ELECRICAL ENGINEERING BITS-9

1.

Multi-layer helical windings are commonly used in the transformers as high voltage windings
 for 110 kV and above 

2.

_______is a negatively charged particle present in an atom.
 Electron 

In a synchronous motor, damper windings are provided on ________?

 stator frame.

We can apply source transformation to voltage source when a resistance is connected to it in

 14 HP.

To eliminate 5th harmonic in the induced voltage phase breadth should be ??

 72°

________is universally used for windings of electrical machines because it is easily workable without any possibility of fracture.
 Copper 

In a paper mill where constant speed is required

 individual drive is preferred

When the rotor speed, in a synchronous machine, becomes more than the synchronous speed during hunting, the damper bars develop ??
 induction motor torque. 

In induction heating ______

 The resistance of charge must be low and voltage applied must be high in order to produce sufficient heat.

Which of the following is the voltage for single phase A.C. system ?
 240 V 

The resistivity of water should not be less than

 2000 Q m

The speed of a superfast train is
 more than 100 kmph 

For 25 kV single phase system power supply frequency is

 50 Hz

Which of the following insulating materials was suitable for low temperature applications ?

 Diatomaceous earth

In DC machine torque depends on which of the following?
 Both armature current (I) and flux (f) 

The steam engine provided on steam locomotives is

 single acting non-condensing type

Maximum power developed by a synchronous motor depends on ___?

 supply voltage and excitation

The thickness of metallic shielding on cables is usually

 0.04 mm

A 3 layer, total diameter of an ACSR conductor is 5 cm. Find the diameter of each strand?
 1 cm 

If a step function is applied to the input of a system and the output remains below a certain level for all the time, the system is

 not necessarily stable

For a particular material the Hall coefficient was found to be zero. The material is
 metal 

To reduce the radio interference which line is/are transposed?

 Either power and telecommunication lines

Which of the following quantities are to be calculated for generator bus?

 Q and d

________electromagnets generally function as holding magnets.

 Portative

For a 3-phase, 4 pole, 50 Hz synchronous motor the frequency, pole number and the frequency are halved. The motor speed will be??
 1500 rpm 

In the cables, the location of fault is usually found out by comparing

 the capacitances of insulated conductors

Which of the following materials is the best conductor of electricity ?
 Copper 

The photo-electric effect occurs only when the incident light has more than a certain critical

 frequency

To measure a resistance with the help of a potentiometer it is

 not necessary to standardise the potentiometer

Suri transmission is

 hydro-mechanical

In case of type-1 system steady state acceleration is

 infinity

The filament of an electric bulb is made of
 tungsten 

The conductivity of a metal is determined by

 the electronic concentration and the mobility of the free electrons

Due to which of the following factors the brush wear rate is altered ?
 all of these 

A cable carrying alternating current has
 
 hysteresis and leakage losses only

Which of the following motor is suitable for frequent starting and stoppings?

 capacitor start motor

PVC stands for
 polyvinyl chloride 

The temperature, under thermal and electrical system analogy, is considered analogous to

 voltage

For a standard frequency the machine operates at a particular speed known as
 synchronous speed 

In a system low friction co-efficient facilitates

 reduced velocity lag error

Which of the following is a semiconductor material ?
 Silicon 

Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto

 60 MW

Full form of VVVF control _______?
 variable voltage variable frequency. 

The usual values of maximum flux densities for distribution transformers using hot rolled silicon steel are
 1.1 to 1.35 Wb/m^2 

Co-efficient of adhesion reduces due to the presence of which of the following ?
 both dew on rails and oil on the rails 

The illumination at a point 5 meters below a lamp in 6 lux. The candle power of the lamp is ___?

 150.

Out of the following which is an insulating material ?
 Paper 

Which of the following methods does not take into account the maximum temperature rise under variable load conditions ?

 Method of average losses

The type 2 system has _____ at the origin.

 two poles

Which of the following should be done to make an unstable system stable ?

