Effects of unbalanced Electrical Load (Part:2)


  • Harmonics in system by UPS:

  • UPS or inverter supplies also perform with poor efficiency and inject more harmonic currents in case of unbalances in the system
  • Decrease Life cycle of Equipment:

  • Unbalanced Voltage increase I2R Losses which increase Temperature. High temperatures, exceeding the rated value of a device, will directly decrease the life cycle of the device and speed up the replacement cycle for the device, and significantly increase the costs of operation and maintenance.
  • Relay malfunction

  • Unbalanced Voltage flows Negative and Unbalanced Voltage of Voltage or Current.
  • The high zero-sequence current in consequence of voltage imbalance may bring about malfunctions of relay operation or make the ground relay less sensitive. That may result in serious safety problems in the system.
  • Inaccurate Measurement

  • Negative and zero-sequence components of voltages or currents will give rise to inaccurate measurements in many kinds of meters.
  • The imprecise measured values might affect the suitability of settings and coordination of relay protection systems and the correctness of decisions by some automated functions of the system.
  • Decrease Capacity of transformers, cables and lines

  • The capacity of transformers, cables and lines is reduced due to negative sequence components. The operational limit is determined by the RMS rating of the total current, due to ‘useless’ non-direct sequence currents the capacity of equipment is decrease.
  • Increase Distribution Losses

  • Distribution network losses can vary significantly depending on the load unbalance.
  • Unbalance load increase I2R Losses of distribution Lines.
  • Increase Energy Bill by increasing Maximum Demand

  • Unbalanced Load increase maximum Demand of Electrical supply which is significantly effects on energy bill. By load balancing we can reduce energy bill.
  • For Energy Consumption Energy Supply Company does not charge on kVA but on kW for Residential customers. This means that they are charged for the “actual” energy used and not charged for the “total” energy supplied. Thus the power factor and Maximum Demand do not impact residential customers.
  • But Commercial, Industrial and H.T Connection charged by its maximum demand . We have to specify the maximum “demand“(in kVA) at the time of connection. During the month if you exceed your maximum “demand” you have to pay penalty (or extra price) for the same. That is the MDI penalty that appears on electricity bills.
  • Let’s assume That Two Company has same approved load of 40 KW and runs 30KW for 100 hours.
  • Electricity charge = 65 Rs per kWh
  • Demand charge = 210Rs per kW
  • Example 1: Company A runs a 30 KW loads continuously for 100 hours but It’s Maximum Demand is 50KW
  • 30 KW x 100 hours = 3,000 KWh
  • Energy Consumption Charge =3000×65=195000Rs
  • Demand difference = 50 KW-40KW=10KW
  • Demand Charges = 10X210=2100Rs
  • Total Bill:  195000+2100=197100Rs
  • Example 2: Company A runs a 30 KW loads continuously for 100 hours but It’s Maximum Demand is 40W
  • 30 KW x 100 hours = 3,000 KWh
  • Energy Consumption Charge =3000×65=195000Rs
  • Demand difference = 40 KW-40KW=0KW
  • Demand Charges = 0X210=00Rs
  • Total Bill:  195000+0=195000Rs
  • Failure of Transformer

  • Three-phase voltage with high unbalanced may cause the flux inside the transformer core to be asymmetrical.
  • This asymmetrical flux will cause extra core loss, raise the winding temperature and may even cause transformer failure in a severe case.
  • Ideally any distribution transformer gives best performance at 50% loading and every electrical distribution system is designed for it. But in case of unbalance the loading goes over 50% as the equipments draw more current.
  • The efficiency of transformer under different loading conditions
  • Full Load- 98.1%
  • Half Load- 98.64%
  • Unbalanced loads- 96.5%
  • For a distribution transformer of 200KVA rating, the eddy currents accounts for 200W but in case of 5% voltage unbalance they can rise up to 720W.
  • Bad / Loose connection of neutral wire

  • In balance Load condition Bad connection of Neutral wire does not make more impact on distribution System but in unbalance load condition such type of Bad neutral connection make worse impact on distribution.
  • The Three Phase power supplies a small a three-floor building. Each floor of this three-floor building is serviced by a single-phase feeder with a different phase. That is the first, second and third floor are serviced by phase R, Y and B. The external lighting load is connected only on R Phase.
  • The supply transformer is rated at 150 kVA and connected delta-grounded wye to provide for 430/220 V three-phase four-wire service.
  • This Transformer has a loose or Bad Neutral connection with the earth.
  • The transformer delivers a load of 35 kVA at 220 V with 0.9 power factor lagging to each floor.
  • During the daytime on, most of the Load of the Building are distributed equally over the three floors which is R Phase=30A, Y Phase =32A, B Phase=38A.
  • In Daytime The Bad connection of Neutral does not effected the Distribution system due to equal load distribution of the System
  • However it is not case in Nighttime. the Load on Y Phase and B Phase are negligible but R Phase Load is high compare to Y and B Phase.
  • In R Phase due to High Electrical Load and The fluorescent lamps flash frequently during the Nighttime of external Lighting Load
  • In Night time a bad electrical contact of the neutral wire of the supply makes the high contact resistance between the neutral wire and connector .which was about 15 kΩ.
  • This extra high impedance caused an unusually high voltage drop in the phase a circuit. In this case, the voltage of phase a dropped from the normal 220V to 182.5V, about 17% based on the nominal voltage. If the contact impedance goes higher than 20 kΩ, it may result in more serious conditions such as extinguishing all lamps.
  • This problem can be removed by fixing the bad connection and keeping the contact impedance near to zero.
Neutral Wire Contact Resistance Voltage across  bad Connection Point Voltage across  Transformer Secondary Side
Day Time Night Time Day Time Night Time
R Y B R Y B R Y B R Y B
Proper Connection (0Ω) 0v 0v 0v 0v 0v 0v 220v 220v 220v 220v 220v 220v
Bad Connection (15Ω) 0v 0v 0v 40v 0v 0v 220v 220v 220v 182v 220v 220v
  • Neutral wire broken

