# Two 3-phase, Y-connected alternators are to be paralleled to a set of common busbars. The armature has a

23 views
Two 3-phase, Y-connected alternators are to be paralleled to a set of common busbars. The armature has a per phase synchronous reactance of 1.7 Ohm and negligible armature resistance. The line voltage of the first machine is adjusted to 3300 V and that of the second machine is adjusted to 3200 V. The machine voltages are in phase at the instant they are paralleled. Under this condition, the synchronizing current per phase will be

(A) 16.98 A (B) 29.41 A (C) 33.96 A (D) 58.82 A

Two 3-phase, Y-connected alternators are to be paralleled to a set of common busbars. The armature has a per phase synchronous reactance of 1.7 Ohm and negligible armature resistance. The line voltage of the first machine is adjusted to 3300 V and that of the second machine is adjusted to 3200 V. The machine voltages are in phase at the instant they are paralleled. Under this condition, the synchronizing current per phase will be 16.98 A

## Related questions

A 500 MW, 3-phase, Y-connected synchronous generator has a rated voltage of 21.5 kV at 0.85 p.f. The line current when operating at full load rated conditions will be  (A) 13.43 kA (B) 15.79 kA (C) 23.25 kA (D) 27.36 kA

A 3 Phase, 60 Hz generator connected in Y connection, generates a line to line voltage of 23900 V. Calculate the peak line voltage.  (A) 13800 V (B) 33800 V (C) 42300 V (D) 23900 V

The three non -inductive loads of 5 kW, 3 kW and 2 kW are connected in a star network between R, Y and B phases and neutral. The line voltage is 400 V. The current in the neutral wire is nearly (a) 11 A (b) 14 A (c) 17 A (d) 21 A

In a certain three -wire Y -connected generator, the phase voltages are 2 kV. The magnitudes of the line voltages will be: A. 2,000 V B. 6,000 V C. 666 V D. 3,464 V

The sequence components of current of a single-phase load connected to a 3-phase system are (A) equal positive and negative sequence components (B) equal positive, negative and zero sequence components (C) vector sum of sequence currents is zero (D) algebraic sum of sequence currents is zero

The power delivered to a 3-phase load can be measured by the use of two wattmeters only when the  (a) load is unbalanced (b) load is balanced (c) three phase load is connected to the source through three wires (d) three phase load is connected to the source through four wires

Two wattmeters are used to measure the power in a 3 -phase balanced system. What is the power factor of the load when one wattmeter reads twice the other ?  (a) 0 (b) 0.5 (c) 0.866 (d) 1

If two 3-phase transformers with unequal voltage ratios are connected in parallel, the result is (A) circulating current on no-load (B) no circulating current on no-load (C) dead short-circuit (D) equal no-load secondary emfs

When two alternators A and B are operating in parallel, the increase in steam supply to alternator A will cause the active power output of (1) Alternator A to be decreased and alternator B to be increased (2) Alternators A and B is not affected (3) Alternators A and B is increased (4) Alternator A to be increased and alternator B to be decreased

A 30 MVA, 15 KV, 1500 rpm, 3 phase synchronous generator connected to a power grid has a synchronous reactance of 9 ohm per phase. If the exciting voltage is 12 kV (line to neutral) and the system voltage is 17.3 kV (line to line), Calculate the maximum power that generator can deliver before it falls out of step (losses synchronous).  (A) 39.952 MW (B) 78.349 MW (C) 16.67 MW (D) 112.89 MW

Two sinusoidal signals having the same amplitude and frequency are applied to the X and Y inputs of a CRO. The observed Lissajous figure is straight line. The phase shift between the two signals would be (1) Zero (2) 90 degrees (3) Either zero or 180 degrees (4) Either 90 degrees or 270 degrees

Two two-port networks are connected in cascade. The combination is to be represented as a single two-port network. The parameters of the network are obtained by multiplying the individual a. z-parameter matrix b. h-parameter matrix c. y-parameter matrix d. ABCD-parameter matrix

A 3-phase star-connected 75 MVA, 25 kV 3-phase synchronous generator has a synchronous reactance of 1.0 p.u. The per unit value to a 90 MVA base and 30 kV is (A) 2/15 p.u. (B) 5/6 p.u. (C) 1.0 p.u. (D) 1.2 p.u.

A 400 V, 15 kW, 4-pole, 50 Hz, Y-connected induction motor has full load slip of 4%. The output torque of the machine at full load is  (A) 1.66 Nm (B) 95.50 Nm (C) 99.47 Nm (D) 624.73 Nm

At a particular instant, the R-phase voltage of a balanced 3-phase system is + 30 V, and the Y-phase voltage is – 90 V. The voltage of B-phase at that instant is (A) + 120 V (B) – 120 V (C) – 60 V (D) + 60 V

In a Y -connected circuit, between each line -voltage and the nearest phase - voltage, there is a phase -angle of: A. 0° B. 30° C. 60° D. 120°

Measurement of power and power factor of a 3-phase system by two wattmeter method can be obtained in case of  1. Balanced load and balanced source  2. Balanced source with 3-phase 3-wire unbalanced load  3. Unbalanced source with 3-phase 3-wire balanced load  4. Balanced source with 3-phase 4-wire unbalanced load  5. unbalanced and unbalanced source    (a) 1 only (b) 2, 3 and 5 (c) 1, 2, 3, 4 and 5 (d) 1, 2, 3 and 5

