Thermal Overload Relays [OLR]

thermal overload relay [olr] is an electrical protection device designed to monitor and protect electric motors from overheating due to excessive current flow. It serves as a safeguard against the risks posed by motor burnouts, which can occur if motors operate for prolonged periods with elevated current levels.

Overload Relay Types. These are classified into two types namely 

thermal overload relay and magnetic overload relay.

A thermal over load relay (OLR) is an electro mechanical relay which is used to protect motors from overloading (or overheating).

How Do Thermal Overload Relays Work?

Thermal overload relays operate on a simple yet ingenious principle. They incorporate a bi-metallic strip that bends when heated. This strip is in direct contact with the motor current. When the motor current exceeds the predetermined safe threshold, the strip heats up, causing it to bend and trigger a mechanical switch. This switch then cuts off power to the motor, preventing further current flow and allowing the motor to cool down.

Importance of Thermal Overload Relays

1-Preventing Motor Damage

The primary purpose of a thermal overload relay is to prevent damage to electric motors. Overheating can lead to insulation breakdown, which can, in turn, result in short circuits, fires, or even complete motor failure. By promptly shutting down the motor when excess heat is detected, these relays contribute significantly to the longevity and reliability of electrical systems.

2-Enhancing Safety

Safety is paramount in any electrical setup. Thermal overload relays play a crucial role in ensuring the safety of personnel and property. By preventing motors from running at unsafe temperatures, the risk of fires or electrical shocks is substantially reduced, safeguarding both people and equipment.

3-Energy Efficiency

Beyond safety, thermal overload relays contribute to energy efficiency. Motors that operate within their optimal temperature range consume less energy and operate more efficiently. This not only reduces operational costs but also has positive environmental implications by minimizing energy wastage.

• dp full form in electrical
• 8085/8086 microprocessor short notes
• UPPCL AE/JE 2021 exam Oscillator Approximate frequency range
• Standard Wire Gauge(SWG)/American Wire Gauge (AWG) notes
• project management MCQ UPPCL-SSC-RRB-UPRVUNL JE and AE Exam

Applications of Thermal Overload Relays

1-Residential Use

In residential applications, thermal overload relays are commonly found in various appliances, including refrigerators, air conditioners, and washing machines. These relays prevent the motors in these appliances from overheating and ensure their smooth operation.

2-Industrial Sector

The industrial sector heavily relies on electric motors to power machinery. Thermal overload relays are vital in this context, protecting motors that drive conveyor belts, pumps, compressors, and other essential equipment from overheating and potential breakdowns.

3-Commercial Buildings

In commercial buildings, such as office complexes and shopping malls, thermal overload relays are integral to the HVAC (heating, ventilation, and air conditioning) systems. They ensure that the motors driving air circulation remain within safe temperature limits, contributing to a comfortable and secure environment.

types of OLR–

There are three types of thermal overload relays –

1-bimetallic,

2-eutectic

3-electronic.

Bimetallic thermal overload relays (sometimes referred to as heater elements) 

FAQs Exam point-