The inverse time … Their time-current characteristic curves are: Definite minimum, CO-6 Moderately inverse, CO-7 Inverse, CO-8 Very inverse, CO-9 Extremely inverse, CO-11 These time-current characteristics are compared in Figure below. The block diagram of the inverse-time overcurrent relay is shown in the figure. Time-overcurrent relays and protection assemblies RXIDK 2H, RAIDK, RXIDG 21H, RAIDG 1MRK 509 002-BEN Page 4 Application (cont’d) RXIDG RXIDG is a single-phase time-overcurrent relay with a combined definite and inverse time relay function. Inverse-Time Overcurrent Relay 3. They are available with standard inverse, very inverse and extremely inverse characteristics. You can use combinations of curve types to achieve the design requirements. Time Overcurrent Relays Fall 2018 U I ECE525 Lecture 11 Extremely Inverse Curve and 50E fuse Time Overcurrent Relays Fall 2018 U I ECE525 Example Lecture 11 Vs Z1 Local Load Local Load Local Load Faulted Line Bus #1 Bus #2 Bus #3 Z3 Z4 Z2 Source R2 R3 R4 • Want the relay on the faulted line, R4, to be the only relay to trip Very Inverse Relay 6. Definite Time Overcurrent Relay 4. 1. Extremely Inverse Time Overcurrent and Earth Fault Relay A high set overcurrent unit (type CAG) can be fitted in the same case to provide instantaneous protection under maximum short circuit conditions (see Application Sheet R-5087). This means that the operating time decreases with increasing current magnitude. Inverse Definite Minimum Time (IDMT) Relays 5. In this type of relays, operating time is inversely changed with the current. Extremely Inverse Relay. These relays can replace the following GE electromechanical & static relay types that require a time overcurrent range of 0.5-15.9 Amps and an instantaneous overcurrent range of 1-159 Amps: IAC51 IAC53 IAC55 IAC57 IAC66 IAC77 IAC95 IFC51 IFC53 IFC57 IFC66 IFC77 IFC95 SFC151 SFC153SFC177 So, high current will operate overcurrent relay faster than lower ones. Inverse-Time Protection. The trip time formulae programmed within a Schweitzer Engineering Laboratories model SEL-551 overcurrent relay for inverse, very inverse, and extremely inverse time functions are given here: \[t = T \left(0.18 + {5.95 \over {M^2 - 1}} \right) \hskip 30pt \hbox{Inverse curve}\] Type CO-8 Inverse Time Relay Type CO-9 Very Inverse Time Relay Type CO-11 Extremely Inverse Time Relay! ADVERTISEMENTS: Depending upon the time of operation, overcurrent relays may be categorized as: 1. In American standard there are five different types of time overcurrent relay. 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