LED Grow LIGHTS

Artificial lighting for plant cultivation is an important factor, which determines the cost and nutritional quality of Greenhouse vegetables. The goal is to provide indoor plants with light that mimics natural sunlight and gives them everything they need to thrive. LED lighting has a capability of growing plants with computer accuracy emitting short wavelength that effects plants and insects. LEDs have consistently proven themselves to be tools extremely efficient for indoor farming and greenhouses.

How do plants grow with LED lighting?

According to Zukauskas etall; Plant’s basic need for light resides within three spectral ranges responsible for photosynthesis, phototropism and photomorphogenesis are three important process in a plants development, respectively. Photosynthesis requires light in the vicinity of the absorption peaks of chlorophylls a and b at 662 nm and 642 nm, respectively), which are the most important photosynthetic pigments. Phototropic processes, which control motion of plant organs in response to light and ensure optimization of biophysical and biochemical reactions, are triggered by light with wavelengths in the range of 400–500 nm. Finally, plant morphogenesis, encompassing processes such as shooting, pigment synthesis and healthy plant development, depends on far-red radiation in the range of ~730–735 nm.

                                            

Generally speaking, the more light the better, but it needs to be the right light. Blue and red wavelengths are more beneficial in plants growth while greens and yellows being least beneficial
are most likely to be reflected back. Grow LEDs are designed to provide light intensity in the range from 400-500nm and 590nm to 720nm to completely cover the requirements for Chlorophyll a and b. This is the range of light that is most critical for flowering. Thousand watt HPS bulbs are relatively poor in intensity throughout the range of red light. By minimizing light energy in the yellow and orange spectrum, the Grow LEDs avoids most of the heat energy losses that are linked to a wide variety of grower problems.

Application area of LED plant growth light

• suitable for the greenhouse lighting, horticulture, Hydroponics, Farm/Flower
• Exhibition/Garden.
• Accelerate the growth of plant, delay or hasten of flowering, germinate
• Pest control and draw of harmful insect
• Sterilization and disinfection of seed.

Benefits of LED Grow lights

Light-emitting diodes (LEDs) present a versatile alternative for artificial greenhouse lighting with numerous advantages.
• Energy Savings with targeted light output: Comparing HID lights, LED grow lights use around 75% less energy. For efficient and healthy growth of plants, led grow light are designed to deliver the colors of light with least power consumption. Unlike other grow lights, which produce inefficient lights for plants, LED lights produce light in the red and blue spectra which plants use for photosynthesis.
• Low Heat Signature: Very little heat is emitted by LED grow lights and mostly the chips are kept cool with modest built-in fans. There is no danger of plants and seedlings getting burned or getting excessively dehydrated. They’re cool enough that crop can be grown underneath them.
• Longevous source of light: Around 50,000 to 100,000 hours of lifespan is offered by LED grow lights. Incandescent and HID lighting don’t have such a long life. HPS grow lights needs replacement as often as every 5000 hours.
• High Efficiency: Nearly two-third of the light produced by HID lamps goes wasted as heat or as light and is not used in photosynthesis. At best, HID lights produces only 35% efficient light. With a good LED Grow Lights, 90% or better efficiency can be achieved as they produce light within the spectra of Photosynthetically Active Radiation (PAR).
• High Payback: These grow life is normally 100,000 hours with full day operation and no degradation in light output. Initial purchase of  led lights will cost a little more money but it will be make up by the long term savings from reduced operational costs and the added yield and growth from the plants. There will be savings over the bulb/ballast replacement costs and expensive heating removal systems of other indoor growing lights.
• Eco-Friendly: Lead or mercury is not found in LED bulbs and they don’t emit harmful radiations like UV radiation, Infrared light.
• Safe & Quiet: LED grow lights don’t offer traditional lighting system risk like shock, fire and burns. They are completely silent as they don’t produce buzzing or humming sound which is a typical feature of ballasts in fluorescent or HID lamps.

