Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039. GWEC EDUCATION PARTNERS: This material is subject to the legal License Agreement signed by your institution. Please refer to this License Agreement for restrictions of use.
After completing this module and all its activities, participants will be able to: Describe the typical power sources found at a cell site. Differentiate between a power plant and a power supply. Explain the technologies, discharge cycle, and life expectancy of various battery sources. Explain the theory and design principles of a power plant in a telephony network.
Power Plant Function Telecommunications equipment is designed to operate from a DC power source. The principle operating voltage is -48 volts, nominal for switching and transport equipment and +24 volts, nominal for wireless radio equipment. The DC power plant performs three major functions: Change the AC source to the required DC voltage and polarity. Store electrical energy in the event of an AC failure. Distribute the DC power to the telecommunications equipment. A DC power battery plant is configured with the rectifiers, batteries and telecommunications loads connected in parallel. As such, the rectifiers will normally supply power to load equipment as well as provide a small amount of power to maintain a fully charged battery. Since the rectifier output, batteries and load equipment are all connected in parallel, the output voltage of the rectifiers is presented to these other elements as well. This configuration is commonly referred to as “floating” the battery strings. During an AC power failure the battery strings will supply power to the telecommunications load equipment for a finite amount of time. The amount of time that the power is being drawn from the batteries is referred to as the “reserve time”. When the AC power is restored, the rectifiers resume supplying power to the telecommunications equipment, as well as recharge the batteries. Power Supply Function A power supply will convert an input source to a useable output, however the output would not have batteries connected to it for energy storage. An example would be the power supply in a PC or the converters within telecommunications equipment frames. There are no provisions for energy storage on the output.
Components A DC power battery plant contains three major components: Rectifiers - The rectifiers change the AC power into a DC source, which can be stored in the batteries. Rectifiers are deployed in sufficient capacities and quantities to: Provide sufficient power to the telecommunications equipment, Recharge the batteries following an AC power failure. Batteries - The batteries are used to store the electrical energy that will be required to supply the telecommunications load equipment during AC power interruptions for a specific amount of time. Batteries also help filter any electrical noise, which may pass through the rectifiers as well as provide a reference voltage for the rectifiers. Additionally, they can supply a large amount of current to activate an overcurrent protection device quickly in the event of a short circuit in the distribution network. Power Board [Pbd] - The power board contains the overcurrent protection devices (fuses or circuit breakers) and is the primary distribution point for the DC current. Also, the power board will house the metering and controls for the DC power battery plant.
Main Battery Only Power Plant A main battery only power plant connects the batteries and rectifiers in parallel with the telecommunications equipment as shown above. The term “main battery” implies that there are no switches inserted between the battery and the power board. In normal operation, the output of the rectifiers supplies the load bus and also keeps the batteries charged. A nominal -48 volt main battery only power plant will usually contain 24 series-connected cells per string. A +24 volt main battery only power plant will contain 12 series-connected cells per string. The rectifier output voltage that is present across the battery strings is referred to as the “Float Voltage”. Battery cells used in telecommunications applications are designed for continuous float operation. In order to ensure that cells are in a fully charged state the voltage presented to the battery must be slightly higher than the open cell voltage. The open cell voltage for a typical low specific gravity (1.215) “flooded” cell is 2.06 volts DC. Therefore, battery manufacturers suggest a float voltage range of 2.17 to 2.26 volts for lead-calcium cells and 2.15 to 2.19 volts for lead-antimony cells. A typical 24 cell power plant equipped with “flooded” lead-calcium cells would have a “float voltage” of 2.17 volts per cell or 52.08 volts DC (2.17 * 24 = 52.08). For a 12 cell power plant equipped with “flooded” lead-calcium cell the “float voltage” would be 2.17 volts per cell or 26.04 volts DC.
