What should you know before buying LED Bulbs (Part:3)

 (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
• The higher the CRI rating is, the better its color rendering ability.
• Color Rendering Index (CRI) is a scale from 0 to 100.Incandescent bulbs are rated at 100 and most LED bulbs are usually rated somewhere between 80 and 85
• CRI scoring of 100 is best and a CRI of zero being the worst.
• CRI of 0: For a source like a low-pressure sodium vapor lamp, which is monochromatic compare to a source like an incandescent light bulb which has CRI of 100?
• CRI of 62: A standard “cool white” fluorescent lamp will have a CRI near 62.
• CRI of 70: Lamps with CRIs above 70 are typically used in office and living environments.
• CRI of 82 to 86: Compact fluorescent lamps are graded at 82-86 CRI, which is considered high quality color rendering. CRI is a more important consideration for retail lighting design than it is for office lighting.
• CRI of 80 and above: It is considered high and indicates that the source has good color properties.
• Incandescent lamps and daylight have a CRI of 100, the highest possible CRI.
• The higher the CRI of the light source, the “truer” it renders color.
• The CRI can only be used to compare two light sources that have the same color temperature. A 5000 K, 80 CRI light source is not necessarily superior to a 4000 K, 70 CRI light source.

Color Rendering Index
Light source	CRI
clear mercury	17
white deluxe mercury	45
warm white fluorescent tube	55
cool white fluorescent tube	65
deluxe warm white fluorescent	73
daylight fluorescent	79
metal halide 4200K	85
deluxe cool white fluorescent	86
metal halide 5400K	93
low pressure sodium	0-18
high pressure sodium	25
100-watt incandescent	100

 

Color Temperature & CRI
Lighting source	Color Temperature	Color Rendering Index
High Pressure Sodium Lamp	2100K	25
Incandescent Lamp	2700K	100
Tungsten Halogen Lamp	3200K	95
Tungsten Halogen Lamp	3200K	62
Clear Metal Halide Lamp	5500K	60
Natural Sun Light	5000K to 6000K	100
Day Light Bulb	6400K	80

 

Color Temperature & CRI
Kelvin	Light Effect	CCT	CRI
Below 3600K	Incandescent Fluorescent (IF)	2750	89
Below 3600K	Deluxe warm white (WWX)	2900	82
Below 3600K	Warm white (WW)	3000	52
3200K to 4000K	White	3450	57
3200K to 4000K	Natural white (N)	3600	86
Above 4000 K	Light white (LW)	4150	48
Above 4000 K	Cool white (CW)	4200	62
Above 4000 K	Daylight (D)	6300	76
Above 4000 K	Deluxe Daylight (DX)	6500	88
Above 4000 K	Sky white	8000	88

 (5) Beam angle:

• How the light spreads out from the bulb (Beam Angle) is very important.
• The beam angle determines how light is spread from the bulb into a given space.
• The beam angle is the degree of width that light emanates from a light source. Specifically: The angle between those points on opposite sides of the beam axis where the intensity drops to 50% of maximum.
• Typically a narrow beam angle is a ‘spot’ of light and called “Spot Light”. While a broader beam angle ‘floods’ with light, called a flood light. There are a number of much more specific designations of beam angle.
• Beam angles of LEDs vary greatly and depend on their application. The shape of an LED bulb determines the direction light is emitted.
• Narrow Spot Beam Angle: 05-15 degrees
• Spot Beam Angle: 16-22 degrees
• Narrow flood Beam Angle: 23-32 degrees
• Flood Beam Angle: 33-45 degrees
• Wide flood Beam Angle: 45+ degrees
• Narrow angle bulbs less than 30 degrees are usually used when placing multiple down lights close to each other, such as in a hallway or when lighting cabinetry.
• Larger beam angles are used with high-power LEDs for floodlighting. If you’re replacing incandescent or halogen lamps with LEDs, make sure the beam angle is similar to the old bulb.
• Very large beam angles are sometimes found in pantries or walk-in wardrobes. As beam angle increases, we require more lumens (light output) to maintain the light’s intensity.

 

  (6) Efficacy (Lumen / Watt):

• It is another important parameter to decide the performance of the LED bulb in terms of lumens.
• It indicates effectiveness of the light bulb by converting electrical energy into visible light energy on watts used by Lighting Bulb; hence efficacy is total lumens per watt.
• Example: 9W light bulb comes with lumens of 800 has an efficacy of 90 Lumens per Watt.
• Incandescent bulbs give us light by passing electricity through a filament which heats up and emits light. In fact, 95% of the energy in these bulbs is lost to heat and only 5% is what produces light Hence, incandescent bulbs produce only 16 lumens / watt.
• CFLs in the way they are built are more efficient and can give us between 50 to 70 lumens / watt (at least 3 times more than incandescent bulbs)
• LED bulbs on the other hand, can output up to 100 lumens / watt – which make them one of the most efficient sources of lighting.

