Cable Tray Designing and Selection

In electrical Systems for laying power cables , cable trays are preferable mode for laying cables over a long distance where digging can’t be feasible or digging cost is very high. Cable trays are also used where space is low. Also cable trays gives aesthetic looks to electrical systems.

There are following recommendations for designing cable trays:-

1.     Always take 10-20% as Spare capacity.

2.     Distances between cables should be from 5 mm to 10 mm.

Now let’s illustrate the same by taking an example:-

Here we will design cable tray for aluminum cables:-

(i)              10 no’s 2.5 mmsq X 4 Core cables

(ii)             25 mmsq X 4 Core 10 no’s cables

Calculation:

For calculations following Table is used:-

Total Outer Diameter :

Diameter of 2.5 mmSq.mm Cable =No of Cable X Outer Diameter of Each Cable

                                                       =10 X 16 = 160 mm

Similarly for 25 mmsq cables = 25X10 =250 mm

Total Diameter of All Cables laying in Tray = (160+250)mm= 410 mm

Now Weight of Cables will be:

Weight of 2.5 Sq.mm Cables =No of Cable X Weight of Each Cable

  =10 X 0.56= 5.6 Kg/Meter

Similarly for 25 mmsq cable= 10X1.11= 11.1 Kg/ Meter

Total Weight of All Cables laying in Tray = (5.6+11.1) Kg/Meter= 16.7 Kg/ Meter

Width of all Cables:

Total Width of all Cables = (Total Cables X min. Distance between Cable) + Cable Outer Diameter in total

Total Width of all Cables = (20 X 5) + 410 = 510 mm

Now after taking 10% Spare Capacity of Cable Tray

Final Width of all Cables = 1.1X510 =561 mm

Now total area of cables

Total Area of Cable =  width of all Cables X Maximum Height Cable

Total Area of Cable =  561 X 25 =14025 Sq.mm

Taking 10% Spare Capacity of Cable Tray

Final Area of all Cables = 1.1X14025 = 15427.5 mmsq.

Now cable tray selected from above calculations is that either we can install 1 no. 600 mm X 50 mm cable tray having weight carrying capacity of 50 kg/ meter, this cable tray has overall area of 30000 mmsq , Or we can install 300 mm X 50 mmsq 2 no. s cable trays with area = 30000 mmsq.

We can even use single 300 mmsq X 50 mmsq cable tray and placing one cable over another.

Usually perforated cable trays are used in electrical systems.

VoLTE technology in JIO; What is VoLTE?

In recent days JIO has generated lot of buzz which offers free calling for lifetime and free internet up to December. There is also new technology associated with JIO is VoLTE. Mobile phone manufacturers are selling phones with VoLTE enabled technology. Now there is curiosity what is VoLTE? and how it is different?

In this below article we will learn what is VoLTE technology all about?:-

VoLTE:-

There is new technology in field of data services. VoLTE is known as Voice over Long-Term Evolution. It is used for providing a uniform format of voice traffic on LTE and other systems including CSFB (Circuit Switched Fall Back) and SV-LTE(Simultaneous Voice Long term evolution). This technology is used for better voice call quality. VoLTE uses 4G technology and it is based on packet switching on the other hand 2G and 3G networks uses circuit based switch.

Now when we make a call using 2G and 3G then there is bandwidth assigned to that call this will not allow to terminate until call ends. On the other hand in VoLTE voice calls are divided into packets and are sent on whole data pipeline which will then get reconstructed at receiving end. As calling is done over whole data pipeline which means better calling using VoLTE technology.

VoLTE is designed for standardizing the system for transferring Voice traffic over Long term evolution.

LTE was basically an IP cellular system used for carrying data. Operators would be able to carry voice either by reverting to 2G / 3G Systems. Operators can use VoIP in one form or another.

LTE will lead disintegration and mismatch not allowing all phones to communicate with each other which will reduce the voice traffic. SMS services are still widely used, often proving a means of set-up for other applications.

Even though revenue from voice calls and SMS is falling, a format for voice over LTE and messaging, it was as necessary to have a viable and standardized scheme to provide the voice and SMS services to protect this revenue.

