AC, DC and Electrical Signals

Alternating Current (AC) | Direct Current (DC) | Properties of signals | RMS values

AC means Alternating Current and DC means Direct Current. AC and DC are also used when referring to voltages and electrical signals which are not currents! For example: a 12V AC power supply has an alternating voltage (which will make an alternating current flow). Anelectrical signal is a voltage or current which conveys information, usually it means a voltage. The term can be used for any voltage or current in a circuit.

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AC from a power supply This shape is called a sine wave.

This triangular signal is AC because it changes between positive (+) and negative (-).

Alternating Current (AC)

Alternating Current (AC) flows one way, then the other way, continually reversing direction.

An AC voltage is continually changing between positive (+) and negative (-).
The rate of changing direction is called the frequency of the AC and it is measured in hertz (Hz) which is the number of forwards-backwards cycles per second.
Mains electricity in the UK has a frequency of 50Hz.
See below for more details of signal properties.
An AC supply is suitable for powering some devices such as lamps and heaters but almost all electronic circuits require a steady DC supply (see below). 

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Direct Current (DC)

Steady DC from a battery or regulated power supply, this is ideal for electronic circuits.

Smooth DC from a smoothed power supply, this is suitable for some electronics.

Varying DC from a power supply without smoothing, this is not suitable for electronics.

Direct Current (DC) always flows in the same direction, but it may increase and decrease.

A DC voltage is always positive (or always negative), but it may increase and decrease.
Electronic circuits normally require a steady DC supply which is constant at one value or asmooth DC supply which has a small variation called ripple.
Cells, batteries and regulated power supplies provide steady DC which is ideal for electronic circuits.
Power supplies contain a transformer which converts the mains AC supply to a safe low voltage AC. Then the AC is converted to DC by a bridge rectifier but the output is varying DC which is unsuitable for electronic circuits.
Some power supplies include a capacitor to provide smooth DC which is suitable for less-sensitive electronic circuits, including most of the projects on this website.
Lamps, heaters and motors will work with any DC supply.
Please see the Power Supplies page for further information.
Power supplies are also covered by the Electronics in Meccano website. 

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Properties of electrical signals

An electrical signal is a voltage or current which conveys information, usually it means a voltage. The term can be used for any voltage or current in a circuit.

The voltage-time graph on the right shows various properties of an electrical signal. In addition to the properties labelled on the graph, there is frequency which is the number of cycles per second.
The diagram shows a sine wave but these properties apply to any signal with a constant shape. 

• Amplitude is the maximum voltage reached by the signal. 
  It is measured in volts, V.
• Peak voltage is another name for amplitude.
• Peak-peak voltage is twice the peak voltage (amplitude). When reading an oscilloscope trace it is usual to measure peak-peak voltage.
• Time period is the time taken for the signal to complete one cycle. 
  It is measured in seconds (s), but time periods tend to be short so milliseconds (ms) and microseconds (µs) are often used. 1ms = 0.001s and 1µs = 0.000001s.
• Frequency is the number of cycles per second. 
  It is measured in hertz (Hz), but frequencies tend to be high so kilohertz (kHz) and megahertz (MHz) are often used. 1kHz = 1000Hz and 1MHz = 1000000Hz.

frequency  =	1	and	time period  =	1
	time period			frequency

·         Mains electricity in the UK has a frequency of 50Hz, 
so it has a time period of ¹/₅₀ = 0.02s = 20ms.

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Root Mean Square (RMS) Values

The value of an AC voltage is continually changing from zero up to the positive peak, through zero to the negative peak and back to zero again. Clearly for most of the time it is less than the peak voltage, so this is not a good measure of its real effect.

Instead we use the root mean square voltage (V_RMS) which is 0.7 of the peak voltage (V_peak):

V_RMS = 0.7 × V_peak   and   V_peak = 1.4 × V_RMS

These equations also apply to current. 
They are only true for sine waves (the most common type of AC) because the 0.7 and 1.4 are different values for other shapes. 
The RMS value is the effective value of a varying voltage or current. It is the equivalent steady DC (constant) value which gives the same effect.
For example a lamp connected to a 6V RMS AC supply will light with the same brightness when connected to a steady 6V DC supply. However, the lamp will be dimmer if connected to a 6V peak AC supply because the RMS value of this is only 4.2V (it is equivalent to a steady 4.2V DC).
You may find it helps to think of the RMS value as a sort of average, but please remember that it is NOT really the average! In fact the average voltage (or current) of an AC signal is zero because the positive and negative parts exactly cancel out!