Parameter of LED Bulbs
Parameter	Average	Good	Best
Lumens/Watt	75	90	100
Power Factor	0.7	0.8	0.9
CRI	60	70	80
LED Life in Hours	15000	25000	50000

 Other Technical Parameter:

(1) Instant Light:

• LED Bulbs must be instant start and gives full Lumens from Starting.
• When turning on CFLs and Fluorescent light bulbs, there is a slight hesitation before brightness is achieved, and some bulbs may flicker during warm up or even during operation.
• Unlike fluorescents, LED bulbs, like incandescent bulbs, reach full illumination as soon as they are turned on.
• LED lights produce a steady light which does not flicker.

(2) Dimming Capability:

• Earlier versions of LED bulbs had the disadvantage of not being dimmable. Today, many LED bulbs are designed to work in dimmable switches which are provided in many lamps and home lighting fixtures.
• Dimmable LEDs cost about 40% more than non-dimmable LEDs of similar wattage

(3) LED Driver:

• The main cause of LED bulb failure is the driver. The driver is a small transformer that steps down the voltage from 230V AC to a much lower DC voltage for the LED.
• It’s usually located inside the back of the bulb. A poor quality driver could result in bulb failure within months. The LED chip itself rarely fails until driver fails.

(4) LED Chip:

• LED chips are manufactured by various big and small enterprises in the world. Some Good Suppliers make LED Chip of highest quality for longer life and more reliability.
• Larger chip provide more lights, good stability against current variations, but it costs more.
• Cheap and small led chip provides less light and stability. Ceramic COB lights are totally different in terms of size; they use multiple small chips to provide more lights and stability.

(5) Weight

• LED lights need good heat dispassion, this can achieved by good amount of aluminum. Aluminum is generally used to provide better heat sink and extends the life of LED chip.
• Thin heat sink can provide more area in less weight, but transfer enough heat for the removal.
• Some lower quality products provide 12 to 20W lights in very low weight in plastic body. These products would not perform well even in small span of time.

(6) Heating:

• Although LEDs don’t produce much heat they can overheat in operation if they’re not cooled correctly. Cheap LED’s are less efficient, produce more heat and are more heat sensitive. Operating above 60°C can damage cheaper LED’s shortening their life, reducing light output and efficiency. Generally the higher the wattage/power of a GU10 LED bulb, the more heat it produces requiring a more thermally efficient bulb body to keep the LEDs cool. Therefore beware of cheap higher wattage bulbs that don’t have a metallic or ceramic finned body. Another issue is that higher wattage thermally efficient LED bulbs may be so large that they are no longer a suitable size.

What should you know before buying LED Bulbs (Part: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

 

 

 

What should you know before buying LED Bulbs (Part:1)

Introduction:

• The market of LED Lights is blooming very fast. Many companies serve LED Bulb to their customer and it is not easy for customer to choose best LED Bulb among them.
• The customer does not aware the technical parameter of LED, so It becomes more difficult to find out the best quality of LED Bulbs.
• With traditional incandescent light bulbs it was simple to get the right light bulb.  If a 60 watt bulb is the broke or fused you have just get another 60 watt. When it comes to LED lighting, it’s very different.  Since LED light bulbs doesn’t use the same amount of power that incandescent bulbs use.
• LED is described in terms of incandescent equivalence so we may see an LED bulb described as a 60 watt equivalent when in reality it only uses about 9.5 watts. This is because LEDs are measured by lumens (the total amount of visible light put out by a light bulb).  There is not a direct mathematical comparison between the lumen ratings used in LEDs and the wattage consumed by an incandescent.
• To choose best LED Bulbs we should consider following technical Parameters.

Parameters for Choosing LED Bulbs

 There are different factors to consider when choosing a suitable LED replacement bulb

Basic Technical Parameters:

• Lumen (Lighting Intensity)
• Watt (Power Consumption)
• Correlated Color Temperature (Light color)
• Color Rendering Index (CRI)
• Beam angle (Spread of light)
• Efficiency (Lumen / Watt)
• Power Factor

Other Parameters:

• Instant Light
• Dimming capacity
• LED Driver
• LED Chip
• Weight
• Heating

 Basic Technical Parameter:

(1)  Lumen (Brightness):

• When we deal with brightness of LED bulb, we must to know Lumens not Watts.
• The amount of light emitted from a light bulb is measured in Lumens.
• When we replace an incandescent or CFL bulb with an LED bulb we should confirm that LED bulb produces the same number of lumens that the old bulb did.
• As a general benchmark, a standard 60-watt incandescent bulb, for example, produces about 800 lumens of light. By comparison, a CFL bulb produces that same 800 lumens using less than 15 watts
• Do not use watts as a measure of brightness.
• Lumens represent the amount of light emitted by a light source, and are a more accurate measure of the brightness of a bulb.
• More lumens mean brighter light, fewer lumens mean dimmer light
• 1 Foot Candle: 1 foot candle of light is the amount of light (Lumen) that generates one foot radius away from Lighting source so 1 Foot Candle= 1 Lumen / Sq.Foot
• 1 Lux: 1 Lux of light is the amount of light (Lumen) that generates one Metert radius away from Lighting source so 1 Lux= 1 Lumen / Sq.Meter

• It is meaningless if we compare lumens between an LED bulb and a CFL to an incandescent bulb. While we are measuring lumens, we also have to consider useful lumens.
• LED gives directional light unlike incandescent, halogen or compact fluorescent bulbs that give out omni-directional light (or light all around the bulb).  If a light bulb emits light in every direction similarly over and beneath, then light that going up can get trapped in the light fitting and totally wasted.
• 50% of light emitted from a CFL or incandescent bulb is trapped inside the fitting and never makes it out and reached to objects. This trapped light is just gets absorbed and wasted as heat.
• The amount of lumens that actually reached at the objects of Room that bulb produces are called as the useful lumens.

