Types of Bushings and Voltage ratings

Bushings are very important component of Transmission system. These are used of providing insulation to equipment.

There are various types of bushings available in the market, bushings are classified according to following:-

(i)                  Type of insulating material used

(ii)                Type of construction

(iii)               Insulation inside bushing

Let’s discuss about the same:-

(i)           Type of Insulating Material Used:-

This classification depends primarily on the application of the bushing, i.e. the purpose for which bushing is used. These can be further classified as:-

(a)    Air-to-oil bushing

In this type of bushing there is air is used as insulation at one end on bushing and oil acts as insulation at other end. In these bushings oil end is approximately half as long as air end as oil dielectric strength is more than two times than air at atmospheric pressure.

(b)   Air-to-air bushing

In This type of bushing  air acts as insulation at both ends and is used for applications where at end is open to atmospheric conditions and other is at indoor conditions.

(c)    Air-to-SF6 bushings

This type of bushing is used for SF6 insulated circuit breakers.

(d)   SF6-to-oil bushings

This type of bushing is used as shift from SF6 bus ducts and oil filled equipment.

(e)   Oil-to-oil bushings

This type of bushing as transition between Oil bus ducts and oil filled equipment.

(ii)                Type of Construction:-

There are two types of bushings depending upon type of construction, these are classified as below:-

(a)    Solid Type bushings also known as Bulk type bushings

(b)   Capacitance graded bushings also known as Condenser type bushings

Let’s discuss about these:-

(a)   Solid Type bushings:-

The kind of bushing, is normally made with a focal conductor and porcelain or epoxy covers at either end and is utilized essentially at the lower voltages through 25 kV.  These bushings are generally utilized as a part of utilizations extending from little distribution transformers and circuit switchgears to vast generator venture up transformers and hydrogen-cooled control generators.

The essential impediment of the strong bushing is its capacity to withstand 60-Hz voltages over 90 kV. Henceforth, its applications are restricted to 25-kV hardware appraisals, which have test voltages of 70 kV. Late applications require low halfway release confines on the 25-kV terminals amid transformer test and have brought about additional limitations on the utilization of this sort of bushing.

In these cases, either an extraordinarily outlined strong bushing, with one of a kind evaluating protecting that empowers low innate halfway release levels, or a more costly capacitance-reviewed bushing must be utilized.

(b)   Capacitance Graded Bushings:-

These bushings are utilized for basically all voltage evaluations over 25-kV voltage and has been utilized for bushings upto 1500-kV voltage.

These bushings utilizes directing layers at foreordained spiral interims inside oil-impregnated paper or some other protection material that is situated in the space between the focal conductor and the protector.

Diverse makers have utilized an assortment of materials and techniques for making capacitance-evaluated bushings. Early techniques were to embed concentric porcelain barrels with metallized surfaces or overlaid pressboard tubes with installed conductive layers. Later outlines utilized conductive foils, commonly aluminum or copper, in oil-impregnated kraft paper.

An elective strategy is to print semiconductive ink (distinctive producers have utilized diverse conductivities) on all or a portion of the oil-impregnated kraft-paper wraps.

The primary components are the focal round conductor, onto which the capacitance-evaluated center is wound; the best and lower protectors; the mounting rib; the oil and an oil-extension top; and the best and base terminals.

Capacitance-reviewed bushings include numerous more specialized and assembling subtle elements than strong bushings and are hence more costly. These points of interest incorporate the protection/directing layer framework, gear to wind the capacitor center, and the oil to impregnate the paper protection.

In any case, it ought to be noticed that the outspread measurement required for the capacitance-evaluated bushing is considerably less than the strong development, and this saves money on material inside the bushing also in the mechanical assembly in which the bushing is utilized. Likewise, from a down to earth stance, higher-voltage bushings couldn't in any way, shape or form be fabricated with a strong development.

(iii)             Type of Insulation inside Bushing

Still another order identifies with the protecting material utilized inside the bushing. As a rule, these materials can be utilized as a part of either the strong or capacitance-evaluated development, and in a few sorts, more than one of these protecting materials can be utilized as a part of conjunction. The accompanying content gives a short portrayal of these sorts:

1. Air-Insulated Bushings

Air-protected bushings for the most part are utilized just with air-protected mechanical assembly and are of the strong development that utilizes air at air weight between the conductor and the protectors.

