Motor monitoring
The objective of implementing measurement devices is to ensure a continuous supervision of operating conditions of motors. The collected data can be used with great benefit for improving Energy Efficiency, extending lifetime of motors, or for programming maintenance operations.
Three levels of sophistication for monitoring scheme are commonly proposed: "Conventional", "Advanced", "High Performance", which can be made accessible, depending on the sophistication and power of the driven machine.
| Measurement | Conventional | Advanced | High Performance |
| Currents | |||
| Average current | |||
| Phase current imbalance | |||
| Thermal capacity level | |||
| Motor temperature (by sensors) | |||
| Phase to phase voltage | |||
| Phase voltage imbalance | |||
| Active power | |||
| Reactive power | |||
| Power factor | |||
| Active energy | |||
| Reactive energy |
Fig. N65b: Classification of protection functions
Here is a list of the most useful variables to be monitored, and the benefit provided by the measurement.
Currents: they are directly responsible for the conductors heating and thus for a possible time life reduction. These are the most important variables to monitor. The current measurement also gives a direct indication on the motor load and stress applied to the driven machine.
Average current: to know the average load of the motor, whether the motor is well adapted to the driven machine or not.
Phase current imbalance: as imbalance is responsible for additional losses in the motor, phase current imbalance is an important variable to monitor.
Thermal capacity level: knowledge of the remaining overload capability and safety margin.
Motor temperature (by sensors): knowledge of the real thermal operating conditions, taking account of motor load, ambient temperature, ventilation efficiency.
Phase to phase voltage: too high or too low phase voltages are responsible of increased motor current for a given load. Voltage monitoring is thus indicating whether the motor is operating in normal conditions or not.
Phase voltage imbalance: as imbalance is responsible for additional losses in the motor, phase voltage imbalance is an important variable to monitor.
Active power: indication of the load level applied to the motor.
Reactive power: indication of the reactive power that could be necessary to compensate by implementation of capacitors.
Power factor: indication of load level of the motor. If Power Factor is > 1: submit your candidacy for the Physics Nobel Prize.
Active energy: possibility to relate the consumed energy to the operating time or the quantity of goods produced by driven machine.
Reactive energy: possibility to determine the necessity of implementation of capacitors in order to avoid payment of penalties to the Utility.
Fig. N65c: Example of motor management system with "High performance" protection and monitoring functions (TeSys T Schneider Electric)
