Transmission Line Overcurrent and Earth-Fault Protection: The normal practice is to use a set of two or three overcurrent relays for protection against phase-to-phase faults and a separate overcurrent relay for protection against single line-to-ground faults. These devices are usually mounted in a metal enclosure attached to an outside wall of the building. In case of a fault, the circuit breaker will open to stop current from flowing through the transmission line.
The normal practice is also to provide some form of electrical connection between the power line and the ground wire at each end of the transmission line. This connection is made with a conductor called a "ground strap". Ground straps are either bare copper wires that are connected together at each end of the transmission line or green aluminum conductors which are often used instead. If a single ground strap is used on a large transmission line, it must be able to carry the load if one branch is taken off the line. So, it must be large enough to handle the maximum expected current in both directions. A ground rod is sometimes used as a substitute for a ground strap. The ground rod should be deep enough so that its outer surface is about 12 inches below the surface where it will not be exposed to damage.
A ground fault interrupter (GFI) is a device used to protect against shock hazards when working with electricity.
As a result, relays connected for earth fault protection differ from those connected for phase-to-phase fault prevention. An overcurrent relay is one that works or picks up when its current surpasses a predefined value (setting value). This type of relay is used where there is a chance of someone being injured by electricity if it gets into the electrical system. Earth faults are usually caused by animals such as monkeys, which sometimes stick their hands into power lines to catch insects.
For example, if you have live power coming in to your house and someone opens a door or window and causes a metal object to contact the ground, this would be considered an earth fault. The person might not even know they opened the door or window but nonetheless, an earth fault has been created. If this circuit is part of a whole house electronic security system, an alarm should go off when this happens. Without this protection, anyone could suffer serious injury or death if they got their hand into a live power line.
The best way to protect yourself from earth faults is to don't open doors or windows on your own house. Also, make sure all your household appliances are switched off and unplugged whenever you leave home.
If you still find yourself affected by an earth fault, a small electrical box located near a door or window would contain a device called an earth rod.
Some of the types of protective relays used in transmission lines are as follows: Relays for Protection: Protective relays detect faults and activate the appropriate control signal, such as the tripping signal. They can also provide alarm signals to indicate a problem so that it can be fixed before additional damage is done.
Remotely Operated Protective Relays (ROPRs): These relays are operated from a remote location by a person who does not have access to the power line corridor. They can only monitor voltage and current. Therefore, they cannot open circuit breakers or perform other functions normally performed by ground-based protective relays.
Multichannel Protective Relays: These devices can monitor several circuits at one time. They usually have 20 or more channels for monitoring different parts of the circuit.
Automatic Grounded (AG) Circuit Breakers: These devices use semiconductor components instead of magnetic cores for opening and closing electrical connections. They operate based on either current or voltage conditions. The advantage of this type of breaker over traditional ground-fault circuit interrupters (GFCIs) is that an abnormal condition on any part of the system will cause all other parts to trip simultaneously rather than only when a single conductor is affected like a GFCI.
A: Phase protection relays are intended to safeguard three-phase loads from mains voltage damage. The phase protection relays are intended to safeguard three-phase loads from mains voltage damage. They do this by opening the relevant circuit in response to any rise above a specified level in any one of the conductor wires that make up the mains power supply. For example, if all three wires were to reach maximum voltage at the same time, the phase protector would open all three circuits to prevent current from flowing through them.
Phase protection relays are designed to operate over a wide range of temperatures. They use thermally activated components to provide instantaneous action when overload conditions occur. These components include magnetic reed switches and thermal fuses. Magnetic reed switches consist of a flat strip of magnetically sensitive material mounted inside a glass tube. When electricity passes through the wire attached to the tube, the magnetic field it creates activates the switch which opens the corresponding circuit breaker or lamp holder.
Reed switches are more reliable than other types of magnetic contactors because they do not suffer from corrosion caused by conductive moisture entering the device. However, reed switches also require periodic maintenance by removing any dust or debris that may interfere with their operation.
Thermal fuses are small capsules of carbonized silk coated with iron oxide.