Earthing Transformer : Construction & Working

• It is a special transformer which provides return path for earth fault on Delta connected transformer.

Construction

• It has primary winding but no secondary winding. 
• It is a core type transformer consists of three limbs. 
• Each limb carries two windings which have equal number of turns. 

Tertiary Winding : Construction & Working

• The three winding transformer as its name suggest consists of three winding : Primary winding, secondary winding and third winding is called as tertiary winding.

Construction

• The construction of three winding transformer is similar to that of core type transformer. 

Zig zag Transformer : Advantages, Application

Zig – Zag Transformer

It is also called as interconnected star connection. The characteristic of zig zag connection is combined characteristics of star and delta connection. There are six windings in the three cores and each core consists of two winding which has equal number of turns. 

• Fig A. shows star connection in which each phase consists of two windings. In order to convert this winding into zig – zag connection.

Connection of Zig Zag Transformer

• The R1 winding of the R phase is connected to Y2 winding of Y phase.
• The Y1 winding of the Y phase is connected to B2 winding of B phase.
• The B1 winding of B phase is connected to R2 winding of R phase.
• Each half winding has 60⁰ phase displacement in the zig zag connection. The vector sum of these windings is 86.6% of the line to neutral voltage.

Triangle ABC

AC² = AB² + BC² – 2 ( AB )( BC ) Cos θ

       = ( a / 2 )² + ( a / 2 )² – 2 ( a / 2 ) ( a / 2 ) Cos 120⁰

       = ( a² / 4 ) + ( a² / 4 ) – ( a² / 2 ) Cos ( 90⁰ + 30⁰ )

       = ( a² / 2 ) + ( a² / 2 ) Sin 30⁰

       = ( a² / 2 ) + ( a² / 4 )

AC = √ 3 ( a ) / 2

      = 0.866 a

      = 86.6 % ( a )

• We can say that 15 % more turns require for normal line to neutral voltage. When three phase currents are in phase and its magnitudes are equal, the ampere turns of R2 phase winding cancelled the ampere turns of B1 phase winding. 
• The ampere turns of Y2 phase winding cancelled ampere turns of R1 phase winding. 
• The ampere turns of B2 phase winding cancelled the ampere turns of Y1 phase winding. 
• This will result in three phases in phase current flows through line to neutral.
• When three phase currents are equal in magnitude and 120⁰ phase displacement with respect to each other, the winding ampere turns are not cancelled out therefore the current does not flow through transformer winding only magnetizing current flows through winding. 
• Therefore, in phase current flows through zig zag transformer winding but 120⁰ out of phase current does not flows through it.

Advantages of Zig Zag Transformer

• It provides neutral connection for delta connected transformer and trap third harmonic current through phase winding. 
• The cost of zig zag transformer is less than that of Scott transformer and star – delta transformer. 
• The application of delta – zig zag transformer is similar to that of star – star and delta – delta transformer because there is not phase shift between primary and secondary winding. 
• The zig zag transformer is effective than the star connected transformer and its internal impedance is low.

Applications of Zig Zag Transformer

• The star – zig zag transformer or delta – zig zag transformer is used for single phase low voltage application. 
• It is also used as grounding transformer because in phase current flows through it. 

You may also like to read these articles

Minimum Clearance between Transmission line Conductor and Earth

Right of Way in the Transmission Line

Construction of Cable

Function of Earth Conductor in the Transmission Line

Methods of Improving String Efficiency

 

Linear and Non - Linear load : Source of harmonics

Linear loads

• It is a load in which impedance remains constant. The current input is sinusoidal if the applied voltage is sinusoidal.

Non linear loads

Capacitor Start and Run Induction Motor

 Capacitor Start and Run Motor

• It consists of starting winding and running winding. 
• The starting winding is connected is in series with capacitor and there is no centrifugal switch it means that the capacitor is permanently connected in the circuit. 

Split Phase Motor and Capacitor Start Induction Run Motor

Split Phase induction motor

• A high resistance is connected in series with the starting winding. 
• The angle between starting current and main current is in the range of 20⁰ to 30⁰.

Capacitor Start Induction Run Motor - Construction & Working

Capacitor Start – Induction run Single Phase Motor

• The phase difference between main winding and starting winding is achieved by introducing an electrolyte capacitor is in series with starting winding. 

Split Phase Motor : Construction & Working

Construction

• The single phase induction motor is not self starting. 
• There is one extra winding placed in the single phase induction motor in order to make the single phase induction motor self starting therefore the single phase induction motor consists of two winding.

Rotating Magnetic Filed by Two Phase Winding

Rotating Magnetic Field

• When three phase supply is given to three phase winding, it produces rotating magnetic field which rotates and synchronous speed. 
• Similarly, when two phase supply is given to the two-phase winding, the rotating magnetic field produced by the winding is given here.

