Polyphase motor design

Motor

Perhaps the most important benefit of polyphase AC power over single-phase is the design and operation of AC motors. As we studied in the first chapter of this book, some types of AC motors are virtually identical in construction to their alternator (generator) counterparts, consisting of stationary wire windings and a rotating magnet assembly. (Other AC motor designs are not quite this simple, but we will leave those details to another lesson).

If the rotating magnet is able to keep up with the frequency of the alternating current energizing the electromagnet windings (coils), it will continue to be pulled around clockwise. However, clockwise is not the only valid direction for this motor's shaft to spin. It could just as easily be powered in a counter-clockwise direction by the same AC voltage waveform:

Motor, induction Motor, synchronous

Notice that with the exact same sequence of polarity cycles (voltage, current, and magnetic poles produced by the coils), the magnetic rotor can spin in either direction. This is a common trait of all single-phase AC "induction" and "synchronous" motors: they have no normal or "correct" direction of rotation. The natural question should arise at this point: how can the motor get started in the intended direction if it can run either way just as well? The answer is that these motors need a little help getting started. Once helped to spin in a particular direction. they will continue to spin that way as long as AC power is maintained to the windings.

Where that "help" comes from for a single-phase AC motor to get going in one direction can vary. Usually, it comes from an additional set of windings positioned differently from the main set, and energized with an AC voltage that is out of phase with the main power:

These supplementary coils are typically connected in series with a capacitor to introduce a phase shift in current between the two sets of windings:

That phase shift creates magnetic fields from coils 2a and 2b that are equally out of step with the fields from coils 1a and 1b. The result is a set of magnetic fields with a definite phase rotation. It is this phase rotation that pulls the rotating magnet around in a definite direction.

Rotating magnetic field Magnetic field, rotating

Polyphase AC motors require no such trickery to spin in a definite direction. Because their supply voltage waveforms already have a definite rotation sequence, so do the respective magnetic fields generated by the motor's stationary windings. In fact, the combination of all three phase winding sets working together creates what is often called a rotating magnetic field. It was this concept of a rotating magnetic field that inspired Nikola Tesla to design the world's first polyphase electrical systems (simply to make simpler, more efficient motors). The line current and safety advantages of polyphase power over single phase power were discovered later.

What can be a confusing concept is made much clearer through analogy. Have you ever seen a row of blinking light bulbs such as the kind used in Christmas decorations? Some strings appear to "move" in a definite direction as the bulbs alternately glow and darken in sequence. Other strings just blink on and off with no apparent motion. What makes the difference between the two types of bulb strings? Answer: phase shift!

Examine a string of lights where every other bulb is lit at any given time:

When all of the "1" bulbs are lit, the "2" bulbs are dark, and vice versa. With this blinking sequence, there is no definite "motion" to the bulbs' light. Your eyes could follow a "motion" from left to right just as easily as from right to left. Technically, the "1" and "2" bulb blinking sequences are 180^o out of phase (exactly opposite each other). This is analogous to the single-phase AC motor, which can run just as easily in either direction, but which cannot start on its own because its magnetic field alternation lacks a definite "rotation."

Now let's examine a string of lights where there are three sets of bulbs to be sequenced instead of just two, and these three sets are equally out of phase with each other:

If the lighting sequence is 1-2-3 (the sequence shown), the bulbs will appear to "move" from left to right. Now imagine this blinking string of bulbs arranged into a circle:

Now the lights appear to be "moving" in a clockwise direction because they are arranged around a circle instead of a straight line. It should come as no surprise that the appearance of motion will reverse if the phase sequence of the bulbs is reversed.

The blinking pattern will either appear to move clockwise or counter-clockwise depending on the phase sequence. This is analogous to a three-phase AC motor with three sets of windings energized by voltage sources of three different phase shifts:

With phase shifts of less than 180^o we get true rotation of the magnetic field. With single-phase motors, the rotating magnetic field necessary for self-starting must to be created by way of capacitive phase shift. With polyphase motors, the necessary phase shifts are there already. Plus, the direction of shaft rotation for polyphase motors is very easily reversed: just swap any two "hot" wires going to the motor, and it will run in the opposite direction!