LTE Voice Options:-

There are following options for Long term Evolution voicing:-

(i)             CSFB known as Circuit switched Fall back

(ii)            SV-LTE Known as Simultaneous Voice LTE

(iii)           VoLGA known as Voice over LTE via GAN

(iv)          One Voice / later called Voice over LTE, VoLTE

Let’s discuss about these:-

(i)             CSFB:- This service has been standardized under 3GPP Specifications. CSFB uses different types of processes and network elements to enable the circuit to fall back to 2G/3G connection before a circuit switched call is initiated. The description also allows for SMS to be carried as this is important for very many set-up procedures for cellular telecommunications. To achieve this handset uses an interface known as SGs which allows messages to be sent over an LTE channel.

(ii)            SV-LTE:   This service allows packet switched LTE services to run concurrently with a circuit switched voice service. This facility provides the facilities of CSFB at the same time as running a packet switched data service. There is a disadvantage associated with this service is that, it requires two radios to run at the same time within the handset which has a serious impact on battery life.

(iii)           VoLGA:- This service was based on the current 3GPP Generic Access Network (GAN) standard, and the aim was to allow LTE users to obtain a steady set of voice, SMS services as they shift between GSM, UMTS and LTE access networks. For mobile operators, the aim of VoLGA was to provide a low-cost and low-risk approach for bringing their primary revenue generating services onto the new LTE network deployments.

(iv)          VoLTE:   This scheme for providing voice over an LTE system develops IMS The IP Multimedia Subsystem,  IMS is a framework for delivering Internet Protocol. It enables a variety of services to be run flawlessly rather than having several different applications operating simultaneously), which enables it to become part of a rich media solution. It was the option chosen by the GSMA for use on LTE and is the standardized method for providing SMS and voice over LTE.

Voice over LTE

When concept of SMS and voice System over LTE using IMS was introduced than it was opposed by many telecom operators as it was complex system involving IMS. It was observed that it is not only complex but also it is far too expensive and burdensome to introduce and maintain the same.

One Voice profile for Voice over LTE was developed by association between over 40 operators. In 2010 GSMA declared that they were supporting the One Voice solution to provide Voice over LTE. To achieve a workable system, a cut down variant of IMS was used. It was felt that this would be acceptable to operators while still providing the functionality required.

The VoLTE system is based on the IMS MMTel concepts that were previously in existence. It has been specified in the GSMA profile IR 92.

VoLTE IP versions

After update from IPv4 to IPv6 version ,VoLTE devices are needed to operate in dual mode which will cater both IPv4 and IPv6.

One of the issues with voice over IP type calls is the overhead resulting from the IP header. To overcome this issue VoLTE requires that IP header compression is used along with RoHC (Robust Header Compression) protocol for voice data packet headers.

Methods for reducing Harmonics in System

There are so many methods available by which harmonics can be reduced in system and power quality can be improved. There are following methods of reducing the harmonics in system:-

(i)                  DC choke

(ii)                By reducing harmonics at loads

(iii)               By using filters

Now let’s discuss about them:-

(i)                 DC choke:-

VFD’s are main source of harmonics generation in a plant. DC choke is used in VFD’s to reduce harmonics. DC choking is an inductance in series with semiconductor bridge circuit. DC choke provides reduction in 5th and 7th Harmonics. DC choke is comparable to an equivalent AC-side line reactor, although the %Total Harmonic Distortion (THD) is somewhat less.

(ii)               By reducing Harmonics levels at Loads and Source:-

In electrical Transmission and distribution system there are lot of equipment’s connected in distribution so there will be harmonics getting in system . So it will become even more important to minimize the harmonics.

If there are harmonics get generated in plant i.e. at source end then it is always best to counter these harmonics at source end. As stated earlier in a plant source of harmonics are VFD’s so harmonics can be reduced installing a Delta-Star Transformer in parallel with Delta- Delta Transformer. This is done to convert two synchronized 6-Pulse VFD’s to a 12-Pulse application. This is done as to reduce 5th and 7th harmonics as there will phase shift of 30 degree in 12 pulse applications instead to 60 degree in 6-pulse application. Delta connected Transformer block the zero sequence harmonics so triple Harmonics are eliminated.

(iii)             By using filters:-

Filters are used to minimize the harmonics levels in distribution systems.  These are used in Plants also. There are following types of filters.

(a)    Passive

(b)   Active

Now let’s discuss about these 2 types of filters

(a)   Passive filters:-

 These types of filters are generally inductors and capacitors. These filters are used to block Harmonics. These are even used to shunt the Harmonics to ground. For a particular type particular application these filters are designed accordingly.