  • The effect of a broken neutral makes voltage imbalance in a Three Phase Four Wire System.
  • For a Three Phase Four Wire System, high neutral wire impedance might enlarge a voltage imbalance (Some Phase Voltage increase while some Phase Voltage decreases).
  • High Voltage damage the equipment connected and even destroy on other hand low voltage effect operation of equipments.
  • The Three Phase star connected lighting loads are fed by a 430 V balanced three-phase voltage source. The fluorescent lamps are all rated at 220 V, 100 W each. The lamps are not equally in R Phase 5 No’s of Bulbs are connected, in Y Phase 3 No’s of Bulbs are connected and on B Phase 3 No’s of Bulbs are Connected. And, the normal impedance of the neutral wire is 1Ω
  • In unbalanced three phase load arrangement, high neutral wire impedance will enlarge the voltage across the neutral wire. The voltages of phases B and C at the load terminal raised to 255 V and 235 V, respectively, and gaining 16.15% and 5.77% based on rated voltage. These abnormally high phase voltages might damage the lamps in phase B and C.
  • On the other hand, the voltage in phase A was reduced from 220V to 185V. That might cause the lamps to flash.
  • If the broken neutral line problem is fixed, then the three phase voltages will go back to normal in near balanced status .however, if the loads are distributed equally to the three phases this problem can also be removed or minimized.
Conditions Voltage across the neutral wire Voltage at  the load terminal
R Y B R Y B
Normal Condition 1v 1v 1v 220v 220v 220v
Neutral Broken 0v 0v 0v 182v 255v 235v
  • Unsuitable capacitor bank installation

  • For reducing energy loss, utilities always force their customers to maintain the power factor within a limit. Penalty will be applied to the customers if their loads’ power factors run outside the limits.
  • Installation of shunt capacitor banks is the most common and cheapest manner to improve the power factor. However, unsuitable installation (single Phase Capacitor instead of Three Phase Capacitor ) may make it worse.
  • The supply transformer is rated at 150 kVA, 11kV/430 V, and supplies a three-phase load of 105 kVA with power factor 0.7 lagging.
  • A single-phase 20KVAR capacitor bank is connected to B phase to improve system power. The impedance of the shunt capacitor bank is 1.805Ωper phase.
  • This kind of single phase Capacitor installation should make the system unbalanced. This unsuitable installation consumes extra real power of 44355 W.
  • The extra real power consumption = 1.732x2XV(RB) / 4xXc =(1.732x2x430) / (4×1.805) =44355W
  • This case shows that the system balance should be considered when installing a capacitor bank to correct the system power factor for a three-phase power distribution system.

 Remedial Action to prevent unbalances Load:

  • All the single phase loads should be distributed on the three phase system such that they put equal load on three phases.
  • Replacing the disturbing equipments i.e. with unbalanced three phase reactance.
  • Reducing the harmonics also reduces the unbalance, which can be done by installing reactive or active filters. These filters reduce the negative phase sequence currents by injecting a compensating current wave.
  • In case the disturbing loads cannot be replaced or repaired, connect them with high voltage side this reduces the effects in terms of percentage and even controlled disturbance in low voltage side.
  • Motors with unbalanced phase reactance should be replaced and re-winded.
  • Distribution of single-phase loads equally to all phases.
  • Single-phase regulators have been installed that can be used to correct the unbalance but care must be exercised to ensure that they are controlled carefully not to introduce further unbalance.
  • Passive network systems and active power electronic systems such as static var compensators and line conditioners also have been suggested for unbalance correction.
  • Load balancing.
  • Use of passive networks and static VAR compensators.
  • Equipment that is sensitive to voltage unbalance should not be connected to systems which supply single-phase loads.
  • Effect of voltage unbalance on ac variable speed drives can be reduced by properly sizing ac side and dc link reactors
  • Tight all Neutral Connections of the System.
  • Install Proper size of Capacitor Bank to the System.
  • Load Scheduling, where the loads in an electrical network are scheduled in a way to turn on and off at precise times to prevent the overloading of any one phase.
  • Manual Load Shifting, where an electrician opens a breaker panel and physically removes the loads from one phase and inserts them onto another phase.
  • Load Shedding, where the loads in an electrical network are immediately turned off in order to instantly “rebalance” the phases. This is usually done by ranking the loads in a network by how long they can be turned off before it affects operations

 

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Effects of unbalanced Electrical Load (Part:1)


Introduction:

  • Generally, three phase balance is the ideal situation for a power system and quality of delivered Electrical Power. However Voltage unbalance may makes worse effect on Power quality of Electrical Power at distribution level.
  • The voltages are quite well balanced at the generator and transmission levels. but the voltages at the utilization level can become unbalanced due to the unequal system impedances, the unequal distribution of single phase loads, asymmetrical three-phase equipment and devices (such as three-phase transformers with open star-open delta connections), unbalanced faults, bad connections to electrical connectors.
  • An excessive level of voltage unbalance can have serious impacts on power quality. In the system the level of current unbalance is several times the level of voltage unbalance. Such an unbalance in the line currents can lead to excessive line losses, losses in the stator and rotor of Motor Malfunctioning of Relay, unsymmetrical measuring of Meters. Voltage unbalance also has an impact on ac variable speed drive systems where the front end converter consists of three-phase rectifier systems
  • Phase balancing is very important and usable to reduce distribution feeder losses and Improve system stability and security

What is unbalance Voltage

  • Any deviation in voltage and current waveform from perfect sinusoidal, in terms of magnitude or phase shift is termed as unbalance
  • In ideal conditions the phases of power supply are 120 degree apart in terms of phase angle and magnitude of their peaks should be same. On distribution level, the load imperfections cause current unbalance which travel to transformer and cause unbalance in the three phase voltage. Even minor unbalance in the voltage at transformer level disturbs the current waveform significantly on all the loads connected to it
  • If three phase voltages have the same magnitude and are in exactly 120deg phase displacement, then the Three-phase voltage is called balanced, otherwise, it is unbalanced.
  • There are no negative- and zero-sequence voltages in a balanced system, only positive-sequence components of balanced three-phase voltage exist. On the contrary, if the system is unbalanced, negative-sequence components or zero-sequence components or both may exist in the system.

