Thursday, November 12, 2009
VACUUM CIRCUIT BREAKER
VACUUM CIRCUIT BREAKERS
Circuit breakers are devices which can automatically break a circuit under fault
conditions and it can make the circuit manually after the fault. Circuit breakers are
classified into different types. One of the main circuit breaker among them is Vacuum
circuit breaker. Here vacuum is used to extinct the arc. Arc extinction is the main process
of a circuit breaker
Before that, it is needy to explain how an arc is produced. Circuit breaker has two
contacts- Fixed and movable, otherwise called as electrodes. Normally the contacts
remain closed but if any fault occurs these contacts open automatically and of course can
be opened manually.
We know that circuit breakers work under the instructions from relay. When the trip coils
from relay energize, circuit breaker identifies fault occurred and hence the contacts are
pulled apart. A high intensity current flows through the contacts of the circuit breaker
before they are opened by the system. At the same instant contacts begin to separate and
causes heavy heat and temperature in between the contacts. This is termed as an arc. This
heat is highly dangerous and can cause heavy damage to the whole system. So it has to be
extinguished in no time.
Vacuum is having superior qualities over other arc quenching medium. It has high
insulating strength. When the contacts are opened in vacuum, the arc is produced in
between them. It got extinguishes quickly since the metallic vapours and ions produced
during the arc rapidly condense on the surface of the circuit breaker contacts, resulting in
quick recovery of dielectric strength.
The contacts of Vacuum circuit breaker and arc shied is mounted inside a vacuum
chamber. The chamber is connected to the control mechanism by means of stainless steel
bellows. A glass vessel is used as the outer insulating body. This is all about its
Vacuum circuit breaker is really the most reliable one with low cost, no fire hazards, no
gas generation, low arc energy, little maintenance and low inertia.
Sunday, November 8, 2009
What is an Actuator?
Actuator is a typical mechanical device used to move or control a mechanism or a
system. This device gains energy for its working from air, electricity or liquid and then
converts it into some kind of motion.
In engineering field actuators have many more applications in different sectors. In this
field actuators are used as mechanisms to provide motion and are again used to stop the
motion of that particular device. So it is clear that actuator just actuates the motion. May
be start or stop, depends on the machine.
In electronics engineering, actuators are subdivisions of transducers. They are used to
transform input signal into motion. Normally input signal would be electrical. E.g.
electrical motors, pistons, relays, pneumatic actuators, piezo electric actuators etc.
Actuators can be sometimes used as hardware components. Different types of actuators
are available like plasma actuators, pneumatic actuators, electric actuators, linear
It’s a type of tool used to put something into automatic action. Actually actuators are used
with number of sources. Depending on the type of actuator we are using, different tools
will be assisting us to put the device to motion. Mostly they are used in office work area
since most of them are used to move valve door in systems.
Sometimes they are used to maneuver certain mechanical devices on work. Depending on
the shape and style actuators are divided into different classes. Linear actuators, valve
actuators, hydraulic actuators are the best known and used among them. Each of them has
assigned functions e.g. hydraulic actuators are used to allow more pressure, size and
movement with the object.
All of these different types of actuators are best when knowing what type of motion
control you need. They also provide speed, Belt drive, acceleration and accuracy with
linear motion No matter what type of actuator is needed, there is a tool that makes it
easier to maneuver a certain object or space in your work area.
DIGITAL SIGNAL PROCESSING (DSP)
What is Digital Signal Processing?
It’s a major branch of science that deals with the representation of signals as symbols or
sequences and after that these signals are getting processed. There are two subfields of
processing available- Analog signal processing and Digital signal processing.
This digital signal processing also includes subfields like audio and speech processing,
sonar and radar processing, sensor array processing, spectral estimation, statistical signal
processing, digital image processing, signal processing for communication systems,
biomedical signal processing, seismic signal processing etc. So from the above
description it’s clear that DSP is a vast branch in engineering field that requires genuine
attention and development.
Generally these processing measures the continuous analog signals and is then converted
into digital form by means of an Analog to Digital converter (A-D converter). For certain,
the required output would be in Analog form, so the signal is then converted to Analog
using Digital to Analog converter (D-A converter). We know that this process is very
complex when compared with analog processing and hence error detection and correction
methods are used to clarify the process.
The main notable advantage of DSP is that it is less affected to noise and hence non
vulnerable. DSP algorithms are carried out in special processors like Digital Signal
Processors which is inbuilt in the systems. Since the process is very lengthy and time
consuming, we usually undergo the process in this type of processors. DSP’s include
microprocessors, digital signal controllers, field programmable gate arrays etc. DSP’s can
be implemented using specialized microprocessors like DSP56000, TMS320 and the
Usually the digital signals are denoted in time domain, frequency domain, spatial domain
etc. With the available characteristics, it is decided that on which domain the signal can
be denoted. Sampling is another important point to be specified. Sampling can be done in
signal processing during two stages discretization and quantization. In the dicretization
stage the space of signals are divided into equivalence classes and quantization is carried
out by replacing the signals with representative signals.
DSP has applications in the fields of audio signal processing, audio compression and in
the fields as mentioned earlier.
What are Lightning Arresters?
Lightning arresters or surge diverters are used to protect the earth screen and ground
wires in an electrical system against direct lightning strokes. They conduct the high
voltage surges to the ground without getting affected to the system. The lightning arrestor
provides a cone of protection which has a ground radius approximately equal to its height
above the ground.
