Why Are Surge Capacitors Tied to Ground?

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SUMMARY

Surge capacitors are essential components in power systems, designed to absorb transient voltages and discharge them back into the system. They are tied to ground to provide a low impedance path for high-frequency surges, such as those caused by lightning strikes. This grounding mechanism protects sensitive circuit components from voltage spikes by diverting surge currents away from critical areas. Surge capacitors also contribute capacitance in motor circuits, helping to offset inductance and improve overall system stability.

PREREQUISITES
  • Understanding of surge capacitors and their function in power systems
  • Knowledge of transient voltage phenomena and their sources
  • Familiarity with grounding techniques in electrical systems
  • Basic principles of inductance and capacitance in motor circuits
NEXT STEPS
  • Research the design and selection criteria for surge capacitors in power systems
  • Learn about transient voltage suppression techniques and devices
  • Explore grounding methods for electrical systems to enhance surge protection
  • Investigate the impact of lightning strikes on electrical infrastructure and mitigation strategies
USEFUL FOR

Electrical engineers, power system designers, and technicians involved in surge protection and circuit stability. This discussion is particularly beneficial for those working with motor circuits and transient voltage management.

kenneth edmiston
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I have a decent understanding of power factor caps, (far from perfect) but I’m not as clear on surge caps.

Surge caps store transient voltages and discharge back into the system?
Why are they tied to ground?
And do they also provide capacitance in the motor circuit they are tied to providing an offset to inductance?

Thanks
 
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Generally - they just absorb the energy of a voltage spike, and technically discharge back to the system, but this is not a significant issue.

Since the V spikes - could be on a single phase, you want this protection relative to ground.
 
Think lightning strikes. They are DC. If you designed the grid, how would you deal with lightning surges?
 
The transients in power systems that surge capacitors are intended to eliminate are composed of higher frequencies than the 50/60/400 Hz power frequency. So the surge capacitor is selected to provide a low impedance path to ground at high frequencies to divert the surge currents away from the part of the circuit you want to protect. Most higher frequency transients coupled into the power system can be diverted to ground (earth) because they come from external sources, like lightning, for example.
 

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