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Worksheetsstar and delta
Total questions: 99
Worksheet time: 50mins
Phase voltages of a star connected alternator are ER = 240∠0o V, EY = 240∠-120o V and EB = 240∠ + 120o V. What is the phase sequence of the system?
RYB
RBY
Power in a Three Phase Circuit = _________.
P = 3 VPh IPh CosФ
P = √3 VL IL CosФ
Both 1 & 2.
In a three phase AC circuit, the sum of all three generated voltages is _______ ?
0
230
415
For a star connected three phase AC circuit ———
Phase voltage is equal to line voltage and phase current is three times the line current
Phase voltage is square root three times line voltage and phase current is equal to line current
In a three phase, delta connection ——-
line current is equal to phase current
Line voltage is equal to phase voltage
In a star connected system, the current flowing through the line is
Greater than the phase current
Equal to the phase current
Polyphase generators produce simultaneous multiple sinusoidal voltages that are separated by
CONSTANT VOLTAGE
CONSTANT PHASE ANGLE
In a three-phase system, the voltages are separated by
0
120
In a Y-connected circuit, the magnitude of each line current is
Three times the phase current
Equal to the corresponding phase current
In a 2 phase generator , electrical displacement among the two phases or windings is ____ degree
120
90
180
Power in a Three Phase Circuit = _________.
P = 3 VPh IPh CosФ
P = √3 VL IL CosФ
Both
A polyphase system is generated by______?
Having two or more generator windings separated by equal electrical angle.
Having generator windings at equal distances
In a three phase AC circuit, power is measured using a Wattmeter
true
false
In a three phase AC circuit, power is measured using a Wattmeter
true
false
The windings of a three-phase supplies are separated by:
90degree
120degree
0degree
The windings of a three-phase supplies are separated by:
0degree
120degree
180degree
Synchronization of A.C. supply means __________
different phase sequence
same phase sequence
Phase sequence indicator gives the maximum value of phase voltages.
true
false
Pure resistor circuit the voltage and current are
They have zero phase difference
Lagging each other
When A.C current passes through a capacitor then the current relationship will be
The current lead voltage by phase angle is 90 degrees
The voltage leads current by phase angle is 90 degrees
AC equivalent of resistance is impedance
true
false
What will you call an impedance with zero phase angle?
resistance
reactance
What is maximum value of power factor?
0
1
Active power and apparent power are respectively represented by?
kW and kVA
kVAR and kVA
Power factor is a ratio of
True power to apparent power
Apparent power to true power
The power factor of capacitive circuits is
Leading
Lagging
The power factor of purely inductive circuits is
Leading
Lagging
The power factor of an ac circuit is equal to
Cosine of the phase angle
Sine of the phase angle
The unit of true power is
Watt
VA
The unit of apparent power is
VA
w
The power factor is
cosΦ
sinΦ
Unit of reactive power
VA
VAR
What is the frequency of ac mains in India?
120Hz
50Hz
60Hz
Amplitude is the maximum value of a current or voltage
True
False
A 1KHz signal has a period of 1ms.
True
False
The instantaneous value is the voltage or current of a waveform at its peak.
True
False
A signal with a 20ms period has a frequency of ____
50Hz
60Hz
The unit of frequency is ____
ampere
Hertz
A current is set to be alternating when it changes in
Magnitude only
Direction only
Both magnitude and direction
RMS stands for ________
Root Mean Square
Root Mean Sum
What is the effective value of current?
RMS current
Average current
Peak value divided by the rms value gives us____
Form factor
Peak factor
Calculate the crest factor if the peak value of current is 10A and the rms value is 2A.
5
2
The form factor is the ratio of
Peak value to RMS value
RMS value to average value
Classification of Power sources are
current source and voltage source
cell and battery
The source which supplies in the form of a current is ________
current source
voltage source
The
source which supplies in the form of a voltage is __________
current source
voltage source
An electric battery consists of several ________
dc source
batteries
electrochemical
cells
The
battery converts chemical energy into ______
electrical energy
mechanical energy
The
battery uses _______ source
AC
DC
Secondary
battery is _________
Rechargeable battery
Non rechargeable battery
The
positive side of fuel cell is ________
anode
cathode
The
negative side of fuel cell is ________
anode
cathode
Primary battery is _________
Rechargeable
Non-Rechargeable
A group of cells is called as_________
Battery
electro chemical cell
The fuel cell will convert _________ into ___________
chemical energy into electrical energy
electrical energy to chemical energy
Hydrogen Oxygen Fuel cells contains two electrodes ______ and _____
Anode and cathode
Hydrogen and Oxygen
Unit of current is ___
Ampere
Volt
Unit of EMF is ____
Volt
Ampere
Unit of potential difference
Ampere
Volt
Unit of energy
Watt
Joules
Unit of power
Watt
Joules
The movement of free electrons is called
current
voltage
The force to move the free electrons is called
EMF
Current
The rate of doing work is called
power
energy
The amount of work done is called
Power
energy
The difference between higher potential and lower potential is called
Potential difference
current
The unit of battery is
A
Ah
volt
Five 2V cells are connected in series. the output voltage is
10V
5V
2V
Five 2V cells are connected in parallel . the output voltage is
2V
5V
10V
Five 10V,200mAh cells are connected in series, the capacity of the battery is
200mAh
1000mAh
Three 10V 100mAh are connected in parallel, the capacity of the batteries is
300mAh
100mAh
The capacity of a cell is measured in
Ah
A
V
The performance of the battery depends on
DOD
temperature
charging and discharging
aging and history
All the above
DOD stands for
Depth of discharge
Definition of done
____ is the fraction or percentage of the capacity which has been removed from the fully charged battery.
DOD
Capacity
If a battery has 250 mAh capacity and provides 2 mA average current to a load, the battery will last___ hours.
answer choices
125hrs
250hrs
10hrs
_____ is a measure of the charge stored by the battery and is determined by the mass of active material contained in the battery.
Battery capacity
Battery life
Dry cells and (most) alkaline batteries are examples of ____ batteries.
primary
secondary
Star connection is also known as__________
Y-connection
Mesh connection
Delta connection is also known as____________
Y-connection
Mesh connection
When electric current is passed, electrons move from:
high potential to low potential.
low potential to high potential.
What is the commercial unit of electrical energy?
Joules
Kilojoules
watt-hour
What is the rate of flow of electric charges called?
Electric potential
electric conductance
Electric current
Which instrument is used for measuring electric potential?
Ammeter
galvanometer
voltmeter
A real voltage source has
Small internal resistance
Infinite internal resistance
An ideal current source has
Zero internal resistance
Infinite internal resistance
A real current source has
Infinite internal resistance
large internal resistance
Zero internal resistance
WHICH DEVICE IS USED FOR MEASURING CURRENT
Ammeter
voltmeter
Unit of resistance is ____
ohm
mho
number of cycles per second is called ___
frequency
time period
Ohm's law state that
V=IR
I=VR
KCL state that
incoming current = outgoing current
algebraic sum of all the voltage drop = algebraic sum of all the EMF
KVL state that
incoming current = outgoing current
algebraic sum of all the voltage drop = algebraic sum of all the EMF
The electrons in the last orbit of an atom are called
free electrons
bound electrons
Potential difference is also called as _____
Voltage
current
Unit of charge is
coulomb
ampere
An atom has 37 protons and 23 electrons, then what is the charge of an atom ?
+14
-14
An atom has 16 protons and 19 electrons, then what is the charge of an atom ?
+3
-3