Rectifiers A rectifier is a solid state device that changes the commercially available AC power into a DC source which can then be stored in the reserve batteries. Rectifiers are available in various output capacities, from 3 Amperes up through 800 Amperes. Rectifiers perform the following functions: Provide DC power to the telecommunications equipment at the required voltage. Maintain a “float” charge on the reserve batteries. Recharge the reserve batteries following an AC power failure. Provide alarm and status conditions to the power plant controller. Sufficient rectifier capacity must be provided to meet the total busy hour* load demand of the telecommunications equipment and to maintain the batteries in a fully charged state. Additional rectifier capacity is also required to recharge the reserve batteries to 95% of their capacity following an AC power failure. To help ensure reliability, one (1) additional rectifier is required as a maintenance spare (N+1). Cell sites would generally employ a number of +24 volt, 100 Ampere rectifiers to meet the total busy hour load demand, recharge and maintenance spare requirements described above. *Busy hour is that hour each day that a telecommunications system serves the maximum traffic load, thereby drawing the most power.
Rectifier Types There are several rectifier technologies employed in telecommunications applications today. The most common are silicon controlled (SCR), controlled ferroresonant, and switchmode. SCR rectifiers are the most mature of these technologies and are primarily used in the 400 – 800 Ampere capacity. Controlled ferroresonant may be the most common rectifier used in larger telecommunications applications with capacities that range from 25 – 400 Ampere. Switchmode rectifier technology is the newest of these technologies. This rectifier employs high frequency technology, which enables the physical size and weight to be reduced significantly when compared to the SCR and ferroresonant rectifiers. For example, a 200 Ampere, 48 volt, switchmode rectifier weighs approximately 65 lbs., compared to a 200 Ampere ferroresonant rectifier at approximately 325 lbs. Therefore, the energy density of the switchmode rectifier (size vs. capacity) is significantly greater. Because of this high energy density, these rectifiers can be incorporated into applications where space is a premium. Another advantage is the modular design and “plug and play” abilities. These rectifiers can be added to a system incrementally simply by plugging them into the system as needed. Also, because of the “plug and play” abilities, a defective rectifier can simply be removed and replaced in a timely manner, thereby significantly improving the time it takes to repair the system or MTTR (Mean Time to Repair). The increased energy density, modularity and ability to replace defective rectifiers in a timely manner proved ideal for remote / unstaffed locations (cabinets, huts, CEVs, cell sites, customer premise, etc.).
Features Telcordia Technical Reference, TR-EOP-000151, Generic Requirements for 24, 48, 130, and 140 Volt Central Office Power Plant Rectifiers and GR-947-CORE, Generic Requirements for a –48 Volt Telecommunications Switchmode Rectifier/ Power Supply define the specific requirements desirable in telecommunications rectifiers. Some of these features are listed below: Adjustable output voltage Maintain output voltage regulation within ±0.25% over an 8-hour period Local and remote voltage sensing with open sense lead protection and alarm Load sharing Automatic output current limiting at full load Output overcurrent protection Internal high voltage shutdown and lockout Pre-charging of output filter capacitors prior to connection of the battery plant Walk-in (Gradual increase of output current when the rectifier is turned on) Output ammeter Voltage test jacks Local and remote on/off control Visual control indicators to show the operating state of the rectifier Selective overvoltage shutdown of rectifier causing an overvoltage condition when initiated by a high voltage signal from the plant Remote alarm and control signals for system operation Rectifier failure alarm Fan failure alarm
There are two technologies of lead-acid storage cells presently use d in telecommunications applications: Flooded Valve Regulated Flooded lead-acid batteries are available in various plate types: Lead-calcium Lead-antimony Pure lead Flooded Lead-Calcium Cells Flooded lead-calcium cells are the most widely used cells in large telecommunications applications. These cells use a flat plate design mounted vertically within the cell jar. Calcium is added to the plate grid to increase the mechanical strength of the plate and these plates are submersed in a liquid sulfuric acid electrolyte. Lead-calcium cells are designed to provide approximately 80 discharge cycles down to 100% of their rated capacity or 20 years of service at 77 ° F with proper maintenance. Typical service life can range from 15 – 18 years. The lead-calcium cells require less maintenance than antimony cells. The low self discharge of the cell requires a small amount of current to keep the cell in a fully charged state. Because of the low current required to charge the cell, the cell produces less gas and in turn the amount of water lost is less than the lead-antimony.
