Join 60,000+ competitive exam aspirants
or with email
Your Cart
Subtotal₹0
Total₹0
Examoogle • User • info@examoogle.com • EE-2024-8821
Chapter 1 of 12 • Page 1 of 248🔒 Protected PDF • Watermarked
Join 60,000+ competitive exam aspirants
Which protection system is used for earth fault in power transformer?
Merz prize protection
Earth fault protection
Both A and B
None of above
Both A and B
Quick Summary: Earth fault protection in power transformers is primarily achieved using differential protection schemes (often referred to as Merz-Price protection) and dedicated Restricted Earth Fault (REF) protection. These systems detect internal winding faults to ground by comparing current magnitudes and phases at transformer terminals.
Earth fault protection in power transformers is primarily achieved using differential protection schemes (often referred to as Merz-Price protection) and dedicated Restricted Earth Fault (REF) protection. These systems detect internal winding faults to ground by comparing current magnitudes and phases at transformer terminals.
Idiff=∣Iˉ1−Iˉ2∣ — The fundamental operating principle of differential protection where Idiff is the relay operating current.
Irestraint=2∣Iˉ1+Iˉ2∣ — The restraint current used in biased differential relays to prevent maloperation during through-faults.
Merz-Price protection utilizes the principle of current balance: under normal conditions, current entering the winding equals current leaving it. When an earth fault occurs, the balance is disturbed, creating a differential current Idiff=I1−I2 that operates the relay. REF protection specifically targets faults near the neutral point where traditional differential protection may have low sensitivity due to limited fault current.
Merz-Price protection is a percentage differential scheme.
REF (Restricted Earth Fault) protection is highly sensitive to faults near the transformer neutral.
Transformers require protection against both phase-to-phase and earth faults.
Biased relays are used to prevent nuisance tripping during external faults.
Provides high-speed operation for internal faults.
Selective, meaning it isolates only the faulted equipment.
Requires high precision in matching Current Transformer (CT) characteristics.
Cannot detect faults outside the protected zone.
Power transformers in generating stations.
Transmission and distribution substations.
Merz-Price is another name for differential protection using Pilot wires.
Option B is technically a subset or the intended application for the protection described in Option A.
C is correct — Both Merz-Price protection (differential) and dedicated Earth Fault protection systems are utilized to detect ground faults in power transformers.
Always remember that differential protection is 'Unit Protection', meaning it covers only the specific zone between the CTs placed at both ends of the transformer winding.