Erratum: Protective Relays: Their Theory and Practice—Vol. 2

Protective and control relays as coal-mine power-supply ACS subsystem

“…However, the direct use of this second, delayed BLP kit provided with a conventional selective time delay is contrary to the requirements [1]. Therefore, backup protection must be operated instantaneously.…”

“…The CASSP algorithm depends on where SC occurs in the mine power supply circuit and the location of the breaker of the circuit providing two sources to power its consumers. [1] prohibits the subsurface use of loop power systems.…”

“…For coal mines, as dust and gas hazardous areas, the Safety Regulations [1] require installation of instantaneous (non-delayed) short-circuit (SC) protection systems in 3-10 kV lines extending from the Central Underground Station (CUS) and underground distribution hubs (UDHs). In cases of net-work failure, protection enables single-shot automatic reclosing (AR) and automatic transfer switches (ATS) if used with equipment locking voltage supply to power lines and facilities in case of insulation damage caused by SC.…”

“…Time coordination between protective relays is unacceptable as provided by the requirements [1], while current coordination between protective relays is impossible due to small lengths (hundreds of meters) of the cable lines in the mine network.…”

The Operator's Assistant--An Intelligent, Expandable Program for Power System Trouble Analysis

“…2. The contacts themselves are activated by relays, the more common types of which are[5],[6] Overcurrent operates when a specified current exceeds a specified threshold Differential operates with a specified delay after the phasor sum of two or more currents exceeds a specified threshold Distance operates with a specified delay when the impedance it sees drops below a specified threshold…”