Flooded Lead-Antimony Cells The lead-antimony cell is similar to the lead-calcium cell, except that antimony is added to the plate grid to increase the mechanical strength of the plate. The lead-antimony cells are designed to provide greater than 200 discharge cycles down to 100% of their rated capacity or 20 years of service at 77 ° F with proper maintenance. Typical service life can range from 13 -16 years. The lead-antimony cells require more maintenance than calcium cells. These cells have a high self discharge rate, which requires a larger amount of current to keep the cell in a fully charged state. Because of the higher current required to charge the cell, the cell produces more gassing and in turn the amount of water lost is more than the lead-calcium cells, hence the maintenance is increased. Pure Lead Cells (commonly referred to as the “Round Cell”) The pure lead cell was designed to minimize physical deterioration inherent in conventional battery design. The plates are submersed horizontally into the cell jar so that the plate growth is upward, rather than outward. Also, the positive plate growth is managed due to the cylindrical design of the jar. By managing the direction of the plate growth, there is less chance of the cells cracking and electrolyte leakage. The expected service life of the round cell is 30 to 40 years, based on accelerated life tests.
Valve-Regulated Lead-Acid Cells (VRLA) Valve-regulated lead-acid cells are the most widely used cells in small telecommunications applications, such as cabinets, remote sites, customer premise, cell sites, etc. These cells utilize either an absorbed fiberglass mat (AGM) or “gelled” technology. The AGM technology employs an immobilized electrolyte that is absorbed into fiberglass mats similar to a sponge. The gelled technology utilizes a gelling agent to immobilize the electrolyte. In either technology there should be no residual liquid electrolyte within the cell. Additional information is contained in Reference Telcordia SR-4228, Certification Requirements for VRLA Battery Strings and 1187-1996 IEEE Recommended Practice for Installation Design and Installation of Valve-Regulated Lead-Acid Storage Batteries for Stationary Applications. These cells operate under a small amount of pressure (approx. 2 – 3 lbs.) in order to recombine oxygen, minimize the water loss and maintain a fully charged cell. As the name implies, these cells are equipped with a pressure relief valve that will operate if the design pressure is exceeded. Since these cells operate under a small amount of pressure they are essentially “sealed” under normal operating conditions, making traditional battery maintenance methods impossible to perform. Some manufacturers refer to these cells as “maintenance free”; although there are alternative methods of maintenance which still need to be performed to ensure satisfactory operation of the battery. Reference 1188-1996 IEEE Recommended Practice for Maintenance,Testing, and Replacement of Valve-Regulated Lead-Acid (VRLA) Batteries for Stationary Applications.
VRLA The service life claims for VRLA cells are generally 10 years, with some manufacturers stating up to 20 years of service at 77 ° F. VRLA cells are designed to provide approximately 30 - 60 discharge cycles down to 100% of their rated capacity and service life, 10 – 20 years respectively. However, in many cases VRLA cells are used in uncontrolled environments or extreme temperature environments, such as outside cabinets. When a battery is used in applications where the temperature is above 77 ° F, the service life of the battery is decreased. For example, a VRLA battery with a 10 year life expectancy placed in a cabinet, in an environment with temperatures above 100 ° F, would only last 2 – 3 years.
Battery Reserve Capacity Battery reserve time is the amount of time a battery plant can provide DC power to the telecommunications equipment within the emergency operating voltage limits of the load equipment served. This reserve time must be based on the busy-hour load plus an additional 20% due to the increase in current present as the constant power load equipment is operated at the low emergency voltage limit. When determining the reserve time required, the following criteria should be considered: Standby generators Permanently mounted on-site standby generators. Use of portable standby generator sets. Staffing requirements for the facility or application (attended or unattended). Reliability of the commercial AC utility service. Travel time for personnel to respond for repair or dispatch a portable standby engine. Company policy may provide directives. State Regulatory or Commerce Commission Requirements.