We know that as frequency increase impedance of an inductor increases on the other hand impedance of capacitor deceases with increased frequency.

There are some disadvantages associated with these filters are that these become ineffective if harmonics changes due to variation in loads.

In AC drives usually line reactors and Transformers are used to reduce the harmonics. If DC bus choke is not used then inductor of suitable capacity is used to reduce harmonics level to significant levels.

Thus passive filter may contains series/ Shunt capacitor/ Inductor network and a series inductor or Transformer. Usually now days in electrical system passive filters are integral part of drive system.

(b)   Active filters:-

Unlike passive filters in which harmnocis are blocked or shunted away , active filters are used to condition the power lines and also known as power line conditioners. In active filters these are condition monitors which sense the harmonic currents electronically and generate the counter waveform corresponding to harmonic current generated. So by this way harmonics currents are cancelled out.

Active filters are used to reduce the harmonics levels as per limited specified by IEEE. So by using these filters power factor of system get improved.

Working of Active filters:-

Active filters are installed in parallel to the loads so as to offset the generated harmonics. In electrical systems Current Transducers are used to provide the control logic according to current waveform to counter harmonics. In Three phase system 2 Current transducers are sufficient for these filters working.

Active filters remove the fundamental frequency from this waveform. The resulting waveform after removal of fundamental frequency is inverted and used to direct the firing of the IGBTs. This inverted waveform is injected back into the ac line.

This will leads to cancellation of cancellation of current Harmonics in electrical systems.

As we know that voltage harmonics are due to current harmonics so since we have redcued current harmonics voltage harmonics are also get reduced.

There are following components of Active filters:-

(a)    Power semiconductors

(b)   DC link capacitors and Bus Bars

(c)    Fuses.

Power semiconductor consists of IGBT pulse width modulation (PWM) at an appropriate switching speed. An internal filter in active filters blocks this frequency from entering the ac lines and decouples the active harmonic filter from the rest of the system so no harmful interaction occurs.

In active filters Rated output current= square root of the sum of the squares of the harmonic and reactive currents at the bus.

If total harmonics > Rating of an active harmonic filter, then additional units can be installed in parallel.

For knowing what are Harmonics and effects on Electrical Systems:-
http://electrialstandards.blogspot.com/2016/09/methods-for-reducing-harmonics-in-system.html

Harmonics and its effects on electrical systems

Harmonics in electrical systems:-

Before discussing about consequences of Harmonics you must know what are harmonics:-

Harmonics are electric current and voltages that causes power quality problems. These are generated due to electronic equipment’s which draws non linear loads with abrupt pulses. These pulses causes distorted current and voltages causes of which will be discussed in this article.

Harmonics are classified according of level of harmonics these are multiple of frequencies such as

2^nd level, 3^rd level, 4^th level, and upto 11^th levels

Where 2^nd level means Harmonics with frequency of 100 HZ

3^rd level means Harmonics with frequency level of 150 HZ

And similar for other levels

Now 2^nd level, 5^th level, 8^th level, and 11^th level will have –ve sequence of currents

3^rd level, 6^th level and 9^th level will have zero sequence of currents

4^th level, 7^th level, 10^th levels will have +ve sequence of currents

Harmonics are now integral part of electricity. Harmonics is also known as pollution in electricity. Now days while power availability is not a big concern so intention now shifts towards quality of electiricity.

There is an increase in harmonics levels in electricity there are following few reasons for harmonics in electricity:-

1.       Increase in non-linear loads such as power electronics equipment’s. Such as VFD, SMPS etc where power is chopped and used as per requirements at low or other frequencies.

2.       There are various other devices which leads to Harmonics in electrical systems such as :-

(a)    Arcing devices

(b)   Ferromagnetic devices

(c)    Appliances

(d)   Electronic switching power converters

There will be following effects due to harmonics in electrical systems:-

(a)    Overheating of electrical equipment’s as more eddy currents are produced due to these harmonic levels.

(b)   Due to overheating and other losses this will leads to reduction in life of equipment

(c)    These harmonics will leads to premature failure of equipment’s

(d)   Harmonics will leads to malfunctioning of equipment’s

(e)   Harmonics will leads to more losses in systems

(f)     Harmonics will leads to interference in communication signals

(g)    Harmonics will leads to Nuisance tripping of circuit breaker and blowing off the fuses.

