Thursday, February 27, 2014

Tuesday, February 25, 2014

Terms AC1 and AC3

  12:49 AM Blogger   No comments   Edit

AC-1 - This category applies to all AC loads where the power factor is more than 0.95. These are primarily non-inductive or slightly inductive loads, such as heating. Breaking the arc remains easy with minimal arcing and contact wear.

 

AC-3 - This category applies to squirrel cage motors with breaking during normal running of the motor.

On closing, the contactor makes the inrush current, which is about 5 to 7 times the rated full load current of the motor.

On opening, the contactor breaks the rated full load current of the motor.

Monday, February 24, 2014

Advantages of LED light bulbs

  11:20 PM Blogger   No comments   Edit

How far the light bulb has come. For years incandescent bulbs were the only game in town. But in more recent times consumers have seen new choices come along, such as compact fluorescent light bulbs (CFLs) and light-emitting diodes (LEDs). Sometimes people prefer a certain type of light bulb for the impact they hope it will have on the environment, and other times people choose bulbs based purely on the kind of light they cast. LEDs compare favorably versus incandescent bulbs in some areas. They produce their light from the movement of electrons across a semi-conductive material, while incandescent bulbs have a filament that glows when heated by an electric current. LEDs are said to last as long as transistors -- that's much longer than incandescent bulbs. LEDs have a typical life span of about 30,000 hours, as opposed to the 750 hours that a traditional incandescent bulb will last.

 

Furthermore, an LED's plastic construction is much more durable than glass bulbs. Their small size enables them to be used in more applications, such as in electronic circuits. However, the biggest advantage of LEDs boast over incandescent bulbs is their greater efficiency. LEDs produce light without heat, saving all of the energy that goes into heating filaments for incandescent bulbs. A 2007 study by the Alliance to Save Energy determined that if half of all incandescent decorative Christmas bulbs were replaced with LED bulbs, for example, this could save the U.S. some $17 billion dollars a year in energy costs.

 

So the LED bulb uses much less electricity and causes much less waste than do their traditional incandescent light bulb counterparts, producing much less carbon dioxide. As with most things, however, there is an unfortunate downside and that's immediate cost. LEDs cost much more per bulb than incandescent bulbs, and regardless of the long-term savings they might offer, it's hard for people (especially during difficult economic times) to put so much of their monthly cash flow into expensive light bulbs. Time, and lower prices, may change that equation, however.

 

Source : How stuff works

Friday, February 21, 2014

KW to Ampere calculation

  7:37 PM Blogger   No comments   Edit

DC kilowatts to amps calculation

The current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by the voltage V in volts (V):

I(A) = 1000 × P(kW) / V(V)


 AC single phase kilowatts to amps calculation

The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by the power factor PF times the RMS voltage V in volts (V):

I(A) = 1000 × P(kW) / (PF × V(V) )


 AC three phase kilowatts to amps calculation
 
 Calculation with line to line voltage
 

The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by square root of 3 times the power factor FP times the line to line RMS voltage VL-L in volts (V):

I(A) = 1000 × P(kW) / (√3 × PF × VL-L(V) )


 Calculation with line to neutral voltage
 

The phase current I in amps (A) is equal to 1000 times the power P in kilowatts (kW), divided by 3 times the power factor FP times the line to neutral RMS voltage VL-N in volts (V):

I(A) = 1000 × P(kW) / (3 × PF × VL-N(V) )


Thursday, February 20, 2014

Understanding Type 2 Coordinated Protection in Motor Branch Circuits

  12:52 AM Blogger   No comments   Edit

The new IEC (International Electrotechnical Commission) standard, publication

947 “Low Voltage Switchgear and Control, Part 4-1: Contactors and Motor Starters,”

has been recognized by UL (Underwriters Laboratories) and is becoming

widely accepted by designers and users of motor control in the U.S. This standard

addresses coordination between the branch circuit protective device and the motor

starter. It also provides a method to measure performance of these devices if a short

circuit occurs. This standard defines two levels of component protection in the

event of a short circuit: Type 1 and Type 2 coordination.

