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Homework answers / question archive / A time grading is provided in following relay system, an alternator rated at 60kV, protected by balanced circulating current system, parallerly a delta -star connected alternator of 6

A time grading is provided in following relay system, an alternator rated at 60kV, protected by balanced circulating current system, parallerly a delta -star connected alternator of 6.6kV, 5MVA, specification is connected. Merz-Price protection scheme is used which operates when relay current exceed 50% of armature current. The neutral of the generator is grounded through a resistance of 8 ohms.

(I) Determine the proportion of the winding which is remain unprotected against faulty conditions.

(II) Determine the percent winding which remain unprotected.

(III) Assume a CT ratio will be 40/120; determine whether the relay will operate or not?

(IV) What should be the specification of the differential protection scheme according to the given system?

(V) Draw the threshold characteristic of the system?

(VI) Determine the average rate of rise of restriking voltage?

(VI) Discuss how the rotar will be protected against the earth fault? A 3- phase, 6 pole, 1000 r.p.m alternator has an air-gap diameter of 42 cm and a core length of 31 cm. A two layer narrow spread(?*δ*? =?72??) winding is employed and the winding is accommodated in 4 slots per pole per phase, with 12 conductors per slot. If the per phase reactance of the alternator at 50 Hz is 10 ?Ω?, calculate the circulating current when the machine is delta connected. Determine the phase and line e.m.f in case the narrow-spread coils are connected to form (a) 2-phase winding and (b) 3- phase star-delta connected winding? Also calculate the percentage increase in per phase r.m.s emf due to harmonic. Also, calculate the ratio of resultant line emf to the resultant phase emf. Draw one complete cycle of the emf generated in a single-turn coil-span of 180 degrees electrical. Determine the rms value of the voltage in the single turn coil? Finally calculate the rms value of the fundamental emf per phase?

A 20 MVA, 6.6KV, 3phase alternator is connected to a 3-phase transmission line. The whole transmission line has a two-machine power system. Two ground faults take place at two different locations. The neutral of the alternator is connected to ground, the alternator is connected with unloaded synchronous generator operating at it's rate, where the fault occurs at the terminals, the sequence component of the fault current are as follows- ?*Ipositive*?=*j*1.5*pu*? , ?*Inegative*?? = -j0.5 pu.

Determine all the types of the faults occured in the circuit. Calculate value of the fault occured. Calculate the resistance and the shunt susceptances of the system. Calculate the voltage and the current at the point of the fault. Determine the types of the relays engage in the whole system. Design the whole system of circuit and also suitable spots for circuit breaker.

Three electrical machines are connected parallarly in synchronism with each other, one is unbalanced star-delta tranformer, one is 3 phase salient pole induction motor and the last one is single pole alternator. They all are connected in ring main system network. The impedance characteristic of whole system is constant. How to find the motors ratings for variable load drives. In the whole system which shaft will be the first one to fail due to fatiguness if the synchronism will be lost. Explain the desired properties for the shaft for the whole system. What is the role of the armature flux of the armature teeth in the whole system. Design the complete commutator segment for the complete system. How many number of parallel paths are possible in the whole system.