Power Electronics Lab Manual With Logo
Power Electronics Lab Manual With Logo
Power Electronics Lab Manual With Logo
Experiment-1(a)
Circuit Diagram:
Waveform:
Tabular Column:
Gate Current Ig =………..mA
Procedure:
Result: The values of VAK and IA are noted down, plotted and SCR forward resistance is
found. The values obtained are verified.
Experiment-1(b)
F o r w a r d
c o n d u c t i o n r e g i o n
V B 0 2
V
V B 0 1
B l o c k i n g s t a t e
R e v e r s e
c o n d u c t i o n r e g i o n
VI Characteristics of DIAC
Tabular Column:
V (volts) I(mA)
Procedure:
Result:
Characteristics of MOSFET
Aim: To draw static characteristic of MOSFET and hence to determine the output
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Power Electronics Lab Manual
Circuit Diagram:
Procedure:
(a) Transfer Characteristics:
Connect the circuit as shown in the fig 2.1 (a).
Set VDS = 10V by varying V1. Keep R1 slightly more than ¼ of the total value.
Vary VGS by varying V2 (keep R2 to minimum position) and note down IDS for every
0.5V variation of VGS till 5V of VGS.
Min VGS voltage that is required for conduction is “Threshold voltage” (VTH).
Tabular Column:
VDS = ……
VGS in volts ID in mA
Tabular column:
VGS=…..V
VDS in Volts ID in mA
RESULT: The transfer characteristics & collector characteristics are obtained and their
respective graphs are plotted and output resistance and Trans conductance are found.
Experiment No 2(b)
VI-Characteristics of IGBIT
Aim:
To plot the VI Characteristics of IGBT.
Circuit Diagram:
Waveform:
Tabular Column:
Transfer Characteristics: VCE=……V
VGE(Volts) IC(mA)
PROCEDURE:
Transfer Characteristics:
Connect the circuit as shown in figure.
Initially Keep V1 & V2 to minimum. Set V1=VCE1 = 10V.
Slowly vary V2 (VGE) and note down Ic and VGE reading for every 0.5V. (V(GE)MAX <
8V)
The minimum gate Voltage VGE, which is required for conduction of IGBT, is called
threshold voltage VTH.
If VGE is less than VTH, very small leakage current flows from collector to emitter. If
VGE is greater than VTH, then collector current depends on VCE magnitude.
Repeat the same for different values of VGE and draw the graph of VGE V/S Ic.
Collector Characteristics:
If Vce is more than Vp, constant Ic flows from the device and this operating region is
called as constant current region.
Repeat the above for different values of VGE and note down Ic v/s Vce.
Draw the graph Ic v/s VGE for different values of VGE.
Result: The transfer characteristics & collector characteristics are obtained and their respective
graphs are plotted. The values of Ic, VGE, VCE are noted down in tabular columns and verified.
Experiment No. 3
Aim: 1. To plot firing angle v/s VDC using RC, firing circuits.
2. To plot input, trigger, load voltage waveforms in an RC Triggering circuit for half and
full wave rectifier circuit.
Apparatus Required: RC firing circuit module, rectifier module, Multimeters, CRO, and patch
Chords.
RC Half –Wave Triggering Circuit:
Circuit Diagram:
Waveform:
Procedure:
Tabular Column:
Waveform:
Procedure:
Tabular Column:
Result:
1. Half and full wave R & RC triggering circuit have been rigged up and output
waveforms have been plotted.
2. Graph of firing angle and Vdc for R & RC triggering circuit have been plotted.
Experiment No.4
Aim:
To rig up and verify the operation of the SCR firing circuit using UJT.
Apparatus Required: CRO probes, Patch cords, UJT trainer kit, Digital Multimeters.
Waveform:
Tabular column:
Fig 4.2(a) Waveforms of UJT Relaxation and Waveforms across SCR and Load.
Tabular Column:
Procedure:
The trainer kit is switched on with an AC supply voltage of 230V and 50Hz.
A probe is connected to the CRO and one point is connected to the ground of the pulse
Transformer primary.
The rectified o/p across the diode is measured at point ‘A’ and is displayed on the CRO.
The voltage across the sneer diode and the capacitor is found out at point B
Note down the waveforms across the capacitor at point ‘C’.