Rotating Magnetic Field: Two Phase Winding

• Let us consider that the two windings P and Q are placed at 90^o with respect to each other. 
• We assume that when the two phase supply is given to the winding, flux produces in each winding is purely sinusoidal. 
• The waveform of the flux is shown in the figure B. 
• The direction of the flux is assumed as positive whereas its opposite sides indicate negative values. The instantaneous value of flux can be given by

F_P = F_m Sin θ

F_Q = F_m Sin ( θ – 90^o )

• The voltage of the winding P is taken as reference or zero degree and winding Q is taken at 90 degree with respect to winding P.

Rotating Magnetic Field: Point 1

The voltage of winding P is zero whereas winding Q is negative as shown in the figure. The voltage of the winding Q negative sign is taken because we assume that the direction of voltage for winding P and winding Q is positive in the first quadrant.

F_P = 0 and

F_Q = –  F_m

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ 0 + ( –  F_m )² – 0

                           =  F_m 

Rotating Magnetic Field: Point 2

The voltage of the winding P and winding Q is 45 degrees but both are in the opposite direction.

F_P = F_m / √ 2 and

F_Q = –  F_m / √ 2

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ F_m² / 2 + F_m² / 2 + 0

                           =  F_m

Rotating Magnetic Field: Point 3

The voltage of the winding P is at 90 degree but voltage of the winding Q is at and winding Q is 180 degree.

F_P =  F_m and

F_Q = 0

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ ( F_m )² + 0

                           =  F_m 

Rotating Magnetic Field: Point 4

The voltage of the winding P is at 135 degree but voltage of the winding Q is at and winding Q is 45 degree but both are in the opposite direction.

F_P = – F_m / √ 2 and

F_Q = F_m / √ 2

Resultant flux F = √ P² + Q² – 2PQCos θ

                           = √ F_m² / 2 + F_m² / 2 + 0

                           =  F_m

                                 

Conclusion

Position of winding	Voltage of winding P	Voltage of winding Q	Phase Difference between two winding
Point 1	0 degree	– 90 degree	90 degree
Point 2	45 degree	–  45 degree	90 degree
Point 3	90 degree	0 degree	90 degree
Point 4	135 degree	45 degree	90 degree
Point 5	180 degree	90 degree	90 degree
Point 6	–  225 degree	135 degree	90 degree

 

We can conclude that the rotating magnetic field produced by two phase winding is constant in magnitude. It rotates at constant synchronous speed in the clockwise direction.

You may also like to read these articles

Minimum Clearance between Transmission line Conductor and Earth

Right of Way in the Transmission Line

Construction of Cable

Function of Earth Conductor in the Transmission Line

Methods of Improving String Efficiency

Torque - Slip Characteristic of the Induction Motor

The torque in the three phase induction motor is given by

• T = KFSE₂R₂ / [ R₂² + ( SX₂ )² ]

Torque at standstill condition ( S = 1 )

• The starting torque does not become zero at starting condition or at

Transistor : Emitter, Base and Collector

Transistor

• It is a semiconductor device in which one semiconductor either P or N is sandwich between a pair of opposite semiconductor. 
• Basically there are two types of transistor: NPN transistor and PNP transistor.

Compare Class A, Class B and Class C Amplifier

Class A Amplifier

• If the collector current flows all the time during full cycle of input signal, the power amplifier is called as class A amplifier.  
• The operating point Q lies at the centre of the load line. 

Compare Step up Chopper & Step down Chopper

Step down Chopper

• The average output DC voltage is always less than the input DC voltage.
• The switching device is connected in series with load.

Compare SCR and Asymmetrical SCR ( ASCR )

SCR 

• It has thousand of volts reverse blocking capacity. 
• However it may not requires in some applications particular in the inverter. 

Compare Natural Commutation and Forced Commutation

Natural Commutation 

• It is also called as phase commutation, line commutation or AC commutation. 
• The natural commutation is only possible in the AC circuit. 

Compare Combinational circuit and Sequential circuit

Combinational circuit

• The output at any time depends only upon present input at that time.
•  The previous input condition does not affect the output. 

Compare Holding current and Latching current

Holding current

• It is defined as the minimum anode current beyond SCR turns off. 
• The holding current is associated with turned off process. 
• The holding current is always less than the latching current. 

Compare Power Transistor and Power MOSFET

MOSFET 

• The MOSFET is a majority charge carrier device. 
• It is a voltage controlled device. 
• The input voltage controls the output current therefore It is a

Compare Transistor and SCR

Transistor

• It has three terminals : Emitter, base and collector.
• It is a three layer, two junction device.
• The transistor is switched on by continuous base current.