Electrical Standards

Sunday, January 8, 2017

Dark lamp method of Synchronization of machines

Synchronization of Machines using dark lamp method:-

If phase sequence of running machine is RYB and incoming machine who is to be synchronized with the system is abc, than synchronization switch would be put across contacts a-R, b-Y, c-B respectively. Simultaneous closure of these switches causes synchronization of incoming machine with the running machine.

In dark lamp method of synchronization , There identical lamp’s L1, L2, L3 are contacted across a-R, b-Y, c-B respectively. Voltage rating of these lamps should be twice the rated line to neutral voltage of the machine. Correct phase sequence can be verified if all the three lamps become dark together and bright together with same intensity of brightness. If same doesn’t happens than by changing any 2 terminals of incoming machine correct phase sequence can be achieved.

Image below shows how to Synchronize machines using dark lamp method:-

If lamps never attain a dark phase but intensity of brightness of lamps changes with time then this indicates that there is high voltage difference. The excitation of incoming machine must be varied so that dark phase of all lamps is obtained.

Various cases during dark lamp method of synchronization

Image above shows how various configurations during that method

For maximum brightness case rating of lamp selected should be 2 times the neutral voltage

If the lamps are dark or glow with the same intensity at all time than it means that frequency of incoming machine has become exactly equal to the frequency of running machine. In that case frequency of incoming machine should be adjusted in such a manner that interval between successive dark phases is maximized. That will ensure that frequency difference has become very low. Under these conditions, direction of dark period would become long enough to correctly anticipate the middle of dark period at which the synchronization switch should be closed to ensure proper synchronization of incoming machine with running machine.

If Magnitude difference between 2 phases is very high than lamp will not be dark

At minimum 30% of rated voltage , we can just see the brightness of lamp.

When frequency of phase difference between phases is same then we can see constant brightness of lamp.

For incoming machine Interval between successive darks must be maximum.

Friday, November 11, 2016

Regenerative,Dynamic and Plugging braking

Brake obviously used to reduce the speed of any moving, rotating equipment’s. In day to day activity we use brakes in vehicles to stop them or reduce the speed of the same.

We come through braking of 2 types:-

(i) Electrical Braking

(ii) Mechanical braking

In mechanical braking speed is reduced by using mechanical process. But in electrical braking both electrical and mechanical systems are used for braking.

Electrical braking system works on the principle of reversing the direction of flux.

In most of systems motor is allowed to slow down and eventually stops after switching off the power supply of the motors. But for certain systems braking are needed to be provided. There are various types of motors such as Induction motors, DC motors, Single phase motors, And Synchronous motors etc. As these all types of motors are different from each other so type of braking method will also differ from each other.

There are following type of electrical braking systems:-

1. Regenerative braking

2. Dynamic braking

3. Plugging

Above stated types will be used for all types of motors, Now let’s discuss about them briefly in this article:-

1. Regenerative Braking

This type of braking is used where speed of the motor exceeds the synchronous speed of the motor. As clear from its name in this braking motor will act like a generator and started generating power which will be used for supplying other loads.

Main principle of this type of braking system is that Rotor must rotate at a speed greater than synchronous speed, than motor starts operating like a generator which will leads to reversal in direction of flow of current and torque thus braking takes place.

Regenerative braking is used with DC and AC drives, now let’s see how regenerative works with these drives:-

(a) DC drive:-

The increase in DC voltage for the DC drive occurs at the armature connection. In DC drives there are both forward as well as reverse bridges; by using this reverse bridge DC energy from the armature will get transferred to the source line. If there are only forward bridges in DC drives than a shunt generator is connected in parallel with armature so as to dissipate this energy into heat.

(b) AC drives:-

As we know that in AC drives power supply connected is first converted to DC and then again into AC for feeding the power to motors. There circuitry is only able to handle power in motoring mode only so whenever motor is in regenerating mode than DC voltage get increased at DC link and drive may get trip so that it can’t damage whole Drive. So there are following ways to handle the excessive energy:-

(i) By providing a bridge converter for regeneration.

(ii) By connecting many drives DC bus bars so that regenerative energy from one motor can be used for other motor.

(iii) By dissipating this energy through heat. By using a resistor.

Disadvantage:-

In this braking motor has to run above synchronous speed that may cause damage to the motor mechanically and electrically.

2. Dynamic Braking:-

In this method resistors are used for braking the motor. In this method motor is disconnected from the power supply and connected across a resistance. Whenever motor is disconnected from the source than inertia will kept rotating the motor, such condition of motor is called self –excited generator and direction of flow of current and torque reverses. In this system there a unit which consists of controller, switching device. Resistors are separated components. This whole unit is rated in Amperes. HP rating of the unit is 20%. Resistors are sized according to applications. In this system chopper is mounted in enclosure and resistor is mounted to 100 feet away.