Note down the trigger waveform across the primary of pulse transformer.
Now the ground is removed and it is connected to the ground of the secondary and note
down Vdc.
The waveform across the SCR and at point ‘D’ is found and plotted.
NOTE: Isolation of primary and secondary sides of pulse transformer is to be strictly
maintained while measurements are carried out.
Experiment No 5
Aim:
To control firing angle / duty cycle using digital triggering.
Apparatus Required: Digital firing circuit, SCR’s (Single or any combination) loads, C.R.O,
Probes.
Waveform:
Procedure:
5. Adjust the potentiometer R in such a way that very small pulse at the Counter O/p is
obtained.
6. Now vary the firing angle from 180o to 0o step by step and observe the variation in
trigger o/p’s Tp and Tn.
7. Connect Tp and Tn to 1 and 2 input of pulse transformer isolation circuit .And we will
get the pulse transformer isolated and amplified outputs at P1 & P1 T2 and T2
respectively.
8. Connect these trigger o/p’s to gate and cathode of SCR’s for different Power circuit’s
as given in the table.
9. Now set the 180o –100o switch to 100% mode (chopper) keep the duty cycle at
99%.
10. Adjust the potentiometer ‘R’ in such a way that a very small pulse output is obtained.
11. Now vary the duty cycle in steps from 99% to 1% and observe the counter o/p and
also observe the time variation between main pulse Pm and auxiliary pulse Pa.
12. Connect Pm and Pa to input 1 and 2 of pulse transformer isolator.
Result: Control of firing angle /duty cycle using digital triggering is found.
Experiment 6
Aim:
i) To observe variation of intensity of light with reference to firing angle.
ii) To plot delay angle V/S VL Load voltage and Conduction angle V/S IL Load current.
Components Required: Patch cords, Multimeters, Isolation Transformer, 10:1 probes, lamp,
Triac Module.
Circuit Diagram:
Procedure:
Tabular Column:
Result: The values of load voltage, firing angle, load current and conduction angle are found and
verified using Triac-Diac combination circuit.
Experiment no. 7
Single Phase Full Controlled Bridge Convertor for R & R-L Load
Aim:
1. To plot Vdc v/s firing angle for R load.
Apparatus Required: Trainer module, Multimeters, CRO, Patch cords Rheostat, and Inductor.
Circuit Diagram:
PROCEDURE:
Rig up the circuit and connect the triggering circuit as shown in the fig 8.1(a).
First connect the circuit for 40V AC tapping as shown in fig8.1 (a)
Adjust the triggering angle α using variable resistance on triggering circuit to observe the
waveform on the CRO.
Connect 0-300 Ω r heostats as load resistance.
Repeat the experiment for various conditions of the load with different tapping of Vp AC
voltage (max 120V).
Pure R load.
R-L load (R load in series with L load).
R-L loads with freewheeling Diode.
T (ms) αTH Vdc (V) Idc (A) α(prac) VdcTH (V) Idc TH (A)
R-L load:
Calculations:
Vdc = (Vm/π) * (1 + cosα)
Idc = (Vm/πR) * (1 + cosα)
(Vm(1 + cosΩ)) / π= Vdc
Vm = (Vdc*π) / (1 + cosα)
Result : The values of Vdc, Idc &α are found out, plotted and verified with expected waveforms.
Experiment 8
DC Chopper
Aim:
1. To rig up DC Jones chopper and to measure the value of load voltage (VLDC).
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Power Electronics Lab Manual
2. To plot the graphs of Frequency V/S VLDC and Duty Cycle V/S VLDC.
Apparatus Required: DC chopper power module-SDCP, Triggering circuit (DC chopper), Load
50Ω rheostat, DMM.
Circuit Diagram:
Output waveform:
Procedure:
a) For R – Load:
1. Connections are made as shown in the figure 9.1(a). Use 50Ώ Rheostat for
R-Load (Freewheeling diode (DM) is to be connected only for RL load).
2. Adjust VRPS output to 10v and connect to DC chopper module.
3. Switch on DC toggle switch of chopper module.
b) R-L Load:
1. Connections are made as shown in fig 9.1 (a). Load is 50Ώ Rheostat in
series with inductor L =25mH or 50mH.