(h)   Harmonics will leads to more vibrations in motor and other equipment’s.

(i)      This will leads to flickering of computers.

There are so many effects of Harmonics on various equipments

When there are harmonics in systems than we can’t be able to get 1 Power factor as there are so many reactive powers associated with these harmonics which will not get compensated using capacitor banks. Even when we try to compensate the same by installation of more and more capacitors then we lose a hafety amount on installation of capacitors and also this will leads to higher losses due to capacitor banks.

Earlier we known that Power factor=  Voltage X Current X Power factor

                                                                         Voltage X Current

Now days due to these Harmonics there are Distortion power factors which will be calculated as below:-

Where THDi Stands for Total harmonics distortion in currents

And THDv Stands for Total Harmonics distortion in voltage.

Now Total Power factor is given as = Power factor X Distortion power factor

As Distortion power factor will never will be unity so Total power factor of system will never will be unity.

                               

There are following effects of harmonics on Transformers and Motors:-

1.       There will be more eddy current loses in Transformers.

2.       Harmonics will leads to more losses due to skin effect.

3.       Harmonics will leads to overheating of coils and that will cause premature failure of Transformers

4.       Harmonics will leads to more Hysteresis and eddy current losses in motors as Hysteresis losses are directly proportional to frequency and eddy current losses are directly proportional to square of frequency.

5.       There will be more winding eddy current losses, High frequency Rotor and stator losses, and tooth pulsations in motors due to harmonics

6.       More harmonics will be leads to more I²R losses in both Transformers and motors

7.       There will be increased over temperature due to these losses and leads to premature failure

There are following effects of harmonics on Cables and Capacitors:-

1.       There will be Higher Proximity effects and Skin effects in cables

2.       There will be additional losses in cables

3.       These will cause additional overheating of cables

4.       This will decrease insulation level of cables

5.       Harmonics will cause increased Resistance

6.       Harmonics will cause derating of cables

7.       Harmonics will leads to higher neutral currents in cables and leads to unbalanced loads on cables.

8.       Harmonics will leads to resonance with 7^th Harmonics in capacitor banks which will leads to lower capacitive reactance.

9.       Harmonics will leads to more electricity bill due to increased losses due to harmonics.

10. Harmonics will leads to more KVA demand as stated earlier due to increased losses.

For reducing harmonics visit link:-
http://electrialstandards.blogspot.com/2016/09/methods-for-reducing-harmonics-in-system.html

                                                           

Electricity from Pototes and Other Fruits and vegetables

Electricity works on an idea that whenever two dissimilar metals bring in contact with an electrolytic solution then there will electron movement in these metals when these metals are connected using a conductor.

All plants consist of fluid which is electrolyte for metals. So using above principle of inserting metals in a fluid will leads to electricity generation.

We have done during childhood for generating electricity from potatoes.

It works on principle that Potatoes contains a liquid in which many water soluble chemicals are present. So these may cause a chemical reaction with one or both of our electrodes. So we will get some electricity from that.

Best result will be obtained while using zinc and copper electrodes.

Let’s discuss about the same experiment:-

For conducting experiment let’s take 8 potatoes. We will take 8 potatoes to get enough electricity to light up a LED.

Now insert different metals of any shapes into these potatoes.

Now by using small wires all potatoes are connected in series. Series connection can be done soldering wires at metal ends or by making after series connections one wire is connected to LED which is taken from last potato and other wire is taken from 1^st potato.

Now this last wire which is connected at one end acts as phase and other wire which is taken from 1^st potato acts as neutral.

You will see that LED starts glowing.

Electricity generated during this process in DC in nature.

We can generate higher amount of electricity using lemons as Lemons are having acidic nature which will leads to metals to react quickly so they will generate more electricity.

So for conducting same experiment for generating electricity half the quantity of potatoes.

When you measure voltage generated by one potato using digital multi-meter you will find that it will shows 1.2 volts so in order to get enough value for glowing a LED at-least 8 potatoes must be used.

Now if you keep connecting LED for long time then you will find that when you cut the potato it will be found black.

Similar experiment can also be applicable for fruits such as oranges and apples.

Electricity from Boiled Potatoes

Recent experiments has also shown that if boiled potatoes are used in experiments than they will produce electricity ten times than raw potatoes.

As boiled potatoes break the resistance which will leads to more smooth passage for electrons.

If you cut the potatoes into 4-5 pieces then efficiency will be increased considerably.

