electronic Devices & Storage Corporation is a division of Toshiba focusing on providing designs for end-product developers as well as semiconductor and drive equipment for automotive, industrial equipment, green energy, and consumer and personal electronic devices. Toshiba’s storage products include cloud-scale and enterprise-level products, and PC hard drives. Semiconductor products include Si Cower devices, MOSFETs, IGBTs, IEGTs, isolators, solid state relays, power management and intelligent power ICs, diodes, bipolar transistors, microcontrollers, automotive devices, ICs for wireless communication equipment, general purpose logic ICs, radio-frequency devices, sensors, and linear image sensors.
Schneider Electric S.E. is headquartered in Rueil-Malmaison, France, and has been operating since 1836. Schneider Electric provides a number of products and services including electrical car charging, energy management software, surge protection devices, load banks, servers and HMIs, valve and valve actuators, feeder automation, grid automation, and SCADA software products, data center cooling and software, home automation and security, light switches, motion control and robotics, signaling units, solar and energy storage, RFID systems, as well as other hardware, services, and software.
Pilz is headquartered in Ostfildern, Germany. Pilz designs components, systems, and services to assist industrial plant and machinery customers globally. Customers include many industries such as metals, pharmaceutical, food, presses, and robotics. Pilz serves customers through 4 venues: products and industries, services, support, and training. Products and services include everything from sensor technology and small controllers to robotics to software and operation monitoring. Services include machinery and workplace safety and international compliance. Support is offered 24/7. Training is available through courses and qualification programs.
ifm efector (ifm) is a subsidiary of ifm electronic, founded in Germany in 1969. ifm has developed, manufactured and marketed sensors and controls technology to industries that include assembly and robotics, automotive, material handling, metal forming, mobile equipment, plastics, and food and beverage. Ifm produces sensors, condition monitoring equipment, image processing, safety technology, industrial communication, IO-link, systems for mobile machines, displays, software, connection technology, voltage supplies, as well as other accessories.
Auburn Armature was founded in 1946 and headquartered in Auburn, New York. Auburn Armature is a distributor of electrical products and was recently purchased by Power-Flo Technologies of New Hyde Park, New York. Services that Auburn Armature provide include training, testing, rebuilding, repair, troubleshooting, and training. Parts that Auburn Armature specialize in include automation systems, AC and DC drives, motor controls, motors, motion controls, connectors, wire, boxes, cables, sensors, relays, transformers, panels, struts, terminal blocks, lighting supplies, and conduits.
Celduc Inc. through Celduc Transfo was founded in 1960 as a manufacturer of transformers. Celduc Inc. is based in, France. Celduc Inc. was officially created in 2020 and headquartered in Centerport, New York. Celduc creates electronics and customized products for industries including railway, plastic, packaging, medical, and electronics. Celduc’s main product lines include solid state relays, magnetic proximity sensors, reed relays & switches, and customized products. Customized products are versions of other products adapted for use in industries with special needs such as nuclear power, aircraft, and agriculture.
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