Reference
1. Zukauskas A, Shur M S and Gaska R 2002 Introduction to Solid-State Lighting (New York: Wiley)

Energy Efficient Motors

In today’s power scenarios we are facing a major power crunch. Day by day gap between demand and supply of electric energy is widening at the rate of 3 %. Bridging this gap from the power supply side is a very difficult and expensive proportion. The only variable way in handling these crises, in addition to the capacity, is the efficient use of available energy which is possibly by using energy efficient drives. Electric motors are industries basic need. Industries consumes about 50% of the power generated in the country and electric motors consume around 70% of the total electricity used in the industrial sector. Majority of the motive loads use squirrel cage induction motor as the driving element  

Most of the motors used in industries are oversized. Even when proper sized motors are used, they are not fully loaded to their capacities. This result into poor efficiency of the motor must be a part of any comprehensive energy conservation effort. This conservation is possible by using the energy efficient motors in place of standard motors .as motors are the largest user of the electrical energy, even small efficiency improvements can produce very large saving across the country. Energy conservation measures taken by individual consumers in this direction will improve the national economy and benefit the environment on global scale.

Electric motor efficiency is the measures of its ability to convert kilowatt of electric power supplied to the motor terminal and the horsepower of mechanical energy taken out of the motor at the rotating shaft. The inefficiency of a motor is the losses taking place in the conversion of electrical energy to mechanical energy.

EFFICIENCY (%) = Watts output

                                  --------------   *100

                                   Watts input

                                =746*HP*100

                                  ----------------

                                  V*I * Power factor

                             =   Input-losses

                                ----------------  *100

                                      Input

Energy-Efficient Motors

An energy efficient motor produces the same shaft output power (KW), but draws less input power (kw) than a standard (lower efficiency) motor. Hence energy efficient motor consumes less electricity than comparable standard motor for any given load.

Energy efficient motors are manufactured with higher quality materials and techniques; they usually have higher services factors and bearing lives, less waste heat output and less vibration

Energy efficient motors must have nominal full load efficiencies that meet or exceed the NEMA standards.

In 1994 the National Electrical Manufacturers Association (NEMA) issued definitions for “energy efficient motors,” which are from 2 to 6 percentage points higher in efficiency than conventional motors. These definitions cover all standard combinations of horsepower (1 to 500 HP), enclosure, and synchronous speed (900 to 3,600 RPM). The efficiency values for T-frame, single-speed, foot-mounted, continuous-rated, polyphase, squirrel-cage induction motors conforming to NEMA designs A and B can be found in NEMA’s “Table 12-10.”

CEE Premium-Efficiency Motors

The Consortium for Energy Efficiency (CEE) has worked with motor manufacturers and experts to develop a new set of guidelines that are even higher than NEMA levels for energy-efficient motors. Motors that meet these guidelines (referred to as “CEE Premium Efficiency ” motors) have 0.8% to 4% higher efficiency than the energy-efficient motors required under EPACT. 890123456789012345678901212345678901234567890123456789

It goes without saying that more-efficient motors will consume less energy and reduce their owners' electric bills over the long run, but a rapid return on investment is most likely when the motors operate at high duty cycles. Motors that operate intermittently may or may not save enough to justify replacement except in cases where utility rates are especially high. But, in evaluating motors that operate at a high duty cycle, or continuously, replacement with energy-efficient motors can usually result in very rapid payback, and save many times their initial cost.

Design differences between Standard and Efficient Motors

Energy-efficient AC motors produce the same output as standard motors, but require less electrical input because they generally are better designed, with closer tolerances, better materials, and improved manufacturing quality. In addition, they usually operate at lower temperatures, last longer, and tolerate abnormal operating conditions better. Although a tremendous variety of AC motors exists, three-phase squirrel-cage induction motors account for over 90 percent of installed motor horsepower. Simple, rugged, reliable, and cheap, they are found in a wide variety of commercial and industrial uses. Energy- efficient motors generally cost 15 to 30 percent more than standard units, although costs for both vary widely. Efficient motors last on average about 15 years, and proper maintenance can extend their lifespan significantly. New energy-efficient induction motors are from one to over six percent more efficient than new standard motors. Because a motor consumes energy worth 4 to 10 times its own cost each year, energy-efficient motors often make economic sense in a wide variety of situations.

It is usually appropriate to consider them when

·       designing new facilities.

·       modifying existing installations or processes.

·       procuring prepackaged equipment.

·       considering rewinding failed motors.

·       replacing oversized (underloaded) motors.

·       setting up an energy management or preventive maintenance program.

·       utility rebates are available.