2. Oil-Insulated or Oil-Filled Bushings

Oil-protected or oil-filled bushings have electrical-review mineral oil between the transmitter and the encasings in strong sort bushings. This oil can be contained inside the bushing, or it can be imparted to the contraption in which the bushing is utilized. Capacitance-reviewed bushings likewise utilize mineral oil, typically contained inside the bushing, between the protecting material and the protectors for the motivations behind impregnating the kraft paper and exchanging heat from the directing lead.

3. Oil-Impregnated Paper-Insulated Bushings

Oil-impregnated paper-protected bushings utilize the dielectric cooperative energy of mineral oil and electric evaluations of kraft paper to deliver a composite material with predominant dielectric-withstand attributes. This material has been utilized broadly as the protecting material in capacitance-evaluated centers for approximately the most recent 50 years.

4. Gum Bonded or - Impregnated Paper-Insulated Bushings

Gum fortified paper-protected bushings utilize a sap covered kraft paper to manufacture the capacitance-reviewed center, while gum impregnated paper-protected bushings utilize papers impregnated with tar, which are then used to create the capacitance-evaluated center. The last kind of bushing has prevalent dielectric attributes, equivalent with oil-impregnated paper-protected bushings.

5. Cast-Insulation Bushings

Cast-protection bushings are developed of a strong thrown material with or without an inorganic filler. These bushings can be both of the strong or capacitance-evaluated types, despite the fact that the previous sort is more illustrative of present innovation.

6. Gas-Insulated Bushings

Gas-protected bushings utilize pressurized gas, for example, SF6 gas, to protect between the focal conductor and the rib. It utilizes the same pressurized gas as the electrical switch, has no capacitance reviewing, and utilizes the measurements and situation of the ground shield to control the electric fields.

Bushing rating and mounting are depended upon type of interface.  HT Bushing above 1000 V are designed as per IS 2099

There are 5 types of interfaces:-

1.       Interface A1

2.       Interface B1 & B2

3.       Interface C1 & C2

4.       Interface D1 & D2

5.       Interface F1, F2 & F3

Short circuit ratings of all above mentioned bushings is as below:-

Interface Type	Contact Type	Current Rating(A)	RMS(kA)			Peak asymmetrical current rating kA
			1 Sec	2 Sec	3 Sec
A1	Pin and Socket	250	12.5	9.0	7.5	31
B1	Pin and Socket	250	12.5	9.0	7.5	31
B2	Pin and Socket	400	16.0	11.3	9.2	40
C1	Bolted	630	28.0	19.7	16.1	70
C2	Bolted	1250	75.0	53.0	43.3	>150
D1	Bolted	800	50.0	35.3	28.8	125
D2	Bolted	1250	75.0	53.0	43.3	>150
F1	Bolted	2500	-	-	-	-
F2	Bolted	630	28.0	19.7	16.1	70
F3	Bolted	1250	75.0	53.0	43.3	>150

Applications of different types of bushings:-

A1 Interface type bushings :-

These types of bushings are useful for equipment insulated with oil fluids such as Transformers, Switchgear, Capacitors.  There are following types of A1 interface type bushings:-
(i) 180AR-1

Voltage Rating- 12 KV, Current Rating- 250A, Dimensions are- 222 X 106 (height X Breadth)

(ii) K180AR-1

Voltage Rating- 24 KV, Current Rating- 250A, Dimensions are- 222 X 106 (height X Breadth)

(iii) 180AR-2

Voltage Rating- 12 KV, Current Rating- 250A, Dimensions are- 284 X 168 (height X Breadth)

(iv) K180AR-2

Voltage Rating- 24 KV, Current Rating- 250A, Dimensions are- 284 X 168 (height X Breadth)

(v) 180AR-3

Voltage Rating- 12 KV, Current Rating- 250A, Dimensions are- 171 X 55 (height X Breadth)

(vi) K180AR-3

Voltage Rating- 24 KV, Current Rating- 250A, Dimensions are- 171 X 55 (height X Breadth)

There is another interface A1 bushing known as In-Air bushing for dry type transformers, Motors , Switchgear and capacitors.

Types of Bushings are

(i)                  180A-24P-O

Voltage Rating- 12 KV, Current Rating- 250A, Creepage Distance (mm)- 630 mm

(ii)                180A-24P-O

Voltage Rating- 24 KV, Current Rating- 250A, Creepage Distance (mm)- 630 mm

Interface B Type Bushings:-

This is useful for Oil fluids such as Transformer, Switchgear & Capacitors.

