Phase Failure (Loss) Thermal Overload Relays
Reviewed by: Jon Lowy, consulting engineer
Description
Phase Failure (Loss) Thermal Overload Relays are protective devices designed to monitor and protect electric motors from damage due to phase loss or imbalance. These relays detect when one or more phases in a three-phase power supply are lost or become imbalanced, and they trip to cut power to the motor, preventing potential damage.
Working Principle
Phase Failure (Loss) Thermal Overload Relays operate by continuously monitoring the voltage and current of each phase in a three-phase power system. When a phase loss or imbalance is detected, the relay trips, cutting off power to the motor. This is crucial because phase imbalance can cause dangerous fluctuations in voltage or current, leading to motor damage. The relays are equipped with features such as ambient temperature compensation and adjustable trip settings, allowing them to provide precise protection tailored to specific motor requirements .
Applications
Phase Failure (Loss) Thermal Overload Relays are commonly used in industrial settings where three-phase motors are prevalent. Specific applications include:
- Pumping Systems: Protecting pumps from running dry due to phase loss, which can lead to mechanical failure.
- Conveyor Systems: Ensuring continuous operation by preventing motor damage from phase imbalances.
- HVAC Systems: Safeguarding compressors and fans from phase-related issues that could cause overheating or mechanical stress.
Advantages over other Thermal Overload Relays
One significant advantage of Phase Failure (Loss) Thermal Overload Relays is their ability to detect phase loss and imbalance, which are leading causes of motor failures. This capability provides an additional layer of protection compared to standard thermal overload relays that may only respond to overcurrent conditions .
Limitations
A limitation of these relays is that they may require manual resetting after tripping due to an overload, which can lead to downtime if not promptly addressed. Additionally, they may not provide adequate protection if only voltage magnitude is monitored without considering phase angle displacement .
Considerations
When selecting Phase Failure (Loss) Thermal Overload Relays, consider the following:
- Initial Costs: These relays may have a higher upfront cost due to their advanced monitoring capabilities.
- Operating Expense: They can help reduce long-term operating expenses by preventing costly motor repairs and downtime.
- Durability and Accuracy: Look for relays with ambient temperature compensation and adjustable settings for enhanced durability and precise protection.
- Replacement and Maintenance Costs: Regular maintenance and timely replacement of relays are essential to ensure continuous protection and avoid unexpected failures .
from Schneider Electric, Automation & Control
TeSys LR97D - Electronic overcurrent relays 0,3 A to 38 A. Direct mounting beneath TeSys Model d contactors up to LC1D38, width 45 mm. Screw clamp or lug connections. External 24 to 230 V AC power supply. Manual or automatic reset. Protection functions: - Overcurrents due to overload or mechanical... [See More]
- Features: Automatic Reset (optional feature); Phase Failure (Loss)
- Operating Temp: -13 to 140
- Full Load Current Range: 0.30 to 1.50
from Mitsubishi Electric Automation, Inc.
Mitsubishi Electric thermal overload relays protect motors and motor circuit conductors against over heating caused by current overloads and or phase-loss. The TH-N and TH-T series relays can be paired with the Mitsubishi Electric contactors or utilized as a stand-alone overcurrent protection... [See More]
- Features: Phase Failure (Loss)
from CARLO GAVAZZI Automation Components
Direct mount on the mini contactors with screw clamp connection. contactor types. DIN rail or screw mountable with the optional base AZ-12H. Small physical size : 44 mm wide. 1NO+1NC trip contacts. Trip class 10A according to IEC60947-4-1. Differential current/Phase failure protection : CGT types. [See More]
- Features: Automatic Reset; Ambient Temperature Compensation; Phase Failure (Loss); Reversal
- Full Load Current Range: 0.10 to 16.00
- Overload Relay Type: BiMetallic
- Trip Class: 10.0
from Schneider Electric, Automation & Control
TeSys LT47 - Electronic overcurrent relays 0,5 A to 60 A. DIN rail or plate mounting. Screw clamp or lug connections. External 24 to 230 V AC power supply. Manual or automatic reset depending on model. Protection functions: - Overcurrents due to overload or mechanical jamming: starting and steady... [See More]
- Features: Automatic Reset (optional feature); Phase Failure (Loss)
- Operating Temp: -13 to 140
- Full Load Current Range: 0.50 to 6.00
from Mitsubishi Electric Automation, Inc.
Mitsubishi Electric thermal overload relays protect motors and motor circuit conductors against over heating caused by current overloads and or phase-loss. The TH-N and TH-T series relays can be paired with the Mitsubishi Electric contactors or utilized as a stand-alone overcurrent protection... [See More]
- Features: Phase Failure (Loss)
from Schneider Electric, Automation & Control
TeSys LR9 - LR9D / LR9F - Electronic thermal overload relays with build-in alarm function from 18,5 kW to 315 kW. 8 ratings. 2 versions: Simplified version: class 10, class 20. Complete version: can be selected as class 10 or 20, with an alarm function enabling tripping to be anticipated by shedding... [See More]
- Features: Ambient Temperature Compensation; Phase Failure (Loss)
- Trip Class: 10.0
- Full Load Current Range: 30.00 to 50.00
- Operating Temp: -13 to 131
from Schneider Electric, Automation & Control
TeSys LR2K - Thermal overload relays 0,06 kW to 5,5 kW. Manual and automatic reset. Sealable flap. Prewiring kit. Terminal block for separate mounting. Remote electrical reset. Can be combined with TeSys k contactors in a 45 mm wide space. Connectors: spring terminal, screw clamp. Class 10 A. [See More]
- Features: Automatic Reset (optional feature); Phase Failure (Loss)
- Trip Class: 10.0
- Full Load Current Range: 0.11 to 0.16
- Operating Temp: -4 to 140
from Schneider Electric, Automation & Control
TeSys LRD - Thermal overload relays up to 75 kW/400 V. Manual and automatic reset. Sealable flap. Prewiring kit. Terminal block for separate mounting. Remote electrical reset. Can be combined with TeSys model d contactors in a 45 mm wide space up to 18.5 kW, 55 mm from 15 to 30 kW. Connectors:... [See More]
- Features: Automatic Reset (optional feature); Ambient Temperature Compensation; Phase Failure (Loss)
- Trip Class: 20.0
- Full Load Current Range: 17.00 to 25.00
- Operating Temp: -4 to 140