services of Excavation and underground in Electricity

HSE and other organisations have produced guidance on electrical safety that is suitable for a wide range of industries and technical competencies. Most of the information produced by the HSE is available for immediate download.

What you need to know ?

When underground cables are damaged, people can be killed and injured by electric shock, electrical arcs (causing an explosion), and flames. This often results in severe burns to hands, face and body, even if protective clothing is being worn.

Damage can be caused when a cable is:

• cut through by a sharp object such as the point of a tool; or
• crushed by a heavy object or powerful machine.

Cables that have been previously damaged but left unreported and unrepaired can cause incidents.

The HSE booklet "Avoiding danger from underground services" gives guidance on how you can manage the risks of digging near underground cables.

The Electricity Networks Association (ENA) publication "Watch It! When digging in the vicinity of underground electric cables also provides advice".

What you need to do ?

Why Work near electricity ?

• Do a risk assessment for the work you are planning, and make sure this covers electrical hazards.
• Learn how to recognise electrical wires. These may be overhead power lines, electrical wiring in a workplace, or cable buried the ground.
• Get an up-to-date map of the services in the area and use it.
• Look for electrical wires, cables or equipment near where you are going to work and check for signs warming of dangers from electricity, or any other hazard. Remember to look up, down, and around you.
• If you will be digging or disturbing the earth or cutting into surfaces, use a cable locator to find buried services and permanently mark the position of services you do find.
• Work away from electrical wiring wherever possible. If you have to work near electrical wiring or equipment, ask for the electrical supply to be turned off. Make sure the power is off, and cannot be turned on again without you agreeing.
• If the electrical supply cannot be turned off, consult a competent person who should be able to advise you on the best way to proceed.
• Identify where it is safe to work. Put up danger notices where there are still live electrical circuits, and warn your co-workers where it is safe to work and where it is not safe. Remember to remove notices at the end of the work.

Information

• A quick guide to protecting yourself

The booklet 'Electricity at work, safe working practices' provides general guidance on working near electricity. Many electricity supply companies will provide advice on how to work safely near electrical distribution equipment. You should contact them directly.

Electrical danger signs

The Nuclear Qualified Instrumentation

Ultra Electronics, Nuclear Sensors & Process Instrumentation (NSPI) has been supplying nuclear qualified temperature sensors, thermowells and transmitters, pressure transmitters and fiber optic modems for more than three decades. We are recognized as a global leader in the technologies we supply, in part because of our intense focus on quality and reliability.
Today, over 80% of all North American reactors rely exclusively on Ultra Electronics, NSPI temperature sensors for critical reactor coolant monitoring. Our nuclear qualified pressure transmitters are used for safety related and BOP measurements at over 20% of US nuclear power plants. Ultra Electronics, NSPI products have been qualified for use in all of the leading reactor technologies, including PWR, BWR, CANDU (PHWR), and APWR.
We are also proud to be team members of the Generation III and III+ reactor technology platforms, including the System 80+, AP600 and AP1000.
In 1989 we acquired the manufacturing rights for the Foxboro N-E10 Series nuclear qualified pressure transmitters. In 1993, we purchased Camille Bauer, Inc (previously known as Westinghouse-Veritrak and Tobar), a major US based manufacturer of pressure transmitters for the nuclear power industry. More recently, we seismically qualified and became the exclusive supplier of the Invensys (Foxboro) N-I/A Series nuclear qualified pressure transmitters. The N-I/A Series combine the advantages of digital electronics with the reliability and performance of ion-implanted, micro machined silicon pressure sensor technology.
We have received the necessary certification to supply critical Class 1E and non classified temperature detectors for civil nuclear equipment in China from the country’s National Nuclear Safety Administration. All overseas companies must obtain certification, formally known as a “Letter of Confirmation on the Registration in the People’s Republic of China of Overseas Organizations Associated with Civil Nuclear Safety Equipment”, or HAF604 Certification, before they can work with civil nuclear safety equipment in China.
Ultra Electronics, NSPI is now globally acknowledged to be the premier supplier of temperature and pressure measurement instrumentation and fiber optic networking solutions to the nuclear power generation industry.
Ultra Electronics, NSPI Nuclear Quality Program:
Our Quality Program meets the stringent needs of the global nuclear power generation industry. In addition to being ISO 9001:2008 registered we are compliant with 10CFR50 Appendix B, 10CFR21, ANSI N45.2, ASME NQA-1, ASME NCA3800 and CSA Can3-Z299.1.