Lumen Chart for Incandescent, CFL,LED
Wattage	Lumens	Useful Lumens
LED 9W	800 lm	800lm
CFL 20W	1000lm	500lm
Incandescent 60W	1000lm	500lm

• There is no rule for how many Lumen is required.It will depend on room size and shape, height of ceilings, colour scheme, type of lamps & fitting.

Area	Lumens/Sq Meter
Kitchen	300 to 400
Kitchen (Task)	700 to 800
Living Room	400 to 500
Hallway	300
Bedroom	300 to 400
Bedroom (Task)	700 to 800
Bathroom	500 to 600
Bathroom (Task)	700 to 800
Reading Area	400

 (2)  Watt (Power Consumption):

• The amount of energy a light bulb consumed is indicated by Watt.
• The watts refer to how much energy a bulb will use.
• The lower the watts, the lower the electric bill. CFLs and LEDs have a lower wattage than incandescent bulbs, but emit the same light output
• Watts measure power consumption, whereas lumens measure light actual brightness..
• Wattage is no longer a reliable way to gauge a light bulb’s brightness.
• In old days, when there was only one basic type of incandescent light bulb was available.consumers could buy the incandescent bulb on the term “watts” .
• Incandescent lamps use the filament material heated to the same temperature, the only way to increase their light output is to increase the wattage. We actually feel difference in brightnes between 60 Watt, 100Watt or 150 Watt light bulbs incandescent bulb.
• When new technology introduce The energy-saving CFL bulbs of 15 Watt CFL bulb produced the same light of a 60 Watt incandescent. A 25 Watt CFL was comparable to a 100 Watt incandescent in light output.
• Generally LEDs produce the same amount of light as an incandescent bulb that has five to six times the wattage.
• LED sources are much more efficient at converting watts to lumens. Different materials can be used within the LED sources with different light extraction efficacy so two different LED sources can consume the same number of watts but having different  lumen output.

Watt	Approximate Lumens
25 Watt	230 to 270
35 Watt	250 to 410
40 Watt	440 to 460
50 Watt	330 to 450
60 Watt	800 to 850
75 Watt	1000 to 1100
100 Watt	1500 to 1600

 

Incandescent Watts	CFL Watts	LED Watts	Lumens (Brightness)
40	8 – 12	4 – 5	450
60	13 – 18	6 – 8	750 – 900
75 – 100	18 – 22	9 – 13	1100 – 1300
100	23 – 30	16 – 20	1600 – 1800
150	30 – 55	25 – 28	2600 – 2800

Cable Construction & Cable Selection- Part:4

Cable Selection Parameters:

 (1) Voltage of Cable:

• The Nominal voltage is to be expressed with two values of alternative current Uo/U in V (volt)
• Uo/U : Phase to earth voltage
• Uo : Voltage between conductor and earth
• U : Voltage between phases (conductors)
• (i ) Low-tension (L.T.) cables — upto 1000 V
• (ii ) High-tension (H.T. ) cables — upto 11,000 V
• (iii ) Super-tension (S.T.) cables — from 22 kV to 33 kV
• (iv ) Extra high-tension (E.H.T.) cables — from 33 kV to 66 kV
• (v ) Extra super voltage cables — beyond 132 kV
•  A low-voltage system usually has a solidly earthed neutral so that the line to earth voltage cannot rise higher than (line volts) ÷ √ 3. Cables for low-voltage use are insulated for 600V rms score to earth and 1000V rms core to core.
• High-voltage cables used in Shell installations are rated 19000/3300V or 3810/6600V or 6600/11000V, Phase/Phase.
• In selecting the voltage grade of cable, the highest voltage to earth must be allowed for. For example, on a normal 6.6kV unearthed system, a line conductor can achieve almost 6.6kV to earth under earth-fault conditions, to withstand this, a cable insulated for 6600/11000V must therefore be used.

 (2) Current carrying capacity:

• The current carrying capacity of a cable is called Ampacity. Ampacity is defined as the maximum amount of electrical current a conductor or device can carry before sustaining immediate or progressive deterioration and is the rms electric current which a device or conductor can continuously carry while remaining within its temperature rating

  (3) Short Circuit values:

• the “short-circuit current rating” is the maximum short-circuit current that a component can withstand. Failure to provide adequate protection may result in component destruction under short circuit conditions.
• Short circuits and their effects must be considered in selecting cables. These cables should have a short circuit rating which is the highest temperature the cable can withstand during an electrical short circuit lasting up to about half a second.

 (4) Type of Conductor:

• Type of Conductor Material Copper or Aluminum is main criteria for selection of Cable

 (5) No of Core:

• No of Core selection is depends upon Power System.
• For Single Phase Power Supply We can use 2 core Cable for Three phase supply we can use 3.5 Core or 4 Core Cable for HV supply We may be use Single Core Cable.

