Differential protection of feeders

by Joost Nusselder | Updated on:  July 24, 2021
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Differential protection is a method for protecting electrical lines. A differential feeder, or the “dummy load” as it’s often called, has an extra line of wire running parallel and grounded to provide added safety in case anything goes wrong with one side of the power supply. The Merz-Price circulating current system was originally developed by two German inventors who came up with this concept while they were working at Siemens on submarine cables!

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What is meant by differential protection?

Differential protection is a unit-type protection for specific zones or equipment. The differential current between the input and output currents can only be high in case of faults internal to that zone, meaning you are more protected from external threats where there will not be as much difference with your power coming into it; this also means if something goes wrong on the inside then you would know because the system alarm should go off at once!

How are feeders protected?

Most feeders are protected from short circuits. In a situation where power is suddenly cut, the circuit breaker nearest to it should open and all other breakers remain closed so that less electricity will flow through an already unstable system in case of another fault elsewhere on the line. It’s important though for this protection to be backed up by adjacent breakers if one fails- otherwise there could still be more faults causing blackouts or worse yet, fires!

Where is differential protection used?

Differential protection is a type of power system insulation that protects against phase-to-phase fault and phase to earth faults. Power transformers are protected by this method, which runs on the principle of circulating current developed in 1898 by Merz & Prize Company. This technique provides an additional measure for protecting high voltage equipment such as those rated at more than 2 MVA capacity from being damaged due to electrical surges or contact with other conductors when it malfunctions.

What are the difficulties of differential protection?

Differential protection is a complex issue, as it takes into account many variables. For example, unmatched transformer characteristics may cause mismatched CTs to trip prematurely or not at all; tapping the circuit causes an imbalance that can result in fires and explosions due to excess current flow (magnetizing of transformers). The magnetizing inrush currents encountered during startups are also difficult for differential protective devices to respond quickly enough when they occur because their response times vary depending on how fast they sense changes within the system. Differential protection has been around awhile and still remains one of our most powerful ways of safeguarding against faults across systems without compromising power quality issues such as voltage dips.

What is the difference between restricted earth fault and differential protection?

The difference between restricted earth fault and differential protection is that one detects phase faults within the Transformer on both primary and secondary sides, while the other only detects earth faults in a zone from Secondary winding to Secondary CTs.

What is percentage differential protection?

The percentage differential protection is a relay that protects the system by working with fractional relation of current. The Current transformer saturation, unequal CT ratios and nuisance trips are all potential problems for an electrician to protect against when installing or maintaining electrical systems.

On which principle differential protection is based?

Differential protection is based on the principle of comparing two or more electrical quantities. For example, a relay whose operation depends on phase difference and magnitude would be able to compare these qualities in order to detect any potential hazards before they have an opportunity for action.

Also read: these are the best frost-free hydrants to consider for your lot

Joost Nusselder, the founder of Tools Doctor is a content marketer, dad and loves trying out new equipment, and together with his team he's been creating in-depth blog articles since 2016 to help loyal readers with tools & crafting tips.
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