Review

AC "induction" and "synchronous" motors work by having a rotating magnet follow the alternating magnetic fields produced by stationary wire windings. Single-phase AC motors of this type need help to get started spinning in a particular direction. By introducing a phase shift of less than 180o to the magnetic fields in such a motor, a definite direction of shaft rotation can be established. Single-phase induction motors often use an auxiliary winding connected in series with a capacitor to create the necessary phase shift. Polyphase motors don't need such measures; their direction of rotation is fixed by the phase sequence of the voltage they're powered by. Swapping any two "hot" wires on a polyphase AC motor will reverse its phase sequence, thus reversing its shaft rotation.

Ohmmeter design

Ohmmeter

Though mechanical ohmmeter (resistance meter) designs are rarely used today, having largely been superseded by digital instruments, their operation is nonetheless intriguing and worthy of study.

The purpose of an ohmmeter, of course, is to measure the resistance placed between its leads. This resistance reading is indicated through a mechanical meter movement which operates on electric current. The ohmmeter must then have an internal source of voltage to create the necessary current to operate the movement, and also have appropriate ranging resistors to allow just the right amount of current through the movement at any given resistance.

Starting with a simple movement and battery circuit, let's see how it would function as an ohmmeter:

When there is infinite resistance (no continuity between test leads), there is zero current through the meter movement, and the needle points toward the far left of the scale. In this regard, the ohmmeter indication is "backwards" because maximum indication (infinity) is on the left of the scale, while voltage and current meters have zero at the left of their scales.

If the test leads of this ohmmeter are directly shorted together (measuring zero Ω), the meter movement will have a maximum amount of current through it, limited only by the battery voltage and the movement's internal resistance:

With 9 volts of battery potential and only 500 Ω of movement resistance, our circuit current will be 18 mA, which is far beyond the full-scale rating of the movement. Such an excess of current will likely damage the meter.

Not only that, but having such a condition limits the usefulness of the device. If full left-of-scale on the meter face represents an infinite amount of resistance, then full right-of-scale should represent zero. Currently, our design "pegs" the meter movement hard to the right when zero resistance is attached between the leads. We need a way to make it so that the movement just registers full-scale when the test leads are shorted together. This is accomplished by adding a series resistance to the meter's circuit:

To determine the proper value for R, we calculate the total circuit resistance needed to limit current to 1 mA (full-scale deflection on the movement) with 9 volts of potential from the battery, then subtract the movement's internal resistance from that figure:

Now that the right value for R has been calculated, we're still left with a problem of meter range. On the left side of the scale we have "infinity" and on the right side we have zero. Besides being "backwards" from the scales of voltmeters and ammeters, this scale is strange because it goes from nothing to everything, rather than from nothing to a finite value (such as 10 volts, 1 amp, etc.). One might pause to wonder, "what does middle-of-scale represent? What figure lies exactly between zero and infinity?" Infinity is more than just a very big amount: it is an incalculable quantity, larger than any definite number ever could be. If half-scale indication on any other type of meter represents 1/2 of the full-scale range value, then what is half of infinity on an ohmmeter scale?

Scale, logarithmic Logarithmic scale

The answer to this paradox is a logarithmic scale. Simply put, the scale of an ohmmeter does not smoothly progress from zero to infinity as the needle sweeps from right to left. Rather, the scale starts out "expanded" at the right-hand side, with the successive resistance values growing closer and closer to each other toward the left side of the scale:

Infinity cannot be approached in a linear (even) fashion, because the scale would never get there! With a logarithmic scale, the amount of resistance spanned for any given distance on the scale increases as the scale progresses toward infinity, making infinity an attainable goal.

