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| Syllabus | |
| 1 | Intro. to the Course |
| 2 | Intro. to Gas and Oil Processing |
| 3 | Gas Processing Methods |
| 4 | Intro. to Water -Hydrolic Cycle |
| 5 | Intro. to Water -Part 2 |
| 6 | Power Generation/ Cogeneration |
| 7 | Electricity Transmission |
| 8 | 8 Missing |
| 9 | 9 Missing |
| 10 | 10Missing |
| 11 | Chemical, Reagents,Tools, Rigging |
| 12 | 12 Missing |
| 13 | Land Use and Reclamation |
| 14 | Instrumentation and Drawings |
| **** Final Exam***** | |
| Resources | |
| Staff E-mail | |
Lesson 7
Safety
Topics |
Electricity Transmission | Basic
Terms
Objectives:
Safety topic-Lockout/Tagout - Authorized Employees
When servicing or performing maintenance on equipment or machinery, you must be sure that the equipment cannot unexpectedly start-up or release stored energy. How do you do this? The procedure for isolating the energy sources is called lockout/tagout.
As employees who service and perform maintenance on the equipment in this facility, you need to know how to avoid the dangers involved when hazardous energy sources are not locked out and/or tagged out. You must know, understand, and perform lockout/tagout properly.
Energy control procedures
Each piece of equipment or machine needs its own lockout/tagout procedure. The procedure contains the steps for shutting down, isolating, blocking and securing machines or equipment to control hazardous energy.
Also, the procedure should include the steps for placement, removal, and transfer of lockout/tagout devices.
Finally, it should contain the requirements for testing and verifying the effectiveness of the lockout/tagout devices and other energy control measures.
An orderly shutdown must be used to avoid any additional or increased hazards when the equipment is stopped. Use the shut down procedures that are established for each individual machine.
Locks
Lockout devices must be durable and substantial.
Locks are standardized for ease of recognition.
The lock must identify the person who applied it. This can be done with a tag.
The use of someone else's lockout device is prohibited.
Tags
Tags must be durable and substantial.
Tags are standardized for ease of recognition including the print and format.
The attachment means for a tag must be:
- Non-reusable.
- ÝAttachable by hand.
- ÝSelf-locking.
- Non-releasable with an unlocking strength of 50 pounds.
The attachment means must be equivalent to a one-piece, all-environment-tolerant nylon cable tie.
The tag's legend includes statements such as Do Not Start, Do Not Open, Do Not Close, Do Not Energize, or Do Not Operate.
Employee training
OSHA regulations contain specific training requirements for employees that are authorized to perform lockout/tagout operations. At 29 CFR 1910.147(c)(7)(i)(A), the rule says that each authorized employee must receive training in the recognition of applicable hazardous energy sources, the type and magnitude of the energy available in the workplace, and the methods and means necessary for energy isolation and control.
Your employer will show you energy isolating devices, locks, and tags that are used in your facility. They will also reveiw the lockout/tagout procedure before requiring you to be familiar with it's practice.
Where to go for more information
OSHA regulations at 29 CFR 1910.147, The control of hazardous energy (lockout/tagout).
Electricity Transmission
- Describe Electricity Transmission
- Describe Electrical Power Distribution within a plant
- Describe Hydroelectric Power
- BTMOSC
- Basic Math Continued
Definition of Transmission
For the purposes of this class Electrical Power Transmission is the transmission of electrical power across long distances. Electrical Distribution is the distribution of electricity within a facility.
The voltages involved in electrical transmission are very high.
Generation Plant
At the generation plant electricity moves from the generator to a switchyard where it is transformed to a higher voltage and sent on to the grid via a transmission line. The transmission line voltage will be between 69 and 500 thousand volts.
High Voltage
The voltage is high to cut line losses. In accordance with ohms law the loss in a line is equal to the resistance times the current squared or IxIxR. As the current increases the power lost is squared. So, it is important to keep the current as low as possible.
