Standards for symbols

Symbols of Electrical Things
Standards for symbols
An electronic symbol is a pictograph used to represent various electrical and electronic devices (such as wires,batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit. These symbols can (because of remaining traditions) vary from country to country, but are today to a large extent internationally standardized. Some symbols represent components which ceased to be used routinely as newer technologies were introduced (such as vacuum tubes)


Standards for symbols

Contents

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• 1 Standards for symbols
• 2 Reference designations
• 3 Gallery of common electronic symbols
  • 3.1 Resistors
  • 3.2 Capacitors
  • 3.3 Transistors
  • 3.4 Diodes
  • 3.5 Vacuum tubes
  • 3.6 Switches
  • 3.7 Miscellaneous
• 4 See also
• 5 References
• 6 External links

Symbols of Electrical Things.

Miscellaneous.

Symbols of Electrical Things.

An electronic symbol is a pictograph used to represent various electrical and electronic devices (such as wires,batteries, resistors, and transistors) in a schematic diagram of an electrical or electronic circuit. These symbols can (because of remaining traditions) vary from country to country, but are today to a large extent internationally standardized. Some symbols represent components which ceased to be used routinely as newer technologies were introduced (such as vacuum tubes).

             
        

Definitions Of Electrical Energy

Definitions Of Electrical Energy

1   Electricity: energy made available by the flow of electric charge through a 


conductor; "they built a car that runs on electric 


2    Electric potential energy, or electrostatic potential energy, is a potential energy 


associated with the conservative Coulomb forces within a defined system of point 


charges. The term "electrostatic potential energy" is preferred here because it seems 


less likely to be misunderstood.


3   The energy associated with electric charges and their movements.


4    The generation or use of electric power measured in kilowatt-hours, megawatt-


hours or gigawatt-hours


5       The quantity of electricity delivered over a period of time. The commonly used 


unit of electrical energy is the kilowatt-hour (kWh).

Power Factor "cosφ".

Power Factor

It is common to define the Power Factor - PF - as the cosine of the phase angle between voltage and current - or the "cosφ".

 The power factor defined by IEEE and IEC is the ratio between the applied active (true) power - and theapparent power, and can in general be expressed as:

PF = P / S         (1)

where

PF = power factor

P = active (true or real) power (Watts)

S = apparent power (VA, volts amps)

A low power factor is the result of inductive loads such as transformers and electric motors. Unlike resistive loads creating heat by consuming kilowatts, inductive loads require a current flow to create magnetic fields to produce the desired work.

Power factor is an important measurement in electrical AC systems because

• an overall power factor less than 1 indicates that the electricity supplier need to provide more generating capacity than actually required
• the current waveform distortion that contributes to reduced power factor is caused by voltage waveform distortion and overheating in the neutral cables of three-phase systems

International standards such as IEC 61000-3-2 have been established to control current waveform distortion by introducing limits for the amplitude of current harmonics.

Example - Power Factor

A industrial plant draws 200 A at 400 V and the supply transformer and backup UPS is rated 200 A × 400 V = 80 kVA.

If the power factor - PF - of the loads is only 0.7 - only

80 kVA × 0.7

    = 56 kW

of real power is consumed by the system. If the power factor is close to 1 (purely resistive circuit) the supply system with transformers, cables, switchgear and UPS could be made considerably smaller.

Any power factor less than 1 means that the circuit's wiring has to carry more current than what would be necessary with zero reactance in the circuit to deliver the same amount of (true) power to the resistive load.

A low power factor is expensive and inefficient and some utility companies may charge additional fees when the power factor is less than 0.95. A low power factor will reduce the electrical system's distribution capacity by increasing the current flow and causing voltage drops.

"Leading" or "Lagging" Power Factors

Power factors are usually stated as "leading" or "lagging" to show the sign of the phase angle.

• With a purely resistive load current and voltage changes polarity in step and the power factor will be 1. Electrical energy flows in a single direction across the network in each cycle.
• Inductive loads - transformers, motors and wound coils - consumes reactive power with current waveform lagging the voltage.
• Capacitive loads - capacitor banks or buried cables - generates reactive power with current phase leading the voltage.

Inductive and capacitive loads stores energy in magnetic or electric fields in the devices during parts of the AC cycles. The energy is returned back to the power source during the rest of the cycles.

Power Factor for a Three-Phase Motor

The total power required by an inductive device as a motor or similar consists of

• Active (true or real)  power (measured in kilowatts, kW)
• Reactive power - the nonworking power caused by the magnetizing current, required to operate the device (measured in kilovars, kVAR)

The power factor for a three-phase electric motor can be expressed as:

PF = P / [(3)^1/2 U I]         (2)

where

PF = power factor

P = power applied (W, watts)

U = voltage (V)

I = current (A, amps)

Typical Motor Power Factors

Power (hp)	Speed (rpm)	Power Factor
		1/2 load	3/4 load	full load
0 - 5	1800	0.72	0.82	0.84
5 - 20	1800	0.74	0.84	0.86
20 - 100	1800	0.79	0.86	0.89
100 - 300	1800	0.81	0.88	0.91

• 1 hp = 745.7 W

END RESULT OF U.P.S

END RESULT

With everything operating at max, I got just short of two hours of battery time. Considering my application consists of two 12V batteries wired in series to give me 24V, I am effectively running off one 24V battery.