 The gain of the system should be increased

In transmission lines distribution constants are _____?
 resistance , inductance and capacitance 

Besides a constant speed a synchronous rotor possesses which of the following advantages ?

 High power factor

Which of the following are integrating instruments ?
 Ampere-hour and watt-hour meters 

Cross magnetization effects which of the following?

 commutation

In a circuit a 33 Q resistor carries a current of 2 A. The voltage across the resistor is
 66 v 

An insulated metal sphere of 20 cm diameter is charged by rubbing with charges 2 × 10-8 C. Potential developed will be _____?

 1800 V.

Commutator in DC generator is used for ________?
 convert AC armature current in to DC 

Due to proximity effect, the increase in conductor resistance is not negligible in _____

 underground cable

Induction heating process is based on which of the following principles ?
 Electro-magnetic induction principle 

Super conductivity can be destroyed by

 application of magnetic field

The material of the heating element for a furnace should have
 high specific resistance 

To measure an A. C. voltage by using an A.C. potentiometer, it is desirable that the supply for the potentiometer in taken

 from the same source as the unknown voltage

In D.C. machines the number of slots per pole usually lies

 between 9 to 16

A 3 stack stepper motor has 12 teeth on stator as well as on rotor. Determine the step size when each stack excited?
 10 degree 

Ohm's law is not applicable to
 vacuum tubes 

In a domestic cake baking oven the temperature is controlled by

 series-parallel operation

The S.I. unit of power is
 watt 

The impurity atoms is semiconductors

 reduce the energy gap

________is an open loop control system.

 Field controlled D.C. motor

In pneumatic control systems the control valve used as final control element converts

 pressure signal to position change

In a stable control system backlash can cause which of the following ?

 Low-level oscillations

Specified quantities of load bus are __________
 P and Q 

A Weston frequency meter is

 moving iron instrument

Wattmeter cannot be designed on the principle of

 moving iron instrument

The property of a conductor due to which it passes current is called
 conductance 

In a superconductor the value of critical density depends upon

 both magnetic field strength and temperature

The electric flux is given D = (2y2 + z) Ix + 4xy Iy + x 1z C/m2. The volume charge density at point (-1,0,3) is

 - 4 C/m3.

The number of passanger coaches that can be attached to a diesel engine locomotive on broad gauge is usually restricted to

 10

Current velocity through a copper conductor is
 of the order of a few ^.s/m 

Maximum power developed in a cylindrical synchronous machine depends on
 synchronous reactance and excitation 

The output of a feedback control system must be a function of

 reference and output

An instrument which detects electric current is known as
 galvanometer 

Properly of low temperature co-eflficient of heating element is desired due to which of the following reasons ?

 Both to avoid initial rush of current and to avoid change in kW rating with temperature

______ is an example of piezoelectric material.

 Quartz

A universal RLC bridge uses

 Maxwell Wein bridge for measurement of inductance and modified De Santy's bridge for measurement of capacitance

A network containing 100 buses in which 10 are the voltage control buses, 5 are fixed shunt capacitor buses, 20 are the reactive power support buses, 6 are the generator buses. Find the size of the Jacobian matrix?

 163×163

The basic elements of a electric drive are
 electrical motor and control system. 

Which of the following is essentially needed while selecting a motor ?

 Starter

By the use of which of the following, high frequency power supply for induction furnaces can be obtained ?

 Motor-generator set

_______ motor is a constant speed motor.
 Synchronous motor 

Advantages of shunt compensation is/are _____?

 It requires less maintanance

A moving iron instrument can be used for
 both D.C. and A.C. 

Which of the following statements is not necessarily correct for open control system ?

 Presence of non-linearities causes malfunctioning

The breakdown of insulation of the cable can be avoided economically by the use of
 both inter-sheaths and insulating materials with different dielectric constants 

If the excitation is reduced, the power factor is _______?

 leading power factor

The simplest and most commony used methode for temperature control is ______

 Transformer tappings.

In electrical-pneumatic system analogy the current is considered analogous to
 air flow rate 

Rotor of a motor is usually supported on _______ bearings.
 ball or roller