This is done by keeping the voltage as high as possible. The generated power is 3 phase alternating current. Three phases are used because it is the most efficient method. In addition to the 3 phases the power company uses the earth as a ground. If you look at the towers you will notice the 3 phases and often a fourth wire higher up. This is a ground wire intended to attract lightning and protect the system.
In order to handle the high voltage the transmission lines must be elevated and separated from each other. Also the lines must be held in place mechanically by insulators with the mechanical strength and electrical resistance necessary for this purpose.
An interesting feature of the insulators is how the electrical surface resistance is increased by the design. Look at slide 7-2. Notice that the insulator has been designed to provide the maximum possible surface distance between the two ends This is because the insulator must be as long as possible to provide maximum insulation.
Transformation
The voltage produced by the generator itself is relatively low, probably 7200 volts or less. Why? Because the generators windings are closely wound an extremely high voltage in the generator would cause arcing. So, the generator has a lower voltage and a higher current.
This power is presented to a transformer in the yard which then steps the voltage up to distribution line voltages. The transformer has two windings, the primary and the secondary. If the primary had 100 windings and the secondary had 200 windings then the transformer would double the voltage.
Grid
Look at slide 7.3 The transmission line exits the switchyard and is presented to the power distribution grid. The grid connects power plants and consumers within a geographical area, such as a state or several states. Because the grid has multiple power plants connected it allows the continuous flow and shifting of power from one area to another to make sure there is adequate power for customers at all times.
Typically it is economical to transmit electricity over distances of up to 300 miles. Near customers the transmission line enters a substation where high voltages are transformed to distribution voltages of 34,500 volts or less and sent to final customers where it is transformed one last time to the final voltage.
Protective Relays
Protective relays are a type of sensor located in black boxes at every substation. When a line is shorted or broken, the relays shut off power on both ends of the line.
The grid's relays de-energizes faulted equipment within 3/60th of a second, or 3 cycles.
It is vital that the fault gets turned off instantaneously, because it sucks out wattage from other parts of the system to feed its leak, causing a shortage to be felt around the region.
Usually each relay must be checked once every 2 to 3 years. On the scheduled maintenance date, the craftsman drives to the substation with computer and test equipment in hand. The craftsman checks the relays, reads the meters' output and installs new equipment if necessary.
Power System Control SCADA (System Control and Data Acquisition)
The grid is constantly monitored to make sure it is functioning properly and power is being delivered.
SCADA equipment provides the telemetry link for these functions. This large network connects every substation on the grid.
This SCADA equipment detects signals, data and disturbances.
For example remotely monitored meters measure the amount of power sold to customers in order to correctly bill them. The number of kilowatt-hours being used at a substation is sent to Central Control for billing of large customers.
Protective relays already mentioned above connected to the SCADA system constantly monitor conditions and send alerts to distant control centers.
Likewise, the number of megawatts of load on a transmission line is sent to the control center for load control.
If there's sudden jump in the load, a signal may be sent to the Generation plants to generate more power. Another system monitors alarms at each substation and sends the information to control centers to check the status of equipment.
Microwave stations, UHF, fiber optic and voice are all used.
Electrical Power Distribution
This course element addresses the distribution of power within a plant. We will use a typical pipeline pump station as our example.
When power is generated locally at a plant or imported from a utility it must be distributed within the facility. The electrical equipment for this purpose will be referred to as the distribution system.
Features of the distribution system.
1 Three phase AC power 480 volts : The most common voltage used in the processing industries.Commonly used on motors from 1/2 to 500 horsepower, when higher power is required, higher voltage motors are employed.
2 Motor Control Centers : These enclosures are protected from the elements and the process itself. This part of the distribution system commonly contains transformers, magnetic motor starters, variable frequency drives, main dis-connects, and other electronic equipment that can be environment sensitive.
3 Power Buses : The main conductors used in the distribution system.
4 Redundant cabling: provides a second power path when needed .
5 A load shed/readd system: This system is used for controlling the power use on the grid. Without some way to control load, black-outs would be inevitable, causeing major disruption to the process.