Three equal impedances are first connected in delta across a 3 -phase balanced supply. If the same impedances are connected in star across the same supply then,

A two-phase generator is connected to two 90Ω load resistors. Each coil generates 120 V ac. The value of current flowing through the common neutral line will be: A. 1.33 A B. 1.88 A C. 2.66 A D. 1.77 A

If the excitation of an alternator operating in parallel with other alternators decreased, its: (1) Power factor becomes more leading (2) Output Kw will change (3) Power factor becomes more lagging (4) Power factor becomes unity

A 3-phase delta connected squirrel cage induction motor when started with a DOL starter has a starting torque of 600 NM. Its starting torque when star delta starter is used:

A 4000 kVA, 11 kV/132 kV delta-star connected 3-phase transformer has reactance, x1 = 0.12 p.u. The actual value of x1 referred to the low voltage side is (A) 0.85 Ω (B) 3.63 Ω (C) 36.3 Ω (D) 252 Ω

A single-phase transformer has a turns ratio of 1 :2 and is connected to a purely resistive load as shown in the figure. The magnetizing current drawn is 1A, and the secondary current is 1A. Ifcore losses and leakage reactances are neglected, the primary current is  A)1.41A B)2A C) 2.24A D)3A

A 3-phase induction motor is running at slip ‘s’. If its two supply leads are interchanged, then the operating slip at that instant will be:

Two waves have frequency of 500 Hz. One is set at its maximum value whereas the other at zero. The phase angle between them will be

In CRO, Lissajous pattern will be a straight line, if the two signals are of same frequency with a phase difference of (a) 0° (b) 180° (c) 360° (d) All of these

The two inputs of a CRO are fed with two stationary periodic signals. In the X-Y mode, the screen shows a figure Which changes from ellipse to circle and back to ellipse with its major axis changing orientation slowly and repeatedly. The following inference can be made from this  A) The signals are not sinusoidal ... but not equal C) The signals are sinusoidal with their frequencies very close but not equal D) There is a constant but small phase difference between the signals

When the phase difference between two sinusoidal quantities is 90° they are said to be ______ A) Phase right angle B) Phase quadrature C) Phase sinuright D) None of these

Which of the following are 3 byte instruction set ? (a) MV 1A, 32 H (b) JMP 2085 H (c) MOV C, A (d) ADD B

A 20-MVA, 6.6-kV, 3-phase alternator is connected to a 3-phase transmission line. The per unit positive-sequence, negative-sequence and zero-sequence impedances of the alternator are j0.1, j0.1 and j0.04 respectively. The neutral of the alternator is connected to ground through an inductive reactor of j0.05 p.u. The per unit positive-, ... The voltage of the alternator neutral with respect to ground during the fault is  (A) 513.8 V (B) 889.9 V (C) 1112.0 V (D) 642.2 V

The armature current on symmetrical 3 phase short circuit of a synchronous machine (salient pole)  (A) has q -axis current only (B) has d -axis current only (C) has both d and q axis currents (D) cannot be divided between q and d axis currents

Each branch of Y-connected load has resistance of 10 Ω. The resistance of each branch of an equivalent ∆-connected load will be   (a) 30 Ω (b) 100 Ω (c) 110 Ω (d) None of these

A differential amplifier has a differential gain of 28000 and CMRR is 60 dB. What will be the value of common mode gain? A) Ac = 0.125 B) Ac = 0.33 C) Ac = 3 D) Ac = 28

Two resistors are said to be connected in series when?

In a two -channel oscilloscope operating in x -y mode, two in -phase 50 Hz sinusoidal waveforms of equal amplitude are fed to the two channels. What will be the resultant pattern on the screen ? (a) An ellipse (b) A parabola (c) Straight line inclined at 45° with respect to x-axis (d) A circle

The main application of delta/zig-zag connected 3-phase transformer is to supply (A) balanced loads (B) unbalanced loads (C) furnace loads (D) single-phase loads

Two 3-phase synchronous generators with reactance 60% and 40% feed a fault current of 1200 A up to short-circuit fault point. The short-circuit current is (A) 1200 A (B) 2400 A (C) 4000 A (D) 5000 A

In a 3-phase 4-wire distribution system three unbalanced but equal magnitude impedances are connected between respective lines and neutral. The magnitude of current in the neutral conductor for RYB and RBY phase sequences are (A) zero (B) same (C) different (D) same in magnitude but differs in phase.

Two transformers with identical voltage ratings are working in parallel to supply common load. The percentage impedance of one transformer is higher compared to that of other. The load sharing between the two transformer will: (1) Be proportional to their percentage impedance (2) Be independent of their percentage impedance (3) Be inversely proportional of their respective impedance (4) Depend on the resistance to leakage reactance ratio of each transformer

Two wattmeter method is employed to measure power in a 3 -phase balanced system with the current coil connected in the A and C lines. The phase sequence is ABC. If the wattmeter with its current coil in A -phase line reads zero, then the power factor of the 3 -phase load will be

Two wattmeters connected to measure the power input to a balanced three-phase circuit indicate 4.5 KW and 3 KW respectively. Find the power factor of the circuit. A. 0.7 B. 0.8 C. 0.95 D. 0

When two alternators are operating in parallel, the cause for circulating current is (A) increase in the excitation of one machine (B) increase in the driving torque of one machine (C) reduction in angular velocity of one machine (D) identical speed/load characteristics of both machines