We still have a question of range for our ohmmeter, though. What value of resistance between the test leads will cause exactly 1/2 scale deflection of the needle? If we know that the movement has a full-scale rating of 1 mA, then 0.5 mA (500 μA) must be the value needed for half-scale deflection. Following our design with the 9 volt battery as a source we get:

With an internal movement resistance of 500 Ω and a series range resistor of 8.5 kΩ, this leaves 9 kΩ for an external (lead-to-lead) test resistance at 1/2 scale. In other words, the test resistance giving 1/2 scale deflection in an ohmmeter is equal in value to the (internal) series total resistance of the meter circuit.

Using Ohm's Law a few more times, we can determine the test resistance value for 1/4 and 3/4 scale deflection as well:

1/4 scale deflection (0.25 mA of meter current):

3/4 scale deflection (0.75 mA of meter current):

So, the scale for this ohmmeter looks something like this:

One major problem with this design is its reliance upon a stable battery voltage for accurate resistance reading. If the battery voltage decreases (as all chemical batteries do with age and use), the ohmmeter scale will lose accuracy. With the series range resistor at a constant value of 8.5 kΩ and the battery voltage decreasing, the meter will no longer deflect full-scale to the right when the test leads are shorted together (0 Ω). Likewise, a test resistance of 9 kΩ will fail to deflect the needle to exactly 1/2 scale with a lesser battery voltage.

There are design techniques used to compensate for varying battery voltage, but they do not completely take care of the problem and are to be considered approximations at best. For this reason, and for the fact of the logarithmic scale, this type of ohmmeter is never considered to be a precision instrument.

One final caveat needs to be mentioned with regard to ohmmeters: they only function correctly when measuring resistance that is not being powered by a voltage or current source. In other words, you cannot measure resistance with an ohmmeter on a "live" circuit! The reason for this is simple: the ohmmeter's accurate indication depends on the only source of voltage being its internal battery. The presence of any voltage across the component to be measured will interfere with the ohmmeter's operation. If the voltage is large enough, it may even damage the ohmmeter.

Review

Ohmmeters contain internal sources of voltage to supply power in taking resistance measurements. An analog ohmmeter scale is "backwards" from that of a voltmeter or ammeter, the movement needle reading zero resistance at full-scale and infinite resistance at rest. Analog ohmmeters also have logarithmic scales, "expanded" at the low end of the scale and "compressed" at the high end to be able to span from zero to infinite resistance. Analog ohmmeters are not precision instruments. Ohmmeters should never be connected to an energized circuit (that is, a circuit with its own source of voltage). Any voltage applied to the test leads of an ohmmeter will invalidate its reading.

Ammeter design

Ammeter design

Ammeter

A meter designed to measure electrical current is popularly called an "ammeter" because the unit of measurement is "amps."

Taking the same meter movement as the voltmeter example, we can see that it would make a very limited instrument by itself, full-scale deflection occurring at only 1 mA:In ammeter designs, external resistors added to extend the usable range of the movement are connected in parallel with the movement rather than in series as is the case for voltmeters. This is because we want to divide the measured current, not the measured voltage, going to the movement, and because current divider circuits are always formed by parallel resistances.

Voltmeter design

Voltmeter design

Voltmeter

As was stated earlier, most meter movements are sensitive devices. Some D'Arsonval movements have full-scale deflection current ratings as little as 50 μA, with an (internal) wire resistance of less than 1000 Ω. This makes for a voltmeter with a full-scale rating of only 50 millivolts (50 μA X 1000 Ω)! In order to build voltmeters with practical (higher voltage) scales from such sensitive movements, we need to find some way to reduce the measured quantity of voltage down to a level the movement can handle.

Let's start our example problems with a D'Arsonval meter movement having a full-scale deflection rating of 1 mA and a coil resistance of 500 Ω:

Distributed Generator System Synchronization

 Synchronization

Distributed Redundant is a common UPS system design used in the market today. This design uses multiple UPS modules that have their output buses cross-connected for multiple power sources to the critical load by static transfer switches. Each static transfer switch will have two inputs. One input will be set as the primary feed for the switch. The other input will be set as the secondary. In the event of a power failure on the primary input of the static transfer switch, it will automatically switch to the secondary source. The switching action is a short duration open transition, typically up to 4ms. The primary and secondary inputs of all the switches will be divided among the outputs of the UPS modules. This is done so that the load is balanced across the entire system. If any one UPS module

were to fail, the static transfer switches that have their primary input fed by the failed UPS will switch input sources. The critical load is then transferred to the outputs of the other good UPS modules. Correct system design will ensure that the remaining good modules will not be overloaded at this time. Both inputs to the static transfer switches must be synchronized to minimize voltage transients during switching.

