Inverse Definite Minimum Time (IDMT) relays are commonly used in electrical systems for the protection of equipment and circuits. These relays are designed to detect and respond to faults or abnormal conditions in a timely manner, thereby preventing damage to the system.

Explanation:
1. Inverse Definite Minimum Time (IDMT)
- The term "Inverse Definite Minimum Time" refers to the operating characteristic of the relay.
- "Inverse" indicates that the operating time of the relay decreases as the fault current increases. This means that the relay operates faster for higher fault currents.
- "Definite" means that the operating time of the relay is determined by a specific time-current characteristic curve.
- "Minimum Time" signifies that the relay will operate within a minimum time for high fault currents, ensuring swift protection.

2. Operating Characteristic
- IDMT relays have a specific time-current characteristic curve, which determines their operating time.
- The characteristic curve represents the relationship between the fault current magnitude and the operating time of the relay.
- The curve is typically plotted on a logarithmic scale, with the current magnitude on the x-axis and the time on the y-axis.
- The curve starts with a high slope at lower fault currents, indicating faster operation. As the fault current increases, the slope decreases, resulting in slower operation.

3. Minimum Time Lag
- The "Minimum Time Lag" in IDMT relays refers to the minimum operating time of the relay for the highest fault current.
- It ensures that the relay operates within a specific time, even for the highest fault current, providing quick protection.
- The minimum time lag is typically set based on the requirements of the system and the equipment being protected.

4. Protection Applications
- IDMT relays are widely used for protecting various electrical equipment and circuits, including transformers, motors, generators, and distribution systems.
- They provide reliable protection against faults such as overcurrent, short circuit, or earth fault.
- By operating within a minimum time for high fault currents, IDMT relays prevent damage to the equipment and minimize downtime.

In conclusion, IDMT relays stand for Inverse Definite Minimum Time Lag relays. They operate on a specific time-current characteristic curve, with a minimum operating time for high fault currents. These relays are essential for protecting electrical systems and equipment from faults.