what is Tertiary winding

What is Tertiary Winding? What is Three Winding Transformer?
In some high rating transformer, one winding in addition to its primary and secondary winding is used. This additional winding, apart from primary and secondary windings, is known as Tertiary winding of transformer. Because of this third winding, the transformer is called three winding transformer or 3 winding transformer.

Advantages of Using Tertiary Winding in Transformer
Tertiary winding is provided in electrical power transformer to meet one or more of the following requirements-

a.) It reduces the unbalancing in the primary due ato unbalancing in three phase load.

b.) It redistributes the flow of fault current.

c.) Sometime it is required to supply an auxiliary load in different voltage level in addition to its main secondary load. This secondary load can be taken from tertiary winding of three winding transformer.

d.) As the tertiary winding is connected in delta formation in 3 winding transformer, it assists in limitation of fault current in the event of a short circuit from line to neutral.

Rating of Tertiary Winding of Transformer:
Rating of tertiary winding of transformer depends upon its use. If it has to supply additional load, its winding cross - section and design philosophy is decided as per load, and three phase dead short circuit on its terminal with power flow from both sides of HV and MV.
In case it is to be provided for stabilizing purpose only, its cross-section and design has to be decided from thermal and mechanical consideration for the short duration fault currents during various fault conditions single line to ground fault being the most onerous.

Purpose of Transformer Core

In an electrical power transformer, there are primary, secondary and may be tertiary windings. The performance of a transformer mainly depends upon the flux linkages between these windings. For efficient flux linking between these windings, one low reluctance magnetic path common to all windings should be provided in the transformer. This low reluctance magnetic path in transformer is known as core of transformer.

Measuring instrument

MEASURING INSTRUMENTS
1.1 Definition of instruments
An instrument is a device in which we can determine the magnitude or value of the quantity to be measured. The measuring quantity can be voltage, current, power and energy etc.

Generally instruments are classified in to two categories.
a.) Absolute Instrument
b.) Secondary Instrument

1.2 Absolute instrument
An absolute instrument determines the magnitude of the quantity to be measured in terms of the instrument parameter. This instrument is really used, because each time the value of the measuring quantities varies. So we have to calculate the magnitude of the measuring quantity,
analytically which is time consuming. These types of instruments are suitable for laboratory use.
Example: Tangent galvanometer.

1.3 Secondary instrument
This instrument determines the value of the quantity to be measured directly. Generally these instruments are calibrated by comparing with another standard secondary instrument.
Examples of such instruments are voltmeter, ammeter and wattmeter etc. Practically secondary instruments are suitable for measurement.

Secondary instruments
a) Indicating instruments
b) Recording Integrating c)Electromechanically
d) Indicating instruments

1.3.1 Indicating instrument
This instrument uses a dial and pointer to determine the value of measuring quantity. The pointer indication gives the magnitude of measuring quantity.

1.3.2 Recording instrument
This type of instruments records the magnitude of the quantity to be measured continuously over a specified period of time.

1.3.3 Integrating instrument
This type of instrument gives the total amount of the quantity to be measured over a specified period of time.

1.3.4 Electromechanical indicating instrument
For satisfactory operation electromechanical indicating instrument, three forces are necessary.
They are
(a) Deflecting force
(b) Controlling force
(c)Damping force

1.4 Deflecting force
When there is no input signal to the instrument, the pointer will be at its zero position. To deflect the pointer from its zero position, a force is necessary which is known as deflecting force. A system which produces the deflecting force is known as a deflecting system. Generally a deflecting system converts an electrical signal to a mechanical force.