Guideline to Design Electrical Network for Building / Small Area.

Guideline to Design Electrical Network for Building / Small Area.

 (1)  Calculate Electrical Load:

• Find out built up area in Sqft.of per flat per House/Dwelling unit.
• Multiply area in Sqft. by Load/Sqft according to following Table

Type of Load	Load/Sqft
Industrial	100 Watt/Sqft
Commercial	30 Watt/Sqft
Domestic	15 Watt/Sqft

• Apply the diversity factor and Compute the load of all dwelling units in the area.

Type of Load	Diversity Factor
Industrial	0.5
Commercial	0.8
Domestic	0.4

• Add the load of common services such as Auditorium, Street Lights, Lifts and Water Pumps etc. For simplicity purpose 0.5kW/dwelling units may be considered as common load.
• Compute the “Total Load” of the area by adding load observed at above.

SELECTION OF MCCB / MCB (LESSON-3)

SELECTION OF MCCB / MCB (LESSON-3)

(E) Others:

 (1) Frequency:

• MCB is designed and used in AC power system of 50 to 60Hz.
• Electromagnetic force of magnetic release is related with power supply frequency so If Frequency is changed than electromagnetic fore of Magnetic element is changed hence MCCB tripping current will be different.
• If we used MCCB for protection in DC circuits than specially design DC circuit MCCB should be used rather than normal type of MCCB.

SELECTION OF MCB / MCCB ( LESSON-2)

 HOW TO SELECT  MCB / MCCB  

A. Utilization category / Characteristic (B, C, D, K, Z curve):

• Characteristic of Trip curves of MCCB tell about the trip current rating of MCCB.
• MCB will trip instantaneously according to their Tripping Characteristic at 0.1 sec.
• There are various type of MCCB
• Type B MCCB
• Type C MCCB
• Type D MCCB
• Type K MCCB
• Type Z MCCB

SELECTION OF MCB / MCCB ( LESSON-1)

SELECTION OF MCB / MCCB

Introduction

MCB or MCCB are widely used in electrical distribution system for ON/OFF Electrical supply and it also gives over current and short circuit protection. Selection of MCB or MCCB involved technical, Mechanical parameters. Some parameters are important but some parameters are confusing and mislead to wrong selection of MCCB. Some parameters are directly affected on cost of MCCB.  

Specification / Name Plate Details of MCB/MCCB:

 Following specifications are required to select appropriate MCB or MCCB.

(A) Current Related:

• Frame Size (Inm): Amp
• Rated current (In/ Ie): Amp
• Ultimate short circuit breaking capacity (Icu): KA
• Rated short-circuit breaking capacity (Ics): % of Icu

(B) Voltage Related:

• Rated voltage (Ue): Volt
• Rated Insulation voltage (Ui): Volt
• Rated impulse withstand voltage(Uimp): KV
• No’s of Pole : SP,DP,TP,TPN,FP

(C) Application Type:

• Utilization Category/ Characteristic : B,C or D curve

(D) Accessories:

• Rotary Handle: Extended/ Direct
• Alarm Contact:
• Shunt Trip:
• Under voltage Trip:
• Mechanical interlocking:
• Manual /Auto operation
• Motorized Operation:

(E) Protection Type:

• Protection : Over current / Short circuit
• Trip Mechanism: Thermal / Magnetic / Solid / Microprocessor
• Trip Mechanism adjustment : Fixed / Adjustable

(F) Others:

