The basics of primary distribution circuits (substation branches, feeders…)

Distribution circuits come in many different configurations and circuit lengths. Most share many common characteristics. Figure 1 shows a typical distribution circuit, and Table 1 shows typical parameters of a... Read more
By EEE, ADBU

The essentials of electric shock protection, earthing systems and RCDs

Protection of persons and livestock against electric shock is a fundamental principle in the design of electrical installations in accordance with BS 7671: Requirements for Electrical Installations, commonly known as... Read more
By EEE, ADBU

Basic Electrical Engineering MCQs

01) Two 100W, 200V lamps are connected in series across a 200V supply. The total power consumed by each lamp will be in Watts :-
A) 25 Watts
B) 50 Watts
C) 100 Watts
D) 200 Watts

A

02) Two electric bulbs have transparent filament of same thickness. It one of them gives 60 W & other gives 100 W, then-
A) 60 W lamp filament has shorter length
B) 100 W lamp filament has longer length
C) 60 W lamp filament has longer length
D) 60 W & 100 W lamp filament have equal length

C

03) Bulb in street lighting are connected in
A) Parallel
B) Series
C) Series parallel
D) end of end

D

04) A piece of copper and another piece of germanium are cooled from room temperature to 80K. The resistance of
A) each of them increases.
B) each of them decreases.
C) copper increases and germanium decreases.
D) copper decreases and germanium increases.

D

05) If a large resistance is connected parallel a small resistance then net resistance will be
A) Greater than the large resistance
B) Smaller than the small resistance
C) Smaller than the greater but larger than the smaller resistance
D) None of the above option

B

06) The speed of a DC motor is
A) Directly proportional to flux and inversely proportional to back emf.
B) Directly proportional to both back emf and flux.
C) Directly proportional to back emf and flux.
D) Directly proportional to back emf and inversely proportional flux.

D

07) In which braking back emf exceeds supply voltage?
A) Regenerative.
B) Dynamic.
C) Plugging.
D) None of these.

A

08) Third pin of a 3 pin plug is thicker and longer due to
A) for designing purpose.
B) for protection purpose.
C) all pins are of same size.
D) none of these.

B

09) Power factor can be defined as
A) both option B and C.
B) cosine of angle between voltage and current.
C) ratio of resistance versus impedance.
D) sine of voltage and current.

A

10)A 60 Hz frequency voltage would case a bulb to turn on and off
A) 60 times per second.
B) 120 times per second.
C) 70 times per second.
D) 80 times per second.

B

August 21, 2017 at 02:09AM by EEE, ADBU

9 power generating units grouped by prime mover you should know about

Many types of power generating plants are in use and possible for the future, including steam plants fueled by coal, oil, or gas, nuclear plants, hydro plants and plants which... Read more
By EEE, ADBU

Differences Between Alternator and Generator

Differences Between Alternator and Generator

Alternator and Generator both are electro-mechanical machines which converts mechanical input to electrical output i.e., electrical energy.Though output of the both machines electrical power, there are some key differences between alternator and generator are there in terms of design type of power etc.

What is the difference between an alternator and a generator?

Alternator vs Generator

Alternator	Generator
Alternator generates only AC power in every condition.	Generator can generates both AC power or DC power But using commutator we convert to DC power. (Can say mostly used for DC power generation.)
Alternator generates higher output than Generator.	Generator generates lower output than Alternator.
Alternator generates alternating EMF at its output terminal.	Generator generates constant EMF at its output terminal. But internally it is alternating in nature.
Alternator has stationary Armature and rotating magnetic field.	Generator has stationary magnetic field and rotating Armature for high voltage output but in case of low voltage output rotating armature and rotating magnetic field are used.
It works on faraday law of electromagnetic induction.	It also works on faraday law of electromagnetic induction.
Alternator has DC field which generates constant magnetic field in Armature.	Generator has permanent magnet which generates constant magnetic field in stator.
In alternator we take supply from its stator.	In generator we take supply from rotor. It is a major difference between alternator and generator.

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advantage of alternator vs generator
alternator vs generator efficiency

August 18, 2017 at 09:48AM by EEE, ADBU

5 special applications of residual current devices (RCDs)

Normally residual current devices (RCDs) are used for protection against direct and indirect contacts. An RCD can detect low leakage currents that could flow through the body of a person.... Read more
By EEE, ADBU

The essentials of MV/HV magnetic voltage transformers

Magnetic voltage transformers are used to provide a secondary signal that is proportional to the actual prevailing primary value. These signals are used to supply measuring instruments, meters, relays and... Read more
By EEE, ADBU

Comparison of Gravity Control and Spring Control

Differences Between Gravity Control and Spring Control

Gravity control or Spring control both are comes under the category of "controlling torques" of an electrical measurement instrument.Before going have a comparison between gravity control and spring control let us have a look at why we need controlling torque in a measurement instrument?