1.4.1 Magnitude effect
When a current passes through the coil it produces a imaginary bar magnet. When a soft-iron piece is brought near this coil it is magnetized. Depending upon the current direction the poles are produced in such a way that there will be a force of attraction between the coil and the soft iron piece. This principle is used in moving iron attraction type instrument.
If two soft iron pieces are place near a current carrying coil there will be a force of repulsion between the two soft iron pieces. This principle is utilized in the moving iron repulsion type instrument.
1.4.2 Force between a permanent magnet and a current carrying coil
When a current carrying coil is placed under the influence of magnetic field produced by a permanent magnet and a force is produced between them. This principle is utilized in the moving
coil type instrument.
1.4.3 Force between two current carrying coil
When two current carrying coils are placed closer to each other there will be a force of repulsion between them. If one coil is movable and other is fixed, the movable coil will move away from
the fixed one. This principle is utilized in electrodynamometer type instrument.

1.5 Controlling force
To make the measurement indicated by the pointer definite (constant) a force is necessary which will be acting in the opposite direction to the deflecting force. This force is known as controlling
force. A system which produces this force is known as a controlled system. When the external signal to be measured by the instrument is removed, the pointer should return back to the zero position. This is possibly due to the controlling force and the pointer will be indicating a steady
value when the deflecting torque is equal to controlling torque.
Td = Tc

1.5.1 Spring control
Two springs are attached on either end of spindle .The spindle is placed in jewelled
bearing, so that the frictional force between the pivot and spindle will be minimum. Two springs are provided in opposite direction to compensate the temperature error. The spring is made of
phosphorous bronze. When a current is supply, the pointer deflects due to rotation of the spindle. While spindle is
rotate, the spring attached with the spindle will oppose the movements of the pointer. The torque produced by the spring is directly proportional to the pointer deflectionθ .
TC ∝θ (1.2)

The deflecting torque produced Td proportional to ‘I’. WhenTC = Td
, the pointer will come to a
steady position. Therefore
θ ∝ I
Since, θ and I are directly proportional to the scale of such instrument which uses spring
controlled is uniform.
1.6 Damping force
The deflection torque and controlling torque produced by systems are electro mechanical. Due to inertia produced by this system, the pointer oscillates about it final steady position before coming to rest. The time required to take the measurement is more. To damp out the oscillation is quickly, a damping force is necessary. This force is produced by different systems.
(a) Air friction damping
(b) Fluid friction damping
(c) Eddy current damping
1.6.1 Air friction damping
The piston is mechanically connected to a spindle through the connecting rod  The
pointer is fixed to the spindle moves over a calibrated dial. When the pointer oscillates in clockwise direction, the piston goes inside and the cylinder gets compressed. The air pushes the
piston upwards and the pointer tends to move in anticlockwise direction.
If the pointer oscillates in anticlockwise direction the piston moves away and the pressure of the
air inside cylinder gets reduced. The external pressure is more than that of the internal pressure.
Therefore the piston moves down wards. The pointer tends to move in clock wise direction.
1.6.2 Eddy current damping
An aluminum circular disc is fixed to the spindle . This disc is made to move in the
magnetic field produced by a permanent magnet.When the disc oscillates it cuts the magnetic flux produced by damping magnet. An emf is induced in the circular disc by faradays law. Eddy currents are established in the disc since it has
several closed paths. By Lenz’s law, the current carrying disc produced a force in a direction opposite to oscillating force. The damping force can be varied by varying the projection of the
magnet over the circular disc.

Single phase motor working theory

Single Phase Induction motor:-

》The single phase induction motor operation can be described by two methods double revolving field theory and cross field theory 113 is perhaps the easier of the two explanation to understand so we will discuss the double revolving theory only

Double revolving field theory:-

》》A single phase AC current supplies the man winding that produce a pulsating magnetic field 》》Mathematically Rakul setting friend would be divided into two field which are rotating in opposite direction
》》 the interaction between the field and current induced in the road Charbagh generates opposing torque

Starting torque:-

》》Single phase motor starting torque is zero  of the pulsating  single phase magnetic flux
》》 the starting of the motor requires the generation of a rotating magnetic flux similar to the rotating flux in three phase motor
》》 two perpendicular coil That Give current 90° out of phase can generate the necessary rotating magnetic field which start the motor
》》There are single phase Motors are built with  two perpendicular winding

》 the best gift is achieved by connecting
• A  resistance
• An inductance or
• A capacitor in series with the starting winding.

