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Motor Protection Devices
Motor Protection Devices for Three-Phase Motors and Critical Loads
ATC Diversified Electronics offers motor protection devices for three-phase motors and electrical loads that require continuous supervision of current, voltage, and operating conditions. The collection includes the MPA2 Motor Protection Analyzer and a range of current transformers for measuring higher motor currents and supporting compatible monitoring and protection systems.
The MPA2 Motor Protection Analyzer continuously monitors three-phase current and voltage and provides configurable protection against common electrical conditions including overload, undercurrent, overvoltage, undervoltage, current unbalance, voltage unbalance, single phasing, phase reversal, frequency shift, and locked-rotor conditions.
For higher-current applications, ATC current transformers provide standardized 5-amp secondary signals across primary current ranges from 30A to 1000A. Together, these products support scalable motor-current measurement and protection for pumps, compressors, conveyors, process equipment, and other critical three-phase loads.
Why Use Advanced Motor Protection?
Monitor Both Current and Voltage: The MPA2 continuously supervises electrical conditions on all three phases, allowing protection settings to respond to abnormalities affecting either current or voltage.
Protect Against Multiple Fault Conditions: Configurable protection includes overload, undercurrent, overvoltage, undervoltage, current and voltage unbalance, single phasing, phase reversal, frequency shift, and locked-rotor conditions.
Account for Motor Heating: The MPA2 incorporates motor thermal-class settings and thermal memory so restart behavior can account for estimated motor heating rather than relying only on whether the electrical fault has cleared.
Reduce Nuisance Trips: Adjustable startup and trip delays allow the protection strategy to account for normal motor acceleration, temporary fluctuations, and high-inertia loads.
Review Motor Operating Data: The MPA2 measures current, voltage, frequency, power factor, real power, reactive power, and energy consumption and provides an LCD interface for viewing motor and electrical information.
Review Fault History: Historical fault information can help maintenance teams determine what electrical condition caused a trip instead of relying only on the condition visible after the motor has stopped.
Extend Current Measurement with CTs: ATC current transformers are available for primary-current ranges from 30A to 1000A and provide 5A secondary outputs for compatible monitoring equipment.
MPA2 Three-Phase Motor Protection Analyzer
The MPA2 Motor Protection Analyzer is a microprocessor-based motor protection relay designed to continuously supervise current and voltage on three-phase motors and other electrical loads. When a configured harmful condition occurs, the MPA2 can deactivate its output until the fault clears, acceptable line conditions return, and the applicable motor thermal conditions permit restart.
In addition to basic current and voltage protection, the MPA2 provides adjustable motor thermal class, fault-recovery settings, startup delay, trip delay, automatic or manual restart modes, high-inertia motor settings, schedule-timer functions, and password protection.
The analyzer also provides measurement and reporting of current, voltage, frequency, power factor, real power, reactive power, energy consumption, motor running time, and recent fault information. MODBUS RTU communication over an available RS485 interface supports integration with compatible supervisory and automation systems.
Current Transformers for Motor Current Measurement
ATC current transformers allow higher primary currents to be represented by a standardized lower secondary current for compatible meters, monitoring relays, and motor-protection devices.
The CT Series is available in ratios from 30/5A through 1000/5A, with multiple bus-bar sizes and accuracy classes from 0.5 through 5. Optional DIN rail clamps are available for compatible installations.
Motor Protection for Pumps and Critical Industrial Equipment
Three-phase motors used on pumps, conveyors, compressors, fans, process machinery, and other critical equipment can be exposed to electrical and mechanical operating conditions that are not addressed by a single protection setting alone. Monitoring multiple current and voltage parameters provides additional information about how the motor and its electrical supply are behaving.
For critical applications, protection settings should be selected based on the motor nameplate, starting characteristics, expected load, system voltage, allowable voltage and current variation, thermal characteristics, process requirements, and the consequences of an unexpected trip or motor failure.
Find the Right Motor Protection Device
Selecting the right motor protection relay or current transformer depends on motor voltage, full-load current, starting current, CT requirements, expected load variation, thermal class, acceptable current and voltage limits, restart strategy, communication requirements, and the specific faults that need to be detected.
Explore the ATC motor protection devices above to compare the MPA2 Motor Protection Analyzer and available CT ratios for three-phase motor, pump, and industrial equipment applications.
Motor Protection Device FAQs
What is a motor protection relay?
A motor protection relay monitors electrical or thermal operating conditions and provides a control response when configured limits are exceeded. Depending on the relay, monitored conditions can include overload, undercurrent, voltage abnormalities, phase conditions, current unbalance, or motor thermal behavior.
What is the MPA2 Motor Protection Analyzer?
The MPA2 is a microprocessor-based three-phase motor protection relay that continuously monitors current and voltage. It provides configurable protection, electrical measurements, fault reporting, thermal modeling, and communication features for motors and other three-phase electrical loads.
What faults can the MPA2 protect against?
The MPA2 provides protection against overload, undercurrent, overvoltage, undervoltage, frequency shift, voltage unbalance, current unbalance, single phasing, phase reversal, and locked-rotor conditions.
What electrical values does the MPA2 measure?
The MPA2 measures current, voltage, frequency, power factor, reactive power, real power, and energy consumption. It also provides reports and operating information through its LCD interface.
What is motor thermal memory?
Thermal memory allows a motor protection device to account for estimated heat that remains in the motor after operation or a protective trip. This helps prevent the restart logic from treating a recently heated motor as though it were completely cool.
Can the MPA2 account for different motor thermal classes?
Yes. Motor thermal class is one of the adjustable protection parameters available in the MPA2, allowing the thermal protection behavior to be configured for the motor and application.
Why does a motor protection relay need a startup delay?
Motors can draw substantially more current during acceleration than they do during normal operation. A properly configured startup delay allows normal starting conditions to occur without immediately producing an unnecessary protective trip.
Can the MPA2 be used with high-inertia motor loads?
Yes. The MPA2 includes adjustable settings for controlling motors with high-inertia loads, along with startup, trip, thermal, and fault-recovery settings that can be configured for the application.
Does the MPA2 store fault information?
Yes. The MPA2 provides historical fault reporting so maintenance personnel can review recent protective events and the electrical conditions associated with them.
Does the MPA2 support communication with a control system?
Yes. An RS485 communication interface using MODBUS RTU is available for the MPA2, allowing compatible automation or supervisory systems to access motor and electrical information.
What is a current transformer?
A current transformer, or CT, converts a higher primary current into a proportional lower secondary current that can be measured by compatible meters, relays, and protection equipment.
What current transformer ratios does ATC offer?
ATC CT Series current transformers are available from 30/5A through 1000/5A, meaning the selected rated primary current is represented by a 5A secondary current at the rated condition.
How do I select a current transformer for a motor?
CT selection should consider the expected motor current, required CT ratio, conductor or bus-bar size, accuracy requirements, monitoring device input, and the electrical installation. The selected CT should provide a suitable measurement range for both normal motor operation and the protection strategy.
Does a motor protection analyzer replace every other motor protection device?
No. Motor protection is application dependent. The MPA2 provides extensive electrical and thermal protection functions, but other devices may still be required for circuit protection, disconnecting means, ground-fault protection, process monitoring, vibration monitoring, seal monitoring, or other application-specific requirements.
How do I choose the right motor protection settings?
Begin with the motor nameplate, system voltage, full-load current, starting characteristics, motor thermal class, expected process load, acceptable voltage and current variation, restart requirements, and applicable equipment or system requirements. Protection settings should be coordinated with the motor, starter, upstream protection, and process.