Class A Commutation ( Current or self or Resonance Commutation )

• The commutating components L and C are used in order to turn off the SCR. 
• When the load resistance of very small value is used, the inductor L and capacitor C are connected in series with load. 
• Similarly the load resistance of high value is used; the load resistance is connected across capacitor. 

Static AC Circuit Breaker

• The basic circuit for the DC time delay relay is shown in the figure A.
• The DC supply V_CC depends upon rating of SCR. The zener diode provides constant voltage for UJT. 
• The voltage across load becomes zero when the SCR is in off condition.  

Static DC Circuit Breaker

• The basic circuit for DC circuit breaker is shown in the figure A. 
• The SCR 1 is main SCR. When it is necessary to break load current, the SCR 1 is turned off.  
• There is no control circuit given in this figure for simplification. 

DC Time Delay Circuit

• The basic circuit for the DC time delay relay is shown in the figure A.
•  The DC supply V_CC depends upon rating of SCR. 
• The zener diode provides constant voltage for UJT. 
• The voltage across load becomes zero when the SCR is in off condition.  
  

AC Time Delay Circuit

• The basic circuit for the AC Time delay circuit is shown in the figure A.  
• Let us consider that the switch is in the reset position. 
• The charging of the capacitor is done through N – (+) C1 – C1 (–) – D2 – R2 – P path during negative half cycle. 

Jones Chopper

• The basic circuit of the Jones chopper is shown in the figure A. 
• The Class D commutation circuit is used in the Jones chopper. 
• The SCR T1 is main SCR whereas SCR T2, diode D1, capacitor C and auto – transformer T makes commutating circuit for SCR T1. 

Morgan Chopper

• The basic circuit for the Morgan chopper is shown in the figure A. 
• The SCR T1 is main SCR whereas diode D1, capacitor C and saturable reactor SR makes commutation circuit for the SCR T1. 
• The exciting current of the saturable reactor is neglected.

Type E Chopper ( Class E Chopper )

• The type E chopper is a four quadrant chopper. 
• The type E chopper is parallel combination of two type C chopper. 
• The combination of chopper CH1, chopper CH2, diode D1 and diode D2 makes one type C chopper and other is made from chopper CH3, chopper CH4, diode D3 and diode D4.

Type D Chopper ( Class D Chopper )

Working

• The two quadrant type B chopper or type D chopper is shown in the figure A. 
• This chopper works in first as well as fourth quadrant therefore the output current remain positive but output voltage may be either positive or negative. 

Type C Chopper ( Class C Chopper )

• The type C chopper is parallel combination of type A and type B chopper. The output voltage is always positive but output current either positive or negative in this type of chopper therefore it works in first as well as second quadrant.

Type B Chopper ( Class B Chopper )

• The type B chopper works in second quadrant it means that the output voltage positive and output current negative. 
• The load current flows through load to supply side.  
• When chopper CH1 is switched on, the output voltage becomes zero

Speed Control of DC Series Motor By Chopper

• The speed control of DC series motor by using chopper is shown in the figure A.  
• This speed control is achieved through constant frequency control or variable frequency control. 
• When chopper CH is switched on, the DC motor gets input supply voltage V_dc. 

Speed Control of Slip Ring Induction Motor By Chopper

• The speed control of the Slip ring induction motor by chopper is shown in the figure A. 
• The ON and OFF time of chopper is adjusted in order to get desirable speed of the motor. 
• The three phase rectifier converts AC into DC. 

Type A Chopper ( Class A chopper )

• The power circuit diagram of the type A chopper is shown in the figure A. The commutation circuit is not shown in this figure A. 
• When chopper CH1 is switched on, the load current flow through path V_DC – CH1 – A – L – B – LAOD – C – D – V_DC.  

Working of the Step Up / Step Down Chopper

•  It is a chopper which can work as step up chopper as well as step down chopper. 
• When the chopper is switched ON during T_ON time, the energy stored in the inductor via path V_dc – CH – L – V_dc.