》 Most frequently used is a capacitor to generate the starting torque

》 Single phase induction motor are classified and name according to the method employed to make them self starting

(I).  split phase induction motor:- started by phase motor section through the use of auxiliary for starting winding
(II). Capacitor Motors:- standard 5 phase motor connection through the use of an auxilliary  and capacitor these are 

classified as:-
(a). Capacitor start induction run motor
(b). Capacitor run induction motor
(c). capacitor start capacitor run induction motor
(III). Shaded pole induction motor:- started by the motion of the magnetic field produced by means of shading coil around

☆ split phase induction motor☆

In this motor having two winding main winding and auxiliary winding ,hence these winding are 90° electrically each other and same 90° phase angle in these  winding. there are main winding having low resistance and high reactance and auxiliary winding have high resistance and low reactance .switch motor when attain 75% of its rated speed.
  》Working:-

Is lags by V because low reactance and high resistance and Im lag V by very large due to high reactance hence its starting torque proportional to sign thita . it disconnect after attain 75% speed from rated .

Centrifugal switch operation:-
                                                        It is connected in series with the head salary winding and mounted on the rotor shaft when the motor started and reaches 75% of synchronous speed centrifugal switch is mechanically  opened and in running condition auxiliary  winding remains  cut out from the circuit
Therefore motor run only with main winding

Characteristics:-

a.) Starting torque 1.5 times to 2 times the full load torque
b.) Starting current 6 to 8 time the full load current
c.) Low operating power factor 0.55 to .65
d.) Low efficiency 60 to 65%
e.) Power rating 1/20 to 1/2 kW
f.) Speed range 2875rpm to 700 rpm

Applications :-
                            It has low starting current and moderate starting torque. It is used for easily started load and typical applications  including fan, saw, washing machine, blower, centrifugal
pumps. etc.

Capacitor induction motor:-
1.) Capacitor start motor
2.) Capacitor run motor
3.) Capacitor start capacitor run motor

Capacitor start motor :-

                                           In this motor electrolytic capacitor used for starting the motor .in this  motor 90° phase angle for starting purpose the motor . Im' and Is' Im lags V' due to high reactance of main winding in there Is'lead V' due to capacitor  Im'and Is' angle is 90° . this motor having high starting torque .it is used in Lathes , drilling , fan, etc.

Cheracteristcs :-
a.) Starting torque 3.5 to 4.5 times the full load torque
b.) ∝30° to 80° from starting torque can be improved
c.) power factor very from 0.65 to 0 .75.
d.)Power rating 1/10 to 3/4 kW

Requirement of capacitor
》 Electrolytic capacitor are used as  starting capacitor value around 50 microfarad to a few hundred micro farad
》 Capacitor designed for extremely short time duty service and is guaranteed for not more then 29 period of operation / hr each period not axceed 3 seconds

Applications :-
This motor has high starting torque and therefore is used for hard start load such as pumps compressor refrigerator units machine tools etc.

Capacitor start capacitor run 

characteristics 

a ) starting torque 3 to 3.5 time the full load
b.) 60% efficiency opprox.
c.) Power factor .09
d.) Power rating 1/8 to 3/4 HP
e.) Pull out torque up to 260% of rated torque

Applications :-
》It combines the advantage of capacitor start and permanent capacitors and used for hard to start loads such compressor ,pump conveyors etc.
》 These motors are often employed requiring a quite operating motor such as in hospitals and  studios

