Correct Answer

Direct FormulaElectricalPower System

Option B

35A

Quick Summary: Given: Plug Setting Multiplier (PSM) = 5, Pickup Current (I_pickup) = 7A

📋 Given

Plug Setting Multiplier (PSM) = 5, Pickup Current ( $I_{pickup}$ ) = 7A

🔢 Formula Used

PSM=FaultCurrent(If)PlugSetting(Ip)PSM = \frac{Fault Current (I_f)}{Plug Setting (I_p)}PSM=PlugSetting(Ip​)FaultCurrent(If​)​

🔢 Step-by-Step Solution

Define the relationship

The Plug Setting Multiplier (PSM) is defined as the ratio of the actual fault current to the pickup current (or plug setting).

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

Rearrange the formula

To find the fault current $I_f$ , rearrange the formula as $I_f = PSM \times I_p$ .

If=PSM×IpI_f = PSM \times I_pIf​=PSM×Ip​

Calculate the fault current

Substitute the given values $PSM = 5$ and $I_p = 7A$ into the equation.

If=5×7=35AI_f = 5 \times 7 = 35AIf​=5×7=35A

✅

B is correct because multiplying the Plug Setting Multiplier of 5 by the pickup current of 7A results in a fault current of 35A.

Core Concepts Used

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Relay Protection Plug Setting Multiplier Fault Current Calculation

💡 EXAM TIP

The PSM is a critical parameter in Inverse Definite Minimum Time (IDMT) relay coordination, directly determining the operating time of the relay on the time-current characteristic curve.

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