Injuries of Electrical

Electrical injuries can be caused by a wide range of voltages but the risk of injury is generally greater with higher voltages and is dependent upon individual circumstances. Torch batteries can ignite flammable substances.
Alternating current (AC) and Direct Current (DC) electrical supplies can cause a range of injuries including:

• Electric Shock
• Electrical Burns
• Loss of Muscle Control
• Thermal Burns

There are posters that give first aid procedures for Electric Shock and Emergency Action, including for burns.
More detailed technical information on electrical injury is given in the standard IEC 60479 "Guide to the effects of current on human beings and livestock - Part 1: General aspects".

Smart Analog Process-Instrument Transmitter with Low-Power Converters and a Microcontroller

By Albert O'Grady & Jim rYAN
An analog transmitter is a field-mounted device that senses a physical parameter such as pressure or temperature and generates a current proportional to the measured variable in the standard range, 4 to 20 mA. Providing the output as a current in a twisted-pair loop has many advantages: the measurement signal is insensitive to noise and is not affected by changes in loop resistance; transmitters meeting the standard are interchangeable; and the power required to energize the transmitter circuits can be derived from a remotely supplied loop voltage. Figure 1 shows a conventional transmitter circuit, consisting of a power supply, a current-manipulating transmitter, and a receiving controller.

 analog transmitter

Transmitter design has responded to the requirements of users for improved performance and versatility, plus reduced cost and maintenance. A second-generation “smart analog transmitter” has a microprocessor (and data conversion), to provide remote memory and computing power (Figure 2). It can condition the signal remotely before converting it to current and transmitting it back to the controller. For example, it can normalize gain and offsets, linearize sensors having known nonlinearities (such as RTDs and thermocouples) by converting to digital, processing with arithmetic algorithms in the µP, converting back to analog and transmitting on the loop as a standard current. This reduces the control room’s signal processing burden, a big advantage if a large number of signals must be dealt with. 

 smart transmitter

The third generation, “smart-and-intelligent” transmitters, add digital communications, which share the same twisted-pair line with the traditional 4-20-mA “dc” signal (Figure 3). The communication channel allows both analog and digital versions of the measured variable to be transmitted over the twisted pair, as well as control signals and diagnostic data relevant to the transmitter, such as calibration coefficients, device ID, and data relevant to fault diagnosis. Transmitter faults can be diagnosed remotely­ very useful for transmitters in hazardous locations.
The Hart protocol is the de facto communication standard used by smart transmitters. It employs frequency-shift keying (FSK) modulation, based on the Bell 202 Standard. Data is transmittedat 1200 bits/s, switching between 2.2 kHz (“0”) and 1.2 kHz (“1”).

inteligent transmitter

Accuracy of Pressure Transmitter

Pressure sensors (including level and flow sensors) are vital to process control and safety in industrial processes. In both the mechanical and electromechanical classes of pressure sensors, the applied pressure is converted into a displacement through an elastic sensing element. A displacement sensor, such as a strain gauge or a differential transformer, is then used to convert the displacement into an electrical signal so it can be displayed on a pressure gauge. The three most commonly used sensing elements for both mechanical and electromechanical pressure sensors are the Bourdon tube, bellows, and diaphragm.
In most applications, pressure sensors and the indicating or recording equipment associated with them are located away from each other to ensure safety and convenience, as in nuclear power plants, where radiation hazards are involved, or in chemical processes, where corrosive or flammable fluids under dangerously high pressures are present.
Two methods are available for remotely transmitting pressure signals from the process to the control room: pneumatic transmission and electrical transmission. In pneumatic transmission, the motion of the elastic element in the pressure sensor is usually converted into a standard 3 to 15 psi pressure signal, which is piped to a remote location. Pneumatic pressure transmitters have two important shortcomings: (1) they have large response lags that can limit the maximum length of transmission, and (2) they require quality air supply, free of moisture and undesirable fluids such as lubricating oil. To overcome the disadvantages of pneumatic transmission, electric transmission systems were developed, in which the motion of the elastic element is typically converted into a 4-20 mA (or 10-50 mA) electrical signal.
Accuracy in Pressure Transmitters

