Measuring High-Frequency Currents in Your Electric Motor

Large electric motors in a factory

Measuring the high-frequency currents in your electric motor is key to understanding your unit’s needs. Is it time to take preventative measures to mitigate additional motor damage? Are you at risk of motor breakdown or malfunction? Here are three of the most common methods for measuring high-frequency currents that will enlighten you about your electric motor, as well as tips on how to protect your motor for a failure-free future.

The Rogowski Coil

The “Rogowski Coil” is a form of alternating current sensor within conductors. The coil sits around the current-carrying conductor within the motor and protects it from any external electromagnetic interference, while providing insight into the motor current.

Because the coil is only capable of measuring the alternating current by itself, you’ll need to integrate an input signal if you need to measure the full current value in your motor. Engineers can create this signal using an internal circuit for the sensor, which comes with the coil.

Rogowski coils are a popular solution for measuring currents because they’re easy to use. The coil isn’t closed and the output doesn’t rely on the coil path, so you can quickly install the sensor without any structural changes. What’s more, these coils are “current transformers,” which means they linearly transfer the current into a level that’s compatible with measurement.

Shunt Resistors

Shunt resistors are otherwise known as “measurement shunts.” Typically, they measure the amount of energy moving through the shunt in the circuit. These components are available for a range of applications, although you will need to make sure to choose the shunt that’s sized correctly for the output and power range of your motor. Depending on your budget, you may be able to purchase a more precise resistor for stronger readings.

Unlike Rogowski coils, a shunt doesn’t wrap around the circuit; it needs to sit within the circuit instead. This can make it harder to install in your system, but it also means you can measure DC currents with a greater level of accuracy.

Hall-Effect Current Sensors

The sensors in a Hall-Effect system address the real current within the circuit. This allows for a more precise insight into how the circuit is performing. To measure frequency, the Hall sensor is placed within the core, inside the magnetic field, and it outputs a voltage that scales to the load that’s in the line. It’s important to note that there are different types of Hall sensor available. For instance, an open-loop sensor uses the Hall-Effect to consider the flowing current, while a closed-loop sensor generates a current to compensate the magnetic field created by the primary current.

Hall-Effect sensors can give engineers a greater level of accuracy when measuring frequency response, and they can also address DC offset. However, they are more expensive than other measurement options, and they also require the input of power for closed-loop systems.

Protect Against High-Frequency Currents

The best way to respond to the presence of high-frequency currents is with the correct preventative measures. Ideally, this will mean installing a common mode choke that mutes the noise caused by high-frequency currents. These choke modes can absorb asymmetrical currents, minimize voltage spikes, and reduce maintenance expenses.

CoolBLUE inductive absorbers are currently the most effective choke modes for variable frequency drives (VFDs), as they are capable of significantly reducing high-frequency currents. In fact, one case study shows that CoolBLUE could reduce 75% of damaging currents at a wind-turbine plant for renewable energy.

Contact Sloan Electric to speak to one of our experts about how CoolBLUE could reduce the high-frequency currents in your motor and protect your investment.

Measuring High-Frequency Currents in Your Electric Motor was last modified: November 17th, 2017 by admin

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Jerry is the owner of Sloan Electromechanical and is active in all aspects of the company. He is passionate about doing the work RIGHT and proposing the best product solution, hence the Sloan team is focused on aligning company values with client values. Please post your questions or comments and Jerry will respond. For a faster or confidential response, please contact Jerry directly 619-515-9691 or LinkedIn
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