What do AC meters show, is it the RMS or peak voltage?

AC voltmeters and ammeters show the RMS value of the voltage or current. DC meters also show the RMS value when connected to varying DC providing the DC is varying quickly, if the frequency is less than about 10Hz you will see the meter reading fluctuating instead.

What does '6V AC' really mean, is it the RMS or peak voltage?

If the peak value is meant it should be clearly stated, otherwise assume it is the RMS value. In everyday use AC voltages (and currents) are always given as RMS values because this allows a sensible comparison to be made with steady DC voltages (and currents), such as from a battery.

For example a '6V AC supply' means 6V RMS, the peak voltage is 8.6V. The UK mains supply is 230V AC, this means 230V RMS so the peak voltage of the mains is about 320V!

So what does root mean square (RMS) really mean?

First square all the values, then find the average (mean) of these square values over a complete cycle, and find the square root of this average. That is the RMS value. Confused? Ignore the maths (it looks more complicated than it really is), just accept that RMS values for voltage and current are a much more useful quantity than peak values.

Some interesting question for normally we founed

BTS SITE EARTHING SCHEME_1

The Induction Motor

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The Induction Motor

The theory of the induction motor is well known [10], so only the basics will be described here. Fig. IM-1 shows a cross-section view of a three-phase induction motor, with the stator and rotor coils represented by concentrated windings. Voltage equations can be written for the stator and rotor phases in terms of self and mutual-inductances. As the rotor moves in figure IM-1, the mutual inductances between the rotor and stator coils will change, because the angle between the axes of the rotor and stator changes. To eliminate the time-varying inductances, the equations are frequently transformed to q-d-0 variables in the arbitrary reference frame. For this simulation, we used a stationary reference frame, which has the advantage of eliminating some terms from the voltage equations. 

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The simulation of the induction motor, is conveniently accomplished by solving for the flux linkages per second in terms of the voltages applied to the machine.  The derivatives of the stator flux linkages are given by equations IM1 to IM3.  In these equations and the following equations, the superscript "s" indicates the stationary reference frame.  The subscript "s" indicates stator quantities, and omega sub b is the base radian electrical frequency. 

 

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Fig. IM-2 shows the Graphic Modeller simulation of the induction motor.  As noted above, the model for the induction motor requires voltages as inputs.  Thus one block consists of a three-phase source that provides a balanced set of three-phase voltages.  The induction motor block is a compound block that contains another level, and will be described in the next paragraph.  The final block in the model is the load torque, which by suitable choice of constants allows constant power, constant torque, horsepower squared, and horsepower cubed loads.  For convenience there are also two strip plot recorders that plot the stator and rotor phase currents.  Double clicking them, after a simulation run, will plot the appropriate variables.
 

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Induction motor simulation in Graphic Modeller

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Double clicking on the induction motor block reveals the next level of detail as shown in Fig. IM-3.  Compound blocks can be used to allow multiple levels in a model.  That has the advantage of keeping the amount of blocks to a reasonable number at any given level of the model.  In this case, the compound block was used so the model could be used as a tool by undergraduates who are not concerned with the simulation equations.  More advanced undergraduate and graduate students, on the other hand can go down a level to understand the theory behind the simulation.

Since the inputs and outputs to the compound block are phase voltages and currents, they must be transformed to the stationary reference frame.  Thus, the leftmost blue block contains the equations to transform the phase voltages to the stationary reference frame, and the q-d-0 stationary reference frame currents to phase currents.  The center green block contains ACSL code representing equations IM-1 through IM-16, and is thus the actual simulation of the electrical portion of the induction motor.  This block also contains constants for the parameters of the machine, which can be changed by the user to represent other machines.  The purple box contains the code for equation IM-17 and determines the speed and position of the rotor as a function of time.  The last block (the right blue one) is another transformation.  In this case the rotor q-d-0 currents are transformed to phase currents in the rotor reference frame.
 

                                                                                                     

 

My Project

Dragon II

Cable Specification

It Is 3.5 Core 25sqmm Cable.
In 3.5 Core 25sqmm Cable Three cable R-Y-B And One Half N cable

Comman Punch Point In Telecom For Elecrical

[1] Air Gap Found in Roxtec.
[2] Air Gap Found In Cable Entry.
[3] Antistatic Mat Not Grounded (Earthed).
[4] ISMB Clit Not Found .
[5] Joint Found In Chiller AC Supply Cable.
[6] AC-FCU Supply Cable Not Routed In Casing.
[7] Cable Tray Not Fixed On Cage With Screaw.
[8] DG LFL Alarm Not Working And Not Connected.
[9] Y-B Link Not Connect In SMPS Input Suplly MCB.
[10] Padestal Not Found For HCT Support.
[11] Fire- Extinguisher Not Fixed On The Cage.
[12] ISMB Clit Nut Bolt Not Tight Properly.