6 Uninterruptible power for critical control systems: UPS systems generally are battery powered inverters that assure constant power for computers and other critical control systems that would be adversly affected by a loss of power.
7 Protective circuit breakers : These devices are designed for equipment and personal protection. In the case of an electric motor, the current limiting device would trip before maximum amps were drawn, damaging the motor.In the case of a GFI of ground fault interruption device, a ground fault would be sensed before the current potential was high enough to cause physical harm.
8 Lifeline generators: These units supply backup power for the plant's lighing and ventilation systems.
Three phase AC power 480 volts
Plant power consists of 3 phase 480 volts AC. This is because the plant has a large number of electrical motors and the best power for electrical motors is 3 phase. 3 phase power provides high torque for starting. Motors are used to operate support pumps and ventilation fans.
Motor Control Centers
The plant is organized into motor control centers. Each area of the plant has a motor control center which distributes power out to the actual end devices.
The motor control centers also contain most of the control relays. For example a motor control center would contain the relay which turns off ventilation fans when a fire is detected.
Each major device powered/controlled by the MCC has an assigned "bucket". The bucket is a hollow box frame which is mounted on the MCC.
The bucket has an access door. On the door would be indicator lights, a circuit breaker switch and perhaps a on/off/auto switch to program the devices function. Some devices are started automatically, for example a sump pump. The on/off/auto switch overides the automatic control. It would allow the operator to force the pump off or on for special reasons. Inside the bucket itself are the motor starter and other controls. The motor starter is energized by a small control voltage. When the motor starter is energized its output contacts complete the 480 volt circuit to the final device.
When we talk about load sheds we will see that this function is implemented at the MCC.
Power Buses
Power buses provide the connection between the generator and the Switchgear and within the Switchgear itself. The bus is constructed from large copper bars mounted in the Switchgear. Connections from the generators and Switchgear components are made to the bus.
Redundant cabling to provide a second power path when needed
The power is sent directly from the power bus to the MCC via heavy cables. A second set of cables is also routed to the MCC but by a different route. Hand operated breaker switches are set to select one path or the other but never both at the same time. This second route would be used after a disaster thus preventing a fire or other problem from disabling the system for a long period of time.
A load shed/readd system
A plant may have 2 out of 4 generators on the power bus at the same time. A sudden generator failure would bring the whole system down due to overloading the remaining on line generator. To prevent this a smart controller detects the generator failure and sheds non critical load at the MCC's. Then the controller starts another generator, loads it and then readds the loads which had been shed.
Uninterruptible power for critical control systems
Some systems such as communications, station control panels, and fire suppression are so critical that they can never be shutdown. A UPS provides constant power to these systems. Normally the UPS is powered by the stations generators. When the generators shut down the UPS draws power from a battery, converts it to AC and applies it to the critical loads.
Protective circuit breakers
All loads are protected by circuit breakers. These circuit breakers are normally located at the MCC. Circuit breakers trip open when an overcurrent occurs. Some of these breakers weigh hundreds of pounds and break huge currents, thousands of amps. The breakers are complex mechanical devices and require a high level of skill to maintain.
Lifeline generators
At a remote plant like a pump station one generator is located far from the others. This is to prevent a generator room fire from destroying all possible generators. These special generators are in their own rooms or outside and are called lifeline generators. They are to provide life support in the harsh arctic environment during emergencies.
Hydroelectric Power
Hydroelectric Power is a renewable resource. Hydropower provides about 96 percent of the renewable energy in the United States.
Other renewable resources include geothermal, wave, power, tidal power, wind power, and solar power.
Hydroelectric powerplants do not use up resources to create electricity nor do they pollute the air, land, or water, as other powerplants may.
Hydroelectric power comes from the flowing waters of winter and spring runoff from mountain streams and clear lakes. Water, when it is falling by the force of gravity, can be used to turn turbines and generators that produce electricity.
