The Relationship Between Grounding, EMI and Power Quality

Key Takeaways

• The relationship between grounding, EMI, and power quality.

• The difference between grounding for safety vs. EMC.

• Design considerations for EMC grounding.

Grounding provides a low impedance path for electromagnetic interference

Grounding, EMI, and power quality are closely related; power quality can be influenced by a variety of events, including electromagnetic interference (EMI). Fortunately, grounding an electric circuit can mitigate the ill-effects of EMI. Grounding provides a low impedance path for electromagnetic interference. When a system is properly grounded, EMI gets deviated from the critical equipment, improving power quality. In this article, we will explore the relationship between grounding, EMI, and power quality in further detail. 

Grounding, EMI, and Power Quality

Sensitive equipment and devices in a dynamic environment are susceptible to electromagnetic interference. The electronic devices, control circuits, signal and power cables, and other associated systems producing electromagnetic fields interact with each other through electromagnetic interference and disrupt normal operations. EMI interacting with electrical and electronic circuits is a serious threat to power quality.

When electrical and electronic circuits are supplied with electrical power of a specified magnitude, frequency, and phase, this allows the device to operate in its intended manner and power quality is ensured. If the EMI in a circuit is disturbing the magnitude, frequency, or phase of the system voltage, then power quality is compromised.

Grounding is one of the techniques to ensure power quality by mitigating EMI. Proper grounding eliminates electromagnetic interference and ensures safe operations as well as electromagnetic compatibility. Grounding determines how the system should react to unintentional faults, transients, and EMI and controls the conducted and radiated emissions in the electronic circuit by offering a low impedance path for high-frequency EMI currents and voltages.  

The Difference Between Grounding for Safety vs. Electromagnetic Compatibility

Before discussing grounding for electromagnetic compatibility (EMC), let’s differentiate it from grounding for safety. Grounding for EMC is different from grounding for safety. Grounding for safety is to safeguard the personnel working on a device. In grounding for safety, the metal body of the device is usually connected to earth’s ground so that the short-circuit or fault current flows to the ground without harming the user. However, the purpose of grounding for EMC is to provide a low impedance current path for EMI and noise currents. The ground reference for EMC grounding is not necessarily earth’s ground, but instead a shield or conductive plane. 

Grounding and Electromagnetic Compatibility

The grounding for EMC defines a reference of zero-voltage and bonds the circuits and other metal enclosures and parts to this reference through a low-impedance connection. The grounding structure prevents unintentional emissions and alleviates the susceptibility of the equipment to EMI. In case of conducted emissions and immunity problems, the grounding system provides both the zero-volt ground reference and the lowest impedance path for insignificant EMI currents. The grounding structures for electromagnetic compatibility are only allowed to take the EMI noise currents and fault currents. A properly utilized ground structure carries EMI currents and fault currents by forming a sufficiently low-impedance loop, thus controlling the unintentional voltage generated from EMI. 

Design Considerations for EMC Grounding 

1. Utilize conductors for grounding structures at the frequencies of interest. The design of the ground structures should focus mainly on defining local zero-volt references at the system frequencies.
2. Design the ground structure as the reference ground plane for the large metallic parts of electronic circuits. The design of the grounding structure should not get mixed up with the design of the shielding enclosure for the devices under consideration. 
3. Never design the grounding structure to carry the phase currents or operational currents in the circuit. The currents flowing in the ground structure cause magnetic flux wrapping, which induces voltages. The induced voltages are capable of driving the ground structure relative to other parts, especially at high frequencies. The ground structure needs to be designed only for carrying unintentional currents. 

Understanding the relationship between grounding, EMI, and power quality help designers achieve electromagnetic compatibility in electrical and electronic devices. The reference ground plane created by EMC design engineers in any product design plays a key role in eliminating unintentional EMI and noise currents. 

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