Difference between UPS & Inverter

• We are heavily dependent upon appliances that run on electricity such as fans, lights, AC, fridge, Computer and so on.
• Whenever there is a power cut, electricity supply to these appliances is cut off and they stop working. However, if we have backup supply devices such as UPS and inverter, we can ensure Power supply to appliances and not bothered with power cuts.
• However, people remain confused with the difference between a UPS and an inverter because UPS and inverters both are providing back up power supplies during main power outage.
• Inverters are preferred more for general electric appliances whose working does not get affected by extended delays in power supply.
• UPS are used for electronics appliances such as computer, servers, workstations, Medical Equipment which perform critical task and cannot tolerate delays in power supply.
• An off-line ups (the standard) switch to the batteries in 3 to 8 milliseconds, after the main power has been lost. While Inverter changes over in about 500 milliseconds.

UPS:

• UPS means uninterrupted power supply.
• Uninterruptible power supply (UPS) provides uninterrupted power to the equipment. It means switching time from power cut to battery power is vey less hence important and critical equipment like computer, desktop .Medical Instruments is not switch off and we can lose data.
• A UPS is a complete system that is consisting of many parts that include batteries, a charge controller, circuitry any transfer switch for switching between the mains and back-up battery, and an inverter. An inverter is needed because the battery can only store DC power and we need to convert that back to AC in order to match the appliances connected in the main power line.
• UPS= Battery charger + Inverter
• UPS is nothing but inverter with inbuilt battery charger.

• UPS give backup only 10 to 20 minutes. The main intention of it is to provide backup only for small time so that you can save the programs and data.
• UPS also gives protection against line abnormalities like Surge, Voltage fluctuation, Under Voltage, Over Voltage, Spike, Noise.

Inverter:

• Inverter circuit simple converters battery DC current to AC and supply
• In inverter inverts the direct current to an alternating current. During normal condition electrical supply is direct feed to the Load. It also takes the supply from the AC source and charges the battery.
• During the power cut, the inverter receives the supply from the battery and convert it DC to AC Power and provides the power supply to the electrical equipment.
• Inverters purpose is to provide power backup to total home appliances, lights, fans.
• Inverter uses flat plate or tubular battery to store electricity. So it requires continuous maintenance, needs to fill the distilled water toppings at regular intervals of time.
• Inverter does not give protection against line abnormalities

Conclusion:

• The UPS and inverter both provide the backup supply to the electrical system. Two major differences between the UPS and inverter are that
• The switching of UPS from the main supply to the battery is very immediate so it is used to provide backup power of important or critical electronics equipment. whereas in inverter the switching from mains supply to battery takes times so it used to provide less important electrical equipment.
• The UPS provide protection to the load against Spike, Voltage fluctuation, Noise while Inverter does not provide any protection to the load.

Simple Calculation of Flood Light, Facade Light, Street Light & Signage Light

Simple Calculation of Flood Light, Facade Light, Street Light & Signage Light:

Introduction:

• Outdoor Lighting can be classified according to the location where it can be installed or its function which use for highlight landscape area.
• Outdoor Lighting can be classified as

1. Flood Lighting,
2. Facade Lighting and
3. Signage Lighting
4. Street Light

(A) General Outdoor Flood Lighting:

• Normally Pole mounted floodlights are used to illuminate general lighting area of parking lots and storage yards. 
• There are three factor should be consider while designing of outdoor flood lighting.

1. Mounting Height.
2. Spacing
3. Aiming Distance.
4. Horizontal Aiming.

1) Mounting Height:

• Mounting height should be one half the distance across the area to be lighted.
• If the area to be lighted is 16 Meter, the lowest recommended mounting height is 8 Meter. 
• Mounting height = 1/2 distance to be lighted
• 1/2 (16 Meter.) = 8 Meter. 

2) Spacing:

• When more than one Luminar / pole is required than distance between two adjacent luminar / Pole is 4 times Mounting height of luminar /pole.
• If the mounting height of luminar /Pole is 8 Meter than distance between adjacent Luminar is 32 Meter.
• Pole Spacing = 4 x mounting height.
• 4 (8 Meter pole) = 32 Meter between poles

3) Vertical Aiming:

• The fixture should be aimed 2/3 of the distance across the area to be lighted and at least 30 degrees below horizontal. 
• If the area to be lighted is 16 Meter across, the recommended aiming point is 10.6 Meter.
• Aiming point = 2/3 Distance to be lighted.
• 2/3 (16 Meter) = 10.6 Meter aiming point
• To minimize glare, the recommended aiming point distance should never exceed twice the mounting height.
• If a pole is 8 Meter high, the vertical aiming point should not exceed 16 Meter.  
• 2 (8 Meter mounting height) = 16 Meter. 