3. Plugging

In this type of braking supply at terminals is reversed which results in generator torque to also get reversed , thus it will leads to decrease in speed. In this method external resistance is used to limit the current. Disadvantage associated with this method is that here power is wasted during braking also.

Friday, November 4, 2016

Principle and Selection of electrical Chimney

Electrical Chimney is now becoming integral part of every house as houses are shrinking so to get natural ventilation becomes very difficult. Before purchasing chimney lot you have to carry out lot of research on internet so as to get best product as per your requirements. There are so many chimneys available in the market which can be selected as per requirements. It is always useful to look into technical specifications, prices , size etc. as per kitchen requirements. Electrical chimneys are basically forced method of ventilation. All chimneys work on the principle of Updraft.

Principle of Working of Chimney

As Stated earlier that chimney works on the principle of updraft. Updraft is nothing but flow of air from bottom to top. Pressure difference will created the required updraft. This required pressure difference is created by chimney. Longer the height or length of pipe in chimney , longer will be the air is forced to travel through it. It must be kept in mind while designing chimney is that , chimney must be sealed from outside along the length of chimney. When there were breaks along the length of chimney then outside air will comes in and draft will not strong. As said earlier without draft chimney will not work.

*Image Source- Amazon.in

Selection of Electrical Chimney:-

There are following parameters which must be kept in mind while selection of a Chimney:-

1. Size of Chimney:-

Chimney size should be more than or equal to size of Gas stove.

2. Chimney capacity/ Suction of chimney:-

(i) If duct length or Distance from chimney to outlet is more than 8 feet than it is recommended to have chimney having Suction more than 1000.

(ii) If duct length or Distance from chimney to outlet is 5-8 feet than it is recommended to have chimney having Suction 700-1000.

(iii) If duct length or Distance from chimney to outlet is up-to 5 feet than it is recommended to have chimney having Suction up-to 700.

3. Cleaning feature:-

There are following of cleaning features available in chimneys:-

(a) Auto Clean Feature:- Pour water and press auto clean button for cleaning the filter from oil and grease.

(b) 3rd generation auto clean Chimney:- In this feature there is no need of adding water , just press the button and heating element will vaporize oil and grease.

4. Selection of filter:-

There are following filter available:-

(i) Baffle Filter

(ii) Aluminum Cassette filter

Now how these filters works are explained as below:-

(i) Baffle filter

The baffle is flow control panel. Baffle filters are made of Stainless steel. In This filter there are many curves through which exhaust gases will move. During this movement of smoke, oil and grease particles will remains on filter. As In case of Cassette filters where oil and grease obstruct the path of air movement in these filters there will not be any obstruction so suction power doesn’t have any effect. These filters requires cleaning after 3-4 weeks.

Advantages of baffle filter

(i) These filters requires less cleaning and low maintenance comparison to Cassette filters.

(ii) These filters have longer life than cassette filters.

(iii) These filters provide more efficiency to chimney in comparison to cassette filters as air flow isn’t restricted by oil and grease.

Disadvantages of baffle filter

(i) As these filters are made from Stainless steel so these filters are heavier than cassette filters so sometimes it may become difficult in detaching baffle filter from chimney

(ii) These filters are more costlier.

(iii) Aluminum Cassette filters:-

In these types of filters there are multiple layers of mesh which retain grease, oil particle from smoke and throw out remaining smoke. When these cassette filters block oil and grease than its holes get blocked which results in reduction of suction capacity. These filters required washing once a week.

Advantages of cassette filter

(a) Cassette filter are cheaper in comparison to baffle filters.

(b) Cassette filters are of lightweight so detaching cassette filter from chimney is so easy.

Disadvantages of cassette filter

(a) These filters required cleaning on regular basis i.e. once a week. If cleaning isn’t done in some cases grease, oil that stick on mesh threads catch fire.

(b) Cleaning cassette filter much difficult than baffle filter.

Auto clean and oil collector are latest features in chimneys.

There is lot of smoke generated while cooking different kinds of foods in kitchen. Sometimes when we are frying or cooking some oily food then lot of smoke get generated chimney just sucks that smoke and through it out.

Now this smoke contains lot of oil which get accumulate inside chimney, so it is required timely cleaning of chimney. Chimney cleaning is quite an effort taking process earlier but with introduction of auto clean features in chimney it hardly takes any effort.

Now chimneys are having oil collector and cleaning button mounted on its display. For auto cleaning just add some water in oil collector part and press auto clean ,now as soon as button pressed auto-cleaning process get started.

Tuesday, November 1, 2016

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:-

Cable Size, weight, Height, Diameter chart

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.

Friday, October 14, 2016

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.