2. Follow the same procedure as listed in steps 2 to 8 above.
3. Readings and output waveform is to be recorded with and without free
wheeling diode.
Tabular columns:
Constant Duty Cycle
Duty cycle: 50%, VIN= 10 to 15V
Experiment No.9
Aim:
Components Required:
DC Motor, Tachometer (Non Contact), Rheostat 50Ω 5A, Speed Control unit, Isolation
Transformer, 10:1 Probe.
Circuit Diagram:
Fig 9.1 Circuit Diagram for Speed Control of a Separately Excited DC Motor
Procedure:
Tabular Column:
(A) Armature Control
Field Voltage Firing VDC IO Speed
(const) Angle θf volts Amps
Result:
1) Speed of a separately excited DC motor is controlled.
2) Graph of
(i) VDC v/s Speed for Field control.
(ii) VDC v/s Speed for Armature control.
(iii) θf v/s VDC v/s Speed in Armature control are plotted.
Experiment No. 10
Apparatus Required: Trainer Kit, CRO, CRO Probes, Multi meters, Patch
Circuit Diagram:
Procedure:
R
ig up the circuit as shown in fig
A pply AC voltage and switch on MCB.
Vary firing angle and note down the o/p voltage and speed.
Plot Vdc v/s ( firing angle) and Vdc v/s speed.
Tabular Column:
Calculations:
Vdc = (Vm/π) * (1 + cosα)
Idc = (Vm/πR) * (1 + cosα)
(Vm(1 + cosα)) / π= Vdc
Vm = (Vdc*π) / (1 + cosα)
Compare the theoretical & Practical Values of Vdc & Idc.
( R = 60Ω), Vm = 80 V.
Procedure:
1. Connect the circuit as shown in the figure.
2. Switch on the mains 230V to Isolation Transformer and TRIAC firing circuit.
3. Switch on the trigger on push button switch (NOTE: Triac firing circuit
potentiometer to be at approximately 90o.)
4. Vary the firing angle, note down the angle and speed of the induction
motor.
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Power Electronics Lab Manual
Tabular Column:
α in degree Vdc (V) Speed in RPM
Result:
1. The speed of induction motor is controlled using TRIAC.
2. Graph of firing angle v/s speed of induction motor is plotted.
Experiment No. 11
Aim:
To rig up and verify operation of Stepper Motor.
Circuit Diagram:
Procedure:
1. Connect the controller o/p A1, A2, B1, B2 to A1 A2 B1 B2 i/ps (respectively) of the Stepper
Motor Module.
2. Connect +ve common terminal to +ve supply.
3. Switch on the power supply to the unit. It displays S-00.
4. Press SET on SMC.
5. Display shows “rpm”(Rev Per Sec).
6. Press ENT for “Speed MODE”.
7. Display “00”.
8. Press INC key to set rpm.
9. Press ENT
10. Displays DR FR (Direction of rotation).
11. Press INC/DEC to change direction of rotation.
12. Press ENT.
13. Displays HF ST or FL STEP.(Step size Half or Full)
14. Use INC/DEC to select step size.
15. Press ENT.
16. Then it displays n…….. Rpm set for speed mode.
17. Press Run/Stop for running or stopping the motor.
Step Mode:
NOTE: Step Lle =1.8 + 0.1 (Non cumulative) Steps/ revolution =200
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Power Electronics Lab Manual
0 1 1 0
1 0 0 0
1 0 1 1
Half Step
A1 (RED) A2 (GREEN) B1 (BLUE) B2 (BLACK)
0 1 0 1
0 0 0 1
1 0 0 1
1 0 0 0
1 0 1 0
0 0 1 0
0 1 1 0
0 1 0 0
Result:
Operation of Stepper Motor has been verified.
Experiment.12 (a)
Parallel Inverter
Aim: To rig up and verify the operation of parallel inverter using SCR.
Apparatus Required: Trainer kit, Probes, Patch cords, Rheostat, and CRO.
Circuit Diagram:
Waveform:
RL =100Ω/50ΩRheostat
SCR’s – 10A/600V.
Diodes – IN 4007, 10A/600V.
Procedure:
Tabular Column:
Result: Parallel inverter circuit is rigged up and output waveforms is plotted and verified with
expected waveforms.
Experiment 12(b)
Series Inverter
Aim:
1) To rig up a Series Inverter using SCR and note down the waveforms.