Efficient motors usually feature some of the following design improvements (individual features depend on the manufacturer and model):

_ 20% to 60% more copper in the windings

_ More and thinner laminations of higher quality steel—35% more electrical

   steel

_ Optimized air gap between stator and rotor

_ More efficient rotor bar designs

_ Improved overall design to reduce windage, friction and stray load losses

_ Reduced fan losses

_ Better quality control during manufacturing

_ Longer core to reduce I2R (resistance) losses

Commercial Induction Motor Classification By Electrical And Mechanical Properties

 The development of the double cage rotor created a  versatility  in the induction motor rotor design that has lead to a variety of slip torque characteristics. By properly proportioning the double cage   winding manufacturers have developed numerous variations of the single or normal cast iron design   .these variations result in the starting torque greater or less than the normal design and also in the reduced starting currents. In order to distinguish   between the various available type, the national electrical manufacturer association has developed a letter system in which each SCIM type is manufactured in accordance with a particular design standard and is placed in a certain class letter  the electrical and mechanical rotor construction properties of the 5 NEMA classes of SCIM is  summarized in the table:

SCIM  Motor Characteristic  By NEMA Class  Letter

NEMA CLASSES	STARTING TORQUE	STARTING CURRENT	SPEED REGULATION	CLASS NAME FOR MOTOR
A	1.5-1.75	5-7	2-4	Normal
B	1.4-1.6	4.6-5	3-5	General purpose
C	2-2.5	3.5-5	4-5	Double cage high torque
D	2.5-3	3-8	5-8,8-13	High resistance

Class A Letter SCIM

The class a motor is a normal or standard SCIM manufactured for constant speed use  .it has large slot areas for good heat dissipation capacity and fairly deep slot rotor bars during the starting period, the current density is high near the rotor surface during the running period the current density is distributed fairly uniformly. This difference makes for some high resistance and low reactance at starting resulting in the starting torque from 1.5 to 1.75 times the rated torque.

 A fairly high starting torque and rotor resistance produces a fairly rapid acceleration towards rated current and speed.

The class A SCIM has the best speed regulation but its starting current, unfortunately varies from 5to7 times the normal rated current, making it less desirable for line starting , particularly in large capacity sizes. In sizes below 5 hp, however the class A SCIM is frequently started across the line. Because of the rapid acceleration, it does not produce extremely high current effects, which are undesirable.

Class Letter B SCIM

The class B SCIM is some times called the general-purpose motor .its slip torque curve resembles the normal class A motor quite easily. Its rotor is embedded some what deeper in slots than the normal class a SCIM and the greater depth tends to increase the  starting and running rotor reactance . The increase in the reactance at the starting reduces the starting torque a little bit but reduces the  starting current  as well.

A slightly lower value of the field excitation is also used on this motor to produce the reduced starting current. Starting current varies from 4.5-5 times the rated current, in the large sizes, above 5 hp, reduced voltage starting is still employed with class of motor. Because of their some what lower starting current and almost equal characteristics, class B SCIM are generally preferred over the class A Motor in the large sizes. Most SCIM are manufactured as class B. Typical applications include driving centrifugal pumps, machine tools and blowers.

 

 Class Letter C SCIM

    The class c is a double cage rotor motor that develops a high starting torque from 2 to 2.5 times the rated torque compared to class a and b and a lower starting current from 3.5 to 5 times the rated current. Because of its high starting torque, it accelerates rapidly. When used with heavy, high inertia loads, however the thermal dissipation of the motor is limited since most of the current concentrates in the upper winding.

                   Under condition of frequent starting, the rotor may have a tendency to over heat    it is better suited to sudden large loads but of a kind having low inertia. This motor continues to develop increased torque with increased slip all the way to maximum torque at standstill .the class C SCIM, however, has poorer speed regulation than class B and A Class c motor application are limited to conditions where starting is difficult, such as in pumps and piston type compressor

.

Class Letter D SCIM

The class letter d type    is known as a higher torque, high resistance rotor motor. The rotor bars are constructed of a high steel alloy, and they are placed in the slots closed to the surface or are embedded in small diameter slots. The ratio of rotor resistance to reactance at starting i8s high than in motors of the preceding class letters .the starting torque of these motors approaches 3 times the rated current, with a starting current from 3 to 8 times the rated load, depending on design. This motor is designed for heavy starting torque duty. But again like the type C it is not recommended for frequent start because of the small cross section and poor thermal dissipating ability, it finds it best5 application in the load such as  shears or punch presses, which call for higher torque with the application of a sudden load. The speed regulation of this motor is poorer of them all.

Class Letter F SCIM

The class f SCIM is known as a double cage, low torque rotor motor. It is designed as the low starting current motor since it is requires the lowest starting current of the all classes from a to d. the class F SCIM has high rotor resistance in both its starting and running winding, tending to increase the starting and running current.