4) Horizontal Aiming:

• When two floodlights is mounted to a single pole then horizontal aiming also must be considered.
• Each floodlight should be vertically aimed according to the two-thirds rule. 
• The floodlights should be aimed up to 90 degrees apart. 

(B) Facade Lighting:

• Normally Facade Lighting are used to illuminate Building area from Outer Side. 
• There are three factor should be consider while designing of outdoor Facade Lighting.

1. Setback
2. Spacing
3. Aiming

1) Setback:

• The recommended setback should be 3/4 times the building height. 
• If a building is 10 Meter tall, the recommended setback is 7.5 Meter from the building. 
• If the locating the floodlight closer to the building will sacrifice uniformity and If setting it further back will result in loss of efficiency.
• Setback distance = 3/4 x Building height
• Setback distance =3/4 x (10 Meter) = 7.5 Meter 

2) Spacing:

• Spacing of floodlights should not be exceeding two times the setback distance. 
• If the setback is 7.5 Meter the floodlights should not be placed more than 15 Meter apart.
• Spacing = 2 x setback distance
• Spacing=2 x 5  = 15 Meter

3) Aiming:

• The floodlight should be aimed at least 2/3 the height of the building.
• If a building is 10 Meter high, the recommended aiming point is approximately 6.6 Meter high. 
• After installation aiming can be adjusted to produce the best fine appearance. 
• Aiming Point = 2/3 x Building Height.
• Aiming Point =2/3 (10 Meter) = 6.6 Meter high

(C) Sinage Lighting:

• Normally Sinage Lighting are used to illuminate Sinage Board either Floor Mounted or Pole Mounted
• There are three factor should be consider while designing of Sinage Board Lighting.

1. Setback
2. Spacing
3. Aiming

1) Setback:

• When using floodlights to light a sinage, the setback should be 3/4 the sign height
• If the sinage height is 18 Meter then the setback distance would be 13.5 Meter. 
• If the floodlight closer to sinage will sacrifice uniformity while setting it further back will in a loss of efficiency.
• Setback distance = 3/4 x sinage height
• Setback distance =3/4 (18 Meter) = 13.5 Meter.

2) Spacing:

• The spacing floodlights should not be exceed two times the setback distance. 
• If the setback is 13.5 Meter, the floodlights should not be placed more than 27 Meter apart. 
• Spacing = 2 x setback distance.
• Spacing = 2 x 5 (Meter) = 27 Meter.

3) Aiming:

• The floodlight should be aimed at least 2/3 up the sign.
• If a sign is 18 Meter tall, then the floodlight should be aimed approximately 12 Meter high. 
• Aiming can be adjusted to produce the best appearance. 
• Mounting a full or upper visor to the floodlight can reduce unwanted glare. 
• Aiming point = 2/3 x sign height
• Aiming point =2/3 (18 Meter) = 12 Meter high

Street Light Pole Height & Spacing (as per CPWD):

• There are four type of Street Light Pole arrangement.
• One side Type.
• Staggered Type.
• Opposite Type.
• Central Type.
• As per CPWD we can calculate Pole Height and Spacing as per under

(1) One side Street Light Pole arrangement.

• Pole Height = Width of Road.
• Pole Spacing = 3 to 4 Times Height of Pole.
• If the Road width is 8 Meter than
• Pole Height=8 Meter
• Pole Spacing =24 to 32 Meter.

(2) Staggered Type Street Light Pole arrangement.

• Pole Height = 0.8 time Width of Road.
• Pole Spacing = 3 to 4 Times Height of Pole.
• If the Road width is 8 Meter than
• Pole Height=6.4 Meter
• Pole Spacing =24 to 32 Meter.

(3) Opposite side Street Light Pole arrangement.

• Pole Height = 0.5 time Width of Road.
• Pole Spacing = 3 to 4 Times Height of Pole.
• If the Road width is 8 Meter than
• Pole Height=6.4 Meter
• Pole Spacing =24 to 32 Meter.

(4) Central Street Light Pole arrangement.

