Consider the following statements with reference to Protective Relays:1.The minimum relay coil current at which the relay operates is called pick-up value.2.The pick-up value of a relay is 7.5 A and fault current is 30 A. Therefore its plug setting multiplier is5.3. An earth fault current is generally lesser than the short-circuit current.4.Induction relays are used with both A.C. and D.C quantities.Which of these statements are correct?

Correct Answer: D - 1 and 3 only

Quick Concept Explanation

Plug setting multiplier is the fault current divided by relay pickup current. PSM=I_fault/I_pickup=30/7.5=4, so the statement claiming 5 is numerically incorrect. Key relation: PSM=I_fault/I_pickup.

Exam focus: Calculate PSM numerically before selecting an option. Common trap: Induction-type relays are not used directly on DC quantities.

Statement-wise Verification

• Statement 1 - Correct.
  The minimum relay coil current at which the relay operates is called pick-up value.
  Plug setting multiplier is the fault current divided by relay pickup current.
• Statement 2 - Incorrect.
  The pick-up value of a relay is 7.5 A and fault current is 30 A. Therefore its plug setting multiplier is
  5. 3. An earth fault current is generally lesser than the short-circuit current. 4. Induction relays are used with both A.C. and D.C quantities. PSM=30/7.5=4, not 5
• Statement 5 - Review.
  3. An earth fault current is generally lesser than the short-circuit current.
  Earth-fault current is often lower than a three-phase short-circuit current because the zero-sequence path adds impedance.
• Statement 4 - Review.
  Induction relays are used with both A.C. and D.C quantities.
  Induction relays require alternating flux and are AC devices.

Core Concept

Protective-relay pickup is the minimum actuating quantity that causes operation. Plug setting multiplier is the fault current divided by relay pickup current. Earth-fault current is often lower than a three-phase short-circuit current because the zero-sequence path adds impedance. Induction relays require alternating flux and are AC devices.

Formula / Key Relationship

PSM=I_fault/I_pickup.

Step-by-Step Check

PSM=I_fault/I_pickup=30/7.5=4, so the statement claiming 5 is numerically incorrect.

Why the Other Options Are Wrong

Option A is incorrect because it includes incorrect statement(s) 2 and omits correct statement(s) 3. Option B is incorrect because it includes incorrect statement(s) 2 and omits correct statement(s) 1. Option C is incorrect because it includes incorrect statement(s) 2, 4 and omits correct statement(s) 3.

Exam Shortcut / Approach

Calculate PSM numerically before selecting an option.

Common Mistake

Induction-type relays are not used directly on DC quantities.

Quick Revision

Pickup PSM Earth Fault and Induction Relay is linked with Protective Relays, Protection and Power Systems. Calculate PSM numerically before selecting an option.