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Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
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For protection of parallel feeders fed from one end the relays required at source end are
Non directional
Directional
Both A and B
None of above
Non directional
Quick Summary: For parallel feeders supplied from a single source, non-directional overcurrent relays are sufficient because fault current in both feeders flows in the same direction (away from the source). Directional relays are unnecessary at the source end because there is no possibility of reverse power flow in this specific configuration.
For parallel feeders supplied from a single source, non-directional overcurrent relays are sufficient because fault current in both feeders flows in the same direction (away from the source). Directional relays are unnecessary at the source end because there is no possibility of reverse power flow in this specific configuration.
Ifault=ZfeedVsource — Fault current calculation for radial/parallel feeders
In a parallel feeder system with a single source, the fault current contribution to any feeder always originates from the source bus. Since the fault current always travels in the forward direction towards the fault location, a standard non-directional overcurrent relay can accurately sense the overcurrent and initiate the trip sequence. Directional relays are specifically designed to respond to power flow in a predetermined direction, which is only required when multiple sources exist or when the fault could be fed from both ends (e.g., ring mains or parallel lines with two-end supplies).
Non-directional relays operate based on the magnitude of current exceeding a set pickup value.
Parallel feeders with one-end supply act as radial feeders in terms of power flow direction.
Directional relays increase cost and complexity without providing additional protection in single-end feed configurations.
In two-end fed parallel feeders, directional relays are mandatory to ensure selectivity.
Lower cost of protection equipment.
Simplified relay coordination logic.
Cannot differentiate between forward and reverse faults if the network topology changes (e.g., adding a second source).
Not suitable for closed-loop systems.
Industrial distribution substations.
Radial overhead transmission line networks.
When parallel feeders are connected to two sources at both ends, directional relays must be installed at both ends of each feeder.
Option B is incorrect because directional relays are only required where reverse current flow is possible during fault conditions.
A is correct — Non-directional relays are sufficient for single-end fed parallel feeders because fault current only flows in one direction from the source.
Always identify the number of sources in a power system diagram; if there is only one source, directional relays are generally redundant for feeder protection.