Shadded pole motor theory of operations :-

 Small motor requiring only small starting torque may be made self starting by using low resistance copper bands called shadding bands. The emf induced in the shadding band cause a current to flow in the band . This current oppose the change of flux to which it is due and thus there is a time lag between the fluxes in the shadded and unshadded portion of the pole . The flux in the shadded portion of tge pole lags the flux in the rottor portion . the result is like a rotating field moving in the direction from the unshadded to the shadded portion of the pole and a starting torque is produced

characteristics :-
a.) Low starting torque 0.4 to 0.8 times the full load torque
b.) Efficiency 35% approximate
c.) Power factor 0.45 approx.
d.) Pull out torque 15% of full load torque
e.) Power rating 1/300 to 20HP ( 2.5 W to 40W)

Applications :- Because their poor starting torque low power factor and poor efficiency such motor are only suitable for low power applications such as for toys, portable fan, electric clock, hair drier, humidifier , photocopy machine etc.

MCQ on Refrigerator & AC 51-105

51. One ton refrigeration corresponds to
(A) 50 kcal/ min✔
(B) 50 kcal/ hr
(C) 80 kcal/ min
(D) 80 kcal/ hr

52. The process, generally used in winter air-conditioning to warm and humidity the air, is called
(A) Humidification
(B) Dehumidification
(C) Heating and humidification✔
(D) Cooling and dehumidification

53. The leaks in a refrigeration system using Freon are detected by
(A) Halide torch which on detection produces greenish flame lighting✔
(B) Sulphur sticks which on detection gives white smoke
(C) Using reagents
(D) Smelling

54. The reduced ambient air cooling system has
(A) One cooling turbine and one heat exchanger
(B) One cooling turbine and two heat exchangers
(C) Two cooling turbines and one heat exchanger✔
(D) Two cooling turbines and two heat exchangers

55. In vapour compression cycle, the condition of refrigerant is saturated liquid
(A) After passing through the condenser✔
(B) Before passing through the condenser
(C) After passing through the expansion throttle valve
(D) Before entering the expansion valve

56. Which of the following refrigerant has the maximum ozone depletion potential in the stratosphere?
(A) Ammonia
(B) Carbon dioxide
(C) Sulphur dioxide
(D) Fluorine✔

57. If the evaporator temperature of a plant is lowered, keeping the condenser temperature constant, the h.p. of compressor required will be
(A) Same
(B) More✔
(C) Less
(D) More/less depending on rating

58. Hydrogen is used in Electrolux refrigeration system so as to _________ the rate of evaporation of the liquid ammonia passing through the evaporator.
(A) Equalize
(B) Reduce
(C) Increase✔
(D) None of these

59. Pick up the wrong statement. A refrigerant should have
(A) Tow specific heat of liquid
(B) High boiling point✔
(C) High latent heat of vaporisation
(D) Higher critical temperature

60. The pressure at the inlet of a refrigerant compressor is called
(A) Suction pressure✔
(B) Discharge pressure
(C) Critical pressure
(D) Back pressure

61. Condensing temperature in a refrigerator is the temperature
(A) Of cooling medium
(B) Of freezing zone
(C) Of evaporator
(D) At which refrigerant gas becomes liquid✔

62. In aircraft, air refrigeration Cycle is used because of
(A) Low weight per tonne of refrigeration✔
(B) High heat transfer rate
(C) Low temperature at high altitudes
(D) Higher coefficient of performance

63. Highest pressure encountered in a refrigeration system should be
(A) Critical pressure of refrigerant
(B) Much below critical pressure✔
(C) Much above critical pressure
(D) Near critical pressure

64. The refrigerant used for absorption refrigerators working on heat from solar collectors is a mixture of water and
(A) Carbon dioxide
(B) Sulphur dioxide
(C) Lithium bromide✔
(D) R-12

65. One ton of the refrigeration is
(A) The standard unit used in refrigeration problems
(B) The cooling effect produced by melting 1 ton of ice
(C) The refrigeration effect to freeze 1 ton of water at 0°C into ice at 0°C in 24 hours✔
(D) The refrigeration effect to produce 1 ton of ice at NTP conditions