2) To record the frequency of operation.
Circuit Diagram:
Procedure:
Waveform:
Tabular Column:
Result:
Experiment-13(a)
Aim:
Apparatus Required: Trainer kit, Probes, Patch cords, Rheostat, and CRO
Circuit Diagram:
Waveform:
Procedure:
Connections are given as shown in circuit diagram.
Switch ON the power supply & Set 10V.
Note down o/p s waveforms across Load, SCR, and Capacitor.
Plot the Graph.
Tabular Column:
Result:
Self Commutation by LC Circuit is rigged up and output waveforms are noted.
Aim:
To rig up a Auxiliary SCR Commutation and note down the waveforms.
Apparatus Required: Trainer kit, Probes, Patch cords, Rheostat, and CRO.
Circuit Diagram:
Procedure:
Connections are given as shown in circuit diagram.
Switch ON the power supply & Set 10V.
Note down O/PS waveforms across Load, SCR1, and SCR2 & Capacitor.
Plot the Graph.
Tabular Column:
Waveform:
Amplitude(Volts) Time(ms)
Result:
Auxiliary SCR Commutation rigged up and output waveforms are noted.
Viva Questions:
V-I CHARACTERISTICS OF SCR
1. What is a Thyristor?
Thyristor is derived from the properties of a Thyratron tube and a Transistor. It is used as
another name for SCR’S. They are power Semiconductor devices used for power control
applications.
2. What are SCR’s?
SCR’s is Silicon controlled Rectifiers. They are basically used as thryristor.
3. Draw the structure of an SCR?
4. What are the different methods of turning on an SCR?
*Anode to cathode voltage is greater than break over voltage.
*Gate triggering
*When dv/dt exceeds permissible value.
*Gate cathode junction is exposed to light.
5. What is Forward break over voltage?
The voltage Vak at which the SCR starts conducting is called as Forward
Break over voltage Vbo. This happens when the junction J2 undergoes
Avalanche breakdown due to high reverse bias on junction J2.
6. What is Reverse break over voltage?
If the reverse voltage is increased more than a critical value, avalanche
Breakdown will occur at J1 and J3 increasing the current sharply. This is
Reverse break over voltage VBO.
7. Why is Vbo greater than VBR?
In SCR the inner two p-n regions are lightly doped due to which the thickness of the
depletion region at junction J2 is higher during forward bias than that of J1 and J3 under
reverse bias.
CHARACTERISTICS OF MOSFET
1. What are MOSFET’s?
Metal oxide silicon di-oxide field effect transistor is a voltage-controlled device. The parts of
MOSFET are gate, drain and source.2.Draw the symbol of MOSFET.
3. What is the difference between MOSFET and BJT?
The MOSFET is a voltage controlled device where as BJT is a current controlled device.
4. What is the difference between JFET and MOSFET?
There is no direct contact between the gate terminal and the n-type channel of MOSFET.
5. Draw the structure of MOSFET.
6. What are the two types of MOSFET?
*Depletion MOSFET - N channel in p substrate.
-P channel in n substrate.
*Enhancement mosfet –virtual n channel in p substrate
-Virtual p channel in n substrate
7. What is the difference between depletion and enhancement MOSFET?
The channel in the center is absent for enhancement type MOSFET but the channel is
present in depletion type MOSFET.The gate voltage can either be positive or negative in
depletion type MOSFET’s but enhancement MOSFET responds only for positive gate voltage.
8. How does n-drift region affect MOSFET?
The n- drift region increases the onstage drop of MOSFET and also the thickness of this region
determines the breakdown voltage of MOSFET.
9. How are MOSFET’s suitable for low power high frequency applications?
MOSFET’s have high on state resistances due to which losses increase with the increase in the
power levels. Their switching time is low and hence suitable for low power high frequency
applications.
10. What are the requirements of gate drive in MOSFET?
*The gate to source input capacitance should be charged quickly.
*MOSFET turns on when gate source input capacitance is charged to sufficient level.
*The negative current should be high to turn off MOSFET.
11. Draw the switching model of MOSFET.
As the collector voltage drops in BJT there is an increase in collector Current and this
substantially increase the power dissipation. This Dissipation is not uniformly spread over the
entire volume of the device but is concentrated in highly localized regions where the local
temperature may grow and forms the black spots. This causes the destruction of BJT. This is
second breakdown.