 (6) Voltage drop:

• It is a primary concern when installing lengths of cables is voltage drop. The amount of voltage lost between the originating power supply and the device being powered can be significant. All cables have resistance, and when current flows in them this results in a volt drop.

 (7) Type of Insulation:

• Type of Cable Insulation Material like, PVC, XLPE, Rubber
• PVC Cable is cheaper than XLPE Cable

 (8) Method of Installation:

• If we lay cable in Ground Armor cable is required but If we lay cable in cable tray We may be used un armor cable to reduce cost of cable.
• I we lay cable on cable tray than shielded cable is required.
• Mutual heating effect due to cable group laying is also consider while selecting a cable. When multiple cables are in close proximity, each contributes heat to the others and diminishes the amount of external cooling affecting the individual cable conductors. Therefore cable de rating is necessary consideration for multiple cables in close proximity.

 (9) Shielded Cable or un shielded Cable

• The choice of a shielded cable or non-shielded cable is depend upon some criteria.
• An area such as a production/factory floor where heavy equipment is being used is a prime example of a place where we might consider a shielded cable.
• Grounding can also be a concern in some installations. If shielded cable is used to connect equipment from two different circuits, a ground loop can occur causing noise on a network line. If the ground voltage difference is great enough it may even cause damage.
• Terminations of the shielded cable must also be made with care, to provide for a smooth dielectric transition from the shielded condition to the unshielded condition
• the substantial space required if shielded cables were used. Shielded cables require a significant amount of space at each end of the cable for installation of the stress cone kit. Also, the minimum bending radius for shielded cables is twelve times cable outside diameter, whereas the minimum bending radius for unshielded cables is only eight times outside diameter (and even less with extra-flexible appliance connection cables used in controllers).
• The two factors, high cost and large space requirements, preclude use of shielded cable in switchgear

 (10) Economics:

• It is also an important factor for selecting the type of cable.
• It is to be kept in mind that the cost of the cable should not be such large that it causes loss and another cable may fetch the same results in low cost and loss.

(11) Environmental conditions:

• Cable operates at its best when it is installed in its optimum environmental conditions.
• For example, Elastomeric Cable is applied in trailing, coal cutter, wind mill, panel wiring, battery cable and such other areas. XLPE cables work good in areas where moisture content is good. Thus, proper cable should be selected so that the system becomes more efficient.

 (12) Applications:

• Low voltage cables with both PVC and XLPE insulation are suitable for indoor and outdoor applications.
• Armored cables are not recommended for tray applications, as they are heavy in weight and extra loads are exerted on the tray.
• Unarmored cables are not recommended for direct buried applications, except if the quoted cables are designed and produced to pass direct burial test requirements (example, direct burial tests described in UL 1277 and UL 1581).
• A PVC jacket is a very stable material against a wide range of chemicals, while HDPE jacketed cables can serve better in wet locations.

 Cable Core Colors Identification

• Single core – Natural
• Two core – Red, Black
• Three core – Red, Yellow and Blue
• Four core – Red, Yellow and Blue and Black
• Five core – Red, Yellow and Blue and Black and Green

 Abbreviation for PVC & XLPE Cable

•  A = Aluminum Conductor.  
• Y = PVC Insulation or PVC Sheath
• 2X = Cross-linked Polyethylene Insulation 
• W = Round Steel Wire Armoring  
• WW = Double Round Steel Wire Armoring
• F = Formed Steel Wire (Strip) Armoring
• FF = Double Formed Steel Wire (Strip) Armouring
• C = Metallic Screening (Usually of Copper)  
• CE = Metallic Screening (Usually of Copper) over each individual core.
• Gb = Holding Helix Tape (of Steel)  
• Wa = Aluminum Round Wire & Aluminum Formed Wire (Strip) Fa Armouring.

Example:

• AYY- Aluminum Conductor, PVC Insulated, PVC Outer Sheathed Heavy Duty Cables.
• AYWY- Aluminum Conductor, PVC Insulated, Round Steel Wire Armored and PVC Outer Sheathed
• AYFY- Aluminum Conductor, PVC Insulated, Flat Steel Wire (Strip) Armored and PVC Outer Sheathed
• AYCY- Aluminum Conductor, PVC Insulated, Metallic Screened and PVC Outer Sheathed
• A2XCY- Aluminium Conductor, XLPE Insulated, Metallic Screened and PVC Outer Sheathed

 Cable Application Standard:

• IEC 60502 (Part 1)”PVC/ XLPE insulated cables” single core /multi-core
• BS 5467 for XLPE insulated armored cables
• BS 7889 for XLPE insulated single core unarmored cables

Cable Construction & Cable Selection- Part:3

(9) Armoring:

