block diagram of a mobile communication system...
September 11, 2013
September 7, 2013
30 Electrical Engineering Formulas!
Download Instruction:
1. Click on the 'Download Now' button
2. Wait for five seconds and then click on ...
Useful Electrical Equations!
Useful Electrical Equations:
· For Sinusoidal Current: Form Factor = RMS Value/Average Value = 1.11
· For Sinusoidal Current: Peak Factor = Max Value/RMS Value = 1.414
· Average Value of Sinusoidal Current (Iav) = 0.637 x Im (Im = Max.Value)
· RMS Value of Sinusoidal Current (Irms) = 0.707 x Im (Im = Max.Value)
· A.C Current = D.C Current/0.636.
· Phase Difference between Phase = 360/ No of Phase (1 Phase=230/1=360°, 2 Phase=360/2=180°)
· Short Circuit Level of Cable in KA (Isc) = (0.094 x Cable Dia in Sq.mm)...
August 29, 2013
Sometimes we have seen that a ceiling fan suddenly starts moving in opposite direction with slow speed, what could be the defect?
The starting winding circuit is open-circuited may be due to burnt winding or damaged capacitor or the running winding is damaged. The fan is running only on one winding. The blades and thrust of air in the room accelerated the blades in opposite direction. As we know that the single phase motors are not self-starting, they will continue to move in the direction in which these are initially accelerated...
July 12, 2013
What are the Functions of Substation Equipment?
Functions of Substation Equipments:
Sl. No.
Equipment
Function
Bus-Bar
Incoming & outgoing circuits Connected to bus-bar
Circuit
Breaker
Automatic switching during normal
or abnormal conditions
Isolators
Disconnection under no-load
condition for safety, isolation and maintenance.
Earthing
switch
To discharge the voltage on deadlines
to earth
Current
Transformer
To step-down...
What is REF relay?
It is restricted earth fault relay. When the fault occurs very near to the neutral point of the transformer, the voltage available to drive the earth circuit is very small, which may not be sufficient to activate the relay, unless the relay is set for a very low current. Hence the zone of protection in the winding of the transformer is restricted to cover only around 85%. Hence the relay is called REF relay...
What are the errors in Current Transformer?
(a) Ratio error Percentage ratio error = [(Nominal ratio – Actual ratio)/Actual ratio] x 100 The value of transformation ratio is not equal to the turns ratio.(b) Phase angle error: Phase angle =180/π[(ImCos δ-I1Sin δ)/nI...
What is an arc? Give the two methods of arc interruption?
Arc is a phenomenon occurring when the two contacts of a circuit breaker separate under heavy load or fault or short circuit condition.
Methods of arc interruption:
High resistance interruption:-the arc resistance is increased by elongating, and splitting the arc so that the arc is fully extinguished
Current zero method:-The arc is interrupted at current zero position that occurs 100 times a second in case of 50Hz power system frequency in ac.
...
What do you mean by current chopping?
When interrupting low inductive currents such as magnetizing currents of transformer, shunt reactor, the rapid deionization of the contact space and blast effect may cause the current to be interrupted before the natural current zero. This phenomenon of interruption of the current before its natural zero is called current chopping...
How to calculate voltage drop?
How to calculate voltage drop:
In situations where the circuit conductors span large distances, the voltage drop is calculated. If the voltage drop is too great, the circuit conductor must be increased to maintain the current between the points. The calculations for a single-phase circuit and a three-phase circuit differ slightly.
Single-phase voltage drop calculation:
Three-phase voltage drop calculation:
OR 3øVD = (SQRT(3)*L*R*I)/1000
VD...
How much voltage drop is Acceptable?
The national Electrical Code (NEC) recommends that the combined voltage drop of the electrical system (brunch circuit and feeders) not exceed 5% for optimum efficiency. This recommendation not only can improve safety but can ensure proper equipment operation and power efficiency. Foe Example, In a 220 volt 5 ampere circuit, this means that there should be no more than a 11 V drop (109 volts) at the furthest outlet when the circuit is fully loaded.
Related Link: How to calculate voltage dro...
July 5, 2013
What are the Components of the power system?
The various components of power system are:
Generator (alternator),
Transformer,
Transmission line,
Induction motor,
Synchronous motor,
Resistive and
Reactive loads.
...
June 8, 2013
Mention The major features of a good protective gear for alternator and transformer
Major
features of a good protective gear
ü High
speedy
ü Selectivity
ü High
sensitivity
ü Stability
ü Simplicity
ü Reliability
...
Write down the Protective System of Alternator and Transformer
Alternator
protection
ü Differential
protection system
ü Balanced
Earth fault protection
ü Stator-inter
run protection
Transformer
protection
ü Using
Buchholz relay
ü Combined
leakage and overload protection
ü Circulating-current
scheme for transformer protection
...
Write down some major Faults of Alternator and Transformer.
Major faults
in Alternator
ü Failure of prime-mover
ü Failure of field
ü Over Current
ü Over Voltage
ü Over Speed
ü Stator Winding faults
ü Unbalanced loading
Major faults in
Transformer
ü Open
circuits
ü Over
heating
ü Earth
Fault
ü Phase-to-Phase
fault
ü Over
Load
ü Phase
to ground fault
ü Incipient
fault
ü High
voltage surge fault
...
How can a circuit element absorb power?
By converting electrical energy into-
Heat (resistors in toasters);
Light (light bulbs);
Acoustic energy (speakers);
Storing energy (charging a battery).
...
June 2, 2013
EEE Project -1 : 15- Step Digital Power Supply
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Its is a simple circuit to obtain variable DC voltage from 1.25V to 15.19V in reasonably small
steps.
Download Instruction:
1. Click on the 'Download Now' button
2. Wait for five seconds and then click on ...
May 30, 2013
Write down some Elements of Protection System.
Protection System Elements:
¤ Protective relays
¤ Circuit
breakers
¤ Current and
voltage transducers
¤ Communications
channels
¤ DC supply
system
¤ Control
cable...
How Do Relays Detect Faults?
¤ When a
fault takes place, the current, voltage, frequency, and other electrical
variables behave in a peculiar way. For example:
o
Current suddenly increases
o
Voltage suddenly decreases
¤ Relays can
measure the currents and the voltages and detect that there is an overcurrent,
or an undervoltage, or a combination of both
¤ Many other
detection principles determine the design of protective relays
...
February 12, 2013
Write down some common applications of Diodes.
Some common applications of Diodes:
Power supply applications
AM (amplitude modulation) detectors
Back-EMF path
Clamping or DC restoration
Clipper or limiter
Non-linear circuits
Logic circuits...
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