1) Controlling torque produces a force equal and opposite to the deflecting force in order to make the deflection of pointer at a definite magnitude. If this system is absent then the pointer will swing beyond its final steady position for the given magnitude and deflection will become indefinite.

2) It brings the moving system back to zero position when the force which causes the movement of the moving system is removed. It will never come back to its zero position in the absence of controlling system. We have some advantages of spring control over gravity control.

Advantages of spring control | Disadvantages of gravity control

Gravity Control	Spring Control
Adjustable small weight is used which produces the controlling torque.	Two hair springs are used which exert controlling torque.
Controlling torque can be varied.	Controlling torque is fixed.
The performance is not temperature dependent.	The performance is temperature dependent.
The scale is nonuniform.	The scale is uniform.
The controlling torque is proportional to sinA (A is angle).	The controlling torque is proportional to 0.
The readings can not be taken accurately.	The readings can be taken very accurately.
The system must be used in vertical position only.	The system need not be necessarily in vertical position.
Proper levelling is required as gravity control.	The levelling is not required.
Simple, cheap but delicate.	Simple, rigid but costlier compared to gravity control.
Rarely used for indicating and portable instruments.	Very popularly used in most of the instruments.

Tags:
Controlling System: Gravity vs Spring Control
Advantages of spring control over gravity control
What is advantages of spring control over gravity control
What is gravity control,spring control?
Controlling torque in measuring instruments

August 13, 2017 at 11:12PM by EEE, ADBU

What is Transfer Function In Control System ?

Transfer Function of Control System

Definition: Mathematically it is defined as the ratio of Laplace transform of output (response) of the system to the Laplace transform of input (excitation or driving function), under the assumption that all initial conditions are zero.

Symbolically system can be represented as shown in the below figure where input is represented as r(t) and output is represented as c(t) and the transfer function of the system is C(s)/R(s).

C(s) ---- Laplace transform of output.
R(s) ---- Laplace transform of input.
Transfer Function G(s)= C(s)/R(s)

Advantages and Features of Transfer Function

The various features of the transfer function are,

i) It gives mathematical models of all system components and hence of the overall system. Individual analysis of various components is also possible by the transfer function approach.

ii) As it uses a Laplace approach, it converts time domain equations to simple algebraic equations.

iii) It suggests operational method of expressing equations which relate output to input.

iv) The transfer function is expressed only as a function of the complex variable ‘s'. It is not a function of the real variable, time or any other variable that is used as the independent variable.

v) It is the property and characteristics of the system itself.  Its value is dependent on the parameters of the system and independent of the values of inputs. Transfer function is to be obtained for a pair of input and output and then it remains constant for any selection of input as long as output variable is same. it helps in calculating the output for any type of input applied to the system.

vi) Once transfer function is known, output response for any type of reference input can be calculated.

vii) It helps in determining the important information about the system i.e. poles, zeros, characteristic equation etc..

viii) it helps in the stability analysis of the system.

ix) The system differential equation can be easily obtained by replacing variable 's' by d/dt.

x) Finding inverse, the required variable can be easily expressed in the time domain.
this is much more easy than to analyse the entire system in the time domain.

Disadvantages of Transfer Function

The few limitations of the transfer function approach called approach are,

i) Only applicable to linear time invariant systems.

ii) It does not provide any information concerning the physical structure of the system. From transfer function, physical nature of the system whether it is electrical, mechanical, thermal or hydraulic, cannot be judged.

iii) Effects arising due to initial conditions are totally neglected. Hence initial conditions loose their importance.

Procedure to Determine the Transfer Function of a Control System

1) Write down the time domain equations for the system by introducing different variables in the system.

2) Take the Laplace transform of the system equations assuming all initial conditions to be zero.

3) Identify system input and output variables.

4) Eliminating introduced variables, get the resultant equation in terms of input and output variables.

August 13, 2017 at 02:20PM by EEE, ADBU

Star to Delta and Delta to Star Conversion (Wye-Delta Transformations)

Star to Delta and Delta to Star Conversion

(Wye-Delta Transformations)

It is easy to calculate equivalent resistance of resistors which are in either parallel or series.Sometimes we may face difficulty in solving equivalent value. There we make use of star to delta or delta to star conversion. It is a powerful tool to simplify the complexity of the network. By applying this we can measurably reduce the problem solving time.

