- pick-up current setting = 1000 A x 0.8 = 800 A.The relay pick-up current value is set at 0.8, time multiplier setting is 7 and the fault current is 8000 A.

These are given by:ДЄn 1000 Amp breaker protected by relay with Standard Inverse characteristic. Tripping times for the various relays are: Standard Inverse (SI)Д¬urrent time characteristics in North America as classified as IEEE Moderately Inverse, IEEE Very Inverse, IEEE Extremely Inverse, US C0 8 Inverse and US CO 2 Short Time Inverse. a standard inverse curve which will trip in 3 seconds at 10 times the current setting). Relay characteristics are sometimes classified according to the tripping time at 10 times the setting current (i.e. I = fault (actual) secondary CT current (A) Each characteristic can be calculated from: The IEC 60255 standard defines four standard current time characteristics вЂ“ standard inverse (SI), very inverse (VI), extremely inverse (EI) and long-time inverse. Tripping Curves IEC 60255 Characteristics More recently static relays have been superseded by first digital relays and now numerical microprocessor based devices. Static relays have no moving parts (hence the name) and operated on the basis of analogue circuitry. While still being reliable and widely used these were superseded by static relays in the early 1980s. Mechanical relays developed in the 1800s were the first form of electrical protection. While over recent years these have been replaced by microprocessor based numerical devices, there are still many older electromechanical relays in service. Electromechanical relays have been the traditional backbone of electrical protection systems.

Cdg34 relay manual