Wednesday, April 18, 2018

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:-
Electric Vehicle chargers

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.

Electric Vehicle chargers

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.


Thursday, October 26, 2017

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) × VL-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) × VL-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
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.

Saturday, September 23, 2017

Working spaces for 600 V equipments installations (NFPA 70)

National Electricity code (NFPA 70) for working spaces while installation of 600 V electrical equipments:-

In this article we will discuss about working spaces of electrical equipment’s for voltage level of 600 Volts, Nominal, or Less.

Spaces required for all Electrical Equipment:-
There should be sufficient Access and working space shall be provided as to do the maintenance and operation of electrical equipment safely.

(A)  Working Space:-
There should be due attention to be taken regarding working space of equipment working at 600 Volts or less. This should comply with working space requirement for examination , adjustment, servicing or maintenance. The working spaces requirement will be shown in table as below:-

(i)                 Depth requirement of Working Space:-

The depth requirement of working space in the direction of live parts shall not be less than that specified in table below unless the requirements of all conditions are met as stated below        . In These cases distances can be measured from the exposed live parts or from the enclosure or from the opening if the live parts are enclosed.

(a)   Dead-Front Assemblies:-
For dead front assemblies such as:-

à Motor control centers
à Switchboards

In these assemblies there will not be requirement of working space in back sides.
In these assemblies all changing parts or adjustable parts such as fuses or switches are accessible from other than back and back sides. Where rear access is required to work on nonelectrical parts on the back of enclosed equipment, a minimum horizontal working space of 762 mm (30 in.) shall be provided.

(b)   Low Voltage:-
When there are exposed live parts having voltages in ranges between 30 Volts RMS- 60 Volts RMS then working space requirement can be reduced only by taking special permission.

(c)    Existing Buildings
If there is requirement of replacement of electrical equipment’s in existing buildings then working space or clearance is per condition 2 mentioned in tables above for dead-front switchboards, panel-boards, or motor control centers located across the passage. Where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the passage from being open at the same time and qualified persons who are authorized will service the installation.

(ii)               Working space requirement across Width :-
The working space requirement across width in front of the electrical equipment shall be the width of the equipment or 762 mm (30 in.), whichever is greater. In all cases, the work space shall permit at least a 90 degree opening of equipment doors or hinged panels; it is more advisable to have space sufficient enough for opening of whole equipment as much allowable by hinge of panel.

(iii)             Working space requirement across Height:-
The working space requirement across height shall be clear and extend from the grade, floor, or platform to a height of 2.0 m (612 ft) or the height of the equipment, whichever is greater. Within the height requirements of this section, other equipment that is associated with the electrical installation and is located above or below the electrical equipment shall be permitted to extend not more than 150 mm (6 in.) beyond the front of the electrical equipment.

Exception No. 1: In existing residence units, service equipment or panel-boards that do not exceed 200 amperes shall be permitted in spaces where the height of the working space is less than 2.0 m (612 ft).

Exception No. 2: Meters that are installed in meter sockets shall be permitted to extend beyond the other equipment. The meter socket shall be required to follow the rules of this section.

(B)  Clear Spaces:-

Working space required shall not be used for storage. When normally enclosed live parts are exposed for inspection or servicing, the working space, if in a passageway or general open space, shall be suitably guarded.

(C)  Entrance space requirement and Egress from Working Space:-

(i)                 Minimum Required:-

At least one entrance of sufficient area shall be provided to give access to and egress from working space about electrical equipment.

(ii)               Large Equipment:-

For an electrical equipment having ampere rating of 1200 amperes or more and over 1.8 m (6 ft) wide that contains overcurrent devices, switching devices, or control devices, there shall be one entrance to and egress from the required working space not less than 610 mm (24 in.) wide and 2.0 m (612 ft) high at each end of the working space. A single entrance to and egress from the required working space shall be permitted where either of conditions stated below are met:-

(a) Unobstructed Egress. Where the location permits a continuous and unobstructed way of egress travel, a single entrance to the working space shall be permitted.

(b) Extra Working Space. Where the depth of the working space is twice that required by table above, a single entrance shall be permitted. It shall be located such that the distance from the equipment to the nearest edge of the entrance is not less than the minimum clear distance specified in table above for equipment operating at that voltage and in that condition.

(iii)             Personnel Doors:-
When there are electrical equipment’s having rated current more than 1200 A or more and also contains overcurrent devices, switching devices, or control devices are installed and there is a personnel door(s) intended for entrance to and egress from the working space less than 7.6 m (25 ft) from the nearest edge of the working space, the door(s) shall open in the direction of egress and be equipped with panic bars, pressure plates, or other devices that are normally latched but open under simple pressure.

(iv)             Illumination:-
Illumination shall be provided for all working spaces about service equipment, switchboards, panel- boards, or motor control centers installed indoors and shall not be controlled by automatic means only.

(v)               Dedicated Equipment Space:-
All switchboards, panel-boards, and motor control centers shall be located in dedicated spaces and protected from damage.

Exception: Control equipment that by its very nature or because of other rules of the Code must be adjacent to or within sight of its operating machinery shall be permitted in those locations.

For indoor electrical equipment’s

(a)    Dedicated Electrical Space:-
The space equal to the width and depth of the equipment and extending from the floor to a height of 1.8 m (6 ft) above the equipment or to the structural ceiling, whichever is lower, shall be dedicated to the electrical installation. No piping, ducts, leak protection apparatus, or other equipment foreign to the electrical installation shall be located in this zone.
Exception: Suspended ceilings with removable panels shall be permitted within the 1.8-m (6-ft) zone.

(b)   Foreign Systems:-
The area above the dedicated space required shall be permitted to contain foreign systems, provided protection is installed to avoid damage to the electrical equipment from condensation, leaks, or breaks in such foreign systems.

(c)    Sprinkler Protection:-
Sprinkler protection shall be permitted for the dedicated space where the piping complies with this section.

(d)   Suspended Ceiling:-.
A dropped, suspended, or similar ceiling that does not add strength to the building structure shall not be considered a structural ceiling.

à Outdoor:-
 Outdoor electrical equipment shall be installed in suitable enclosures and shall be protected from accidental contact by unauthorized personnel, or by vehicular traffic, or by accidental spillage or leakage from piping systems. The working clearance space shall include the zone. No architectural appurtenance or other equipment shall be located in this zone.

(vi)             Locked Electrical Equipment Rooms or Enclosures:-

Electrical equipment rooms or enclosures housing electrical apparatus that are controlled by a lock(s) shall be considered accessible to qualified persons.