The surge diverters consist of a spark gap in series with a nonlinear resistor. The function
of non linear resistor is very important. As the gap sparks over, due to the over voltage,
the arc would get short circuited and may cause power flow current in the arrester. Since
the characteristic of the resistor is to offer high resistance to high voltage, it prevents the
effect of a short circuit. After the surge is over, the resistor offers high resistance to make
the gap non-conducting.
One end of the arrestor would be connected to the terminal of the equipment to be
protected and other end would be grounded. The length of the spark gap is set in such a
way that normal line voltage is enough to cause an arc across the gap but high voltage
would break down the air insulation and form an arc.
Different types of surge diverters are available depending on the purpose. Some of them
are Rod gap arrester, Horn gap arresters, Multigap arresters, Expulsion type lightning
arrester and valve gap arrester. Each of them has variety of range of operating conditions.
Wednesday, October 28, 2009
What are Acoustic Couplers?
The term acoustic means sound. This is a device used in telecommunication field for
coupling electrical signals by acoustical means. Its main working is related to our
telephone. Acoustic coupler is a terminal and interface device to link data terminals and
radio sets with telephone. Acoustic couplers are used to transmit data over telephone lines
using modems. This is a device onto which telephone handset is placed to connect
computer to the network, a modem will be also there. Modems that do not use acoustic
coupler can some times be called as Direct Connected Modems
The link between the terminals and telephones can be achieved by means of acoustic
signals rather than through electrical connections. In 1956 acoustic couplers came into
use in our telephone industry till then this industry was a closed system wholly controlled
and owned by Bell systems.
At first acoustic couplers were sensitive to external disturbances and noises. Direct
electrical connections to telephone networks were made legal in early times. But rapidly
preference got secured to the modem connecting method and hence acoustic couplers are
used widespread. At times acoustic couplers are no longer used since now a days,
telephones can be directly connected to modem instead of connecting to modular
telephone connectors. Better connections can be established by avoiding unwanted
breakage in signals. Still acoustic coupler modems can be useful in some situations like,
in a hotel room where telephone cable is anchored in the walls.
Wednesday, October 28, 2009
What is a VARISTOR?
The name varistor came from variable resistor. Varistor is a pure electronic component
used to protect circuits from transient over voltages making the circuit triggered. The
function of a varistor is to provide increased current when voltage becomes excessively
high. Varistor is also known as Voltage Dependent Resistor (VDR) since it depends on
The most common type we are dealing with now days is Metal Oxide Varistor (MOV). It
is just like a Unijunction Transistor, since it allows current flow only in one direction. It
contains mass of ceramic grains enclosed between two metal plates. The boundary
between and its neighbour forms a diode junction. So when a small voltage is applied
across the electrodes, only a small current passes due to the reverse break down at the
junctions. Similarly when a large voltage is applied, due to thermionic emission large
current passes through the junction. This behavior results in nonlinear current voltage
Varistor can absorb surge in some ways but to some to extent. A typical surge protector
power strip can be made using MOV’s. A varistor provides no equipment protection from
inrush surge current. A varistor doesn’t control such events. Varistors have many
applications on different electronic circuits. It can replace ordinary resistor in almost all
functions, basically it can vary its resistance. So using varistors we can control voltage
and current to the circuit. Thus we can protect the circuit from internal damage and
severe short circuits.
SCADA is the acronym of Supervisory Control And Data Acquisition. It is used in the
fields of data acquisition and monitoring in industries. SCADA is a pure software
package and not having any hardware components. It is the monitoring section of a
process and the decision making section. It controls all the process taken while doing a
Normally we use couplet of software, e.g. SCADA- PLC couplet. Here SCADA acts as
master and PLC acts as slave. SCADA gives instructions and PLC obeys as per the order.
In short control is safe in SCADA hands. It’s more convenient if we use the couplets
even if SCADA alone can do all the operations alone.
SCADA operations are categorized under three below explaining sections. Such as-
industrial, infrastructure and facility based processes. Industrial process includes
manufacturing, production, power generation etc. Infrastructure based process means
water treatment, waste water collection, refining etc. Facility process includes building,
airport and all public sector processes.
SCADA mainly consists of five subsystems. Each is assigned to perform a particular
task. The five subsystems are:
+ HMI or Human Machine Interface- This is an apparatus used to supply data to the
human operator and through this he could able to monitor and control
+ A supervisory computer system- This is used to acquire data and to send commands to
+ RTU or Remote Terminal Unit- These are connected to sensors to do a process,
Converts sensor signals to digital data and sends this data to the supervisory system.
+ PLC or Programmable Logic Controller- used as field devices in a process, since they
are economical, flexible, versatile and much configurable than general purpose RTU’s.
+ Communication- Many modes of communication are available. Communication
connects supervisory systems to RTU’s.
Three generation SCADA software is available. They are First generation or Monolithic,
Second generation or distributed, Third generation or Integrated. Now third generation is
SCADA has applications on energy management system, multi tasking, automation,
industrial control systems, data exchange, pipeline transport, graphical design etc.
SCADA made almost all sections under its control tactically. Mainly we use this software
in automation purposes. This software is freely available and another advantage is no
programming is needed. So even a person who is not good in programming can handle
SCADA well and efficiently.