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...

Introductory Circuit Analysis (13th Edition)

13th Edition

ISBN:9780133923605

Author:Robert L. Boylestad

Publisher:Robert L. Boylestad

Chapter1: Introduction

Section: Chapter Questions

Problem 1P: Visit your local library (at school or home) and describe the extent to which it provides literature...

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Consider the system shown in the single-line diagram of Figure (3). All reactances are shown in per unit to the same base. Assume that the voltage at both sources is 1 p.u. a Find the fault current due to a bolted- three-phase short circuit at bus 3 b- Find the fault current supplied by each generator and the voltage at each of the buses 1 and 2 under fault conditions 0.06 p.u. 0.2 p.u. 0.04 p.u. 0.25 p.u. 0.2 p.u. 0.2 p.. 0.2 p.u. 0.06 p.u. 0.25 p.u. Figure (3) Single-line diagram ele ver ele 888 ele 0.06 p.u. 0.25 p.u.
-The symmetrical fault occurs in the terminals of the synchronous generator. Find the direct axis transient reactance of the synchronous generator under the transient period for the data given below, Leakage reactance(Xl)= 1.3 ohm, Armature reactance (Xad)= 1.6 ohm and field reactance (Xf)=5.4 ohm. 2.10 2.53 1.23 4.00 -The existing condition of the power system can be determined by _____________ analysis. Short Circuit Stability Power Flow Transient
Explain the principles of power system protection, including the role of relays and circuit breakers in safeguarding the grid.
A 600 KVA generator with X"a = 0.22 per unit is connected to a bus through a circuit breaker, as shown in the following figure. Connected through circuit breakers to the same bus are three synchronous motors rated 200 KVA, 2.5 KV, 1.0 power factor, with X"a = 0.15 per unit. The motors are operating at full load, unity power factor and rated voltage, with the load equally divided among the machines. (a) Find the rated symmetrical short-circuit current in Amperes, which must be interrupting breakers A and B for a fault at point P. Simplify the calculations by neglecting the Prefault current. M. GHA B
A radial system shown in figure below is fed from a supply of 220 Volt. All impedance values are referred to 220V side (3 phase). When a three phase fault occurs at E, relay D will operate with 0.4 second longer than relay at E. Determine TSM (Time Setting Multiple) at A, B C and D by taking discrimination time (DT) equal to 0.4 second, and TSM at C is already set equal to 0.05. The protection data is as given in figure while IDMT relay characteristic is as in table.
A resistance of 8 Ohms is used to ground a 30-MVA, 11 kV alternator. Its relay is set to operate when a 2.2 A out of balance current occurs. The CTs have a ratio of 1000/6. If we consider the reactance of the alternator to be negligible, how much percentage of the stator winding is protected against earth faults? To make this 95%, what is the minimum value of earthing resistance to be used?
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Contribution of fault analysis in power system netwrok?
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How do power system protection and relay systems work to ensure the safety and reliability of the grid during faults and disturbances?
A 100-MVA, 18-kV generator is connected to a transformer. The generator has reactances of 19%, 26% and 130% and time constraints of Td" = 0.035 sec, Td' = 2.0 sec and TA = 0.2 sec. A 5-cycle breaker is connected between the generator and the transformer. A three=phase short circuit occurs between the breaker and the transformer when the generator is operating at 5% above rated voltage and at no-load. Calculate a. The minimum instantaneous symmetrical fault current which the breaker interrupts (kA) b. The instantaneous asymmetrical fault current (kA) which the breaker interrupts assuming maximum DC offset
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