 

This Product Data Bulletin describes:

 

_ How to conformto the new standard using motor controls built to meet

NEMA and IEC standards

_ Related benefits associated with Type 2 coordination

The IEC standard for motor starters and contactors, 947-4-1, defines two levels of

protection/coordination for the motor starter (contactor and overload relay) under

short circuit conditions. Each level of protection is achieved by using a specific

combination of motor starter and short circuit protective device.

_ Type 1 Coordination

Under short circuit conditions, the contactor or starter shall cause no danger

to persons or installation and may not be suitable for further service

without repair and replacement of parts.

_ Type 2 Coordination

Under short circuit conditions, the contactor or starter shall cause no danger

to persons or installation and shall be suitable for further use. The risk

of contact welding is recognized, in which case the manufacturer shall indicate

the measures to be taken in regards to equipment maintenance.

Faults in electrical systems are most likely to be of a low level, which are handled

well by motor controllers built to meet Type 1 coordination standards. After the

fault is cleared, the only action necessary is to reset the circuit breaker or replace

the fuses. In situations where available fault currents are high and any period of

maintenance downtime is crucial, a higher degree of coordinated protection may

be desirable.

Many industries are dependent upon the continuous operation of a critical manufacturing

process. In these conditions, it is especially important to understand that

Type 1 protection may not prevent damage to the motor starter components. In order

to ensure that high level fault or short circuit does not interrupt a critical process,

it may be prudent to consider implementation of Type 2 coordination in the

selection and application of low voltage motor controllers.

Type 2 coordination, which has no equivalent U.S. standard, does not permit damage

to the starter beyond light contactwelding, easily separated by a screwdriver or several

coil operations. Type 2 coordination does not allowreplacement of parts (except fus-

es) and requires that all parts remain in service. Beyond providing basic electrical and

fire protection, it also minimizes lost production, reduced productivity and unscheduled

disruptions resulting fromdowntime needed to replace or repair a starter.

 

SQUARE D Product Data Bulletin

Wednesday, February 19, 2014

Why Are Copper Bus Bars Plated?

  11:38 PM Blogger   No comments   Edit

Even though copper is the most popular choice for use in bus bars, and used very often in other electrical applications because it is more resistant to rust and corrosion than other metals, this doesn’t mean that it won’t oxidize over time.

 

When metals oxidize, the resistance in the conductive metal will increase, requiring more power to be used to carry current along the surface. When the copper oxidizes beyond a certain point, the metal can begin to flake and fall apart.

 

Many metals are plated in order to help them retain their positive qualities and attributes. When it comes to copper bus bars, plating is an important factor in longevity as well as maintaining the integrity of the conductive surface. When copper bus bars are not plated, over time the surface will oxidize. When that occurs, then more power is required to push electricity along the surface because the oxidized surface simply doesn’t conduct as well as a smooth, plated surface.

 

Plating, using tin or silver acts as a coating over the surface of the copper, helps to protect the copper from oxidizing. While this will not completely prevent oxidizing over a long period of time, it will dramatically reduce the effects of such oxidization. The reason why tin and silver is commonly used in the plating technique for copper is that both metals are considered soft metals, easier to work with when plating, and more importantly they don’t offer a great deal of resistance to electrical conductivity.

 

Which is better? Tin or Silver?

 

Throughout the industry there are different thoughts about which metal is better for plating copper, tin or silver. 10 microns of tin will outperform 1 micron of silver. With the price of silver climbing, tin becomes more economical, even though ten times the amount of tin will be required to do the same job.

 

When using silver to plate copper bus bars, a minimum of 3 microns should be used, and preferable 6 microns. On top of that, an anti-tarnish would need to be applied as well to protect the finish. In most fixed bus bar applications, tin is recommended. Silver should be used for moving bus bar parts in which arcing may be a concern.

 

For both tin and silver plating, anti-tarnish is important to keep the surface clean and conductive. When working with copper bus bars, plating is essential not only for longevity, but also integrity and safety.

