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February 22, 2017

What will happen when power factor is leading in the distribution of power?

If there is a high power factor, i.e if the power factor is close to one:

  1. Losses in the form of heat will be reduced;
  2. The cable becomes less bulky and easier to carry, and very cheap to afford, &
  3. It also reduces over heating of transformers.

What are the functions of Protective Relays?

Figure: Protective Relaying System

Functions of Protective Relays:

  • To detect the faults. For Example: Short circuits.
  • To detect abnormal operating conditions. For example: Overloads, unbalances, low voltage or frequency.
  • To Initiate the operation of the circuit breaker to isolate the defective element from the rest of the system, thereby protecting the system from damages consequent to the fault.
  • To Control and supervision. For example: Automatic reclosing, bus transfer, synch-check.

February 21, 2017

List of Acronyms on Digital Electronics


ACDS advance combat direction   system.
ACRO (or CRO) auxiliar cathod readout.
ALT key —alternat key.
A/N —alphanumeric.
APA —all points addressable.
AM —amplitude modulation.
ASCII   —American Standard Code for Information Interchange.
ASTAB automated status board.
ASW —antisubmarine   warfare.
BC —broadcast.
BDU —basic display unit.
BER —bit error rate.
BITE built-in test equipment.
BPS —bits per second.
C2P —Command and Control Processor.
CAG —central automated status board generator.
CCAEP computer-controlleaction entrpanel.
CDB —central data buffer.
C-DITEG commodigital television graphics generator.
CDS —combat direction system.
CED consolelectronic drawer.
CEG —centraequipmengroup.
CGA —color graphics adapter.
CIGARS console internally generated and refreshed symbols.
CIU —computeinterface unit.
CONICS circles and ellipses.
CP —clock pulse.
CPS —cycles per second.
CRO —TV monitor.
CRT —cathode-ray tube.
CTRL —control.
dB —decibels.
DCC —display control console.
DCI —direct computer interface.
DDEU digital data entry unit.
DDI (1) digital data indicator; (2) digital display indicator.
DITEG digital television graphics generator.
DIV —diversity.
DLRP Data Link Reference Point.
DMU —display multiplexer unit.
DRAC digital radar azimuth converter.
DSC —digital scan converter.
DTS —data terminal set.
EDAC error detection and correction.
EF word —external function word.
EGA enhance graphic adapter.
EMI/RFI —electromagnetic   interference/radio frequency interference.
EPROM —erasable, programmable read-only memory.
ESC key —escape key.
FM —frequency modulation.
GUI —graphic user interface.
HF —high frequency.
HVPS —high voltage power supply.
HZ —hertz.
I/O —input/output.
IFF/SIF —identification, friend or foe/selective identification feature.
JTIDS Join Tactica Informatio Distribution System.
J-SERIES MESSAGE The fixed format messages containing tactical data and commands that are used to exchange information over the JTIDS system.
JU —JTD Unit.
LCD —liquid crystal display.
LCLV liquid crystal light valve.
LED indicator light-emittin diod indicator.
LINK-4A The tactical digital data link for controller-to-controlled aircraft communications.
INK-11—The tactical digital data link for communications among a multiple number of units.
LINK-16 The tactical digital data link for communication among a multiple number of units.  This link is a secure, jam resistant, nodeless, high-capacitlinky that uses the JTIDS terminal.
LSB —Lower Side Band.
LSD —large screen display.
VPS low voltage power supply.
MDA —Monochrom Displa Adapter.
M-SERIES MESSAGES Link-1 messages.
NCS —Net Control Station.
NCT —Net Cycle Time.
NICP Networ Interfac Control Program.
N-SERIES MESSAGES The “normalized” messages exchanged between the C2P computer and the ADCS computer.
NTDS naval tactical data system.
ODR —output data request.
OJT —on-the-job training.
OSC —operations summary console.
PA/SG pulsamplifier/symbol generator.
PC —personacomputer.
PEFT peripheraequipment functionatest.
PIO —periphera I/O
PIXEL picturelement.
PMS —planned maintenancsystem.
POFA programmeoperations functional appraisal.
PPI —plan position indicator.
PPLI —precise participant location and identification.
PPU —projection plotting unit.
PROM programmablread-only memory.
PU —participatinunit.
RAC —radar azimuth converter.
RAM —randoaccess memory.
RC —Roll Call.
RDDS radar data distribution switchboard.
RELNAV relative navigation.
RF —radio frequency.
RGB red, blue, green.
ROM read-only memory.
ROM BIOS ready-onlmemorbasic input output system.
R-SERIES MESSAGES Link-4messages from the controlled aircraft that are sent in response to a control message
SAC —sonar azimuth converter.
SCG —sensor converter group.
SDDS sensodata distribution switchboard.
SG —symbogenerator.
SRAC synchro radar azimuth converter.
SVGA super videographics array.
TDM —tactical   DITEG   module.
TDS tactical data system.
TFT —thin film transistor.
TMG —test message generator.
TN —trac number.
TQ —track quality.
TSLO third salvo lock out.
TTL —transistor-transistor logic.
TVC —television converter group.
TVSC television scan converter.
UHF —ultra-high frequency.
USB —upper side band.
V/C word —velocity/category word.
VDT —video display terminal.
VFK panel variable function key panel.
VGA video graphics array.
V-SERIES MESSAGES Link-4control messages sent from the controlling station to the controlled aircraft.
VSS —video signals simulator.
XGA —extended graphics array.