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Causes of unbalance Voltage

  • Switching of three phase heavy loads results in current and voltage surges which cause unbalance in the system.
  • Unequal impedances in the power transmission or distribution system cause differentiating current in three phases.
  • Any large single phase load, or a number of small loads connected to only one phase cause more current to flow from that particular phase causing voltage drop on line
  • With continuous operation of motor’s in various environment cause degradation of rotor and stator windings. This degradation is usually different in different phases, affecting both the magnitude and phase angel of current waveform
  • A three phase equipment such as induction motor and Transformer with unbalance in its windings. If the reactance of three phases is not same, it will result in varying current flowing in three phases and give out system unbalance.
  • A current leakage from any phase through bearings or motor body provides floating earth at times, causing fluctuating current.
  • Unbalanced incoming utility supply
  • Unequal transformer taps settings
  • Large single phase distribution transformer on the system
  • Open phase on the primary of a 3 phase transformer on the distribution system
  • Faults or grounds in the power transformer
  • Open delta connected transformer banks
  • A blown fuse on a 3 phase bank of power factor improvement capacitors
  • Unequal impedance in conductors of power supply wiring
  • Unbalanced distribution of single phase loads such as lighting
  • Heavy reactive single phase loads such as welders

 How to calculate unbalance

  • %voltage unbalance= 100x (maximum deviation from average voltage) / (average voltage)
  • Example: With phase-to-phase voltages of The System is 430V, 435V, and 400V.
  • The average Voltage=(430+435+400)/3=421V.
  • The maximum Voltage deviation from Average Voltage=435-421=14V
  • %voltage unbalance=14×100/421=3.32%
  • The permissible limit in terms of percentage of negative phase sequence current over positive sequence current is 1.3% ideally but acceptable up to 2%.

 Effects of unbalance Voltage on System and Equipment:

  • The factors for voltage unbalances can be classified into two categories: normal factors and abnormal factors.
  • Voltage imbalances due to normal factors, such as single-phase loads and three-phase transformer banks with open star-open delta connections, can generally be reduced by properly designing the system and installing suitable equipment and devices.
  • Abnormal factors include series and shunt faults of circuits, bad electrical contacts of connectors or switches, asymmetrical breakdown of equipment or components, asynchronous burnout of three phase power fuses, single-phase operation of motors, etc. The abnormal factors just mentioned above might result in critical damage of systems and equipment.
  • Increase Neutral Return Current

  • The unequal distribution of loads between the three phases of the system cause the flow of unbalanced currents in the system, that produce unbalanced voltage drops on the electric lines. This increase in neutral current which cause line losses.
  • If the system has balanced phase then Neutral current flow will be less on a system. We can save thousands to millions of rupees money by reduce losses be the reducing the neutral current flow in the system
  • Thus unbalance in LV distribution network resulting in increase of neutral current.
  • Voltage or Current Shift

  • If the system is unbalanced, negative-sequence components or zero-sequence components or both may exist in the system.
  • The resistance for negative sequence current is 1/6th of the positive sequence current, which means a small unbalance in voltage waveform will give more current and thus losses.
  • Excessive power loss

  • The unbalance Voltage always causes extra power loss in the system. The higher the voltage unbalance is the more power is dissipated means higher power bills.
  • The imbalance of current will increase the I2R Losses
  • Let’s look at a simple exercise, In balance System The Load current in R Phase=200A, Y Phase=200A,B Phase=200A and in Unbalance System The Load current in R Phase=300A, Y Phase=200A,B Phase=100A,Consider Resistance of line are same in both case and all phases.
  • In Balanced System:
  • Total Load current =R+Y+B = 200+200+200=
  • Total Losses =R(I2R)+Y(I2R)+B(I2R)=40000+40000+40000=120,000Watt.
  • In Un Balanced System:
  • Total Load current =R+Y+B = 300+200+100=
  • Total Losses =R(I2R)+Y(I2R)+B(I2R)=90000+40000+10000=140,000Watt.
  • Here Total Load current is same in both case but Losses in unbalance system is more than balance system.
  • An unbalance of 1% is acceptable as it does not affect the cable. But above 1% it increases linearly and at 4% the de-rating is 20%. This means – 20% of the current flowing in the cable will be unproductive and thus the copper losses in the cable will increase by 25% at 4% unbalance.
  • Motor failure