Series battery connection

I was extremely happy with the time it gave me. Under normal office operating conditions, had I switched one computer off while the power was down and used the other for tasks that are nothing more stressful than spreadsheets, I am quite sure I could get at least double the time out of it, if not more.

It took just on four hours to recharge the batteries. I restarted the PC’s immediately after reverting back to mains so everything was on while the unit was recharging the batteries. I’m not sure if leaving the computers off would have made a big difference to the charge up time.

In conclusion, I would have to say I am extremely happy with my UPS.
I paid R 3,003.00 for it. That included the batteries and the battery housings. In US dollars, at our current exchange rate, that translates to around $411.00

The beauty of this system is if you get an inverter that has the same features as the one I got, you can custom fit it with batteries of your choice and then add as many as you need in parallel depending on what application and backup time you need. With a bit of research and common sense, it should be easy to make your own backup unit with a few lead-acid batteries that can be bought from the local battery retailer.

Parallel battery connection

PUTTING TOGETHER A UPS OF YOUR OWN

As my unit was already made up for me, I am not going to go through a step by step dialogue on how to make one of these from scratch. Using my unit as a guide, I’m hoping that I am able to provide you with sufficient specifications, diagrams and pictures for you to make your own setup or be able to make an informed decision should you wish to go out and buy one, or have one made.

For this project you will need the following hardware:

• A DC-to-AC inverter, with auto line-to-battery transfer and integrated charging system.
• 12V semi-sealed lead acid batteries or valve regulated lead acid batteries (VLRA) which are completely sealed.
• Polyethylene battery box (This is optional although highly recommended from a safety aspect.)
• AC wiring no less than 18-gauge copper wire and rated for 167°F (75°C) or higher cut to the desired length.
• Battery cables no less than 10-gauge and rated for 167°F (75°C) or higher.
• Metal battery terminals to fit the positive and negative contacts on your particular model of battery.
• Ring cable terminals to secure the battery cables to the DC input connecter on the back of the inverter

I would suggest getting the cables made up at your local auto electrician as it involves the use of specialized crimping tools, which unless you already have in your toolbox, seem to be an unnecessary outlay for the single use you would have for them on this project.

The back of my inverter unit is very clearly marked and shows exactly where to connect the various terminals. The following diagram and close-up of the wiring on my unit should hopefully provide a sufficient guide.

To the left, are the terminals for the DC input(battery terminals). This would take the 10-gauge wire that runs from the positive and negative terminals of the batteries. It is advisable to keep the length of these cables as short as possible. Using cables that are too small in diameter or too long will cause a resistance buildup and could stress the inverter, resulting in lower efficiency, lower peak output power, and reduced surge power. At worst, the cable could generate sufficient heat to start a fire.

Place the correct polarity battery ring terminal over the battery terminal plate at the rear of the unit. This should be marked with a + or – It may also be coloured red or blue. Do not place any additional items like washers or nuts between the terminal plate and the cable ring as overheating may occur. The terminal stud (screw) is not designed to carry current. Make sure to tighten the cable ring to the terminal plate with the appropriate nut to ensure maximum connectivity.

Next up is the AC input supply. My unit provides a three station terminal block to connect the wires from the AC inlet (wall socket plug) to the inverter. The positioning for the wires have been clearly marked as HOT (positive) NEUTRAL (negative) and GROUND (earth). You would need to check the wiring colour code for your country or region before attempting to connect the wires to the terminal block. As mentioned, a minimum of an 18-gauge cable should be used. Most general purpose three core extension wires would suffice. The length of this cable is not as crucial as the cabling to the battery terminals and may be cut to a length that suits your application.

To the right of the unit is the output socket. This may take on various configurations depending on the appliance standard for your country or region. The cable that came with my unit ended with a single kettle plug connection, which was useless for my application, so I cut it off and replaced it with a multi-plug adapter. If you can find an extension lead that fits the inverters outlet and has sufficient sockets to meet your requirements, you may not have to adapt it like I did.

That is effectively all there is to putting your own UPS together. Depending on your needs and budget, you could build a UPS that provides monstrous battery capacity. Your only limitations would be weight, the need for portability, and sufficient ventilation.

There is presently no short-term solution for the electricity supply problem in South Africa.
Without spending a small fortune, the Inverex 1000 with deep discharge lead-acid batteries is the best solution for me. During the day, we can keep the office going without any downtime. In the evening, we can have fun and never get stuck sitting in the dark with nothing to do.

SETTING UP THE TEST OF U.P.S

SETTING UP THE TEST.

For my test application I rigged up the two PC’s, the ADSL Router, the wireless router, a 19” widescreen LCD monitor, a 17” CRT monitor, and the 4-in-1 laser printer.

