Over Current Relay Setting Calculator

Calculator

An Overcurrent Relay Setting Calculator is a online calculator tool that determines the proper relay settings to safeguard electrical circuits against excessive current flow. 

Proper relay settings provide fault detection, coordination, & system stability, which prevents equipment damage and reduces downtime.

An Overcurrent Relay Setting Calculator assists in determining precise relay settings by inputting 

• Rated Current, 
• Plug Setting Multiplier (PSM), and 
• Time Dial Setting (TDS), 

ensuring proper safety and synchronization in electrical systems.

Calculating the settings for an overcurrent relay is an essential step in electrical engineering. 

This calculator makes the procedure easier, providing an effective method to determine the relay settings required for best protection. 

This post explains you through the calculator’s usage, formula, and solved examples.

Formula

The formula for determining the overcurrent relay settings is given below:

Relay Setting = (PSM X Rated Current) / TDS

Where

PSM – Plug Setting Multiplier (PSM)

• Specifies the pickup current for relay operation.
• Common values include 50%, 75%, 100%, 125%, and 150% of rated current.

TDS – Time Dial Setting (TDS)

• Controls the delay in the relay tripping.
• Adjusted to account for collaboration with upstream and downstream relays.

Rated Current

How to Calculate Over Current Relay Setting?

Step-1: Enter the Rated Current in the appropriate input field.

Step-2: Choose the Plug Setting Multiplier (PSM) depending on the desired pickup current.

Step-3: Select the Time Dial Setting (TDS) for proper relay performance.

Step-4: Calculate the Relay Operating Time utilizing standard time-current curves (IEC/IEEE).

Step-5: Adjust the settings to guarantee optimum cooperation with other protective devices.

Importance of Overcurrent Relay Settings

• Protects transformers, wires, and motors from high currents.
• Enables only the nearest relay to trip, preventing unwanted power interruptions.
• Maintains system stability and prevents cascading failures in the electrical network.
• Improves safety by lowering the risk of fire & equipment failure caused by overcurrent circumstances.

An Overcurrent Relay Setting Calculator allows electrical engineers to precisely calculate relay settings, assuring dependable protection & efficient system performance.

Solved Example

How do you calculate the relay setting for a electrical system with a rated current of 1250 A, a Plug Setting Multiplier (PSM) of 150%, & a Time Dial Setting (TDS) of 0.25 seconds?

Given

Rated Current = 1250 A

Plug Setting Multiplier (PSM) = 150%

Time Dial Setting (TDS) = 0.25 seconds

Formula

Relay Setting = (PSM X Rated Current) / TDS

Solution

Relay Setting = (150 X 1250) / 0.25

Answer

Relay Setting = 7500.00 A

What is the PSM Setting?

Plug Settings Multiplier (PSM) t is the ratio of the actual fault current in the relay working coil to the pick-up current, or relay current setting. 

The Plug Setting Multiplier (PSM) shows the level of the fault. 

The plug setting multiplier is only utilized in electromagnetic relays and not numerical relays.

What is an Overcurrent Relay?

An overcurrent relay is a safety device. It is designed to activate when the current in the circuit exceeds a predefined threshold value. This device can detect inappropriate current levels.

What is an Overcurrent Relay Setting?

An overcurrent relay setting is a percentage-based ratio of overcurrent to load current.

What is the function of an overcurrent relay in an electrical system?

An overcurrent relay is a device that detects and interrupts excessive current flows in electrical systems, preventing damage from overloads (or) short circuits. 

It works by sensing the current and activating a trip mechanism when it surpasses a predetermined threshold.

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