How To Identify Where Star Delta Transformation Is Required? 

• Delta, or Δ (also known as the 'Pi' or π) configuration, and
• Star connected network which has the symbol of the letter 'Y' (also known as the  'T') configuration.
• In the below picture you can observe the connection of delta or 'Pi' configuration, star or 'T' configuration.

Delta Configuration

Star Configuration.

Delta (Δ) to Star (Y) Conversion 

In delta to star conversion, the delta connected elements will be converted to star connection in order to simplify the network analysis.Transforming from delta to star introduces one additional node.

Star (Y) to Delta (Δ) Conversion 

In  star to delta conversion, the star connected elements will be converted to delta connection in order to simplify the network analysis.Transforming from star to delta removes one node.

Star-Delta Transformation

Delta-Star Transformation

Star-Delta Transformation / Delta-Star Transformation can be used to any type of electrical component.Star to delta conversion formula have been given above.Delta wye transformation problems with solution pdf will be added (Stay Tuned).

August 13, 2017 at 01:43AM by EEE, ADBU

10 equipment you MUST recognize in every distribution substation

Distribution substation is a substation from which electric supply is distributed to the different users. In a substation there are numbers of incoming and outgoing circuits each having its isolator,... Read more
By EEE, ADBU

The most common methods of measuring the resistance of an earth electrode

When an earth electrode system has been designed and installed, it is usually necessary to measure and confirm the earth resistance between the electrode and “true Earth”. The most commonly... Read more
By EEE, ADBU

Practical advices for positioning of circuit breakers inside LV switchboard

Mounting of the different mechanical and electrical components (enclosures, busbars, functional units – circuit breakers, etc.) which constitute the LV switchboard defined by the original manufacturer must be carried out... Read more
By EEE, ADBU

MV network diagrams for feeding secondary switchboards and MV/LV transformers

Let’s take a look at the main MV network diagrams and structures used to feed secondary switchboards and MV/LV transformers. The complexity of the diagrams differs, depending on the level... Read more
By EEE, ADBU

Choice of Site For Hydro-Electric Power Stations

Factors Affecting Hydroelectric Plant Location

Hydroelectric power / Hydro-power plant is one of the eco-friendly power generation systems.It has less running cost and high efficiency (around 50%, compared to thermal plant much better). Site selection of hydroelectric power plant depends on some factors in order to give efficient output in terms of overall performance and economic.

Site selection of Hydroelectric power plant. 

What are the points to be considered while selecting the sites of hydroelectric power plant?

The following points should be taken into account while selecting the site for a hydro-electric power station : 

(i) Availability of water.

Since the primary requirement of a hydro-electric power station is the availability of huge quantity of water,  such plants should be built at a place (e.g., river, canal) where adequate water is available at a good head.

(ii) Storage of water.

There are wide variations in water supply from a river or canal during the year.  This makes it necessary to store water by constructing a dam in order to ensure the generation of power throughout the year.  The storage helps in equalizing the flow of water so that any excess quantity of water at a certain period of the year can be made available during times of very low flow in the river.   This leads to the conclusion that site selected for a hydro-electric plant should provide adequate facilities for erecting a dam and storage of water.

(iii) Cost and type of land.

The land for the construction of the plant should be available at a reasonable price.  Further, the bearing capacity of the ground should be adequate to withstand the weight of heavy equipment to be installed.

(iv) Transportation facilities.

The site selected for a hydro-electric plant should be accessible by rail and road so that necessary equipment and machinery could be easily transported. It is clear from the above mentioned factors that ideal choice of site for such a plant is near a river in hilly areas where dam can be conveniently built and large reservoirs can be obtained.

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August 02, 2017 at 03:01PM by EEE, ADBU

How to install a manual transfer switch for a backup system in 16 steps

A manual transfer switch is installed next to the main service panel to override the normal electrical service with power from a backup generator during a power outage. Manual transfer... Read more
By EEE, ADBU

What is Difference between UPS & Inverter

Introduction:

• We are heavily dependent upon appliances that run on electricity such as fans, lights, AC, fridge, Computer and so on.
• Whenever there is a power cut, electricity supply to these appliances is cut off and they stop working. However, if we have backup supply devices such as UPS and inverter, we can ensure Power supply to appliances and not bothered with power cuts.
• However, people remain confused with the difference between a UPS and an inverter because UPS and inverters both are providing back up power supplies during main power outage.
• Inverters are preferred more for general electric appliances whose working does not get affected by extended delays in power supply.
• UPS are used for electronics appliances such as computer, servers, workstations, Medical Equipment which perform critical task and cannot tolerate delays in power supply.
• An off-line ups (the standard) switch to the batteries in 3 to 8 milliseconds, after the main power has been lost. While Inverter changes over in about 500 milliseconds.