  • In general, a three-phase motor fed by a balanced three-phase voltage with only positive-sequence component which produces only positive-sequence torque.
  • Reduce Motor life by heating: Extra loss due to voltage imbalance will heat the motor windings, by increasing the operating temperature of Motor leads to the breakdown of winding insulation and might finally in motor failure. This may also decompose the grease or oil in the bearing and de-rate the motor windings. The voltage unbalance of 3% increases the heating by 20% for an induction motor.
  • Winding insulation life is reduced by one-half for each 10°C increase in operating temperature
  • Vibration of Motor: The negative-sequence voltage caused by voltage imbalance produces opposite torque and leads to motor vibration and noise. Severe voltage imbalance may even result in motor collapse.
  • Reduce Motor Life: Heat generated by Unbalance Voltage may also reduce the Motor life
  • Reduce Efficiency: In induction motors connected to unbalanced supply, the negative sequence currents flow along with positive sequence current resulting in decreased percentage of productive current and poor motor efficiency. Any unbalance above 3% hampers the motor efficiency.
Motor Efficiency %
Motor Load % Full Voltage Unbalance
Nominal 1% 2.5%
100 94.4 94.4 93.0
75 95.2 95.1 93.9
50 96.1 95.5 94.1
  • Assume that the 100-HP motor tested was fully loaded and operated for 800 hours per year with an unbalanced voltage of 2.5%. With energy priced at 23Rs/KWH. the annual energy and cost savings calculation are
  • With Normal Voltage
  • Annual Energy Consumption=100HPx0.746X800X(100/94.4)x23=1454068Rs
  • With Unbalanced Voltage
  • Annual Energy Consumption=100HPx0.746X800X(100/93)x23=1475957Rs
  • Annual Cost Savings = 1475957-1454068=21889Rs
  • Overall savings may be much larger because an unbalanced supply voltage may power numerous motors and other electrical equipment.
  • Tripping of Motor: Negative phase sequence current flowing due to unbalance can cause faults in the motor, resulting in, tripping or permanent damage of the electrical equipment
  • Reduce Capacity: For motors, an unbalance of 5% will result in capacity reduction by 25%.
  • Tripping of VFD Drives: The variable frequency or speed drives connected to an unbalanced system can trip off. VFD treats high level unbalances as phase fault and can trip on earth fault or missing phase fault.

What is Fixture’s Beam Angle & Beam Diameter (Part-2)


How to Measure Beam Diameter at Floor:

  • If we install lights at a certain height then how much light will be on the surface will be calculated by following equation.
  • Diameter of light Speared on Floor = 0.018 × Beam angle × The distance
  • For example if we need to calculate the diameter of light for a spotlight of 14° at 3 meter distance.
  • Diameter of Light Spread on Floor=0.018×14×3=0.756
  • As light moves away from a light source, it spreads out and becomes less intense.
  • The beam spread chart below gives a quick reference for common light angles and distances.

Beam Spread at various Beam angle and distance

Beam Angle At 5 Feet At 10 Feet At 15 Feet At 20 Feet
10° 0.9 feet 1.8 feet 2.7 feet 3.6 feet
15° 1.35 feet 2.7 feet 4.05 feet 5.4 feet
20° 1.8 feet 3.6 feet 5.4 feet 7.2 feet
25° 2.25 feet 4.5 feet 6.75 feet 9 feet
40° 3.6 feet 7.2 feet 10.8 feet 14.4 feet
60° 5.4 feet 10.8 feet 16.2 feet 21.6 feet
90° 8.1 feet 16.2 feet 24.3 feet 32.4 feet
120° 10.8 feet 21.6 feet 32.4 feet 43.2 feet

Lamp has Same Lumen but Different Lux due to change in Beam Angle:

  • Amount of Lux at Floor is depending upon Distance between lamp and working floor and Beam Angle of Lamp.

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  • If the Lumens and distance between working plan and lamp is the same for all the four lights having beam angle of 10°,28°,38° and 60°.
  • The amount of Lux at working plan is different. At narrow beam angle 10° it is more Lux at the center of Light (1390 Lux) and it will be reduce as we move from the center. While for wide angle 60° it is less Lux at the Center (39 Lux).

Narrow Beam Angle have Good Light (Lux) at Central

  • A LED light bulb with a narrower beam angle may also seem brighter but the overall total luminous flux (Lumen) will be the same as the same LED light bulb with a lens which produces a wider beam angle. The brighter light is created by focusing the light within a more localized area, much like a magnifying glass can be used to focus the light of the sun. This is sometimes referred to the angular intensity of the light. 
  • If we use a narrower beam angle, we will increase light intensity but reduce the size of the area being illuminated for the same height.
  • The 10 degree beam will be brightest in the center; however, the lux drops very fast away from the center. Thus, it totally is wrong to conclude that 10 degree beam is brighter than the 60 degree beam and hence10 degree beam is a better light.
  • The 60 degree beam has low center lux because it has more light spread over a larger area. The 10 degree beam is good to provide spot lighting. The 60 degree beam may be good for different lighting ambiance.

Illumination as per Distance (Inverse Square Law of Illumination):

  • Only natural light provides even illumination on earth even though it pass from clouds, environment and shadows.
  • But all artificial light are affected from various factor and when the distance increases from the light source then the illuminance reduces according to distance.
  • This is phenomena is called the inverse square law of illumination where the illuminance falls to a quarter of its value if the distance is doubled.

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  • As the luminous flux (Lumen) travels away from the light source the area over which it spreads increases, therefore the illuminance (lux) must decrease. The relationship is called as the inverse square law.
  • Illumination (E) = Lighting Intensity (Lumen) / (Distance)2
  • The inverse square law describes how the intensity of a light is inversely proportional to the square of the distance from the light source (the illuminator).
  • As light travels away from the point source it spreads both horizontally and vertically and therefore intensity decreases. In practice this means that if an object is moved from a given point, to a point double the distance from the light source it will receive only a ¼ of the light (2 times the distance squared = 4).
  • Taking this theory further, if an object at 10m from a light source receives 100 LUX, moving the object to 40m, it will receive only 1/16th of the light (4 times the distance, squared = 16) resulting in the object receiving only 6.25 LUX.

What is Fixture’s Beam Angle & Beam Diameter (Part-1)


Introduction:

  • Lamps are available with multiple beam angle options hence Beam angle is an important factor in lighting design.
  • The beam angle is the width of light that is emanated from the bulb and it is measured in degrees and can vary according to the different styles of bulbs.
  • The beam angle of the Light is mainly depend ceiling height or distance of an object from the light source, and the lux level (brightness) which is required for a particular object or floor area.

Light Terminology

  • Lumens:

  • Lumen is the total amount of light emitted by that lamp in all directions.
  • The luminous flux (Lumen) is provided by lamp manufacturers and common lumen values are included on the lamp.