In the 1920's, hydroelectric plants supplied as much as 40 percent of the electric energy produced. Hydroelectric power presently supplies about 11 percent of the electrical generating capacity of the United States. Hydropower responds quickly to rapidly varying loads or system disturbances, which base load plants with steam systems powered by combustion or nuclear processes cannot accommodate.
58 powerplants throughout the Western United States produce an average of 42 billion kWh (kilowatt-hours) per year, enough to meet the residential needs of more than 14 million people.
This is the electrical energy equivalent of about 72 million barrels of oil.
The efficiency of today's hydroelectric plant is about 90 percent. Hydroelectric projects have long lives relative to other forms of energy generation, and hydroelectric generators respond quickly to changing system conditions.
HOW HYDROPOWER WORKS
Generating Power
To generate electricity, water must be in motion. This is kinetic (moving) energy. When flowing water turns blades in a turbine, the form is changed to mechanical (machine) energy. The turbine turns the generator rotor.
Some powerplants are located on rivers, streams, and canals, but for a reliable water supply, dams are needed. Dams store water for later release for such purposes as irrigation, domestic and industrial use, and power generation. The reservoir acts much like a battery, storing water to be released as needed to generate power..The dam creates a "HEAD" or height from which water flows. A pipe (penstock) carries the water from the reservoir to the turbine. The fast-moving water spins the turbine.
How Power is Computed
The actual output of energy at a dam is determined by the volume of water released (discharge) and the vertical distance the water falls (head). So, a given amount of water falling a given distance will produce a certain amount of energy. The head and the discharge at the power site and the desired rotational speed of the generator determine the type of turbine to be used.
This pressure is measured in pounds per square inch. More head or faster flowing water means more power..
Turbines
There are two basic types of turbines (impulse and reaction), with many variations.
A reaction turbine is a horizontal or vertical wheel that operates with the wheel completely submerged, a feature which reduces turbulence. In theory, the reaction turbine works like a rotating lawn sprinkler where water at a central point is under pressure and escapes from the ends of the blades, causing rotation. Reaction turbines are the type most widely used.
An impulse turbine is a horizontal or vertical wheel that uses the kinetic energy of water striking its buckets or blades to cause rotation. The wheel is covered by a housing and the buckets or blades are shaped so they turn the flow of water about 170 degrees inside the housing. After turning the blades or buckets, the water falls to the bottom of the wheel housing and flows out.
Environmental Effects
Hydropower is not free from adverse environmental effects. Considerable efforts have been made to reduce environmental problems associated with hydropower operations, such as providing safe fish passage and improved water quality.
Low-head Hydropower
A low-head dam is one with a water drop of less than 65 feet and a generating capacity less than 15,000 kW. Large, high-head dams can produce more power at lower costs than low-head dams, but construction of large dams may be limited by lack of suitable sites, by environmental considerations, or by economic conditions. In contrast, there are many existing small dams and drops in elevation along canals where small generating plants could be installed. New low-head dams could be built to increase output as well. The key to the usefulness of such units is their ability to generate power near where it is needed, reducing the power inevitably lost during transmission..
Peaking with Hydropower
Demands for power vary greatly during the day and night. These demands vary considerably from season to season, as well.
Nuclear and fossil fuel plants are not efficient for producing power for the short periods of increased demand during peak periods. Their operational requirements and their long startup times make them more efficient for meeting baseload needs.
Since hydroelectric generators can be started or stopped almost instantly, hydropower is more responsive than most other energy sources for meeting peak demands. Water can be stored overnight in a reservoir until needed during the day, and then released through turbines to generate power to help supply the peakload demand.
Pumped Storage
Like peaking, pumped storage is a method of keeping water in reserve for peak period power demands. Pumped storage is water pumped to a storage pool above the powerplant at a time when customer demand for energy is low, such as during the middle of the night. The water is then allowed to flow back through the turbine-generators at times when demand is high and a heavy load is place on the system.
