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Protecting Motors Against Overload Conditions Using “I-squared-T” Methods

 

 
The goal of an effective motor overload protection scheme is to protect the motor from damage while allowing it to operate normally up to its thermal limit. Ideally such a scheme would be based on a direct measurement of internal motor temperatures. Unfortunately the temperature at different points within a given motor varies widely and it is thus difficult to accurately measure 'hot spot” temperatures. An alternative overload protection method monitors power flow to the motor and keeps track of the magnitude and duration of overload events. Such a method can provide excellent performance without the need for direct measurement of motor temperature. Since power delivered to the motor flows through the drive amplifier, an overload protection scheme based on power flow is well suited to implementation within the amplifier.
Products & Services
Overload relays prevent an electric motor from drawing too much current and overheating; includes thermal and solid state overload types. Search by Specification | Learn more about Thermal Overload Relays
Motor contactors are relays with large current capacity for connecting and disconnecting a motor from the power supply. Typically, motor contractors are multi-pole for control of all current carrying conductors. Search by Specification | Learn more about Motor Contactors
DC motor starters combine a controller (most often a contactor) with overload protection, allowing a motor or motor-controlled equipment to be turned on and off. Search by Specification | Learn more about DC Motor Starters
Electric linear actuators have an output rod that provides linear motion via a motor driven ball screw, lead screw, or ACME screw assembly. The actuator's load is attached to the end of a screw or rod and is often unsupported. Search by Specification | Learn more about Linear Actuators
Motor starters and contactors are motor-starting devices. They combine a contactor with overload protection and are designed for starting AC or DC motors. Search by Specification | Learn more about Motor Starters and Contactors
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Topics of Interest
MOTOR INSULATION Insulation systems must be used in a motor to electrically insulate the windings from the mechanical parts of the motor as well as to insulate the phase winding conductors from one... (Read More)
IEC Ratings At this point, it would be helpful to briefly review IEC motor ratings and then compare IEC with NEMA. The motor market today has become more global, with IEC rated motors on equipment... (Read More)
Over Temperature Conditions Placing the motor into overload conditions is one cause of over-temperature. High ambient temperatures and dirty or clogged air filters on the machine or motor blowers... (Read More)
Protection and Ratings Motor Protection The typical method of starting a three-phase induction motor is by connecting the motor directly across the power line. Line starting a motor is done with a... (Read More)
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