How Does the Grounding System Work in Aircraft & Submarines?

How is Grounding in AC/DC Systems Used for Protection in Aircraft, Ships, and Submarines?

Aircraft, ships, and submarines represent significant investments and require advanced levels of electrical protection. These vehicles, including airplanes, fighter jets, navy ships, aircraft carriers, cruisers, and submarines, use both AC and DC power systems. To protect their electrical systems, they employ specialized bonding and grounding (earthing) methods, which differ from traditional Earth-grounded systems.

Since these vehicles are isolated from Earth, they cannot rely on conventional grounding techniques. Instead, their grounding systems are designed to mitigate electrical faults, reduce electromagnetic interference (EMI), and ensure safety and reliability in isolated environments.

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Grounding in AC Systems

In conventional AC systems, grounding is provided through the equipment grounding conductor (EGC), also known as the earth continuity conductor, which connects to the grounding electrode system (GES). The EGC bonds various machines and metal components, creating a pathway for fault current to return to the ground rod or earth electrode during a fault. This grounding method protects both equipment and personnel.

Grounding in DC Systems

In typical DC systems, grounding may not be required for low-voltage sources, such as solar panels and batteries, which are isolated from Earth. However, high-voltage DC applications exceeding 60V, such as generators and rectifiers, require separate grounding and bonding systems to ensure safety and proper device operation.

Earthing and Grounding in Aircraft

Most aircraft utilize a 400 Hz, 115/200 V three-phase AC power system for main power. However, DC power is also used for certain systems, like the electro-hydrostatic actuator system (EHA), due to its stability and control, as well as for charging the aircraft’s battery, which serves as backup power in case of main power failure.

In aircraft, grounding provides a stable reference point and minimizes electrical interference, despite lacking a direct Earth connection. The airframe serves as the grounding plane, providing a reliable return path for the DC system and reducing EMI. Grounding also helps protect the system from static electricity buildup and lightning strikes.

Aircraft grounding, often called a “floating ground” or “aircraft ground,” includes the following components:

1. Return Path for Electrical Circuits: The airframe serves as a common return path for many electrical systems, creating a stable reference point.
2. Static Discharge Protection: High-speed airflow can cause static electricity to accumulate on an aircraft’s surface. Static wicks discharge this electricity safely into the atmosphere.
3. Lightning Protection: Aircraft structures incorporate conductive materials to withstand and redirect lightning strikes safely across the fuselage and away from sensitive systems and passengers.

For grounded aircraft (when not in flight), Aircraft Grounding Receptacles (AGR) are used for safety during parking, refueling, and maintenance. These receptacles have a high current-carrying capacity and are corrosion-resistant, providing protection against static electricity and enabling safe connections to ground power and main electrical supplies.

Earthing and Grounding in Submarines

Submarines typically use AC power distribution systems similar to land-based setups. Some also use DC power cables for long-distance transmission, as AC cables face limitations from capacitive currents. Nuclear submarines, powered by nuclear reactors, generate steam to drive turbines that power both propulsion and electrical generators.

In submarines, the hull serves as the grounding plane for DC systems, providing a stable electrical reference and managing EMI in the conductive seawater environment, which is crucial for systems like sonar. Grounding in submarines also prevents galvanic corrosion, a significant risk in marine environments.

Key components of submarine grounding include:

1. Hull Grounding: The metal hull acts as a grounding plane and reference for onboard electronics, similar to an aircraft’s airframe. This setup is essential for consistent electrical operation in a saltwater environment.
2. Isolation to Prevent Corrosion: Due to seawater’s corrosive nature, specialized grounding techniques minimize galvanic corrosion, protecting both electrical systems and the hull.
3. Noise and EMI Management: Grounding systems limit EMI and noise, ensuring clear signal transmission for sensitive systems like sonar and communications.

The surfaces of submarine vessels and ships are protected by an Active Shaft Grounding (ASG) system. This system is designed to shield the vessel from underwater extremely low-frequency electromagnetic (ELFE) signals. These signals are generated by the modulated current flow between the cathodic protection system and the ship’s propellers, as well as the electromagnetic fields and currents produced by hull corrosion.

The electric potential difference between the anode (cathodic protection system) and cathode (propeller or other exposed metal) creates a Static Electric (SE) field, also referred to as the Underwater Electric Potential (UEP). The strength of this field is proportional to the level of current flowing between the electrodes and the distance between them.

A current path exists from each anode to the propeller shaft, which then flows along the shaft before grounding to the hull through the shaft bearings. When activated, the ASG system provides a low-resistance path for this current, bypassing the shaft bearings to prevent wear.

The ASG system uses electronic components to actively ground the shaft to the hull through a slip-ring brush assembly. The system measures the shaft-to-hull potential via one slip-ring assembly, and this signal, after amplification, is used to control a high-current power supply. This supply then draws current out of the shaft through a second slip-ring assembly. By stabilizing the shaft-to-hull resistance, the system minimizes variations in current between the cathodic protection anodes and the hull, effectively eliminating the ELFE signature.

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