• Code: IS: 7098 / IS: 3975 / IEC:60502 / BS:6622/BS:7835.
• Material: metallic or non-magnetic Alumimium, Steel wire/strip.
• Used for : LV, MV & HV Cables
• The armor provides mechanical protection against crushing forces.
• Armor also can serve as an Earth Continuity Conductor (ECC).
• The armoring type could be:
• Mechanical protection of the cable is provided by a single layer of wire / Strip strands laid over the bedding. Steel wire / Strip is used for 3-core or 4-core cables, but single-core cables have aluminum wire armoring.
• When an electric current passes through a cable it produces a magnetic field (the higher the voltage the bigger the field). The magnetic field will induce an electric current in steel armor (eddy currents), which can cause overheating in AC systems. The non-magnetic aluminum armor prevents this from happening.
• Magnetic Material’s armoring for 3Ph System: With 3-core or 4-core cables the vector sum of the currents in the conductors is zero, and there is virtually no resultant magnetic flux. In Multi-core armored cables have either single layer of Galvanized Steel wire Armor or Galvanized steel strip applied over inner sheath with left hand lay.
• Non Magnetic Material’s armoring for 1Ph System: This is not so however for a single-core cable, where eddy-current heating would occur if a magnetic material was used for the armoring. The material has to be non magnetic for armoring as in this case of return current is not passing through the same cable. Hence it will not cancel the magnetic lines produced by current. These magnetic lines which are oscillating in case of A.C. systems will give rise to eddy currents in magnetic armoring and hence armoring will become hot, and this may lead to failure of the cable. Hence Single core cables for use on A.C systems are armored with single layer of nonmagnetic (Aluminum) material.
• Armoring is Mostly following Type
• SWA – Steel wire armor, used in multi-core cables (magnetic),
• AWA – Aluminum wire armor, used in single-core cables (non-magnetic).
• Tinning or galvanizing is used for rust prevention. Phosphor bronze or tinned copper braid is also used when steel armor is not allowed.
• As strip construction is economical, the manufacture always provides steel strip armoring unless wire armoring is specified.
• As per IS: 1554 Round Wire armoring is provided in cable where calculated diameter under amour is upto13mm. Above this the amour is either steel wire or steel strip of size 4.00X0.80mm.

 (10)Over Sheath (Outer Jacket):

•  Code: IS: IS:7098 / IEC:60502 / BS:6622/BS:7835.
• Material: PVC Flame Retardant / Flame Retardant Low Smoke / Zero Halogen (LSOH), High density Polyethylene HDPE, Halogen Free Flame Retardant (HFFR)
• Used for : LV, MV & HV Cables
• Purpose:
• It is the outer protection part of the cable against the surrounding environment.
• Protected against water ingress, Protection against termite, Protection against UV and Protection against differing soil compositions.
• It is applied over armoring in case of armored cable and over inner sheath in case of unarmored cable called as “Outer Sheath”.
• The standard sheath color is Black other colors such as Red , Light Blue can also be provided
• High-voltage cables are identified by outer sheaths colored red; a black sheath indicates a low-voltage cable
•  The following are the electrical property may be consider while selecting a outer Sheath Materials
• Dielectric Strength: Cable Sheath may be semiconducting or insulating.
• Discharge and Tracking Resistance: When a non shielded cable rests upon or comes into contact with a ground plane, the ground plane acts as the outer plate of the capacitor, made up of the conductor, insulation and the ground plane. Discharges and tracking may cause erosion of the Outer Sheath material.
• Material: A major consideration in selecting Outer Sheath may be a thermoplastic or thermosetting material. Mostly a thermoplastic jacket is less expensive. However, thermoplastics will melt at some elevated temperature and, thus, could run or drip from the cable under extreme conditions.
• Thermoset materials will not melt and run or drip at elevated temperatures.

 Comparison of Cable:

 PVC Insulated Cable:

•  PVC insulation becomes stiff making it difficult to fold and the soft PVC loosens its softening agent over years, making it brittle and prone to rip.
• Even at the time of disposing, burning PVC emits toxic dioxin, which is responsible for causing cancer and does, when dumped scantly dissolve
• PVC is thin insulation mainly used in LT side cables and XLPE is thick insulation used in MV & HT cables.
  

XLPE Insulated Cable:

•  Higher Current Capacity: XLPE has higher current carrying capacity as
• Higher Temperature Withstand Capacity: It can withstand higher temperature compared to PVC cable.
• Higher Overload Capacity: XLPE have high overload capacity.
• Low Dielectric Constant: XLPE has lower dielectric and constant power factor.
• Light weight & Small Bending Radius :XLPE cables are lighter in weight, has smaller bend radius, and hence lesser installation cost.
• Higher Short Circuit Capacity: XLPE has higher short circuit rating. XLPE can withstand higher & lower temperatures insulation is usually thinner but the resistance is higher.
• Higher Moisture Resistance: XLPE also has a higher moisture & chemical resistance.
• Cable Installation Job for XLPE is easier than PVC insulated cables because of less Wt, less Diameter and Less Bending radius.
• The Volume Resistivity (ohm-cm) for XLPE is way higher than the PVC cables which are of the order of XLPE cables has insulation resistance of 1000 times compared to PVC cables.

 Elastomer Insulated Cable:

•  Elastomer cables are preferred for flexible application and in congested locations where the bending radius are very small. Elastomer cables are available from low voltage up to 33 kV grade.
• Elastomer cables are also available with rigid copper conductors and having properties like Fire Survival, Zero Halogen and Low toxicity FS properties.

