Setting formula for definite time and inverse time overcurrent protection - Database & Sql Blog Articles

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Time limits in electrical protection systems are crucial for ensuring the safety and reliability of circuits. There are two main types of time limits: definite time limit and inverse time limit.

Definite Time Limit: This type of protection has a fixed time delay, regardless of the current level. It is used when a consistent response time is required, such as in applications where rapid tripping is not necessary.

Inverse Time Limit: In this case, the response time decreases as the current increases. The higher the current, the faster the protection system will act. This type is commonly used in overcurrent protection to allow for temporary overloads without unnecessary tripping.

According to IEC standards, inverse time limits are further categorized into three types:

• Standard Inverse Time Limit: t = 0.14 * tp / ((I/Ip)^0.02 - 1)
• Very Inverse Time Limit: t = 13.5 * tp / ((I/Ip) - 1)
• Extreme Inverse Time Limit: t = 80 * tp / ((I/Ip)^2 - 1)

Here, "tp" represents the pickup time, "I" is the actual current, and "Ip" is the pickup current. The exponents (^0.02 and ^2) indicate the power of the respective values.

This classification helps engineers select the most appropriate protection mechanism based on the application's requirements, ensuring both performance and safety in electrical systems.