Pressure of Pump Versus Head

I found this article written by Larry Bachus recently (Jan 2008) and find it is pretty simple but useful. It gives us a simple idea the difference between pump pressure and head.

Cheat Sheets: Pump Secrets Lost in Time
The Relationship Between Pressure & Head

Early in my career I worked in a steel mill. One day, my boss gave me a purchase chit, put me in a company truck, and told me to go into town and buy a pump for cooling water. He said to get a pump that develops 30 PSI.

At the pump shop, the clerk showed me a pump that develops 70-ft of head. I thought, “Who cares about 70-ft? I need 30 PSI.” I didn’t know the relationship between head and pressure. I’m not alone.

Pump industry people use the term “head”;

maintenance people use the term “pressure”.

What is head? What is pressure?

In simple terms, they are the same. The terms head and pressure are interchanged in conversations regarding pumps. But they are different, with different definitions.

Meaning of "Pump Head"

This is another simple and useful article shared by Larry Bachus (Feb 2008) Understandinng of "pump head" would leads you converse easily with pump manufacturer

Cheat Sheets: 2.31 or .433?
The Numbers May Be Different, But the Result Is the Same

No, it’s not a new song by the band Chicago. (Remember “25 or 6 2 4”?) These numbers are the conversion factors that relate pump head with pressure. As established in my previous column (“Pump Secrets Lost in Time,” Jan. ’08), head is a measure of energy. The units of energy are expressed in feet or meters. Pressure is a force applied to a unit of area, such as a pound of force applied to a square inch of area, or PSI. For water, we can say that had in feet divided by 2.31 is pressure in PSI, and pressure in PSI multiplied by 2.31 is head in feet. Stated mathematically:

Head (ft.)/2.31 = PSI and PSI x 2.31 = Head (feet)

It is equally correct to convert head into pressure and vice versa with the factor .433. Head in feet multiplied by .433 is pressure in PSI, and pressure divided by .433 is head in feet. Mathematically:

Head (feet) x .433 = PSI and PSI/.433 = Head (feet)

Provide Pressure Transmitter at Pump Suction

Many years ago, i have seen pressure transmitter with alarm located at the pump suction line. I have spend a lot of time to figure out what is real purpose of this pressure transmitter ?

Why provides Pressure Transmitter (PT) with Low pressure alarm (PAL) at pump suction line ?

Power Factor of Calculation

As was mentioned before, the angle of this “power triangle” graphically indicates the ratio between the amount of dissipated (or consumed) power and the amount of absorbed/returned power. It also happens to be the same angle as that of the circuit's impedance in polar form. When expressed as a fraction, this ratio between true power and apparent power is called the power factor for this circuit. Because true power and apparent power form the adjacent and hypotenuse sides of a right triangle, respectively, the power factor ratio is also equal to the cosine of that phase angle. Using values from the last example circuit:

It should be noted that power factor, like all ratio measurements, is a unitless quantity.
For the purely resistive circuit, the power factor is 1 (perfect), because the reactive power equals zero. Here, the power triangle would look like a horizontal line, because the opposite (reactive power) side would have zero length.