 Rubber Insulated Cable:

•  Rubber insulation remains in the best condition after a long span of time,say,25-30 years and remain soft and pliable even when the temperature is low.
• Rubber Cables are predominantly used in special applications like, mining, ship wiring, transportation sector and Defense applications & earth moving machines.
• These materials have the potential to be recyclable since they can be molded , extruded and reused like plastics, but they have typical elastic properties of rubbers which are not recyclable owing to their thermosetting characteristics

Cable Construction & Cable Selection- Part:2

(5) Insulation Screen:

• Code: IS:7098/IEC:60502/ BS:6622/BS:7835
• Material: Extruded thermo set semi-conducting compound, Carbon paper and carbon loaded polymer.
• Used for : Cable from 6 to 30kV (MV & HV Cables)
• Purpose:
• An extruded layer of semi conducting is applied over the insulation layer to insure that the electric stress is homogeneous around the insulated core. The semi conducting layer shall be firmly bonded to the outer layer of the insulation layer.
• The Purpose of Insulation screen is same as Conductor Screen.
• The Purpose of Insulation Screen is to reduce voltage stress at the interface between the conducting and insulating component
• A cylindrical, smooth surface between the insulation and Metallic shield
• Insulation screen is a layer of black cross linked semi conductive compound of approx 1mm thickness and is either fully bonded to the insulation layer, or can be “cold strippable” by hand.
• When terminating or jointing the cables, it is necessary to remove a part of the insulation screen.

 (6) Bedding (Inner Sheath):

•  Code: IS: 7098, 1554 / IEC: 60502 / BS: 6622 / BS: 7835.
• Material: Thermoplastic material i.e. PVC, Polyethylene, thermosetting (CSP) compound
• Used for : LV, MV & HV Cables
• Purpose:
• It could be also called inner sheath or inner jacket, which serves as a bedding under cable armoring to protect the laid up cores and as a separation sheath.
• Inner sheath is over laid up of cores.
• It gives Circular Shape of the cable and it also provides Bedding for the armoring.
• IS:1554 permits following two methods of applying the Inner Sheath of thermoplastic material i.e. PVC, Polyethylene etc., Which is not harder than insulation.
• Inner sheath is provided by extrusion of thermoplastic over the laid up of cores
• Inner sheath is provided by wrapping at thermoplastic tape.
• All multi-core cables have either extruded PVC inner sheath or thermoplastic wrapped inner sheath, which is compatible to insulation material and removable without any damage to insulation. Single core cables have no inner sheath.

 (7) Water blocking Taps:

•  Water blocking is used to prevent moisture migration.
• Water blocking tapes or Swelling powder should be applied between the conductor strands to block the ingress of water inside the cable conductor (if required).
• Water blocking Methods to be considered are as follows.
• Powders: Swell able powders are used as longitudinal water blocks in cables to prevent longitudinal water penetration. These powders swell and expand sufficiently upon contact with water to form a gel-like material to block the flow of water.
• Water-Blocking Tapes: A water-blocking tape is usually a nonwoven synthetic textile tape impregnated with, or otherwise containing, a swell able powder.
• Sealed Overlap: To ensure a seal of the overlap, hot-melt adhesives can be used. These adhesives can be extruded or pumped into the overlap seam of a longitudinally formed metallic tape before the seam is closed during cable manufacture.

 (8) Metallic Screen:

•  Code: IS: 7098 /IEC:60502 / BS:6622/ BS:7835.
• Material: Nonmagnetic metallic materials Copper Wire / Tape or Aluminum Wire / Strip
• Used for : MV & HV Cables
• Purpose:
• Medium Voltage & High-voltage cables have an earthed metallic screen over the insulation of each core.
• This screen consists one or multi layers of a lapped Conductive copper wires, copper tape or metallic foil, lead, aluminum helically with overlap over insulation screen.
• The metallic shield needs to be electrically continuous over a cable length to adequately perform its functions of electrostatic protection, electromagnetic protection, and protection from transients, such as lightning and surge or fault currents.
• (1) Shield Electromagnetic radiation: A metallic sheath is used as a shield to keep electromagnetic radiation in the Cable.
• The main function of the metallic screen is to nullify the electric field outside of the cable – it acts as a second electrode of the capacitor formed by the cable. The screen needs to connect to earth at least at one point along the route.
• The capacitive charging current and induced circulating currents which are generated under normal operating conditions will be drained away through the screen.
• (2) Earth Path: It also provides a path for fault and leakage currents (sheaths are earthed at one cable end).
• The screen also drains the zero-sequence short circuit currents under fault conditions; this function is used to determine the required size of the metallic screen.
• Lead sheaths are heavier and potentially more difficult to terminate than copper tape, but generally provide better earth fault capacity.
• (3) Water Blocking: The other function of Metallic sheaths is to water block and form a radial barrier to prevent humidity from penetrating the cable insulation system.
• (4) Mechanical Protection: It also provides some degree of mechanical protection to cable.
• Cable shields are nonmagnetic metallic materials. The two materials typically used for metallic shields are aluminum and copper. Aluminum requires a larger diameter as a wire or a thicker cross section as tape to carry the same current as copper. At equivalent current-carrying capacity, an aluminum shield will be lighter in weight but about 40% larger in dimensions

 Different Types of Metallic Screen:

 (A) Concentric Copper Wire screens /Tapes

• Advantages:
• Lightweight and cost effective design.
• High short-circuit capacity.
• Easy to terminate.
• Drawbacks:
• Low resistance of screen may necessitate need for special screen connections to limit the circulating current losses.
• Does not form a complete moisture barrier unless water swell able tapes are used under and/or over the copper wires.