66. The dry bulb temperature during sensible heating of air
(A) Remains constant
(B) Increases✔
(C) Decreases
(D) None of these

67. Vertical lines on pressure-enthalpy chart show constant
(A) Pressure lines
(B) Temperature lines
(C) Total heat lines✔
(D) Entropy lines

68. During heating and dehumidification process, dry bulb temperature
(A) Remains constant
(B) Increases✔
(C) Decreases
(D) None of these

69. The evolution of heat of solution takes place in ammonia absorption plant when
(A) Ammonia vapour goes into solution✔
(B) Ammonia vapour is driven out of solution
(C) Lithium bromide mixes with ammonia
(D) Weak solution mixes with strong solution

70. In a pressure enthalpy chart, the space to the left of the saturated liquid line represents
(A) Wet vapour region
(B) Superheated vapour region
(C) Sub-cooled liquid region✔
(D) None of these

71. In vapour compression cycle, the condition of refrigerant is high pressure saturated liquid
(A) After passing through the condenser
(B) Before passing through the condenser
(C) After passing through the expansion or throttle valve
(D) Before entering the expansion valve✔

72. In a bootstrap air evaporative cooling system, the evaporator is provided
(A) Between the combustion chamber and the first heat exchanger
(B) Between the first heat exchanger and the secondary compressor
(C) Between the secondary compressor and the second heat exchanger
(D) Between the second heat exchanger and the cooling turbine✔

73. The COP of a domestic refrigerator
(A) Is less than 1
(B) Is more than 1✔
(C) Is equal to 1
(D) Depends upon the make

74. The air cooling system mostly used in transport type aircrafts is
(A) Simple air cooling system
(B) Simple evaporative air cooling system
(C) Bootstrap air cooling system✔
(D) All of these

75. The higher temperature in vapour compression cycle occurs at
(A) Receiver
(B) Expansion valve
(C) Evaporator
(D) Compressor discharge✔

76. Dry bulb temperature is the temperature of air recorded by a thermometer, when
(A) It is not affected by the moisture present in the air✔
(B) Its bulb is surrounded by a wet cloth exposed to the air
(C) The moisture present in it begins to condense
(D) None of the above

77. In refrigerators, the temperature difference between the evaporating refrigerant and the medium being cooled should be
(A) High, of the order of 25°
(B) As low as possible (3 to 11°C)✔
(C) Zero
(D) Any value

78. The evaporator changes the low pressure liquid refrigerant from the expansion valve into
(A) High pressure liquid refrigerant
(B) Low pressure liquid and vapour refrigerant
(C) Low pressure vapour refrigerant✔
(D) None of these

79. Choose the correct statement
(A) A refrigerant should have low latent heat
(B) If operating temperature of system is low, then refrigerant with low boiling point should be used✔
(C) Pre-cooling and sub-cooling bf refrigerant are same
(D) Superheat and sensible heat of a refrigerant are same

80. Carbon dioxide is
(A) Colourless
(B) Odourless
(C) Non-flammable
(D) All of these✔

81. Reducing suction pressure in refrigeration cycle
(A) Lowers evaporation temperature
(B) Increases power required per ton of refrigeration
(C) Lowers compressor capacity because vapour is lighter
(D) All of the above✔

82. The coefficient of performance of a domestic refrigerator is ________ as compared to a domestic air-conditioner.
(A) Same
(B) Less✔
(C) More
(D) None of these

83. If a gas is to be liquefied, its temperature must be
(A) Increased to a value above its critical temperature
(B) Reduced to a value below its critical temperature
(C) Equal to critical temperature✔
(D) None of the above

84. The capacity of a domestic refrigerator is in the range of
(A) 0.1 to 0.3 TR✔
(B) 1 to 3 TR
(C) 3 to 5 TR
(D) 5 to 7 TR