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  • Lux:

  • It is amount of illumination intensity in specified direction of specified area.
  • Lumen is related to lux. one lux is one lumen per square meter.
  • 1 lux = 1 lumen/m² 
  • Lux is simply the amount of lumens in a specified area.

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  • Lux is measured on a distance of 1 or 10 meters.

Difference between Lumen and Lux:

  • The difference between the lumen and lux is that the lux takes into account the area over which the luminous flux (Lumen) is spread.
  • A flux of 1000 lumens, concentrated into an area of 1 square meter lights with a luminance of 1000 lux.
  • The same 1000 lumens, spread out over 10 square meters, produces a dimmer illuminance of only 100 lux.
  • Mathematically, 1 lux = 1 lm/m2.
  • Lumens are measured in all directions from the light source. This is not the best measurement to describe how bright a light is going to be on a specific area.
  • To perfect describe How much lights going to on Specified area ,luminance lux or foot-candle are used.
  • Lux changes according to beam angle and height

Difference between Beam Angle, Field Angle and Cut off Angle:

Beam Angle:

  • The beam angle is the degree of widththat light emits from a light source.
  • Beam Angle is the angle of the light between two points of 50% of Maximum intensity.
  • It helpful in knowing how much “usable” light the fixture puts out in a fairly even field.

Field angle:

  • It is the angle between the two directions opposed to each other over the beam axis for which the luminous intensity is 10% that of the maximum luminous intensity.
  • In certain fields of applications the field angle was formerly called beam angle.
  • This angle tells you how far the light reaches until it (basically) fades into the darkness.

Cut off Angle:

  • This the angle which encompasses all forward light emitted by the directional lamp.

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Relation between Beam Angle and Filed Angle:

  • The Beam and Field Angles determine how a spot light lights the surrounding area.
  • Normally, the field angle should be 180 degrees, because that creates a softer transition at the edge of the beam angle.
  • If we change the default field angle to 180 to 75 this should give better results and it tighter angle, then over rider it.

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Selecting Beam Angle for various Applications:

  • Beam angle is an important factor in lighting design and Lamps are often available with multiple beam angle options.
  • The beam angle of the Light we choose is determined initially by the ceiling height or distance of an object from the light source, and the lux level (brightness) that is required for a particular object or floor area.

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  • Smaller beam angles (25° to 45° degrees):

  • It will produce a more focused beam of higher intensity and are more suited to spot lighting in commercial or artistic applications.
  • Buildings with very high ceilings of 3m or greater may also benefit from more focused beam angles.
  • Medium beam angle (40 degrees):

  • This is a medium spread beam that offers a good combination of intensity and coverage.
  • Wider beam angles (60 degrees):

  • Very popular for Down lights. A 60 degree beam can be used more effectively in larger rooms. Although the wider beam spread doesn’t provide more light, it does spread the light out further. If we need higher brightness, higher lumen output down lights will be required as a down lights for a good level of uniformity.
  • Larger beam angles (60° to 135° degrees):

  • It will produce a broader beam suited for most residential applications or ambient lighting in commercial applications.
  • They are also useful in lower ceiling applications (< 3m). Whereas a 45° beam spread may be more useful in higher ceiling applications or for corridor lighting.
  • A bulb with a wide beam angle ensures to get a really clear, even light.
  • The spread of light makes no dark areas in the room; and can allow you to use fewer bulbs.
  • Very Larger beam angles (120° degrees):

  • LED light bulbs of 120° or greater are used in high light dispersion applications in place of traditional incandescent or CFL light bulbs or T5, T8 and T12 fluorescent tubes. While 60° to 90° LED light bulbs are more common halogen down light replacements.

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Various Beam Angle as per Applications

 (MR Type) Flood Light (PAR Type)  Spot Light Descriptions Applications
<7° <15° Very Narrow Spot Highlight a small statue or figure on display in a museum or in a jewelry store to make diamonds “pop.”
5° to 15° 15° to 30° Narrow spot Special or sale item or in landscape bullets illuminating a sign or garden feature.
16° to 22° 30° to 60° spot Used in stores to highlight a special or sale area or outdoors to illuminate an architectural feature.
23° to 32° 60° to 90° Narrow flood highlight a display table, while homes might use this bulb in recessed eyeball lights to illuminate a painting
32° to 45° 90° to 120° flood Pendant lights in coffee shops to recessed lights in living rooms.
45° to 60° 120° to 160° Wide flood Common in many general illumination applications from motion-sensing lights above garage doors to recessed cans in auditoriums and movie theaters.
>60° >160° Very wide flood used to illuminate without highlighting any particular object or area. They’re good options for outdoor flood lighting and low-ceiling recessed lights.

 

Ceiling Height and Beam angle

Ceiling Height Beam Angle
2.5 to 3.5 meters 60° beam angle
3.5 to 4.5 meters 38° or 40° beam angle
5 meters 24° to 30° beam angle

Calculate Lighting Fixture’s Beam Angle and Lumen


Example 1: Calculate Lighting Fixture’s Lumen and Diameter of Illumination at surface having following details.

  • Required illumination at surface is 1390 Lux
  • The distance from Lighting Fixture to illumination surface is 3 Meter.
  • The Fixture Beam Angle is 10 Degree.

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Calculation:

  • Required Lux at Surface (E2) =1390 Lux.
  • Distance between Lighting Fixture and Surface (D) = 3 Meter.
  • Fixture Beam Angle (ϕ)= 10°
  • Irradiance at 1.0 meter (E1)= DxDxE2
  • Irradiance at 1.0 meter (E1)=1390x3x3 =12510 Lumen / M2
  • Irradiance at 1.0 meter (E1)= 12510 Lumen / M2
  • Solid Angle of The Lamp (Ω) =2xπx(1-COS(ϕ/2))
  • Solid Angle of The Lamp (Ω) =2×3.14x(1-COS(10/2)) =6.28x(1-0.996)
  • Solid Angle of the Lamp (Ω) =0.0239 Steradian.
  • Required Lumen of Lighting Fixtures= E1x Ω
  • Required Lumen of Lighting Fixtures=12510×0.0239
  • Required Lumen of Lighting Fixtures=299 Lumen.
  • Illumination Diameter at surface =0.018xDx ϕ
  • Illumination Diameter at surface =0.018x3x10
  • Illumination Diameter at surface =0.54 Meter.