Working of Step up Chopper

Step up Chopper

• The step up chopper is one in which output DC voltage is greater than the input DC voltage.  
• The basic diagram for the step up chopper is shown in the figure A.

Firing angle Control of SCR By the UJT Full Wave Circuit

• The firing angle control of SCR by UJT full wave circuit is shown in the Figure A. 
• The firing angle during each positive half cycle has same value in this circuit. 

Firing of SCR By the UJT half Wave Circuit

• The firing angle control of SCR by UJT is shown in the Figure A.
• When switch SW is on, the charging of capacitor C1 is done through resistor R1. 
• When the voltage across capacitor becomes equal to peak point voltage, the UJT turns on.  

Commutation Methods of the SCR Power point

Download : Commutation methods of SCR

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RC Phase Shift Control

• Figure A shows circuit for the RC phase shift control. 
• It consists of one step down transformer which consists of center taped secondary winding. 
• The RC circuit is connected in series with transformer secondary winding. 

RL Phase Shift Control

• Figure A shows circuit for the RL phase shift control. 
• It consists of one step down transformer which consists of center taped secondary winding. 

Chopper Configuration

The configuration of chopper is done according to direction of output voltage and output current.

Type A Chopper

• The output voltage and current both are positive in the Type A chopper.
•  It works in the first quadrant. 

Methods of Chopper Output Voltage Control

There are following methods to control output voltage of the chopper.

Constant frequency control ( Pulse width modulation control )

• The chopping frequency is kept constant in this method therefore it is called as constant frequency control. 

Light Dimmer Circuit OR Fan Regulator Circuit OR AC Load Control Using TRIAC - DIAC

• The fan regulator circuit using TRIAC – DIAC is shown in the figure.
• The TRIAC and DIAC are bi – directional therefore they are used for alternating circuit. 
• The R_L is load resistance / lamp or two terminal of single phase winding.

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Working Principle of DC Chopper

Function of DC Chopper

• The function of the DC chopper is to convert fixed DC into variable DC. A DC chopper is connected between supply source and load. 
• The variable output voltage is obtained by switching on and off SCR at regular interval. 

Wiring Diagram of Twin Tube Light

Twin Tube light

The wiring diagram of twin tube light is shown in the Figure. The Twin tube light is generally used in the textile industry / diamond factory where high level of illumination required.

Wiring Diagram of Twin Tube light

If you do not know how to connected wiring of twin tube light, it is very easy because this diagram is already shown in the old chokes. Here the ballast indicates choke in the wiring diagram.

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Schematic and Wiring Diagram of Stair Case Wiring

                       

Here, the schematic and wiring diagram of staircase wiring is shown in the Figure. There are 2 two way switches used in this diagram and they are connected such that when one switched is change its position, lamp is ON or OFF.

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Control Circuit of Automatic Star Delta Starter

Working of automatic Star Delta starter control circuit

• Press ON push button
• The star contactor coil gets supply through phase R – OFF push button – ON push button – T NC – star contactor coil – D1 ( NC of delta coil ) – phase Y. 

Control Circuit of Forward Reverse Starter

Working of Forward  – Reverse starter control circuit

Forward direction

• Press ON Push button ( F ON )
• The forward contactor coil gets supply through phase R – OFF push button – R2 – forward contactor coil – ON push button F – phase Y.

Control Circuit of Direct ON Line Starter

Working of Direct on Line Starter Control circuit

• Press ON Push button. 
• The main contactor coil gets supply through phase R – OFF push button – ON push button – main coil – phase Y. 

Control Circuit of Semi Automatic Star Delta Starter

Working of semi automatic star delta starter control circuit

• Press ON Push button
• The star contactor coil gets supply through phase R – OFF push button – ON push button – star contactor coil – D1 ( NC of delta ) – phase Y.