 

Copyright :

http://blog.prv-engineering.co.uk/2012/05/why-are-copper-bus-bars-plated/

 

Tuesday, February 18, 2014

IEC 60364 Electrical Installations for Buildings

  9:12 PM Blogger   No comments   Edit

IEC 60364 Electrical Installations for Buildings is the International Electro technical Commission's international standard on electrical installations of buildings. This standard is an attempt to harmonize national wiring standards in an IEC standard. The latest versions of many European wiring regulations (e.g., BS 7671 in the UK) follow the section structure of IEC 60364 very closely, but contain additional language to cater for historic national practice and to simplify field use and determination of compliance by electrical tradesmen and inspectors. National codes and site guides are meant to attain the common objectives of IEC 60364, and provide rules in a form that allows for guidance of persons installing and inspecting electrical systems.

The standard has several parts:

 

Part 1: Fundamental principles, assessment of general characteristics, definitions

Part 4: Protection for safety

Section 41: Protection against electric shock

Section 42: Protection against thermal effects

Section 43: Protection against overcurrent

Section 44: Protection against voltage disturbances and electromagnetic disturbances

Part 5: Selection and erection of electrical equipment

Section 51: Common rules

Section 52: Wiring systems

Section 53: Isolation, switching and control

Section 54: Earthing arrangements, protective conductors and protective bonding conductors

Section 55: Other equipment

Section 56: Safety services

Part 6: Verification

Part 7: Requirements for special installations or locations

Section 701: Electrical installations in bathrooms

Section 702: Swimming pools and other basins

Section 703: Rooms and cabins containing sauna heaters

Section 704: Construction and demolition site installations

Section 705: Electrical installations of agricultural and horticultural premises

Section 706: Restrictive conductive locations

Section 708: Electrical installations in caravan parks and caravans

Section 709: Marinas and pleasure craft

Section 710: Medical locations

Section 712: Solar photovoltaic (PV) power supply systems

Section 713: Furniture

Section 714: External lighting

Section 715: Extra-low-voltage lighting installations

Section 717: Mobile or transportable units

Section 740: Temporary electrical installations for structures, amusement devices and booths at fairgrounds, amusement parks and circuses

 

Wikipedia

Friday, February 14, 2014

Wednesday, February 12, 2014

Electrical Switchboard Routine Tests

  11:11 PM Blogger   No comments   Edit

Physical Check

·         Visual check for any physical damages on the enclosures, paint removal and breakage on components

·         Paint shade as per the approved drawings.

·         Cable feeding provisions

·         General layout of the panel.

·         Check whether all the components are fitted.

·         Check for the Labels and nomenclature

·         Size of Bus bars

Dimensional Check

·         Over all dimensions with approved drawings.

·         List of components its layouts

·         Labels descriptions

Wiring and Control Circuit Check

·         Instrument panel wiring.

·         Control circuit wiring.

·         Power wiring.

·         Protective circuits

·         Rating of breakers

·         Rated voltage of all components

·         Rating of Fuses

Mechanical Operations

·         ON/OFF operations of the circuit breakers by manually.

·         Draw out operations of the withdrawable breakers

·         Breaker interlocking mechanism

·         Electronic protection device of the breakers

·         Operations of the control components like control switches, limit switches etc.

·         Operations of the door interlocking mechanism.

Electrical Operations

·         Electrical ON/OFF operations of the circuit breakers.

·         Electrical functioning of Starters.

·         Operations of components, contactors, control relays, push buttons, indications lamps etc.

·         Checking of electrical interlocking and sequences.

·         Checking of instruments

·         Checking additional protection relays as Ground Fault & Earth Leakage

Torque Test

·         Check all joints of electrical current carrying parts to ensure the tightness by torque range

·         Bus bar joints

·         Breaker terminals

Insulation Resistance Test

·         To check the protective measure of the insulation value

·         To check the continuity of the circuits.

Dielectric Test

Dielectric Test is conducted as per IEC on the power circuits (excluding controls, instruments and electronic components etc.) The test voltage 2.5KV is applied for a period of 1 min. in between

·         1. Phase and phase

·         2. Phase and neutral

·         3. Phase, neutral and earth

 

Tuesday, February 11, 2014

Tuesday, February 4, 2014

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