7. What is switching speed?
The time taken to turn on or turn off a power device is called switching Speed.
8. Can we observe the transfer and collector characteristics of IGBT on CRO?
No. Because the waveform which is to be observed on the CRO should vary with respect to
time otherwise we can see only a straight line on the CRO.
9. What is punch through IGBT?
The IGBT’s which have n+ buffer layer present are called punch through IGBT.They have
asymmetric voltage blocking capabilities and have faster turn off times. Hence they are used in
choppers and inverters.
10. What is non-punch through IGBT?
The IGBT’S without n+ buffer layer are called non-punch through IGBT’s. They
havesymmetric voltage blocking capabilities and are used
for rectifier applications.
resistor?
The limiting resistor Rmin is placed between anode and gate so that the peak gate
current of the thyristorIgm is not exceeded.
4. What is the maximum firing angle of RC-triggering and why?
Ans) Maximum firing angle is 180°. This is because capacitor voltage and AC line voltage differ
in phase. By adjusting the value of R it is possible to vary the delay in turning on the SCR from 0
to 10 msec and hence vary the firing angle from 0° to 180°.
UJT FIRING CIRCUIT FOR HWR AND FWR CIRCUITS.
1. What is an UJT and draw its equivalent circuit?
UJT-uni junction transistor. It has only one type of charge carriers. It has three terminals emitter,
base 1 and base 2. (‘Duo base’ as it has 2 bases)
2. Why is an UJT used in SCR firing circuit?
The voltage at base 1 of UJT is smaller than the voltage needed to trigger the Scrim the voltage
is high, then it will trigger the SCR as soon as the ac supply is on.
3. Why is the isolation needed between Thyristor and firing circuit?
The trigger circuit operates at low power levels (5-20 volts) whereas thyristors operate at high
voltage levels (250 volts). Hence if the Thyristor acts as a short the entire 250volts get applied
across the firing circuit causing damage. Hence isolation is needed.
The capacitor discharges through emitter, base and primary of the pulse transformer.
20. What is relaxation oscillator?
When the capacitor discharges to a valley voltage, the UJT turns off and capacitor starts
Charging again. This mode of working of UJT is called relaxation oscillator.
21. Draw the static characteristics of UJT.
22. What is negative resistance?
After the capacitor charges to Vp it starts discharging. During this period the voltage V
decreases with increase in current, hence this portion of V-I characteristics is called
negative resistance.
23. What is interring base resistance?
Inter base resistance is the resistance between 2 bases.
24. What is intrinsic standoff ratio?
Intrinsic standoff ratio=Rb1/(Rb1+Rb2). Its value ranges between .52 to .81.
The merits are that they are simple without commutation circuits, high efficiency and less
maintenance.The demerits are that the load current is asymmetric (phase control) and hence
harmonics are present and intermittent supply of power in on-off control.
10. Why is the trigger source for the two Thyristor isolated from each other
in a single-phase voltage controller?
When one Thyristor is on, the other should be off. Both the Thyristor should not conduct at a
time.
DC Chopper
1. What are choppers?
A dc chopper converts directly from dc to dc and is also known as dc-dc converter.
2. What does a chopper consist of?
It can be a power transistor, SCR, GTO, power MOSFET, IGBT or a switching device.
3. On what basis choppers are classified in quadrant configurations?
The choppers are classified depending upon the directions of current and voltage flows. These
choppers operate in different quadrants of V-I plane. There are broadly following types of
choppers: class a chopper (first quadrant); class B (second quadrant)
Class C and class D (two quadrant choppers), class C in II quadrant and I whereas class D in IV
quadrants, and I class E is four quadrant operator.
4. What are different control strategies found in choppers?
The different control strategies are pulse width modulation, frequency modulation and
current limit control, variable pulse width and frequency.
5.Explain the principle of operation of a chopper?
A chopper acts as a switch, which connects and disconnects the load, hence producing variable
voltage.
6. What are the advantages of DC choppers?
* High ripple frequency, so small filters are required.
*Power factor is better.
*Efficiency is better.
*Small and compact.
*The dynamic response of choppers is fast due to switching nature of the device.