(B) Aluminum foil laminate

• Advantages:
• Lightweight and cost effective design.
• Moisture proof radial barrier.
• Drawbacks:
• Low short circuit capacity.
• More difficult to terminate – requires special screen connections.

(C) Extruded lead alloy sheath

• Advantages:
• Waterproofing guaranteed by the manufacturing process.
• Excellent resistance to corrosion and hydrocarbons (suitable for oil and gas plants).
• Drawbacks:
• Heavy and expensive.
• Lead is a toxic metal whose use is being restricted in some countries.
• Limited capacity for short circuits.

Cable Construction & Cable Selection- Part:1

Cable Construction:

Parts of Cable:

1. Conductor (For LV/MV/HT Cables)
2. Conductor Screen (For MV/HT Cables)
3. Filler & Binding Tapes (For LV/MV/HT Cables)
4. Insulation (For LV/MV/HT Cables)
5. Insulation Screen (For MV/HT Cables)
6. Separation Tape (For MV/HT Cables)
7. Bedding (Inner Sheath)
8. Metallic Sheen (For MV/HT Cables)
9. Armor (For LV/MV/HT Cables)
10. Outer Sheath (For LV/MV/HT Cables)
11. Water Blocking Tapes –Optional (For MV/HT Cables)
12. Insulation Tapes–Optional (For MV/HT Cables)

(1) Conductors:

• Code: IS:8130 / IEC 60228/ BS 6360
• Material: Class 2 – Annealed Plain / Tinned Copper / Aluminum.
• Used for : LV ,MV & HV Cables
• Purpose:
• Usually stranded copper (Cu) or aluminum (Al) is used.
• Copper is denser and heavier, but more conductive than aluminum.
• Electrically equivalent aluminum conductors have a cross-sectional area approximately 1.6 times larger than copper, but half the weight.
• The size of the copper / Aluminum conductor forming one of the cores of a cable is expressed in square millimeters (mm2), and the current rating of the cable is dependent upon the cross-sectional area of each core.
• Multi core Aluminum or copper conductor are produced by two Shapes
• Circular Conductor: multi layers of stranded wires are assembled together to make circular shape.
• To achieve a circular conductor, the number of strands follows a particular progression: 3, 7, 19, 37, 61, and 127 etc, the diameter of each strand being chosen to achieve the desired cross-sectional area of whole conductor.
• Circular Shape conductor is normally available used up to 200mm2
• Segment Conductor: Five segments of compacted conductor in triangle shape of 72 degree are assembled together with separation of non metallic tapes to reduce the skin effect which reduce the AC conductor resistance.
• Larger sizes have conductors with the strands laid up in a segmental formation; this Cables achieves a better space factor and reduces the overall diameter of the cable. It also reduces the inductance of the cable due to decreased spacing between phases
• Segmental conductor is normally available from 1000 mm2 and above

 (2) Conductor Screen (Semi Conductor Screen):

• Code: IS:7098/IEC:60502/ BS:6622/BS:7835
• Material: Extruded thermo set semi-conducting compound, Carbon paper and carbon loaded polymer.
• Used for : Cable from 6 to 30kV (MV & HV Cables)
• Purpose:
• This screen consists of a lapped copper tape or metallic foil usually less than 1.0mm in thickness, which is the interface between the conductor and the insulation (PVC, XLPE).
• The Main Purpose of Conductor Screen is to maintain a uniformly divergent electric field, and to contain the electric field within the cable core.
• Conductor Screen is semi-conducting material because Semi-conducting materials do not conduct electricity well enough to be a conductor but will not hold back voltage. It “smoothes” out the surface irregularities of the conductor. The conductor shield makes the voltage on the inside of the insulation the same
• Semiconducting screening materials are based on carbon black that is dispersed within a polymer matrix. The concentration of carbon black needs to be sufficiently high to ensure an adequate and consistent conductivity.
• The incorporation must be optimized to provide a smooth interface between the conducting and insulating portions of the cable.
• The smooth surface is important as it decreases the occurrence of regions of high electrical stress.
• Control Electrical Field: Conductor Screen is control the electric field within the insulation and thus the same voltage gradient across it. It also avoids any interaction of the electric stresses due to the voltages on different phase conductors within the same cable.
• Reduce Voltage Stress Conductor Screen helps to reduce voltage stress at the interface between the conducting and insulating components.
• A typical construction for a medium voltage cable consists of an aluminum conductor covered by a screening layer, then by a polyethylene or ethylene propylene rubber insulation followed by a further screening layer.  The coefficient of expansion of the insulation layer is typically ten times greater than that of the aluminum and when the cable is at its maximum operating temperature of 90ºC, a large enough gap can formed to allow electrical discharges to occur.  The semi-conducting layer then serves to even out the stresses associated with these discharges, which would otherwise attack the insulation at specific points.