• Frequency;
• Reference temperature: (if different from 30°C)
• Pollution degree:
• Suitability for isolation:
• Type of Mounting arrangement
• Electrical Life Cycles:
• Mechanical Life Cycles:
• Dimension: mm
• Weight: Kg
• Reference Standard: IEC: 60947-1/2, IS: 13947-1/2

 (A) Current Related:

  (1) Frame Size (Inm): 

• Breaker Frame Size indicates the basic framework of the Plastic shell of MCCB that can hold the biggest rated current.
• It is the maximum current value for which the MCCB is designed (upper limit of the adjustable trip current range) and it also determines the physical dimensions of the device.
• There are varieties current ratings MCCB for the same series frame Size.
• For example, DX100 Frame Size MCCB for rated current of 16A, 20A, 25A, 32A, 40A, 50A, 63A, 80A, 100A.
• Same DX225 Frame Size MCCB for rated current of 100A, 125A, 160A, 180A, 200A, 225A.
• In above DX100 and DX225 has two Type of frame Size for rated current of 100A, but the shape and size of breaking capacity of circuit breakers is not the same.

 (2) Rated Current (In /Ie):

• It is the current value above which overload protection is tripped.
• For MCB it is fixed while in MCCB the rated current is an adjustable range instead of a fixed value.
• Standard rating of MCB is 1A, 2A, 3A, 4A, 6A, 10A, 13A, 16A, 20A, 25A, 32A, 40A, 50A, 63A, 100A for MCB.

(B) Voltage Related:

 (3) Ultimate short-circuit breaking capacity (Icu):

• Breaking capacity can be defined as the maximum level of fault current which can be safely cleared.
• It is the highest fault current that the MCCB can trip without being damaged permanently.
• The MCCB will be reusable after interrupting a fault, as long as it doesn’t exceed this value.
• It is indicate operation reliability of MCCB
• This parameter may increase or decrease the cost, so it should be properly decided. Breaking capacity should be higher than the possible fault level. For domestic application fault level may be 10kA.

(4) Operating short-circuit breaking capacity (Ics):

• It is expressed as a percentage ratio of Icu and tells you the maximum short-circuit current if a circuit breaker can break three times and still resume normal service.
• The higher the lcs, the more reliable the circuit breaker
• It is the maximum possible fault current that the MCCB can clear. If the fault current exceeds this value, the MCCB will be unable to trip and another protection mechanism must operate.
• If a fault above the Ics but below the Icu occurs, the MCCB can interrupt it successfully but will need a replacement due to the damage suffered.
• The Main difference between Ultimate Short Circuit (Icu) and Service Breaking Capacity (Ics) that Icu (Ultimate Braking Capacity) means Circuit breaker can remove the fault and remain usable but Ics (Service Braking Capacity) means Circuit breaker can remove the fault, but it may not be usable afterwards.
• For example, if a circuit breaker has an Ics of 25,000 Amperes and an Icu of 40,000 Amperes:
• Any fault below 25kA will be cleared with no problem.
• A fault between 25kA and 40kA will cause permanent damage when cleared.
• Any current exceeding 40 kA can’t be cleared by this breaker.

 (5) Rated working voltage (Ue):

• It is the continuous operation voltage for which the MCCB is designed.
• This value is typically equivalent or close to a standard system voltage.
• In three phase it is usually 400V or 415 V. For single phase it is 230V or 240V.

(6) Rated Insulation voltage (Ui):

• It is the maximum voltage that the MCCB can resist according to laboratory tests.
• It is higher than the rated working voltage, in order to provide a margin of safety during field operation.

(7) Rated impulse withstands voltage (Uimp):

• It is the value of transient peak voltage the circuit-breaker can withstand from switching surges or lighting strikes imposed on the supply.
• This value characterizes the ability of the device to withstand transient over voltages such as lightning (standard impulse 1.2/50 μs).
• Uimp = 8kV means Tested at 8 kV peak with 1.2/50μs impulse wave.