Example 2: Calculate Lighting Fixture’s Beam Angle and Illumination Diameter at surface having following details.

  • Required illumination at surface is 22 Lux
  • Lighting Fixture Lumen is 1547 Lumen.
  • The distance from Lighting Fixture to illumination surface is 4 Meter.

Calculation:

  • Required Lux at Surface (E2) =22 Lux.
  • Distance between Lighting Fixture and Surface (D) = 4 Meter.
  • Irradiance at 1.0 meter (E1)= DxDxE2
  • Irradiance at 1.0 meter (E1)=4x4x22 =352 Lumen / M2
  • Irradiance at 1.0 meter (E1)= 352 Lumen / M2
  • Solid Angle of The Lamp (Ω) = Lumen of Lighting Fixtures / E1
  • Solid Angle of the Lamp (Ω) =1547 / 352
  • Solid Angle of the Lamp (Ω) =4.394 Steradian.
  • Solid Angle of The Lamp (Ω) =2xπx(1-COS(ϕ/2))
  • 39 =2×3.14x(1-COS(ϕ/2))
  • Fixture Beam Angle (ϕ)=145°
  • Illumination Diameter at surface =0.018xDx ϕ
  • Illumination Diameter at surface =0.018x4x145
  • Illumination Diameter at surface =10.44 Meter.

Example 3: Calculate Lux Level and Illumination Diameter at surface having following details.

  • Lighting Fixture Lumen is 299 Lumen.
  • The distance from Lighting Fixture to illumination surface is 3 Meter.
  • The Fixture Beam Angle is 10 Degree.

Calculation:

  • Required Lux at Surface (E2) =1390 Lux.
  • Distance between Lighting Fixture and Surface (D) = 3 Meter.
  • Fixture Beam Angle (ϕ)= 10°
  • Solid Angle of The Lamp (Ω) =2xπx(1-COS(ϕ/2))
  • Solid Angle of The Lamp (Ω) =2×3.14x(1-COS(10/2)) =6.28x(1-0.996)
  • Solid Angle of the Lamp (Ω) =0.0239 Steradian.
  • Lumen of Lighting Fixtures= E1x Ω
  • 299= E1x0.0239
  • Irradiance at 1.0 meter (E1)= Lumen of Lighting Fixtures / Ω
  • Irradiance at 1.0 meter (E1)=299 / 0.0239
  • Irradiance at 1.0 meter (E1)= 12506 Lumen / M2
  • Lux at Surface (E2) = E1 / (DxD)
  • Lux at Surface (E2) =12506 / (3×3)
  • Lux at Surface (E2) =1389.5 Lux
  • Illumination Diameter at surface =0.018xDx ϕ
  • Illumination Diameter at surface =0.018x3x10
  • Illumination Diameter at surface =0.54 Meter.

Thumb Rules-14 ( Quick Reference Demand-Diversity Factor)


 

Diversity Factor (NBC)

Type of Load

Type of Building

Individual House Hold , Individual Dwelling of a Block Small Shops, Stores, Offices & Business Premises Small Hotels, Boarding Houses, etc
Lighting 66% of  total current demand 90% of total current demand 75% of total current demand
Heating and power 100% of total current demand up to 10 A+ 50 % of any current  demand in excess of 10 A 100% of full load of largest Appliance + 75% of Remaining appliances 100% of full load of largest appliance+ 80% of second largest appliance + 60% of remaining appliances
Cooking appliances 10 A +30 percent full load of
connected cooking appliances in excess of 10 A + 6 A if socket-outlet incorporated in the unit
100 % of full load of largest appliance + 80% of full load of second largest appliance + 60% of full load of Remaining appliances 100 % of full load of largest appliance + 80 % of full load of second largest appliance + 60% of full load of Remaining appliances
Motors (other than lift motors which are subject to special consideration)   100% of full load of largest Motor + 80% of full load of second largest motor 100 % of full load of largest Motor + 50%of full load of remaining motors
Water heater (instantaneous) 100 % of full load of largest Appliance + 100%of full load of second largest appliance + 25 %of full load of remaining appliances 100 % of full load of largest Appliance + 100%of full load of second largest appliance + 25 %of full load of remaining appliances 100 % of full load of largest Appliance + 100%of full load of second largest appliance + 25 %of full load of remaining appliances
Water heater (thermostatically controlled) No diversity    
Standard arrangements of final circuits in accordance with good practice 100 percent of the current demand of the largest circuit + 40 percent of the current demand of every other circuit 100 percent of the current
demand of the largest circuit + 50 percent of the current demand of every other circuit
 
Socket outlets other than above and stationary equipment other than those listed above 100% of the current demand of the largest point + 40%of the current demand of every other point 100% of the current
demand of the largest point+ 75 % of the current demand of every other point
100%of the current demand of the largest point
+ 75%of the current demand of every point in main rooms (dining rooms, etc) + 40 % of the current demand of every other point
After calculating the electrical load on the above basis, an overall load factor of 70 to 90 percent is to be applied to arrive at the minimum capacity of substation.