The computer that connects to the 19” LCD monitor runs with an AMD 64 3000 chip at 2GHz, 1GB RAM, a Radeon X800 graphics card, two 80GB hard-drives and two CD/DVD drives. Along with the standard keyboard and optical mouse, it also has the laser printer plugged into it.

The second computer connects to the 17” CRT and hosts an AMD 64 3500 at 2.2GHz, 1GB RAM, an Nvidia 7800GT graphics card, a single 80GB hard-drive and one CD/DVD drive. The standard keyboard and optical mouse completes the roundup.

I run Folding@Home on both computers, so the CPU’s are already running at 100 percent capacity. To put extra strain on the setup, I got my son to play a succession of FPS games on the second rig and I printed out 20 pages of full page print, pictures, and spreadsheets from various files on the first computer. Then for good measure, I downloaded a huge game demo file from the computer farthest away from the wireless router (about 30 feet) to make sure it was working hard too. The rest of the uptime was spent playing an FPS LAN on the two computers.
At this stage it must be noted that the Inverex 1000 comes with deep discharge, overcharge, and overload protection, so under normal operating conditions there should be no fears of overloading the system. I was about to see if it could handle what I threw at it.

FACTORS TO CONSIDER WHEN MAKING A PURCHASE.

FACTORS TO CONSIDER WHEN MAKING A PURCHASE.

The technician that put my setup together would at this point argue that he did not sell me an true inverter. To a large extent, I would agree with him. Inverters usually run independent of a main electricity supply, so they do not normally come standard with a 110/230V plug that you can connect to a wall socket. My unit plugs into the mains and uses an integrated charging system to automatically switch the unit to batteries when the power dips below a pre-determined voltage and back to mains when power is restored. It also re-charges the battery once it has dropped below optimum voltage. Pretty much how a UPS functions, so what are the differences?

Well, price for one. A quick search on the Internet showed me I was getting excellent value for money. An industrial type UPS rated to provide backup power for the 4-5 hours I required would have cost me a lot more than I paid for my setup.

On the subject of pricing, when making your choice it’s important to note that there are two types of UPS’s and inverters. One produces a pure-sine wave and the other a modified-sine wave.
The pure or true-sine wave is the closest you can get to the power produced by the public utility power grid system. The modified or square-sine wave models (mine falls into this category) are the most common of the inverters and are much cheaper than their thoroughbred cousins. Be sure to check which model you buying before settling on price.

Apart from a few exceptions, the modified-sine wave inverters will run just about any household appliance. Laptops and desktop computers have no problem running off these.

Another difference I found, and probably the most significant, is the fact that my model and most other inverters like it does not have any built in surge protection against lightening strikes and power spikes. It is essential to run the inverter/UPS through a surge protection unit.

A lot of the better off-the-shelf UPS’s come with monitoring software which enables you to interface with your PC via a USB cable. This is one feature you will be very hard pressed to find when shopping for inverters or UPS of this nature.

Your standard home UPS (600 VA) only has a 0.5 or 1 amp charger at best.
The models from the Inverex range come with a much larger charge capacity (up to 8 amps) which enables you to recharge a large battery to 80 percent of its capacity within 6-8 hours.

IN SEARCH OF A SOLUTION FOR SUPER U.P.S

IN SEARCH OF A SOLUTION For Super U.P.S

It is with this background that I went in search of a decent, cost effective UPS that could run all the electronics in the office for at least a few hours. I quickly came to realize two things:

1. There are no intermediate UPS. You either get the off-the-shelf cheapies or lay out a small fortune. The cheapies are designed for one or two home computers (readily available in most computer stores). Generally these contain “gell cell” batteries which are cheap, don’t leak and are very standardised. They provide only back-up time and little or no protection. The small-fortune variety are much larger and suited for a small- to medium-sized business.

2. Most decent home-use UPS are designed to provide a clean power source, eliminating under and over voltage as well as electrical noise. They are generally not intended to provide hours of backup time. Five to 15 minutes seems to be the norm.

My search eventually led me toBocal Electronics, a local company who specializes in UPS, standby systems and associated products. That’s where I learned about DC-to-AC inverters. Their function is to take power from a battery source, normally 12 or 24 volts DC, and convert it to anything from 110 to 230 volts AC. This is ideal in remote locations where there is no power grid to tap into and allows you to run just about any electrical appliance off a battery.

The unit I bought is the Inverex 1000 with a 1000VA / 600W capacity. It is essentially a DC-to-AC inverter with auto line-to-battery transfer and an integrated charging system. It can serve as an UPS, standalone power source or an automotive inverter. It’s also quite compact, with a footprint roughly the size of a sheet of paper, slightly over 3″ tall, and weighing under four pounds. With those specifications, you may have guessed it does not come with its own dedicated battery storage and that’s where it gets interesting. Provided you stick to the DC voltage rating of the unit, use the same type of batteries (typically lead-acid) with the same Amp Hour(ah) rating, you can pretty much use any combination of battery in parallel or series to meet your specific requirements.

My unit came fixed to the top of the battery housing and comprised of two 12V 45 ah semi-sealed lead-acid batteries, wired in series to produce a total of 24V. The batteries that came with my setup are deep discharge batteries and are well suited for UPS applications.