(8) Number of Poles:

• No of Pole for MCCB depends on Single Phase & Three Phase Power Controlling /Protection
• Single Pole (SP) MCB: 
• A single pole MCB provides switching and protection for one single phase of a circuit.
• Used: for Single Phase circuit
• Double Pole (DP) MCB: 
• A two Pole MCB provides switching and protection both for a phase and the neutral.
• Used: for Single Phase circuit
• Triple Pole (TP) MCB: 
• A triple/three phase MCB provides switching and protection only to three phases of the circuit and not to the neutral.
• Used: for Three Phase circuit
• 3 Pole with Neutral (TPN (3P+N) MCB): 
• A TPN MCB, has switching and protection to all three phases of circuit and additionally Neutral is also part of the MCB as a separate pole. However, Neutral pole is without any protection and can only be switched.
• Used: for Three Phase circuit with Neutral
• 4 Pole (4P) MCB: 
• A 4 pole MCB is similar to TPN but additionally it also has protective release for the neutral pole. This MCB should be used in cases where there is possibility of high neutral current flow through the circuit as in cases of an unbalanced circuit.
• Used: for Three Phase circuit with Neutral

Read also

Demand Factor-Diversity Factor-Utilization Factor- Load Factor

Effects of High VoltageTransmission Lines on Humans and Plants

Direct OnLine Starter

Star-Delta Starter

Electrical Insulation Resistance (IR) Values

Vector Group of Transformer

Parallel Operation of Transformers

Electrical Interview questions

How to Test & Check a Capacitor with Digital Multimeter and Analog AVO Meter.

PROTECTION SETTING OF MCCB (LESSON-2)

 Over load , Shirt circuit & Ground Fault Protection (LESSON-2) 

(2) For Short Circuit Protection (Magnetic Setting):

  (C) Short Time pickup Current Setting (Im):

• Short time protection is time-independent.
• It is determines or sets the level of fault current at which the short-time trip delay countdown is actuated.
• Short Time Pick up Value (Im) (multiplied by the ampere rating) sets the short circuit current level at which the circuit breaker will trip after the set time delay.
• The short-time pickup (Isd) sets current level (below instantaneous trip level) at which circuit breaker will trip after the preset time delay.
• Standard Practice for Setting:
• No trip for a current below 80% of the short time setting
• Trip for a current equal to 120% of the short time setting
• The trip time is Less than 0.2 s for a short time protection with no time delay and equal to the value of the time delay tsd for a protection with time delay

PROTECTION SETTING OF MCCB (LESSON-1)

Protection setting of  MCCB ( Over load , Shirt circuit & Ground Fault Protection (LESSON-1)

Introduction:

• There are various types of protections setting in MCCB, which define various protection of Electrical Network.
• In MCCB we can set most of protection are adjustable according to Electrical Load profile.
• The main adjustable Setting in MCCB are
• Over current Setting
• Short Circuit Setting
• Ground Fault Setting

Meaning of each selector switches of MCCB

• As Per Standard IEC 60947-2 defines the names of the selector switches.

Setting	Adjustment	Protection For
Ir	Long time Pick up Current Setting (or thermal Setting). This is a multiplication coefficient of the rating of the device. (Ir=xIn)	Protection against overloads
tr	Long time delay Setting in seconds, enabling in particular the starting current of a motor to be tolerated. (tr=Sec)	Protection against overloads
Im / Isd	Short time (Magnetic Setting). This is a multiplier of the Ir setting, often 1.5 to 10 times the Ir current (im=xIr)	Protection against short circuits.
tm / tsd	Short time delay Setting, enabling in particular the discrimination (time) to be increased with downstream feeders and the magnetization peaks of a transformer or a motor to be tolerated. It is recommended that the I²t selector switch is set to the ON position.(tm=Sec)	Protection against short circuits.
Ii	Instantaneous current Setting. Protecting the installation against strong short circuits (dead short circuits) by instantaneous tripping without Time Delay and self-protection of the circuit breaker. The Ii > Isd.	Protection against Dead Short circuits.
Ig	for monitoring the earth fault current circulating in the Phase and Earth conductor in TNS systems	Earth protection
tg	Earth protection time delay	Earth protection
I delta n	Adjustment of the sensitivity of the earth leakage protection	Earth leakage protection
delta t	Earth leakage protection delay.	Earth leakage protection