85. The lowest thermal diffusivity is of
(A) Iron
(B) Lead
(C) Aluminium
(D) Rubber✔

86. In a vapour compression cycle, the refrigerant immediately after expansion valve is
(A) Liquid
(B) Sub-cooled liquid
(C) Saturated liquid
(D) Wet vapour✔

87. Which of the following statement is correct for ammonia as a refrigerant?
(A) It is toxic to mucous membranes.
(B) It requires large displacement per TR compared to fluoro carbons.
(C) It reacts with copper and its alloys.
(D) All of these✔

88. Critical pressure of a liquid is the pressure
(A) Above which liquid will remain liquid✔
(B) Above which liquid becomes gas
(C) Above which liquid becomes vapour
(D) Above which liquid becomes solid

89. The optimum effective temperature for human comfort is
(A) Higher in winter than in summer
(B) Lower in winter than in summer✔
(C) Same in winter and summer
(D) Not dependent on season

90. Formation of frost on evaporator in refrigerator
(A) Results in loss of heat due to poor heat transfer✔
(B) Increases heat transfer rate
(C) Is immaterial
(D) Can be avoided by proper design

91. A one tonne refrigerating machine means that
(A) One tonne is the total mass of machine
(B) One tonne refrigerant is used
(C) One tonne of water can be converted into ice
(D) One tonne of ice when melts from and at 0° C in 24 hours, the refrigeration effect is equivalent to 210 kJ/min✔

92. The suction pipe diameter of refrigerating unit compressor in comparison to delivery side is
(A) Bigger✔
(B) Smaller
(C) Equal
(D) Smaller/bigger depending on capacity

93. The coefficient of performance (C.O.P.) of a refrigerator working as a heat pump is given by
(A) (C.O.P.)P = (C.O.P.)R + 2
(B) (C.O.P.)P = (C.O.P.)R + 1✔
(C) (C.O.P)P = (C.O.P)R - 1
(D) (C.O.P)P = (C.O.P)R

94. Presence of moisture in a refrigerant affects the working of
(A) Compressor
(B) Condenser
(C) Evaporator
(D) Expansion valve✔

95. During heating and humidification, the final relative humidity of air
(A) Can be lower or higher than that of the entering air✔
(B) Is lower than that of the entering air
(C) Is higher than that of the entering air
(D) None of the above

96. Which of the following cycles uses air as the refrigerant?
(A) Ericson
(B) Stirling
(C) Carnot
(D) Bell Coleman✔

97. The curved lines on a psychrometric chart indicates
(A) Dry bulb temperature
(B) Wet bulb temperature
(C) Dew point temperature
(D) Relative humidity✔

98. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process
(A) Involves no change in volume
(B) Takes place at constant temperature
(C) Takes place at constant entropy
(D) Takes place at constant pressure✔

99. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be
(A) Positive
(B) Negative✔
(C) Zero
(D) None of these

100. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration
(A) 0.1 to 0.5 h.p. per ton of refrigeration
(B) 0.5 to 0.8 h.p. per ton of refrigeration
(C) 1 to 2 h.p. per ton of refrigeration✔
(D) 2 to 5 h.p. per ton of refrigeration

101. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is
(A) 0.376
(B) 0.4
(C) 0.6✔
(D) 0.67

102. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.
(A) More✔
(B) Less
(C) Equally
(D) Unpredictable

103. Most thermostatic expansion valves are set for a superheat of
(A) 5°C✔
(B) 10°C
(C) 15°C
(D) 20°C

104. In a refrigeration system, heat absorbed in comparison to heat rejected is
(A) More✔
(B) Less
(C) Same
(D) More for small capacity and less for high capacity

105. A thermostatic expansion valve in a refrigeration system
(A) Ensures the evaporator completely filled with refrigerant of the load✔
(B) Is suitable only for constant load systems
(C) Maintains different temperatures in evaporator in proportion to load
(D) None of the above