This means that the operating time decreases with increasing current magnitude. 1. The time-current characteristic curve is different for inverse time, definite time, and instantaneous relays. 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 Inverse-Time Protection. Extremely Inverse Relay. 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). You can use combinations of curve types to achieve the design requirements. Very Inverse Relay 6. They are available with standard inverse, very inverse and extremely inverse characteristics. Inverse-Time Overcurrent Relay 3. 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. The block diagram of the inverse-time overcurrent relay is shown in the figure. Definite Time Overcurrent Relay 4. Instantaneous Overcurrent Relay 2. I commonly use inverse-time, definite-time, and instantaneous elements, all on the same relay. Inverse Definite Minimum Time (IDMT) Overcurrent Relay. The type CDG 24 relay is a CDG 14 with an instantaneous unit. In this type of relays, operating time is inversely changed with the current. ADVERTISEMENTS: Depending upon the time of operation, overcurrent relays may be categorized as: 1. 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 3. 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. These relays operate when the current exceeds the pick-up value and with an operating time that varies inversely the magnitude of the current. In American standard there are five different types of time overcurrent relay. The inverse time … Type CO-8 Inverse Time Relay Type CO-9 Very Inverse Time Relay Type CO-11 Extremely Inverse Time Relay! So, high current will operate overcurrent relay faster than lower ones. 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: \[t = T \left(0.18 + {5.95 \over {M^2 - 1}} \right) \hskip 30pt \hbox{Inverse curve}\] Inverse Definite Minimum Time (IDMT) Relays 5.