IEC 801-4:1988 Level 4 4kv, 2.5 kHz applied directly to IEC 255-22-4:1992 Class IV 4 kV, 2.5kHz applied directly to IEC 255-22-1:1988 Class III circuits and case. High frequency disturbance 2.5 kv peak between independent IEC 255-11:1979 ac ripple on the dc supply.ģ. AC ripple on DC supply The unit should withstand 12% IEC 255-11:1979 The unit should withstand aĢ. Incorrect operation may be either failure to trip or false tripping, the cause of it may be poor application, incorrect setting, personnel error, or equipment malfunction.ġ. Relay performance is generally classified, as (1) correct, (2) no conclusion, (3) incorrect. Supplementary relays such as signal relays, time relays, contact multiplier relays. Indirect-acting relays, those operate through auxiliary relays. Secondary relays connected through C.Ts and P.Ts. According to the method of connection to the power circuit Operating principle: Current balance, Percentage, Multi restraint, product, Solid state, Static, Microprocessor, Electromechanical, Thermal Performance characteristics: Distance, Directional over-current, Inverse time, Definite time, Under-voltage, Over-voltage, Ground or phase, High or low speed, phase comparison, Directional comparisonģ. Inputs: Current, Voltage, Power, Frequency, Pressure, Temperature, Flow, and vibration. According to input quantity, operating principle and performance characteristic. Protective relays, monitoring relays, reclosing relays, regulating relays, Auxiliary relays, synchronizing relaysĢ. Protection costs are considered high when considered alone, but they should be evaluated in the light of the much higher cost of the equipment they are protecting and the cost of an outage and/or the loss of the protected equipment. The simpler the protection system the greater is its reliability. Quick disconnection of a short-circuit, decreases the amount of damage incurred, maintains the machines running in synchronism (A high speed relay will operate in 3 cycles) The capability of the protection system to respond to abnormalities in normal operating conditions The ability of the protection system to “select” (search out) the point at which the fault appears and switch it out of the circuit by tripping the nearest circuit breaker. Generally, enhancing security tends to decrease the dependability and vice versa. SECURITY relates to the degree of ability that a relay system will avoid miss operation. ![]() DEPENDABILITY is the certainty of correct operation in response to system trouble. RELIABILITY HAS TWO ASPECTS I.E., DEPENDABILITY & SECURITY ![]() RELIABILITY, SELECTIVITY, SENSITIVITY, SPEED OF OPERATION, SIMPLICITY, AND ECONOMICS ARE SOME TERMS COMMONLY USED TO DESCRIBE THE OBJECTIVE OF SYSTEM PROTECTION. IT IS RATHER MINIMISING THE DURATION OF THE TROUBLE AND LIMITING THE DAMAGE. THE CAUSES OF THESE ABNORMAL CONDITIONS INCLUDE THE PRIMARY ROLE OF ELECTRICAL PROTECTION SYSTEM IS TO DETECT AND ISOLATE ABNORMAL CONDITIONS.ĪBNORMAL CONDITIONS EXPERIENCED IN POWER SYSTEMS ARE FAULTS, OVERLOADS, AND EQUIPMENT FAILURES. ROLES OF PROTECTION IN ELECTRICAL SYSTEM.
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