 

Demand Factors (As Per Table 220.42  NEC)

Type of Occupancy Electrical Load Demand Factor
Dwelling units First 3000 VA 100%
From 3001 to 120,000 VA 35%
Remainder over 120,000V A 25%
Hospitals First 50,000 VA or less 40%
Remainder over 50,000 VA 20%
Hotels and motels, including apartment houses without provision for cooking by tenants First 20,000 VA 50%
20,001 VA to 100,000 VA 40%
Remainder over 100,000 VA 30%
Warehouses storage First 12,500 VA 100%
Remainder over 12,500 VA 50%
All others Total volt-ampere 100%

 

Non-dwelling Lighting Loads Demand Factors (As Per 220.44  NEC)

Type of Occupancy Electrical Load Demand Factor
Non-dwelling Receptacle Loads First 10KVA 100%
Remainder over 10KVA 50%

 

Diversity (The Electricians Guide 5th Edition by John Whitfield)

Type of final circuit Type of premises
Households Small shops, stores, offices Hotels, guest houses
Lighting 66% total demand 90% total demand 75% total demand
Heating and power 100% up to 10 A + 50% balance 100%X + 75%(Y+Z) 100%X + 80%Y + 60%Z
Cookers 10 A + 30% balance + 5 A for socket 100%X + 80%Y + 60%Z 100%X + 80%Y + 60%Z
Motors (but not lifts)   100%X + 80%Y + 60%Z 100%X + 50%(Y+Z)
Instantaneous water heaters 100%X + 100%Y + 25%Z 100%X + 100%Y + 25%Z 100%X + 100%Y + 25%Z
Thermostatic water heaters 100% 100% 100%
Floor warming installations 100% 100% 100%
Thermal storage heating 100% 100% 100%
Standard circuits 100%X + 40%(Y+Z) 100%X + 50%(Y+Z) 100%X + 50%(Y+Z)
Sockets and stationary equip. 100%X + 40%(Y+Z) 100%X + 75%(Y+Z) 100%X + 75%Y + 40%Z
X = the full load current of the largest appliance or circuit
Y = the full load current of the second largest appliance or circuit
Z = the full load current of the remaining appliances or circuits

 

Diversity factor for Building (Horizon Power)

No of customer Diversity factor
1 3
2 2.57
3 2.2
4 2
5 1.89
6 1.8
7 1.74
8 1.71
9 1.69
10 1.64
11 1.61
12 To 14 1.57
15 To 17 1.5
18 To 20 1.46
21 To 23 1.42
24 to 26 1.4
27 To 29 1.38
30 To 59 1.37
≥60 1

 

Demand Factor (The Electricians Guide Fifth Edition) by John Whitfield)

Area Demand Factor
Office / School 40%
Technical Blocks / Hospital 50%
Air Port / Banks / Department Store / Shopping Center / Public Place 60%
Restaurants / Factories (for 8 Hours Shifts) 70%
Workshops / Factories (for 24 Hours Shifts) 80%
Arc Furnace 90 % TO 100%
Arc Welding 20 % TO 50%
Compressor 20 % TO 50%
Conveyor Crane 90 % TO 100%
Had tool 20 % TO 40%
Paper Mills 50 % TO 70%
Induction Furnace 80 % TO 100%

 

Demand Factor As per No of Appliances

No of Appliances (A) Less than 3.5 KW (B) 3.5 KW to 8.5 KW (C) Less 12 KW
1 80% 80% 8%
2 75% 655 11%
3 70% 55% 14%
4 66% 50% 17%
5 62% 45% 20%
6 59% 43% 21%
7 56% 36% 22%
8 53% 35% 23%
9 51% 34% 24%
10 49% 32% 25%
11 47% 32% 26%
12 45% 32% 27%
13 43% 32% 28%
14 41% 32% 29%
15 40% 32% 30%
16 39% 28% 31%
17 38% 28% 32%
18 37% 28% 33%
19 36% 28% 34%
20 35% 28% 35%
21 34% 26% 36%
22 33% 26% 37%
23 325 26% 38%
24 31% 26% 39%
25 30% 26% 40%
26 To 30 30% 24% 15KW+1KW for Each
31 To 40 30% 22%
41 To 50 30% 20% 25KW+0.75KW for Each

 

51 To 60 30% 18%
More Than 60 30% 16%
       

 

Lighting Demand for Building (As per NBC)

Lighting demand for buildings should be considered as per type of building.
Where nothing is specified, for lighting demand of any type of building a maximum of 13 W/m2 of all built-up areas including balconies.
Covered parking areas may be considered at 3.23 W/m2 including balconies, service areas, corridors, etc, may be considered with very basic diversity of 80 % to 100 %.
Power requirements shall be considered at least 55 W/m2 with an overall diversity not exceeding 50 %. These shall be excluding defined loads such as  lifts,  plumbing  system,  fire  fighting  systems, ventilation requirement, etc.

Thumb Rules-13 ( Quick Reference Earthing -CPWD)


 

Earthing Strip for Sub-Station Equipment

CPWD-TABLE VIII

Type of Installation Earth Electrode Earth Strip
Indoor sub-station with HT panel, Transformer capacity up to  1600  KVA, LT panel, D.G Set. Copper Plate 25 x 5 mm Copper Strip
Indoor sub-station with HT  panel, Transformer  capacity  above  1600  KVA, LT panel, D.G Set Copper Plate 32 x 5 mm Copper Strip
HT Outdoor sub-station Copper Plate 25 x 5 mm Copper Strip
LT Indoor sub-station with generator Copper Plate 25 x 5 mm Copper Strip
LT   switch   room   with Main   LT  D.B Copper Plate 20 x 3 mm Copper Strip

 

Neutral Earthing of Transformers and Generators

CPWD-TABLE VIII

Type of Installation Earth Electrode Earth Strip for Neutral
Transformer  of  capacity  up  to  1600 KVA Copper Plate 25 x 5 mm Copper strip
Transformer  of  capacity  above  1600  KVA Copper Plate 32 x 5 mm Copper strip
Generating set of all capacity Copper Plate 26 x 5 mm Copper strip
Type of Installation Earth Electrode Earth Strip for Neutral
Transformer  of  capacity  up  to  1600 KVA Copper Plate 25 x 5 mm Copper strip

 