• Pole Height = 0.8 time Width of Road.
• Pole Spacing = 3 to 4 Times Height of Pole.
• If the Road width is 8 Meter than
• Pole Height=4 Meter
• Pole Spacing =24 to 32 Meter.

Optimum step size selection guidelines in APFC panels

Optimum step size selection guidelines in APFC panels:

Major part in the design of APFC panels is the selection of step size of capacitor banks and number of steps. The right selection of step size and number of steps plays a significant role in the performance as well as cost of the APFC panel. This article focuses on the need and ways of good step size (maximum and minimum sizes) selection and number of steps.

1. Maximum step size selection:

The maximum capacitor rating in an APFC panel depends up on the following:

i. Maximum amount of load variation that happens in the industry at a time: Large load variations demand bigger capacitor steps so that target power factor is achieved in short time, by less number of switching operations.

ii. Current and voltage transient withstand capabilities of the system:

•     Current transients: Switching of big capacitors (usually above 100 kVAr) introduces large magnitude of inrush current (current transients) for a small duration. This results in high thermal and electrical stress on capacitors, short circuit protection devices and mainly, the switching device. This may lead to their nuisance tripping and premature failures.
•       Voltage transients: Switching of big capacitors may cause transient over voltages, which might result in failure of sensitive electronic devices. Thus, the maximum size of the capacitor step is a trade-off between the points i and ii. Practically acceptable maximum possible rating in any APFC panel shall be 100 kVAr. If this 100 kVAr rating capacitor is switched using power contactor, the peak inrush current may reach as high as 75 kA. Hence, the capacitors should be switched using either capacitor duty contactors or thyristor switching module.

However, thyristor switching module or capacitor duty contactor for 100 kVAr rating is not readily available. Hence, the best way to switch a 100 kVAr bank is by connecting two 50 kVAr TSM / contactor in parallel, each with a separate physical 50 kVAr capacitor banks. The control supply to both the 50 kVAr TSM/contactors shall be common (one relay output of the controller), so that both of the devices are triggered at the same time. To achieve this, the common output of the APFC relay should be programmed as 100 kVAr. Hence, physically they are two separate 50 kVAr banks, whereas electrically they behave as a single 100 kVAr bank.

2. Minimum step size selection:

The minimum capacitor rating depends on how precise the power factor needs to be maintained. This minimum kVAr rating depends upon the minimum current sensitivity (typically around 2.5%) of the APFC controller. However the change in PF due to these minimum selected kVAr rating would be usually in the 3rd or 4th decimal places (depending on panel size or kVAr requirement), whereas the electricity board is concerned only with the first two digits of PF (like 0.99).

Typically many industries want the desired target PF to be unity (exactly 1.00), in order to get incentives from some EBs. But practically, the optimum target PF has to be 0.96 to 0.99. These are healthy levels of power factor as it will have safety margin that avoids the leading power factor as well as any dangerous harmonic amplification (due to more capacitance in the system).

Hence, as a rule of thumb, the minimum kVAr rating in an APFC panel can be chosen to be 5-10% of overall rating of APFC panel. For smaller rating APFC panels (up to 100 kVAr), the smallest step can be 5 kVAr and for bigger rating APFC panels (above 600 kVAr and up to 1000 kVAr) the minimum rating can be 25 kVAr.

3. Number of steps / branches in APFC panels:

Once the minimum and maximum kVAr rating of the APFC panel is selected, the number of branches can be decided upon based of the following:

i. Technology of APFC controllers: APFC controllers shall be self optimized intelligent switching where the controller calculates the exact kVAr requirement and switches ON / OFF the appropriate capacitors irrespective of the capacitors already in circuit.

Traditional controllers employing linear or circular switching require more number of smaller

steps (like 1:2:2:…) for effective power factor correction. Whereas the latest controllers can have a mix of large and small steps reducing the number of steps in capacitor bank as well as the cost of associated switchgear.

ii. Size & cost of APFC panel: More the number of steps more will be the cost of APFC panel, due to more number of switchgear, bigger size of panel and others.

An APFC panel should have:

a. Maximum number of electrical steps (combination of physical steps) to ensure more accurate and flexible power factor correction

b. Minimum number of physical steps to reduce the size and cost of the panel

DISCLAIMER:

For accurate compensation, the load profile of the industry needs to be studied. This gives an indication of the size of peak loads, base loads, possible harmonics, power factor and thus, helps determine step sizes based on load variations. In some cases, the load requirements can also be established from equipment lists.