power in electric

We know that reactive loads such as inductors and capacitors dissipate zero power, yet the fact that they drop voltage and draw current gives the deceptive impression that they actually do dissipate power. This “phantom power” is called reactive power, and it is measured in a unit called Volt-Amps-Reactive (VAR), rather than watts. The mathematical symbol for reactive power is (unfortunately) the capital letter Q. The actual amount of power being used, or dissipated, in a circuit is called true power, and it is measured in watts (symbolized by the capital letter P, as always). The combination of reactive power and true power is called apparent power, and it is the product of a circuit's voltage and current, without reference to phase angle. Apparent power is measured in the unit of Volt-Amps (VA) and is symbolized by the capital letter S.
As a rule, true power is a function of a circuit's dissipative elements, usually resistances (R). Reactive power is a function of a circuit's reactance (X). Apparent power is a function of a circuit's total impedance (Z). Since we're dealing with scalar quantities for power calculation, any complex starting quantities such as voltage, current, and impedance must be represented by their polar magnitudes, not by real or imaginary rectangular components. For instance, if I'm calculating true power from current and resistance, I must use the polar magnitude for current, and not merely the “real” or “imaginary” portion of the current. If I'm calculating apparent power from voltage and impedance, both of these formerly complex quantities must be reduced to their polar magnitudes for the scalar arithmetic.
There are several power equations relating the three types of power to resistance, reactance, and impedance (all using scalar quantities):

Power Factor Correction

When the need arises to correct for poor power factor in an AC power system, you probably won't have the luxury of knowing the load's exact inductance in henrys to use for your calculations. You may be fortunate enough to have an instrument called a power factor meter to tell you what the power factor is (a number between 0 and 1), and the apparent power (which can be figured by taking a voltmeter reading in volts and multiplying by an ammeter reading in amps). In less favorable circumstances you may have to use an oscilloscope to compare voltage and current waveforms, measuring phase shift in degrees and calculating power factor by the cosine of that phase shift.
Most likely, you will have access to a wattmeter for measuring true power, whose reading you can compare against a calculation of apparent power (from multiplying total voltage and total current measurements). From the values of true and apparent power, you can determine reactive power and power factor. Let's do an example problem to see how this works: (Figure bellow) 

Power in Resistive and Inductive AC Circuits

Consider a circuit for a single-phase AC power system, where a 120 volt, 60 Hz AC voltage source is delivering power to a resistive load: (Figure bellow)

 Ac source drives a purely resistive load.

Power Factor Correction

When the need arises to correct for poor power factor in an AC power system, you probably won't have the luxury of knowing the load's exact inductance in henrys to use for your calculations. You may be fortunate enough to have an instrument called a power factor meter to tell you what the power factor is (a number between 0 and 1), and the apparent power (which can be figured by taking a voltmeter reading in volts and multiplying by an ammeter reading in amps). In less favorable circumstances you may have to use an oscilloscope to compare voltage and current waveforms, measuring phase shift in degrees and calculating power factor by the cosine of that phase shift.
Most likely, you will have access to a wattmeter for measuring true power, whose reading you can compare against a calculation of apparent power (from multiplying total voltage and total current measurements). From the values of true and apparent power, you can determine reactive power and power factor. Let's do an example problem to see how this works: (Figurebellow)

Dimmer Lamp

Disclaimer

I disclaim everything. The contents of the articles below might be totally inaccurate, inappropriate, or misguided. There is no guarantee as to the suitability of said circuits and information for any purpose whatsoever other than as a self-training aid.

Some Light Dimmer History

Light dimming is based on adjusting the voltage which gets to the lamp. Light dimming has been possible for many decades by using adjustable power resistors and adjustable transformers. Those methods have been used in movie theatres, stages and other public places. The problem of those light controlling methods have been that they are big, expensive, have poor efficiency and they are hard to control from remote location.
The power Electronic have proceeded quickly since 1960. Between 1960-1970 thyristors and triacs came to market. Using those components it was quite easy to make small and inexpensive light dimmers which have good efficiency. Electronics controlling also made possible to make them easily controllable from remote location. This type of electronic light dimmers became available after 1970 and are nowadays used in very many locations like homes, restaurants, conference rooms and in stage lighting.

How Modern Light Dimmers Work