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If fault current is 30A and peak up current is 7.5A then PSM is

Correct Answer

⚙️ TE • Technical Direct FormulaElectricalPower System

Option A

Quick Summary:

Given: Fault current $I_{f}$ = 30A, Pickup current $I_{p}$ = 7.5A

📐MAMath SolutionDirect Formula

📋 Given

Fault current $I_{f}$ = 30A, Pickup current $I_{p}$ = 7.5A

🔢 Formula Used

PSM=IfIpPSM = \frac{I_f}{I_p}PSM=Ip​If​​

🔢 Step-by-Step Solution

Identify given parameters

Identify the primary parameters required for Plug Setting Multiplier (PSM) calculation: the fault current $I_f = 30A$ and the relay pickup current $I_p = 7.5A$ .

If=30A,Ip=7.5AI_f = 30A, I_p = 7.5AIf​=30A,Ip​=7.5A

Apply PSM formula

The Plug Setting Multiplier is defined as the ratio of fault current flowing in the relay coil to the pickup current.

PSM=IfIpPSM = \frac{I_f}{I_p}PSM=Ip​If​​

Calculate the result

Substitute the given values into the formula: $PSM = 30 / 7.5 = 4$ .

PSM=307.5=4PSM = \frac{30}{7.5} = 4PSM=7.530​=4

✅

A is correct because the ratio of the fault current to the pickup current results in a PSM of 4.

Core Concepts Used

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Relay Protection Plug Setting Multiplier Fault Analysis

💡 EXAM TIP

PSM is a critical factor in determining the operating time of an IDMT relay; higher PSM values lead to faster operation times according to the inverse characteristic curve.

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