  Setting of each Protection switch of MCCB

 (1) For Low level Fault / Over Current Protection (Thermal Setting):

  (A) Long-Pickup Current Setting (Ir):

• It is determines the continuous ampere rating of the breaker.
• Long time protection is time-dependent.
• Long Pickup (Ir) value (multiplied by the ampere rating (In) of MCCB) sets the maximum current level which the circuit breaker will carry continuously.
• If MCB is 1000A Rating but Full Load current is 800A than MCCB Rating can be changed from 1000A to 800A by setting it 0.8, Now Ir=0.8XIn =0.8×1000=800Amp
• If the current exceeds this value for longer than the circuit breaker will trip at the set delay time.
• Long time protection is inverse time type (with I2t constant)
• The long-time pickup (Ir) is adjustable from 4 to 1.0 times the sensor plug rating (In)
  

• Standard Practice for Setting:
• No trip for a current below 105% of Ir
• Trip in less than two hours for a current equal to for
• 120% of Ir for an electronic trip unit and for
• 130% of Ir for a thermal-magnetic trip unit
• For a higher fault current, the trip time is inversely proportional to the fault current value.

(B) Long-Time delay Setting (tr):

• Long time delay (tr) sets length of time that the circuit breaker will carry a sustained overload before tripping.
• The delay bands are labeled in seconds of over current at six times the ampere rating.
• Long-time delay is an inverse time characteristic in that the tripping time decreases as the current increases.
• The long-time delay (tr) sets the length of the time that the circuit breaker will carry an over current (below the short-time or instantaneous pickup current level) before tripping.
• The Long time delay can be set to I2t On and I2t OFF settings.
• (A) I2t Response:I2t Out ,For coordination with other circuit breakers with electronic trip devices and for coordination with thermal-magnetic circuit breakers.
• (B) I2t Response: I2t In ,For coordination with fuses and upstream transformer

KNOW BEFORE BUYING LED BULBS ( LESSON :3)

 know before buying LED Bulbs  

 (4) Color Rendering Index (CRI):

• There are two standard measurements for the color characteristics of light: “color rendering index” (CRI) and “color temperature”, which expresses the color appearance of the light itself.
• Color rendering index measures the ability of a light bulb to reproduce colors.
• CRI is described How artificial light source is able to render the true color of objects as seen by natural outdoor sunlight which has a CRI of 100

KNOW BEFORE BUYING LED BULBS ( LESSON :2)

 know before buying LED Bulbs ( LESSON :2)

(3) Correlated Color temperature (CCT):

• Color temperature refers to the light’s color characteristics.
• Color Temperature is measured in Kelvin.
• It refer to the warmness or coolness of the light that bulb produces.
• The color temperature of a light source is a numerical measurement of its color appearance.
• This temperature is based on the principle that any object will emit light if it is heated to a high enough temperature and that the color of that light will shift in a predictable manner as the temperature is increased.
• Color temperature is a description of the warmth or coolness of a light source. When a piece of metal is heated (temperature increases) the color of light it emits will change. This color begins as red in appearance and graduates to orange, yellow, white, and then blue-white to deeper colors of blue.
• Color Temperature is not an indicator of lamp heat.
• The sun, for example, rises in morning at approximately 1800 Kelvin and changes from red to orange to yellow and to white as it rises to over 5000 Kelvin at high noon. It then goes back down the scale as it sets in evening.
• The warm white ranges from about 2700k to 3800k, natural white ranges from 3800k to 4800k, pure white or daylight from about 4800k to 6000k. Cool white starts from around 6000k upwards.
• Colors and light sources from the red/orange/yellow side of the spectrum are described as warm (incandescent) and those toward the blue end are referred to as cool (natural daylight).
• In Color Temperature Value higher Kelvin temperatures (3600–5500 K) are consider cool and lower color temperatures (2700–3000 K) are considered warm.
• When choosing a color, the two considerations are important one is color rendering (How well the light shows the true color of objects) and temperature.