February 20, 2017

What are the Characteristics, Power Ranges and Applications of different types of AC & DC Motors?

Characteristics, Power Range and Applications of some AC & DC Motors:

Motor Types
Power Range
DC Motors
DC shunt motor
Constant flux constant speed motor creates moderate torque at start.

Up to 200 hp
Machine tools like lathes, milling machines, grinding machines, centrifugal and reciprocating pumps, blowers, and fans.
DC series motor
Creates dangerously high torques at low speeds and should be always connected to the load; speed can be varied.
Up to 200 hp
Preferred for traction-type loads; employed in electric locomotives, conveyors, cranes, elevators, trolleys.
Permanent magnet
DC motor
Higher efficiency, smaller size and simpler architecture; magnets can become demagnetized due to excessive use and overheating; produces lower torque.
Up to 10 hp
Power windows in automobiles, computer peripherals.
Separately excited
Can be controlled either by varying the voltage applied to the field winding or by varying the voltage applied to the armature; can produce high torques.
Up to 100 hp
Traction applications, to control the speed and torque of the motor by changing both armature voltage and stator current.
AC Motors
Three-phase induction motor (Squirrel cage rotor)
Moderate starting torque. Simple robust and maintenance free construction. Speed control by addition of rotor resistance is not possible.
1–5000 hp
Lathe machines, water pumps, grinders, printing machines, large refrigeration and air-conditioning units, small compressors.
Three-phase induction motor (Slip ring rotor)
Very high starting torque. Speed control by rotor resistance possible. High cost. Complicated construction which requires maintenance due to use of slip rings and brush.
1–5000 hp
Cranes, hoists, elevators, large compressors, industrial fans and blowers.
Three-phase synchronous motor
Constant speed irrespective of load, need of a starting device, need for two different excitation sources, variable frequency drives required for speed control.
Up to 50,000 hp
Motor generator sets, timing devices, centrifugal pumps, textile mills, cement mills, rolling mills.
Special Types of Motors
induction motor
Simple and rugged construction.
Up to 5 hp
Fans, water pumps, and refrigerators.
Stepper motor
Smooth rotation, linear relation between electrical input and step rotation.
Used for precise position control in printers, floppy disk drives, robotics, process control, machine tools.
Brushless DC motor
No maintenance required, long life, high reliability and efficiency, low inertia and friction, low starting torque and high costs, ability to run at speeds as high as 50,000 rpm.
Up to 300 hp
Video recorders, computer peripherals, biomedical instruments, commercial ovens, film processing equipment, printing technology, and material handling equipment.
Universal motor
High-power-to-weight ratio, can produce high starting torque, can operate at very high speeds, suits wide variety of applications demanding different torques, shorter lifespan.
Used exclusively
in fractional
Small appliances like mixers, blenders, drills, saws, vacuum cleaners, sewing machines.

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