 UPS:

• UPS means uninterrupted power supply.
• Uninterruptible power supply (UPS) provides uninterrupted power to the equipment. It means switching time from power cut to battery power is vey less hence important and critical equipment like computer, desktop .Medical Instruments is not switch off and we can lose data.
• A UPS is a complete system that is consisting of many parts that include batteries, a charge controller, circuitry any transfer switch for switching between the mains and back-up battery, and an inverter. An inverter is needed because the battery can only store DC power and we need to convert that back to AC in order to match the appliances connected in the main power line.
• UPS= Battery charger + Inverter
• UPS is nothing but inverter with inbuilt battery charger.

• UPS give backup only 10 to 20 minutes. The main intention of it is to provide backup only for small time so that you can save the programs and data.
• UPS also gives protection against line abnormalities like Surge, Voltage fluctuation, Under Voltage, Over Voltage, Spike, Noise.

Inverter:

• Inverter circuit simple converters battery DC current to AC and supply
• In inverter inverts the direct current to an alternating current. During normal condition electrical supply is direct feed to the Load. It also takes the supply from the AC source and charges the battery.
• During the power cut, the inverter receives the supply from the battery and convert it DC to AC Power and provides the power supply to the electrical equipment.
• Inverters purpose is to provide power backup to total home appliances, lights, fans.
• Inverter uses flat plate or tubular battery to store electricity. So it requires continuous maintenance, needs to fill the distilled water toppings at regular intervals of time.
• Inverter does not give protection against line abnormalities

Difference between UPS and Inverter:

 

Comparison of  UPS and Inverter
Descriptions	UPS	Inverter
Definition	UPS means Uninterruptable Power Supply.	Inverter is a device which converts DC electricity to AC
Function	It is an electric circuit (device) which instantly backs up power supply for a gadget. The gadgets works continues to work on smoothly and there is no damage to it.	Inverter consist circuitry which converts AC to DC and stores in the battery. When power supply goes off, that DC power is converted back to AC and is transmitted to the respective electronic gadget.
Principles	It first converts AC to DC Power to charge the battery than Convert DC Power to AC Power (Inverter) and this AC power is supplied to Load. However, UPS monitors the input voltage level and processes it in terms of voltage regulations. UPS= Battery charger + Inverter	Inverter converts DC power (stored in its battery) to AC Power supplied to the devices. Normally AC Power charges the battery .It uses relays and sensors to detect when to use DC power or AC Power, for DC power.
Back up Time	Power Back up for Short Duration	Power Back up for Long Duration
Types	(a) Offline UPS, (b) Online UPS and (c) Line-interactive UPS.	(a) Square Wave, (b) Quasi Wave, (c) Sine Wave
Main Part	Rectifier/charger, Inverter ,controller	Inverter and controller.
Switch over Time	3 to 8 milliseconds.	500 milliseconds.
Voltage Fluctuations	While voltage fluctuations in input supply can be adjusted by the UPS, the output voltages are desired to be as smooth as possible. In smoothing the voltage outputs, UPS are considered better as compared to inverter.	Inverter does not give protection against voltage fluctuations
Circuitry Sophistication	UPS circuitry is far more sophisticated than that of inverter’s	Inverter has Simple circuit then UPS
Pricing	UPS more expensive than an inverter.	Inverter is less expensive than UPS
Application	UPS are used for electronics Application such as computer, servers, Network Switches, workstations, Medical Equipment, Processing Equipment which perform critical task and cannot tolerate delays in power supply.	Inverters are preferred more for general electric Application which working does not affected by extended delays in power supply.
Protection	UPS provide protection against voltage spikes, voltage drops, instability of the main frequency and harmonic distortions	Inverter does not provide protection against Line abnormalities.
Battery	Used sealed maintenance free (SMF) battery	Used flat plate or tubular battery
Battery Maintenance	Do not require any maintenance.	Requires continuous maintenance, needs to fill the distilled water toppings at regular intervals of time
Energy Consumption	More due to constant battery Charging	Less

Conclusion:

• The UPS and inverter both provide the backup supply to the electrical system. Two major differences between the UPS and inverter are that
• The switching of UPS from the main supply to the battery is very immediate so it is used to provide backup power of important or critical electronics equipment. whereas in inverter the switching from mains supply to battery takes times so it used to provide less important electrical equipment.
• The UPS provide protection to the load against Spike, Voltage fluctuation, Noise while Inverter does not provide any protection to the load.

August 01, 2017 at 08:28PM