Answer By true or false• The line-to-line short circuit is the highest short circuit current that can occur in a low voltage installation• A 3-phase bolted short-circuit is a short circuit of considerable impedance• The short circuit rating of an electrical equipment is the prospective symmetrical fault current at a nominal voltage towhich an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria• If the total power of 3-phase motors running simultaneously is higher than 25 % of the total power of transformers, theinfluence of motors must be taken into account.• The motors concerned in short circuit calculations are the 3-phase motors only; single-phase-motor contribution beinginsignificant.• The breaking capacity of the circuit breaker must be less than the maximum three phase bolted short circuit that iscalculated at a certain point• When short circuit occurs, the internal impedance causes voltage to drop from no-load condition (U_20) to bring it to Unwhen the transformer delivers Isc. In normal conditions, this impedance limits the voltage to a value, given in multiplesof Un.• Breaking Capacity is the level of current that the circuit breaker can interrupt without damaging itself electrically orstructurally and without causing an electric arc with unacceptable duration.• A 3-phase bolted short circuit current results in a sudden raise in voltage• To calculate the 3-phase bolted short circuit current at a certain point we should calculate first the impedance of all thecomponents downstream that point.• The Bolted three phase short circuit is used to determine thermal withstand rating of the cables, and the breakingcapacity setting of a circuit breaker.• Short circuit calculations must be done on each point of the installation to determine the nominal rating of the circuitbreakers.Choose...Choose...Choose...Choose...Choose...Choose...Choose...Choose...Choose...Choose...Choose...Choose...

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Answer By true or false • The line-to-line short circuit is the highest short circuit current that can occur in a low voltage installation • A 3-phase bolted short-circuit is a short circuit of considerable impedance • The short circuit rating of an electrical equipment is the prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria • If the total power of 3-phase motors running simultaneously is higher than 25 % of the total power of transformers, the influence of motors must be taken into account. • The motors concerned in short circuit calculations are the 3-phase motors only; single-phase-motor contribution being insignificant. Choose... Choose... Choose... Choose... Choose...

Answer By true or false • The line-to-line short circuit is the highest short circuit current that can occur in a low voltage installation • A 3-phase bolted short-circuit is a short circuit of considerable impedance • The short circuit rating of an electrical equipment is the prospective symmetrical fault current at a nominal voltage to which an apparatus or system is able to be connected without sustaining damage exceeding defined acceptance criteria • If the total power of 3-phase motors running simultaneously is higher than 25 % of the total power of transformers, the influence of motors must be taken into account. • The motors concerned in short circuit calculations are the 3-phase motors only; single-phase-motor contribution being insignificant. Choose... Choose... Choose... Choose... Choose...

Electric Motor Control

10th Edition

ISBN:9781133702818

Author:Herman

Publisher:Herman

Chapter14: Phase Failure Relays

Section: Chapter Questions

Problem 1SQ: What is the purpose of phase failure relays?

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