There are following types of bushings:-

(i)                  400T1

Voltage Rating- 12 KV, Current Rating- 400A

(ii)                K400T1

Voltage Rating- 24 KV, Current Rating- 400A

(iii)               M400T1

Voltage Rating- 36 KV, Current Rating- 400A

(iv)              400AR-1

Voltage Rating- 12 KV, Current Rating- 400A

(v)                K400AR-1

Voltage Rating- 24 KV, Current Rating- 400A

(vi)              M400AR-1

Voltage Rating- 36 KV, Current Rating- 400A

(vii)             400AR-2

Voltage Rating- 12 KV, Current Rating- 400A

(viii)           K400AR-2

Voltage Rating- 24 KV, Current Rating- 400A

(ix)              M400AR-2

Voltage Rating- 36 KV, Current Rating- 400A

(x)                400AR-8

Voltage Rating- 12 KV, Current Rating- 250A

(xi)              K400AR-8

Voltage Rating- 24 KV, Current Rating- 250A

(xii)             M400AR-8

Voltage Rating- 24 KV, Current Rating- 250A

There is another type of Interface B type switch is specifically used for SF6 circuit breakers.

Similarly there are other Interface type bushings and have same applications only difference is in their mounting designs , voltage rating and current rating.

Electric Vehicle chargers and running cost of electric vehicles

Electrical vehicles seems to becoming reality as there is increased focus on reducing pollution and reducing dependency on petroleum products. But there are many challenges while going with electric vehicles such as time required for charging the vehicles and space required for parking the vehicles and also higher cost of electric vehicles in comparison to other vehicles. There is also challenge for long driving as while driving long charging of vehicles will be required after few intervals, which required considerable time for charging again. There is lot of infrastructure and electricity is required to cater all these problems.

Cost of driving electric vehicle is very low in comparison to petroleum products.

There are few terms you must know before going through in details:-

On Board Charging:-

There are chargers which are factory fitted and are known as on board chargers and there are 2 types of charging devices for the same:-

(i)                 Level-1 Charger:-

The slowest form of charging. Uses a plug to connect to the on-board charger and a standard household (120v) outlet. This setup provides between 2 and 5 miles per hour. While this does not sound at all impressive, it can work for those who travel less than 40 miles a day and have all night to charge.

(ii)               Level-2 Charger:-

These chargers converts alternating current (AC) power from the wall to Direct current (DC) power as batteries are required DC for charging. The speed of charging the vehicle varies most commonly there are following on board chargers:-

(i)                 6.6 kW on-board charger for battery electric vehicles

(ii)               3.3 kW on-board charger for hybrid electric vehicles

For faster charging off-board chargers are used.

These types of chargers use an EVSE to provide power at 220v or 240v at the output for upto 30 amps current. These chargers will charge the vehicle for upto 10-25 miles in an hour of charging at home or at a public station.

There is one another charging which is known as Level 3 charging and it is also known as DC fast charging. Usually these charges are similar to Gas filling dispenser sized machine.

There isn’t any single standard for fast charging of vehicles and Tesla well know name in the field of electric vehicles is using supercharger Network. Nissan Leaf is using CHAdeMO technique for faster charging. These fast chargers can charge 80% of vehicle within 30 minutes.

Costing for charging vehicles:-

Customers who are using the electric vehicles always prefer to charge vehicles at home and most often level 2 chargers are recommended.  These chargers are usually cost around $500-$600 depending upon the manufacturer. Depending upon the electricity cost charges will be applicable accordingly. In US there are incentives for both commercial and home chargers. Almost 30% of charging station cost is covered up by tax credits and other rebates given by government.

Nissan Leaf costs around $1 for every 25 miles which is very much lower cost than Petrol, Diesel and in-fact CNG or other Gasoline products.

Tesla Model S which can go upto 250 miles during complete charging and it will take around $10 for complete charging, which will cost around 25 miles per $1.

If you are using level 2 chargers at home which will charge vehicle on 8-9 hours than cost will be even much lower.

Time required for charging an electric car:-

Time required for charging electric cars is usually higher than filling up gasoline at fuel station, at fuel station it usually take 10-15 minutes in filling up fuel in vehicles. There are following details of vehicle which can run after one hour of charging with level 2 chargers:-

(i)                 Nissan Leaf: 11-22 miles

(ii)               Ford Focus Electric: 22 miles

(iii)             Volkswagen e-Golf: 24 miles

(iv)              BMW i3: 28 miles

(v)                Tesla Model S: 29-60 miles

(vi)              Chevy Volt: 11 miles

With DC fast charging of vehicle will be even faster details of the same as below:-

(i)       Nissan Leaf: 60-95 miles in 30 minutes

(ii)     Ford Focus Electric: (no fast-charging)

(iii)    Volkswagen e-Golf: 60-83 miles in 30 minutes

(iv)   BMW i3: 60-82 miles in 30 minutes

(v)     Tesla Model S: 170 miles in 30 minutes

With level 1 charger you can obtain four miles an hour, thus required lot of time for charging for electric vehicle.

