Control, Monitoring and Protection of High Voltage Motors

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HV Motor Control Panels

High voltage motors are essential components in many industrial and commercial applications, such as pumps, compressors, conveyors, and other heavy-duty equipment. However, these motors are susceptible to various electrical faults and failures that can cause downtime, damage, and safety hazards. Therefore, controlling and protecting high voltage motors is crucial to ensure their reliable and safe operation and prevent costly repairs or replacements.


Here are some reasons why high voltage motor control and protection is important:

  1. Preventing electrical faults - High voltage motors can experience various electrical faults, such as overvoltage, undervoltage, overcurrent, phase imbalance, and ground faults. These faults can cause overheating, insulation breakdown, winding damage, and other issues that can lead to motor failure. Therefore, motor protection devices such as overload relays, fuses, circuit breakers, and protective relays are necessary to detect and isolate these faults and prevent them from damaging the motor. 
  2. Enhancing safety - High voltage motors can pose a safety hazard to personnel working nearby, especially in case of faults or failures. For instance, a ground fault can create a shock hazard, and a phase-to-phase fault can cause an arc flash or explosion. Motor protection devices can help reduce these risks by quickly disconnecting the power supply and isolating the motor from the system. 
  3. Improving uptime and productivity - High voltage motors are often critical components in industrial processes that require continuous operation. Any motor failure or downtime can cause production losses, schedule delays, and revenue losses. Motor protection devices can help minimize the downtime and repair time by detecting and isolating the fault quickly, reducing the risk of extensive damage to the motor or other equipment. 
  4. Compliance with regulations and standards - High voltage motors are subject to various regulations and standards that require them to be protected and monitored adequately. For instance, the National Electrical Code (NEC) in the US mandates the use of motor protection devices to prevent motor overload, and other standards like IEC and IEEE provide guidelines for selecting and applying these devices.




Starting mode selection table for the most common applications



"Motor protection" groups all the protection devices used to prevent serious damage due to abnormal operating conditions at supply, motor or process level. The protection devices to be installed are chosen according to the following criteria:
  • operating conditions; 
  • importance of the operation performed by the motor; 
  • the degree of dependability required; 
  • the relative cost of the protection device with respect to the motor; 
  • the likelihood of the faults considered occurring. 
  • the type of load driven; 
  • disturbances which could occur on the network; the type of motor protected.


The principle of protection for high voltage motors is to detect and isolate faults that can cause damage or failure to the motor and the connected equipment. The protection devices used for high voltage motors are designed to monitor various parameters such as voltage, current, temperature, and insulation resistance, and to trip the motor or the associated switchgear when the values exceed the predefined thresholds.

Here are some principles of protection for high voltage motors:

  1. Short circuit protection - Short circuit protection is designed to detect and isolate faults caused by short circuits in the motor or the connected circuitry. Short circuit protection devices such as fuses, circuit breakers, and protective relays monitor the current and trip the circuit if the current exceeds the specified limit.
  2. Overload protection - Overload protection is designed to detect and isolate faults caused by excessive current draw in the motor. Overload protection devices such as overload relays, electronic overload relays, and thermal elements monitor the motor's current and trip the circuit if the current exceeds the specified limit. 
  3. Overvoltage and undervoltage protection - Overvoltage and undervoltage protection devices are used to monitor the voltage supplied to the motor and trip the circuit if the voltage exceeds or falls below the specified range. These devices protect the motor from damage caused by voltage fluctuations or voltage sags. 
  4. Phase imbalance protection - Phase imbalance protection is used to monitor the current in each phase of the motor and trip the circuit if the current in one or more phases exceeds the specified limit. This protects the motor from damage caused by phase unbalance or phase loss. 
  5. Ground fault protection - Ground fault protection is used to detect and isolate faults caused by current leakage to ground. Ground fault protection devices such as ground fault relays.
  6. Overheating protection - Overheating protection is used to monitor the temperature of the motor and trip the circuit if the temperature exceeds the specified limit. Overheating can cause insulation breakdown, winding damage, and other issues that can lead to motor failure. 
  7. Insulation resistance protection: Insulation resistance protection is used to monitor the insulation resistance of the motor and trip the circuit if the insulation resistance falls below the specified limit. Low insulation resistance can indicate insulation breakdown or contamination, which can lead to motor failure. 
  8. Bearing protection: Bearing protection is used to monitor the vibration and temperature of the motor's bearings and detect and isolate faults caused by bearing wear, lubrication failure, or misalignment. Bearing protection devices such as vibration sensors, temperature sensors, and bearing isolators can prevent premature bearing failure and extend the motor's life. 
  9. Phase sequence protection: Phase sequence protection is used to ensure that the motor is connected to the power supply in the correct phase sequence, which can affect the motor's direction of rotation and the performance of the connected equipment. Phase sequence protection devices such as phase sequence relays and phase monitors monitor the phase sequence and trip the circuit if it is incorrect.




The selection of protection devices and principles for high voltage motors should consider the motor's application, size, operating conditions, and the level of protection required. The appropriate protection devices should be chosen and installed to ensure safe, reliable, and efficient motor operation and protect the motor and the connected equipment from faults and failures.

~ End


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Source: Schneider Electric

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