The reservoir acts much like a battery, storing power in the form of water when demands are low and producing maximum power during daily and seasonal peak periods. An advantage of pumped storage is that hydroelectric generating units are able to start up quickly and make rapid adjustments in output. They operate efficiently when used for one hour or several hours.
Future Potential
The hydropower resource assessment by the Department of Energys Hydropower Program has identified 5,677 sites in the United States with acceptable undeveloped hydropower potential. These sites have a modeled undeveloped capacity of about 30,000 MW. This represents about 40 percent of the existing conventional hydropower capacity.
Basic Terms of Maintenance, Operations and System Components
Alternating Current An electric current changing regularly from one direction to the opposite.
Ampere The common unit of measurement of electrical current.
Baseload The minimum constant amount of load connected to the power system over a given time period, usually on a monthly, seasonal, or yearly basis.
Baseload Plant A plant, usually housing high-efficiency steam-electric units, which is normally operated to take all or part of the minimum load of a system, and which consequently produces electricity at an essentially constant rate and runs continuously. These units are operated to maximize system mechanical and thermal efficiency and minimize system operating costs.
Bus (buswork) A conductor, or group of conductors, that serve as a common connection for two or more electrical circuits. In powerplants, buswork comprises the three rigid single-phase connectors that interconnect the generator and the step-up transformer(s).
Capacity The amount of electric power delivered or required for which a generator, turbine, transformer, transmission circuit, station, or system is rated by the manufacturer.
Circuit A conductor or a system of conductors through which electric current flows.
Current (Electric) A flow of electrons in an electrical conductor. The strength or rate of movement of the electricity is measured in amperes.
Dam A massive wall or structure built across a valley or river for storing water..
Demand The rate at which electric energy is delivered to or by a system, part of a system, or a piece of equipment. It is expressed in kilowatts, kilovolt amperes, or other suitable units at a given instant or averaged over any designated period of time. The primary source of "demand" is the power-consuming equipment of the customers.
Direct Current Electric current going in one direction only.
Distribution System The portion of an electric system that is dedicated to delivering electric energy to an end user. The distribution system "steps down" power from high-voltage transmission lines to a level that can be used in homes and businesses.
Generator A machine that converts mechanical energy into electrical energy.
Head The difference in elevation between the headwater surface above and the tailwater surface below a hydroelectric powerplant under specified conditions.
Hydroelectric Power Electric current produced from water power.
Hydroelectric Powerplant A building in which turbines are operated, to drive generators, by the energy of natural or artificial waterfalls
Kilowatt-Hour (kWh) The unit of electrical energy commonly used in marketing electric power; the energy produced by 1 kilowatt acting for one hour. Ten 100-watt light bulbs burning for one hour would consume one kilowatt hour of electricity.
Kinetic Energy Energy which a moving body has because of its motion, dependent on its mass and the rate at which it is moving.
Load (Electric) The amount of electric power delivered or required at any specific point or points on a system. The requirement originates at the energy-consuming equipment of the consumers.
Megawatt A unit of power equal to one million watts. For example, it's the amount of electric energy required to light 10,000 100-watt bulbs.
Ohm The unit of measurement of electrical resistance. The resistance of a circuit in which a potential difference of one volt produces a current of one ampere.
Peakload The greatest amount of power given out or taken in by a machine or power distribution system in a given time.
Pumped-Storage A plant that usually generates electric energy during peak-load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. When additional generating capacity is needed, the water can be released from the reservoir through a conduit to turbine generators located in a power plant at a lower level.
Reservoir An artificial lake into which water flows and is stored for future use.
Volt (V) The unit of electromotive force or potential difference that will cause a current of one ampere to flow through a conductor with a resistance of one ohm.
Watt (W) The unit used to measure production/usage rate of all types of energy; the unit for power. The rate of energy transfer equivalent to one ampere flowing under a pressure of one volt at unity power factor.
Watthour (Wh) The unit of energy equal to the work done by one watt in one hour.
Go to the basic math link and study pages 56 thru 60. Session 7 quiz will contain questions on this material.
Copyright © 2001 DMTC. All rights reserved..