The class F motor was designed to replace the class B motor .the class F produces the starting current of about 1.25 times the rated torque and low starting currents from 2 to 4 times the rated current.

This class motors are manufactured generally In size above 25 hp for across the line service because of the relatively    high starting and running rotor resistance, these motor have poorer speed regulation  then the class B motors, low over load capacity n and usually low running efficiency, when started with light load, however the low starting currents eliminates the necessity for reduced voltage equipment, even in large sizes.

When To Consider Energy Efficient Motors

In general Energy Efficient Motors should be considered in the following circumstances;

(1)-Making electric motors energy efficient has never had greater incentives than today.

(2)-New installations, both separate and as part of packages such as HVAC system and low voltage system.

(3)-When major modifications are made to facility or a process

(4)-Instead of rewinding older, standard motors.

(5)-As part of a preventive maintenance or energy conservation plan.

(6)-Standard motors operating at low load replaced by low rated energy efficient motors

(7)-Standard motor is old, number of rewinds are more and frequent.

Features Of Energy Efficient Motors

*Highest efficiency.

*Lower operating cost.

*Lower demand charges.

*It has higher overload capacity.

*Suitable for operations at higher ambient temperature.

*Fewer power factor corrections

*Lower branch circuit losses.

*Reduced air-conditioned load.

*Saving increases with time

*Confirmation with NEMA standards of protection and control.

*Cooler and quieter operation

*Longer insulation life. Energy Efficient Motor’s winding run about 20⁰ C cooler which increases insulation life by four times.

*Improved bearing life: Energy Efficient Motor bearings run about 10⁰ C cooler than standard motors bearings, which doubles the life.

*Less starting thermal stress

*Higher service factor.

*Better suited for energy management systems.

*Energy Efficient Motor performs better under adverse conditions of abnormal voltage conditions like unbalanced voltages.

*Efficiency of Energy Efficient Motor remains almost constant from 50% to 100% of load

Energy Efficient Motors are manufactured some times using the same frame as standard motors, but can have any or all of the features as enumerated below to comply with the standard for energy efficient motors:

·       Higher quality and thinner steel laminations in the stator.

·       More copper in the windings.

·       Optimized air gap between the rotor and stator.

·       Closer matching tolerances.

·       Greater length of rotor and stator frame.

  

Efficiency Considerations    

While comparing two motors, consistent measures of efficiency should be used. “Nominal” efficiency is the best. This value is obtained through standard testing. Minimum or guaranteed efficiency is slightly lower to take into account typical variations in efficiency within a population of motors

                   Load losses and hence efficiency of any motor varies in accordance with motor loads. General design motors obtain their maximum efficiency at approximately 75% of their rated load .the motor efficiency increases as load increases and motor efficiency will reach its peak value at around 75% load. The efficiency of the motor with a load that is beyond 75% is dependent on the motor manufacturers design.

An A.C 3 phase induction motor has five components of energy losses, which are presented below:

Percentage Of Motor Components Loss

(1)-Stator Copper Loss                     37%

(2)-Rotor Copper Loss                     18%

(3)-Iron Loss                                     20%

(4)-Friction & Windage Loss            9%

(5)-Stray Losses                                16%

   

Copper Loss

Depends on the effective resistance of motor winding:

*Caused by the current flowing through it.

*It is equal to I²R.

*Proportional to load.

* Is equal to statorI^2 R loss+ rotor I^2R   loss.

Iron Loss

Depends on the magnetic structure of the core and results from a combination of hysteresis and eddy current effect due to changing magnetic fields in the motors steel core.

*Voltage related.

* Constant for any particular motor irrespective of load.

Friction And Windage Losses

*These losses occur due to the friction in the bearing of the motor.

* The windage losses of the ventilation fan, other rotating element of the motor.

* Depends on the bearing size, speed, type of bearing, lubrication used and fan blade profile.

*Constant for given speed irrespective of load.

Stray Losses

*Very complex and load related.

*Arise from harmonic and circulating current.

*Manufacturing process variations can also add to stray loses.