Earthing Strip for Bus Trunking and Rising Main

CPWD-TABLE VIII

Type of Installation Material of Main Conductor Earth Strip
Bus   trunking   up   to   2500   Amp   capacity Copper/ Aluminum 2 No 25 x 5 mm Copper Strip
Bus   trunking   above   2500   Amp   capacity Copper/ Aluminum 2 No 32 x 5 mm Copper Strip
Bus  trunking for  generating set and LT panel Copper/ Aluminum 2 No 25 x 5 mm Copper Strip
Rising main up to 400 Amp capacity Copper/ Aluminum 2 No 20 x 5 mm Copper Strip
Rising  main  above  400  Amp  and  up to 800 Amp Copper/ Aluminum 2 No  20 x 3 mm Copper Strip

 

The Size of Earthing conductors

As per CPWD

Size of phase conductor Size of Earthing conductor of the same material as phase conductor
Up to 4 sq.mm. Same size as that of phase conductor
Above 4 sq.mm. up to 16 sq.mm. Same size as that of phase conductor
Above 16 sq.mm. up to 35 sq.mm. 16 sq.mm.
Above 35 sq.mm. Half of the phase conductor

 

Materials and Sizes of Earth Electrodes

CPWD-TABLE IX

Type of Electrodes Material Size
Pipe GI medium class 40 mm dia 4.50 m long (without any joint)
Plate (i) GI 60 cm x 60 cm x 6 mm thick
(ii) Copper 60 cm x 60 cm x 3 mm thick
Strip (i) GI 100 sq. mm section
(ii) Copper 40 sq. mm section
Conductor (i) Copper 4 mm dia (8 SWG)
Note :  Galvanization of GI items shall conform to Class IV of IS 4736 : 1986.

 

Minimum Sizes of Earthing Conductors for Use Above Ground

CPWD- TABLE X

Material and Shape Minimum Size
Round copper wire or copper clad steel wire 6 mm diameter
Stranded copper wire 50 sq. mm or (7/3.00 mm dia)
Copper strip 20 mm x 3 mm
Galvanized iron strip 20 mm x 3 mm
Round Aluminum wire 8 mm diameter
Aluminum strip 25 mm x 3 mm

 

Minimum Sizes of Earthing Conductors for Use Below Ground

CPWD- TABLE XI

Material and Shape Minimum Size
Round copper wire or copper clad steel wire 8 mm diameter
Copper strip 32 mm x 6 mm
Round galvanized iron wire 10 mm x 6 mm
Galvanized iron strip 32 mm x 6 mm

 

Selection of Type of Earthing Electrodes

As per CPWD

Type of electrode Application
GI pipe Internal electrical installations like Distribution Board and Meter Boards (in residential quarters), feeder pillars and poles etc.
GI plate (i) For Fire Fighting pumps and water supply pumps.
(ii) Lightning conductors.
Copper plate Neutral earthing of transformers/ generating sets.
Strip/ Conductor Locations where it is not possible to use other types.

 

Number of Earth Electrodes

As per CPWD

Equipment No of Earthing
For neutral earthing of each transformer 2 sets
For body earthing of all the transformers, 2 sets
HT/LT Panels and other electrical equipment
in the Sub-station/ power house
For neutral earthing of each generating set 2 sets
For body earthing of all the generating sets, 2 sets
LT panels, other electrical equipment in the generator room

 

Size of protective conductor

As per CPWD

Size of phase conductor Size of protective conductor of the same material as phase conductor
Up to 16 sq.mm. Same as Phase Conductor  Size
16 to 35 sq.mm. 16 sq.mm.
35 sq.mm Half Size of Phase Conductor

 

Earthing Points

As per CPWD

Earthing Description
Location for Earth Electrodes Normally  an  earth  electrode  shall  not  be  located  closer  than  1.5  m  from  any  building.
Installation of Pipe Pipe electrode shall be buried in the ground vertically with its top at not less than 20 cm below the ground level
Installation of Plate Plate electrode shall be buried in ground with its faces vertical, and its top not less than 3.0 m below the ground level.
The strip or conductor The strip or conductor electrode shall be buried in trench not less than 0.5 m  deep
More Earthing Electrode When more than one electrode (plate/pipe) is to be installed, a separation of not less than 2 m shall be maintained between two adjacent electrodes.
Earthing Electrode  If the electrode cannot be laid in a straight length, it may be laid in a zigzag manner with a deviation upto 45 degrees from the axis of the strip. It can also be laid in the form of an arc with curvature more than 1 m or a polygon
Earthing Pit Cover A cast iron / MS frame with MS cover, 6 mm thick, and having locking arrangement shall be suitably embedded in the masonry enclosure.
Earthing Wire Protection  The  earthing  conductor  from  the  electrode  up  to  the  building  shall  be  protected  from mechanical injury by a medium class, 15 mm dia. GI pipe in the case of wire, and by 40 mm dia, medium class GI pipe in the case of strip. The protection pipe in ground shall be buried at least 30 cm deep (to be increased to 60 cm in case of road crossing and pavements)
No of Earthing Conductor Two protective conductors shall be provided for a switchboard carrying a 3-phase switch gear there on.
Earthing Electrode  No earth electrode shall have a greater ohmic resistance than 5 ohms as measured by an approved earth testing apparatus. In rocky soil the resistance may be up to 8 ohms.
Earthing Resistance Each   of   the   earth   stations   should   have   a   resistance   not   exceeding   the product  given  by  10  ohms  multiplied  by  the number  of  earth  electrodes  to be  provided  therein.  The  whole  of  the  lightning  protective  system,  including any  ring  earth, should  have  a  combined  resistance  to  earth  not  exceeding 
10 ohms without taking account of any bonding
More Earthing Resistance If the value obtained for the whole of the lightning protection system exceeds 10 ohms, a reduction can be achieved by extending or adding to the electrodes, or by  interconnecting  the  individual  earth  terminations  of  the  down  conductors  by  a  conductor

 

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