GLAND STUDY

Why Use Cable Glands?
- To firmly secure cable entering a piece of equipment
- To maintain the ingress protection of the piece of equipment (minimum of IP54 for "e" and "n" type enclosures. Where the enclosure wall thickness is less than 6mm a sealing washer or thread sealant will be required to maintain IP54 protection)
- To maintain earth continuity between a piece of equipment and any armouring in the cable
- To ensure containment of an internal explosion in flameproof equipment

British Standard for Cable Glands
The Code of Practice for selection, installation and inspection of cable glands used in electrical installations is covered in British Standard BS 6121-5 1989 Mechanical cable glands.

Cable Gland Selection
When selecting cable glands, always consider:
- Electrolytic action between two dissimilar metals (gland and enclosure). Shortened lifetime for the glands and the cable entries can result if incompatabile materials selected.
- Degreee of Ingress Protection required
- Certification of gland for use in Hazardous areas
- Standard gland or barrier gland required
- Size of cable being terminated
- Size of cable entry on peice of equipment
 
What is a Barrier Gland?
Barrier glands are similar to normal cable glands, except a compound sealant material is used to seal around the individual cores of the cable ensuring the inside of the cable is gas tight as well as the outside.

When Should a Barrier Gland be Used?
There are numerous details to consider when deciding if a barrier gland should be used. A useful rule of thumb is; if the hazardous area requires IIC apparatus, or if the volume of the enclosure is greater than 2 litres then it is likely you will need to use a barrier gland.
BS EN60079-14 ElectricalAapparatus for Explosive Gas Atmospheres Part 14 - Electrical Installations in Hazardous Areas (other than Mines) provides a detailed selection process for deciding if a barrier gland is required.
 

Electrical formula

Short To Full name

Abbreviation           Expansion
ACDB                                                 Alternate Current Distribution Box
AMF                                                   Auto Mains Failure
AQA                                                   American Quality Assessors
AVM pads                                          Anti Vibration Mould pads
AGL                                                   Above Ground Level
BB                                                      Battery Bank
BIS                                                     Bureau Of Indian Standards
BOM                                                  Bill Of Material
BTS                                                    Base Trans Receiver Station
BV & DV                                           Build Vendor & Delivery Vendors
CELL Site                                          Composition Of Tower, DG and Shelter
CDMA                                               Code Division Multiple Access
CPRI                                                  Centre Of Power Research Institute
CT & PT                                            Current & Potential Transformer
CVCL                                                Certificate Generator Set
DG Set                                               Diesel Generator Set
Day Markings                                     Orange & White pint bands on tower
DPR                                                   Daily Progressive Report
EAT                                                   Electrical Acceptance Testing
EGB                                                   External Grounding Bus Bar
FA                                                      Final Acceptance
FCU                                                   Fan Control Unit
FS                                                      Foll Scope
FTA                                                   First Time Acceptance
GBT                                                   Ground Base Tower
GI                                                      Galvanized Iron
GSM                                                  Globar System Mobilization
ICAO                                                 International Code Of Aviation Organization
IGB                                                    Internal Grounding Bus Bar
ISO                                                    International Organization Of Stanards
ISO-9001 & 14001                            9001 represents Quality & 14001 Environment
ISMB                                                 I Section Medium Beam
MCB                                                  Miniature Circut Board
MHz                                                   Mega Hertz
MIS                                                    Management Information System
MW Antenna                                      Micro Wave Antenna
NGL                                                   Normal Ground Level
Night Beacom                                     Aviation Lamp
OFC                                                   Optical Fibre Cable
O & M                                               Operations & Maintenance
O & E M                                           Operations & Equipment Mainenance
OPC                                                  Ordinary Portland Cement
PABX                                                Public Automatic Branch Exchange
PCB                                                   Printed Circuit Board
PCC                                                   Plain Cement Concrete
PCM                                                  Phase Change Material
PIU                                                    Power Interface Unit
PM                                                    Project Management
PMC                                                 Project Management Consultancy/ Company
PPC                                                  Pozzalana Portland Cement
RC                                                    Rate Contract
RCC                                                 Reinforce Cement Concrete

About Electrical Engineering

Electrical Engineering is part of Engineering.Electrical engineering is a field of EngineeringThe field first became an identifiable occupation in the late nineteenth century after commercialization of the electric telegraf and electrical power supply. It now covers a range of subtopics including power, electronics, Control system, signal processing and telecommunications.

