Short-Circuit Calculations and Relay Coordination Applied to Cement Plants

5191 Words21 Pages
IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. IA-10, NO. 1, JANUARY/FEBRUARY 1974 57 Short-Circuit Calculations and Relay Coordination Applied to Cement Plants D. K. SHAH AND G. A. SHANNON Abstract-Today's codes and regulations make a coordinated power system a must for cement plants, both new ones and also the older plants. Short-circuit calculations must be made for ali possible fault points in the system. Based on calculated fault currents, ali the system protective devices must be applied and coordinated properly to achieve a coordinated power system. INTRODUCTION T HE importance of a coordinated electrical power system for an industrial plant cannot be stressed enough. Today it is not only good engineering and plant operating practice to require a coordinated power system, it is the law. The inception of the Occupational Safety and Health Act of 1970 and subsequent amendments establishes the 1971 National Electrical Code (NEC) as the electrical standard for inspection of all new installations as well as modifications or revisions to existing installations. Article 110, Sections 9 and 10, of the 1971 NEC reads as follows: 110-9. Interrupting Capacity. Devices intended to break current shall have an interrupting capacity sufficient for the voltage employed and for the current which must be interrupted. 110-10. Circuit Impedance and Other Characteristics. The overcurrent protective devices, the total impedance, and other characteristics of the circuit to be protected shall be so selected and coordinated as to permit the circuit protective devices used to clear a fault without the occurrence of extensive damage to the electrical components of the circuit. This fault may be assumed to be between two or more of the circuit conductors; or between any circuit conductor and the grounding conductor or enclosing metal raceway. SHORT-CIRCUIT

More about Short-Circuit Calculations and Relay Coordination Applied to Cement Plants

Open Document