Over Current Relay Setting Calculator
Calculate optimal overcurrent relay settings for motors, transformers, and feeders. Determine pickup current, time dial, and protection coordination accurately.
Over Current Relay Setting Calculator:
An overcurrent relay is a device that is used to guard electrical appliances against current overload. The Over Current Relay Setting Calculator calculates the best pickup current, time dial settings based on the load current, service factor, and the type of relay. When relay settings are properly set, they provide safe, selective, as well as reliable protection of the motors, transformers, and feeders.
Over Current Relay Setting Tools formula
The Over Current Relay (OCR) Setting Calculator is a tool that calculates the correct settings of the overcurrent protection devices that are applied in electrical systems. It computes pickup current, relay operating time, and provides proper coordination between the upstream and downstream protective devices using such inputs as full load current (FLC), service factor, relay multiplier, and time dial setting (TDS).
Electrical engineers, substation operators, and technicians should have this tool to guard against overcurrent conditions associated with transformers, motors, and feeders. Proper settings of the relays eliminate nuisance tripping, damage to equipment, and selective protection. The calculator accommodates the inverse time relays and definite time relays, and as such can be set correctly using the IEEE/IEC standard.
Work & Installation — Input to Output Summary
Work:
- Calculates OCR settings for protective relays.
- Supports motor, transformer, and feeder protection.
- Helps ensure selective coordination and system safety.
Installation:
- Add HTML input fields for FLC, service factor, relay multiplier, and TDS.
- Include JavaScript formulas:
Pickup current = FLC × service factor × relay multiplier
Operating time = TDS × relay characteristic constant (from standard curves) - Display pickup current (A) and relay operating time (s).
Input:
- Full load current (FLC, A)
- Service factor (SF, decimal)
- Relay multiplier (K, per relay characteristic)
- Time dial setting (TDS, optional)
- Relay type: Inverse / Definite time
- Pickup current (A)
- Relay operating time (s)
- Relay coordination recommendation (optional)
Testing and Final Adjustments
Test sample motors and transformer ratings: e.g., Motor FLC = 50 A, SF =1.1, K=1.2. Pickup current = -66 A. Test operating time with IEC inverse curves or a definite time formula. Make sure that the calculator can work with SF and TDS in the form of decimal numbers. Check unit consistency (A current, s time). Add zero or negative input error handling. Make it mobile responsive by optimizing for real-time updates as the inputs change. Visualization of relay characteristics vs operating time may be optional. After testing, round-off, and layout engineering and educational applications, make sure that OCR settings are correct in all typical protection cases.
Frequently Asked Questions - Over Current Relay Setting Calculator:
What is an overcurrent relay?
An overcurrent relay protects equipment by detecting and tripping on excessive current.
What is pickup current?
Pickup current is the minimum current at which the relay starts operating.
How is relay operating time calculated?
Operating time depends on the relay's time dial setting and characteristic curve.
What is time dial setting (TDS)?
TDS adjusts the operating time of a relay to coordinate with other protective devices.
Can this calculator be used for motors?
Yes, it calculates OCR settings for motors, transformers, and feeders.
What is a relay multiplier?
The relay multiplier is used to scale pickup current based on relay settings and load.
What is service factor?
Service factor accounts for motor overload and allowable operating margin.
Why is selective coordination important?
Selective coordination ensures only the faulted section trips without affecting the rest of the system.
Does it support inverse time relays?
Yes, both inverse time and definite time relays are supported.
What units are used for OCR settings?
Pickup current is in amperes (A) and relay operating time in seconds (s).