(1) Soft White / Warm White (2700K- 3000K):

• Warm light is preferred for living spaces because it is more flattering to skin tones and clothing.
• Recommended for indoor general and task lighting applications.
• Living rooms
• Bed rooms
• Rooms decorated in earthy tones (reds, oranges, and yellows)
• It gives effect like incident or halogen Light.

(2) Natural / Cool White (3500K- 4500K):

• Cool light is preferred for visual tasks because it produces higher contrast than warm light.
• Recommended for use in Domestic Applications.
• Warmer Whites are preferable in living and dining areas as well as reception areas to create a more relaxed environment.
• Natural Whites are preferable for kitchens and bathrooms where tasks are performed.
• Suitable for work areas where contrast is important.
• Kitchen
• Bath rooms
• Rooms decorated in airy, fresh hues (blues, greens, whites)
• It gives effect like Fluorescent Light.

(3) Bright White (4500-5000K):

• Recommended for use in:
• Office
• Study Room

(4) Daylight / Full Spectrum (5000K- 6500K):

• Recommended for use in:
• Garage
• Office
• Industrial and hospital areas.

  

Lighting Source CCT
Source	Color temperature in Kelvin
Skylight (blue sky)	12,000 – 20,000
Average summer shade	8000
Light summer shade	7100
Typical summer light (sun + sky)	6500
Daylight fluorescent	6300
Xenon short-arc	6400
Overcast sky	6000
Clear mercury lamp	5900
Sunlight (noon, summer, mid-latitudes)	5400
Design white fluorescent	5200
Special fluorescents used for color evaluation	5000
Daylight photoflood	4800 – 5000
Sunlight (early morning and late afternoon)	4300
Brite White Deluxe Mercury lamp	4000
Sunlight (1 hour after dawn)	3500
Cool white fluorescent	3400
Photoflood	3400
Professional tungsten photographic lights	3200
100-watt tungsten halogen	3000
Deluxe Warm White fluorescent	2950
100-watt incandescent	2870
40-watt incandescent	2500
High-pressure sodium light	2100
Sunlight (sunrise or sunset)	2000
Candle flame	1850 – 1900
Match flame	1700
Skylight (blue sky)	12,000 – 20,000
Average summer shade	8000
Light summer shade	7100
Typical summer light (sun + sky)	6500
Daylight fluorescent	6300
Xenon short-arc	6400
Overcast sky	6000
Clear mercury lamp	5900
Sunlight (noon, summer, mid-latitudes)	5400
Design white fluorescent	5200
Special fluorescents used for color evaluation	5000
Daylight photoflood	4800 – 5000
Sunlight (early morning and late afternoon)	4300
Bright White Deluxe Mercury lamp	4000
Sunlight (1 hour after dawn)	3500
Cool white fluorescent	3400
Photoflood	3400
Professional tungsten photographic lights	3200
100-watt tungsten halogen	3000
Deluxe Warm White fluorescent	2950
100-watt incandescent	2870
40-watt incandescent	2500
High-pressure sodium light	2100
Sunlight (sunrise or sunset)	2000
Candle flame	1850 – 1900
Match flame	1700

 

CCT – Correlated  Color  Temperature
Kelvin	Associated Effects	Type of Bulbs	Appropriate Applications
2700°	Warm White, Very Warm White	incandescent bulbs	Homes, Libraries, Restaurants
3000°	Warm White	most halogen lamps, Slightly ‘whiter’ than ordinary incandescent lamps	Homes, Hotel rooms and Lobbies, Restaurants, retail Stores
3500°	White	Fluorescent or CFL	Executive offices, public reception areas, supermarkets
4100°	Cool White		Office, classrooms, mass merchandisers, showrooms
5000°	Daylight	Fluorescent or CFL	Graphic industry, hospitals
6500°	Cool Daylight	Extremely ‘white’	Jewelry stores, beauty salons, galleries, museums, printing