    Electrical engineering may include Electronic Engineering.

Types of Engineering Careers

.There are many types of field in Engineering

.Which type field you choice Or  interest

Following are many field.
1)Electrical Engineering
2)Mechenical Engineering
3)Civil Engineering
4)Electronics & Comunication Engineering
5)Computer Engineering
6)Aeronautical Engineering
7)Architectural Engineering
8)Auto mobile Engineering

Interview Question for Elecrical

Some time we Thinking That "What Question Ask in interview And College test

Below Some Questions Given

1) How Transformar Work?
2) What diferce between "Current" And "Voltage"?
3) Principal Of Newton?
4) How Induction Motor Work?
5) Types Of Circuit Breaker?
6) Working Funtion Of SF6 Circuit Breaker?
7) Types of Wiring Used In Home?
8) Types of Wiring Used In Industrial?
9) Types of Transmition Line?
10) Draw the Diagram for Trasmition Line.

Coming Soon For More
And Ansew the Question.

Punch Point In Telecom For Elecrical {PART-2}

In Part-1 We Show Some Punch point In this we Know more Punch point.

Lets Know Following More Punch point

11) Battery Bank not grouted in Battery chiller (Shelter 1X1)
12) SMPS MCB (Y & B phase MCB) short by 10 sq mm instead of 16 sqmm & lugs not used.
13) Ac cut out not sealed properly.
14) Air gap found in shelter cut out below AC unit
15) DG automation not complete.
16) Earth chamber not found
17) EB Power MCCB 63 A used instead of 100 A.
18) AC Foundation otta plaster work not completed
19) Poll Mount not installed
20) Feature Expendable Ac MCB (ACDB-DCDB) supply cable connection not done.
21) OD cable trey grouting not done properly (pedestal done on ground level)
22) light & plug point cable connected with out lugs & Joint found in cable
23) Joint found in light & plug point cable.
24) Shelter cable entry hole not sealed.
25) Shelter (PIU) cable entry not sealed
26) SMPS  MCB not working properly (80 A DC load MCB).
27) oint found in B cooler (AC)cable.
28) Remark :- LFL alarm not working ( Old DG)
29) SFU not installed.
30) Roxtec not available.

More Punch point See Part-3

Punch Point In Telecom For Elecrical {PART-1}

In Telecom Elecrical Punch point found.
Following Are Punchpoint.
1) Door Seanser Not Working.
2) Battery Chiller grouting not done properly.
3) grouting not done properly.
4) Cage Cable Tray not fixed with the cage panel With screwed.
5) Y-B Link not Connect In SMPS Supply MCB.
6) Padestal not found for HCT support.
7) DG Not work in auto mode .
8) PIU Automation not completed.
9) DG fuel sensor not found, So fuel alarm not check.
10) LLOP, HCT/HWT, LFL Alarm not working in DG.

Electrical interview Question @ Answers.

Question 1 ):- What Is The difference between Isolator and Circuit Breaker?

Answers ):-    Isolator is a off load Device which is used for isolating the downstream circuits from Upstream circuits for the reason of any maintenace on downstream circuit.It is manually operated and does not contain any solenoid unlike circuit breaker. it should not be operated while it is having load.First the load on it must be made zero and then it can safely operated. it Specification only rated current  given.But circuit Breaker is onload automaticdevice used for breaking the circuit in case of abnormal condition like short circuit , Over load etc., It is three specification 1 is rated current and 2 short circuit breaking capacity And 3 is instantantneos tripping current.


Question 2 ):- Why In Earth Pin Is Big Than Other In (Power)plug Socket?

Answers ):-  Because Device Short Circuit Current  Direct Grounded.
                     Device Not Damage.


Question 3 ):-  Tell Me How Many Types Of  Earthing?

Answers ):-   Follwing Are Earthing Types. There are many types of earthing.
                    1)Piepe Earthing
                    2)Plate Earthing.
                    3)Chemical Earthing.
                    4)Spring Earthing.
What is the difnd Circuit Breaker?

Question  4 ):-  Write Types Of Circuit Breaker?

Answers ):-    Follwing Are Types Of Circuit Breaker.
                      1) Oil Circuit Breaker
                      2) Air Blast Circuit Breaker
                      3) Sulphur Hyxoflouride (SF6)Circuit Breaker
                      4) Vacuum Circuit Breaker

 Question  5 ):-   Continue...