Even you can light up a room using boiled potatoes for over one month.

For knowing about discovery of electricity visit link"-
http://electrialstandards.blogspot.in/2016/07/discovery-of-electricity-how.html 

Synchronous Generators Prime movers; Steam turbine; Hydraulic turbine & diesel engines

Synchronous machines construction depends upon type of prime mover used in machines. There are following types of prime movers used in power generation:-

1.       Steam turbines

2.       Hydraulic Turbines

3.       Diesel Engines

Let’s discuss them :-

1.     Steam turbine:-

These types of synchronous machines have high speed.  Generators driven by steam turbine are also called Turbogenerators. Maximum speed of Turbogenerators is 3000 RPM as per formula

Frequency= PN/ 120;

Where P is no. of poles

N is no. of revolutions

In 2 Pole machine at 50 HZ frequency Speed of Turbogenerator comes out to be= 50X120/ 2= 3000 RPM

With Such high speed lower value of armature diameter is to be designed. Lower diameter is selected to limit the centrifugal forces which have very much influence on the generator design.

Peripheral Speed of a Machine is given by formula as below:-

Peripheral Speed(V)= πDn  m/Sec

Where D is diameter of rotor in meters

n=speed of rotor in revolutions per second

As we have seen from above formula that Peripheral Speed increases with increase in diameter as both are directly proportion to each other, With increase in diameter centrifugal forces increases. So diameter should be kept low.

Due to this high speed diameter of 2 pole machine is limited to 1.2 meter which will give peripheral speed of about 175 m/s.

Also for turbogenerators cylindrical rotor construction is to be used instead of salient pole as in Salient pole construction is impractical in turbogenerators due to high mechanical forces.

In these alternators efficiency is very high. Turbo-generators are available upto rating of 1000 MW.

2.     Hydraulic Turbines:-

Power plants using hydraulic turbines are Hydro Power plants these power plants uses Synchronous generators driven by Hydraulic turbines. Hydraulic turbines are driven by water heads. There are 3 types of hydraulic turbines due to different levels of water head availability.

Types of Hydraulic turbine used according to head height are as below:-

(i)                  For Water heads of 400 Meter and above- Pelton Wheel design to be used

(ii)                For water heads upto 380 meter – Francis turbine design to be used

(iii)               For water heads upto 50 meter- Kaplan turbine design to be used

As water heads not so much high so speed of turbine is low varies from 50 to 500 rpm. So get such low rpm salient pole alternators are used for the same. No. of poles in these generators are 12 onwards.

Also further Pelton type turbine design can be Horizontal or vertical shaft type. Usually Horizontal Shaft design is more commonly used.  For high power low speed synchronous generators are usually installed for low water heads power plants are generally built with vertical shaft.

There are following fundamental types for vertical shaft Hydro generators:-

(i)                 Suspended Type:-

In this type thrust bearing is at upper bracket above alternator rotor

(ii)               Umbrella Type:-

In this type bearing is mounted on lower bracket on the turbine cover, Mostly umbrella type construction is used to reduce generator weight and height of power plant. As in suspended type where bearing is used on upper bracket it has to be bigger in size as it has to withstand both generator and turbine load, also it has to withstand water reaction. This will leads to higher generator weight and height of power plant.

These type of generators have rating upto 750 MW.

3.       Diesel Engines:-

These are most widely used in small commercial and industrial establishments also known as Diesel generators. They are usually of small rating. These are horizontal type,  Since these are slow speed machines so salient pole construction is used for the same. Torque generated during its operation is non-uniform so it makes the synchronous generator sensitive to torque variations.

Why Power isn't generated at Higher Frequency i.e. greater than 50/ 60 HZ??

There is more often a question arises while you are dealing with electrical systems.
As you know that for alternators (Synchronous generators)
Frequency=  No. of Pole X Speed of Machine

                               120
So increasing the frequency of power generation you have to either increase the no. of poles or increase the speed of alternator.
Now if you increase no. of poles than diameter of machine will increase considerably to accommodate increased no. of poles. Also if machine diameter is increased to accommodate no. of poles then you can't rotate the machine at higher speed as centrifugal forces and vibration forces will be very high. Mechanical strength requirements of machines will also be very high.

Now for increasing speed of alternator you have to provide higher input which will leads to very high maintenance as deterioration happens at such a higher input. So alternator should be mechanically very strong .