 

Efficiency Improvement

Efficiency is the measure of the effective ness with which a motor converts electrical energy into mechanical energy, which is measured by watts input versus watts output. In the conversion process, watts are lost by transformation into heat, which is dissipated through the frame. To improve efficiency:

Watt losses must be reduced through optimized design,

Improved material section and quality control

To reduce watt loss the main areas are:

1-Iron

2-Stator

3-Rotor

4-Friction and windage

5-Stray load loss

Iron

There are two ways to improve the efficiency

*Improved steel properties

Standard motors use low carbon laminated silicon steel for the rotor and stator. Such steel typically has electrical losses at 6.6 watts/kg. High efficiency motors are built with high-grade silicon steel which typically reduces hysteresis and eddy current losses by half to only about 3.3-watt/ kg.

*Thinner laminations

Reducing laminations thickness in rotor and stator steel also lowers eddy current losses. Improved insulation between laminations, when applied with enhanced quality control further reduces these losses. The use of thinner laminations results into decrease in core losses from 10 to 255 depending on method of processing the laminations steel and the method of assembling the magnetic core. Longer core adds more steel to design, which reduces the losses due to lower operating flux densities.

Stator And Rotor Copper Loss

This can be done by the two ways:

*Increased conductor volume

Older standard motors employ aluminum or copper conductor of a size no longer than that needed to deliver the required horsepower. High efficiency motors utilize bigger copper conductor to lower the winding resistance with the conductor sized 35 to 40% larger than needed to simply satisfy the motor output horse power requirement.

*Modified slot design

To accommodate the larger volume of copper in the windings and required additional slot insulations, the slot crossectional area is increased. Longer stator core length yields an important additional benefit in the form of improved motor power factor.

Friction And Windage Loss

More efficient fan design

*Use of low loss fan design reduces losses due to air movement.

*Use of better quality bearings and lubricating materials reduces friction losses.

*In energy efficient motors the heat producing losses are low hence it is possible to reduce ventilation requirements which in turn will reduce the windage losses resulting into further improvement of the efficiency.

* Energy efficient motor design incorporates a small cooling fan resulting into quieter operation.

Stray Losses

*Use of optimized design and strict quality control procedures minimizes the stray losses.

*Proper proportionate of rotor and stator slots.

*Having small slot opening.

*Using optimum air gap.

Air Gap

Narrowing air gaps

Air gap dimensions are optimized to reduce magnetizing currents and associated losses resulting into improvement of power factor.

There are some other methods by which we can improve the efficiency these are:

*Use Of High Permeability Steel

Use of high permeability steel will ensure lower mmf for passing the same amount of flux and resulting into reduction in magnetizing current.

*Inner Laminations Insulations

Insulated laminations gives rise to eddy current losses. High quality insulation like hybrid organic, inorganic coating of L3 type should be used, which help to keep the eddy current losses to minimum. These insulation materials can withstand very high annealing temperature. In excess of 700^O F and can be used on semi finished sheet.

*Rotor Turning

To ensure air gap concentricity, it is common practice to turn the rotor to size from the motor shaft centers. This can burr over the laminations and turn the surface of rotor into a conducting sheet for many years this was considered as un important because the rotor operated at slip frequency and it would limit this loss.

More recent research work done by Mueller et al has shown, however that the loses on the rotor surface are predominantly high frequency losses caused by stator slotting. This results in the high frequency flux ripple which can be 10% of the fundamental flux and the iron losses arising from a23rd harmonics can be more than twice that of the fundamental frequency iron loss.

The best solution is to punch laminations to size, but this is not usually practical on larger sizes. If rotor turning is possible then means have to be developed for separating the laminations at the rotor surface during and after turning operations.

*Mechanical Stresses

Mechanical stress in sheets/laminations can increase the losses. The stator frame exerts a radial force on the stator core. If radial force is increased beyond a certain limit, the iron losses increases sharply. So ways have to be found for anchoring the core back to the frame with minimum radial force.

*Rotor Die Casting

 The circumference of the punched rotor slot presents a un insulated surface area when the rotor is die cast with conductors it forms conducting bridges between the adjacent laminations. These have the effect of increasing the stray losses and eddy current losses. Worse the conductivity of the bridges is highly variable and gives rise to inconsistencies in product performance for many years. The method to minimize this problem has been to deep die cast rotors into the cold water immediately after casting and hope that the differential concentration rates of the steel and aluminum will cause to separate. More recently a Japanese manufacturer has published details of the rotor slots insulation method, which makes use of the resistive residues left by a phosphate loaded lubricant oil and very consistent results are claimed. Theoretical and practical tests and efforts are continuing in this field.

*Copper Rotor Motor

Incorporation of copper for conducting bars and end rings of the induction motors in place of aluminum would results in attractive improvement in motor energy efficiency