7. Define duty cycle.
The duty cycle of chopper controls its output voltage. The value of duty cycle lies
between 0 and 1 and is given by Ton/(Ton+Toff).
8. How can ripple current be controlled?
Ripple current is inversely proportional to the frequency and hence can be controlled by
having higher frequency.
9.What is step up chopper?
If the output average voltage is greater than the supply voltage, then the chopper is called step
up chopper.
10. On what does the commutating capacitor value depend on?
It depends on the load current.
11. What are the disadvantages of choppers?
*They can operate only at low frequencies.
*The commutation time depends on the load current.
*The output voltage is limited to a minimum and maximum value beyond which we
cannot get the output voltage.
12. How do they have high efficiency?
DC choppers uses switching principle, hence they have high efficiency.
13. What are the applications of dc choppers?
Battery operated vehicles, switched mode power supplies, traction devices, lighting and lamp
controls, trolley cars, marine hoists, and forklift trucks. Mine haulers etc.
Speed Control of Separately Excited DC Motor
1. What is principle of dc motor?
An electric motor is a machine, which converts electrical energy into mechanical energy. Its
action is based on the principle that when a current carrying conductor is placed in a magnetic
field it experiences a mechanical force whose direction is given by flemings left hand rule and
whose magnitude is given by F=BIL N.When the field magnets of a multipolar dc motor are
excited and its armature conductors are supplied with current from supply mains they experience
a force tending to rotate the armature .By Fleming’s left hand rule it is noted that each conductor
experiences a force which tends to rotates the armature in anticlockwise direction. These forces
collectively produce a driving torque (or twisting moment), which sets the armature rotating.
2. How can the speed of the series motor controlled?
*flux control method
-field divertors
-Armature divertor
*variable resistance in series with the motor.
3. What are the advantages of field method?
*economical,more efficient
*It gives speeds more /above the normal speed.
4. Whatarethe disadvantages of field method?
Commutation becomes unsatisfactory.
5. What are the factors controlling speed?
Speed can be controlled by controlling flux,resistance,voltage.
6. What is the significance of back emf?
When the motor armature rotates the conductors also rotates and hence cut flux. Therefore emf
is induced and direction is in opposition with the applied voltage (Fleming’s right hand rule).
Because of its opposing direction it is referred to as back emfEb. V has to drive Ia against the
opposition of Eb.The power required to overcome this opposition is EbIa.
7. What is torque?
Torque is twisting or turning moment of a force about an axis.The torque developed by
the armature of a motor is armature torque. The torque available for useful work is knownas
shaft torque (available at the shaft).
8. How can dc motors be classified?
*seperately excited
*self excited.
9. What are the main losses in motors?
*stator losses
*rotor losses
*mechanical losses
10. Why are starter used in dc motor?
Initially Eb =0 and R is usuallly very small,therefore the armature current is very high
which could damage the motor.Hence starters which is basically a resistance connected in series
with the motor.
11. What is the parameter that is being varied by varying the firing angle?
The armature voltage is varied which inturn varies the speed of the motor by varying the firing
angle.
12. What are the operating modes of dc motor?
Motoring, regenerative braking, dynamic braking, plugging.
PARALLEL INVERTER
1. What are inverters and what are its applications?
DC to AC converters is known as inverters. The function of an inverter is to change a DC input
voltage into AC output voltage of desired magnitude and frequency. Inverters are widely used in
industrial applications like variable speed AC motor drives, induction
heating, stand-by power supplies and uninterrupted power supplies.
2. Why is the circuit called parallel inverter?
The circuit is called parallel inverter because the commutating capacitor is in parallel with the
primary winding of the output transformer whose secondary is fed to the load.
3. What is the main classification of inverters?
Inverters can be broadly classified into two types namely, Single-phase inverters and three phase
inverters. Each type can use controlled turn-on and controlled turn-off devices (eg. BJT’s and
MOSFET’s etc) or forced commutation thyristers depending on application.
SERIES INVERTER
1. What are series inverters?
Inverters in which the commutating elements are permanently connected in series with the load
resistance.
2. What are the commutating elements in the above circuit?
L and C are the commutating elements.
3. What is the condition for selecting commutating element?
They are selected in such a way that the current flow through series connected elements R, L,
C is under damped