• Uniform Electrical Field: A Black semi-conducting tape is used to maintain a uniform electric field and minimize electrostatic stresses in MV/HV power cables.
• The external surfaces of the conductor may not be smooth, particularly for stranded conductors, so this layer provides a smooth surface at the same potential as the conductor to keep the electric field consistent all the way around the surface. Without this layer, any small peaks or troughs could cause concentrations of electrical energy which could create small arcs, and over time could erode the insulation layer and cause failure of the cable.
• Reduce Electrical Flux line around the each core: : It Provide a cylindrical, smooth surface between the conductor and insulation
• Semi-conducting compounds also have the effect of filling in the interstices of the conductor giving a smooth surface for the insulation.  This reduces the electrical flux lines around each individual wire that make up the conductor, which can reduce the stress by 10-15%.  

(3) Filler & Binding Tap (Laying-Up):

• Material: Non Hygroscopic PVC / Poly propylene Fiber to maintain roundness of cable.
• Used for : LV,MV & HV Cables
• Purpose:
• In case of three core cables, the three cores are laid up with polymer compound or non-hygroscopic fillers like polypropylene (PP) fillers and a binder tape is applied with an overlap to provide a circular shape to the cable.
• These binder tapes can be of PVC or foamed Polyethylene.
• Inner Sheath (Bedding) for Armored Cables. Extruded layer of PVC or PE is applied over the laid up cores for armored cables.

(4) Insulation:

• Code: IS: 7098, 8130, 14494 / IEC: 60502 / BS: 6622/BS: 7835.
• Material: PVC, XLPE, Rubber, Elastomer, EPR.
• Used for : LV ,MV & HV Cables
• Purpose:
• Insulation main Purpose is to withstand the electrical field applied to the cable for its design life in its intended installed environment
• This will be an extruded layer of XLPE, Elastomer, Rubber or PVC applied over conductor screen under triple extrusion process along with conductor screen and insulation screen.
• There are different Type of Insulation Material used for cable but widely used are

 (A) Cross-linked polyethylene: (XLPE)

• They are known as PEX or XLPE Cable. It is form of polyethylene with cross links.
• XLPE creates by direct links or bonds between the carbon backbones of individual polyethylene chains forms the cross linked polyethylene structure.
• The result of this linkage is to restrict movement of the polyethylene chains relative to each other, so that when heat or other forms of energy are applied the basic network structure cannot deform and the excellent properties that polyethylene has at room temperature are retained at higher temperatures.
• The cross linking of the molecules also has the effect of enhancing room temperature properties.
• The useful properties of XLPE are temperature resistance, pressure resistance (stress rupture resistance), environmental stress crack resistance (esc), and resistance to UV light, chemical resistance, oxidation resistance, room temperature and low temperature properties.
• XLPE cables work for the working voltage of 240 V to 500 KV.
• The Jacketing Material can be of PVC / Flame Retardant / Flame Retardant Low Smoke / Zero Halogen (LSOH).
• Applications: Fire Survival, Under Water Cables, Underground burial, installation on trays and ducts.

 (B) Polyvinyl chloride (PVC)

• They are known as PVC insulated cables are widely used in various fields.
• PVC’s relatively low cost, biological and chemical resistance and workability have resulted in it being used for a wide variety of applications.
• For electric cables the PVC is mixed up with plasticizers. PVC has high tensile strength, superior conductivity, better flexibility and ease of jointing.
• PVC is a thermoplastic material, therefore care must be taken not to overheat it; it is suitable for conductor temperatures up to 70°C. PVC insulated cables should not be laid when the temperature is less than 0ºC because it becomes brittle and is liable to crack.
• Applications: Low voltage copper conductor PVC cables are extensively used for domestic home appliances wiring, house wiring and internal wiring for lighting circuits in factories, power supply for office automation, in control, instrumentation, submarine, mining, ship wiring applications etc.

(C) Elastomer Insulated cable

• These cables are suitable for use where the combination of ambient temperature and temperature-rise due to load results in conductor temperature not exceeding 90°C under normal operation and 250°C under short-circuit conditions.
• This insulation shall be so applied that it fits closely on the conductor (with or without either separator or screen) but shall not adhere to it. The insulation, unless applied by extrusion, shall be applied in two or more layers and it is applicable to cables with a rated voltage up to 1 100 volts.
• Applications: Welding Cables, Ship wiring cables, Pressure Tight Cables and cables for submerged connection, Railways locomotives and coach wiring cables, Mining Cables.

(D) Polyvinyl chloride (EPR).

• For high-voltage cables the insulation is ethylene propylene rubber (EPR) and for low-voltage cables it is polyvinyl chloride (PVC).
• EPR has good electrical properties and is resistant to heat and chemicals; it is suitable for a conductor temperature up to 85 ºC.

(E) Rubber Insulated cable

• These are used in electric utilities such as the generation and transmission of electricity. Long service life under normal environment in Nuclear and conventionally powered generating stations plus safety considerations are the significant factors of these electric appliances.
• When exposed to fire, Silicon offers circuit integrity, low smoke evolution, and freedom from halogen acids.