There are following incentives and points to kept in mind while buying electric vehicles:-

(i)                 Know the incentives available:-

You should know what are the subsidies available in the market with e-vehicles. You must know the final price before buying vehicle, you must also know about maintenance cost and running cost of vehicle. You must compare running cost of vehicle with various fuels available in the market and know about buyback period of purchasing e-vehicle. There are lower charges offered by various power supply companies on power consumption for charging electrical vehicles which makes them even more economical.

(ii)               Get your electrical system ready for charging e-vehicle:-

Before installing the charging station you must know about ampere of charging station. You should install the charging station which can handle upto 30A for fast charging.

(iii)             Know about charging station near you:-

You must know about level 2 charging station near your job, park or regular stop. This will help you to charge your vehicle quickly when you are at work or relaxing somewhere.

 

Three power calculations from single phase and three phase loads

Three phase power calculations when you have Both Single and Three Phase loads in System:-

While calculating three phase loads where  there are both single phase and three phase loads there are so many confusions arises such as how single phase and three phase loads comes at same platform while calculating total load.

This is can be simplified in below stated article:-

In electrical systems power is always additive i.e. if we have connected load in each single phase of 20 KW then total three phase power requirement will be 60 KW. There is often confusion arises while studying that if you have Three phase power of 90 KW then it means power will be 90 KW in each phase but same is not true as it means power will be 30 KW in each phase.

This can be illustrated by doing calculations in reverse order also:-

Three Phase Power calculations for Line to Line Voltage:-

Three phase power(KW) = √3 × PF × I_(A) × V_L-L (V) / 1000

Where PF= Power Factor

I(A)= Phase current in Amperes

VL-L= Line to Line RMS Voltage

Three Phase Power calculations for Line to Neutral Voltage:-

Three phase power(KW) = 3 × PF × I_(A) × V_L-N (V) / 1000

Power factor is usually taken as 1 for Resistive loads

Power factor is usually taken as 0.85 for Induction motors at full loads and 0.35 for no loads.

Now lets take three phase load of 90 KW, now if you consider this load to be equal to 90 KW in each phase then current in each phase will be= 90000/(1.732 X230X0.8)= 282 A

So every-time if you have to calculate total power then  just add single phase load and three phase load then cumulative will be your three phase load requirement.

In a balanced power system if there is total P having power factor pf and line to line voltage as VL

Then single phase power will be P(Single Phase)= P/3

Single Phase apparent power will =P/(3Xpf)

Phase current= Apparent Power

                              VLN

Then Phase current(A) =

1.732=  which comes as VLN=VL/

While doing above calculations efficiency must also be taken care.

These calculations given above are done considering three phase balanced load, which means that there will be same current and power consumption in each phase.  This is mostly applicable for electrical motors and transmission lines but in domestic loads where most of load is single phase this may not be effective. But above calculations will hold good for any industry.

This can be further simplified by assuming three motor of 90 KW. Now if you assume that there is 90KW load in each phase then you will get 270 KW overall load (Adding 90 KW of each phase) then you will pay for only 90 KW electricity charges then this will be huge savings as by withdrawal of 270 KW you have to pay only for 90 KW.

This means if you have a motor which is consuming a given KW then KW per winding is to be divided by 3 which are similar for three phase transformers where transformer is supplying given KVA then KVA in each winding will be third of total power.

Advantages of Three Phase power Over single phase power

There are following advantages of three phase power above single phase power:-

1.     When we use three phase power than frame size of required machine of same rating get reduce in comparison to when we use single phase power. It means frame size of machine get reduced.

2.     Single phase motors are not self-starting and required auxiliary means of starting the same but three phase motors are self-starting.

3.     Three phase motors have higher power factor and higher efficiency in comparison to single phase motors.

4.     Three phase motors of same rating as of single phase motors are smaller in size which will leads to lower cost , lighter in weight, lower in maintenance cost.

5.     Even in transmission lines for same amount of power at same voltage three phase transmission line requires lesser conductor material in comparison to single phase transmission lines. Thus three phase transmission system becomes cheaper. This will also leads to reduction in cross-sectional area of conductor. Thus leads to lower installation cost.

6.     Single phase motors have pulsating torque whereas polyphase system has uniform torque.

7.       It is quite easier to have parallel operation of three phase generators in comparison to single phase system.