Telecommunications power plants employ cells connected in a series within a battery string and parallel battery strings in a power plant. Cells in a battery string are connected in series, therefore the voltage of each cell is additive to provide the operating voltage of the system (24 Volt, 48 Volt, etc.). When the battery strings are connected in parallel, the voltage of the system remains the same, but the available discharge current is additive and the amount of battery reserve time is increased. The available battery reserve will be impacted based on: Physical size of the cells used Rated electrical capacity of the cells Number of battery strings connected in parallel Power plants should be configured with a minimum of two battery strings to meet the desired battery reserve time. This will allow one of the battery strings to be taken off-line for maintenance purposes while still providing a limited amount of battery reserve time. To increase the reserve time, additional parallel battery strings could be added to the power plant or the smaller capacity battery strings could be replaced with larger ones. Ideally, all of the battery strings within a power plant would be of the same size / capacity and from the same manufacturer.
Discharge Curves This figure illustrates a typical discharge curve for a main battery only DC power plant. The amount of reserve time is a function of the ampere capacity of the battery string, the quantity of battery strings and the minimum operating voltage of the equipment served. The discharge time begins once the rectifiers cease to operate due to an AC power failure. The discharge time ends once the voltage reaches the low emergency operating limit of the equipment served plus any voltage losses in the power distribution network. This voltage will be when the first piece of equipment in the office fails or the “highest low emergency limit”. Note: The low emergency operating limit of telecommunications equipment will vary within a manufacturers portfolio as well as from manufacturer to manufacturer. Equipment suppliers should be consulted for actual values. The voltages shown in this figure are measured at the batteries. The voltage available to the telecommunications equipment would be less due to the losses in the power distribution cables.
Battery Age Battery cells are designed to provide reserve capacity over their useful service life. The service life of a battery is also affected by temperature, the number of discharge cycles and the level of maintenance performed. A well maintained battery operating in a 77 ° F environment is designed to reach 80% capacity at the end of its service life. When the cell reaches 80% of its original capacity, it is no longer considered reliable and should be replaced. Note: When batteries are operated in temperatures greater than 77 ° F , the life of the battery will decrease. Operating the batteries at lower temperatures will decrease the reserve capacity. As illustrated above, a new battery has slightly less than 100% capacity. Over time the capacity will reach just over 100% and then begin to deteriorate. The capacity will slowly deteriorate until the battery reaches approximately 75% of its service life, at which time the capacity will begin to deteriorate more rapidly.
Power Board Power boards contain the voltage and amperage meters, rectifier control, local and remote alarm annunciation, and circuit protection devices that feed the downstream secondary distribution devices or telecommunications equipment. The main power board is the point of interface between the rectifiers, batteries and telecommunications equipment. As such, the power board is equipped with a controller which monitors the operation of the power plant. When an alarm is present within the power plant, the controller will transmit an alarm to the Network Operations Center or designated alarm reporting center.
Controller The controller will monitor the rectifiers for failures, and will control them for selective high voltage shutdown, energy management, load sharing and voltage control. Distribution circuit protection (circuit breakers or fuses) is monitored as well. Local visual indicators on the controller will identify the source of the alarm. Typical failure alarms are: Rectifier failure Rectifier fan failure Fuse or circuit breaker failure Control fuse failure Controller failure The controller is equipped with adjustable alarm thresholds to monitor the “float voltage” of the plant. These alarm thresholds may be adjusted as required. When the voltage alarm thresholds have been exceeded local visual indicators on the controller will identify the alarm. Typical voltage alarms are: Low voltage 1 / Battery on discharge Low voltage 2 High voltage 1 High voltage 2
Microprocessor Control Many power plants may employ microprocessor controllers. These microprocessor controllers provide the monitor and control functions as described earlier, as well as offer remote access, storage of historical information, and data acquisition. A microprocessor controller can monitor, control and store data from numerous peripheral devices / systems for statistical information and alarm reporting. Alarm reporting can be via conventional alarm reporting methods, modem or an internal data network. Microprocessor controllers will: Monitor the status of the power plant Record system current drains on discharge Record branch DC distribution feeders current drains Record the battery voltage Record the input voltage to major DC distribution feeders Monitor AC input voltage Monitor other peripheral data points Group alarms into categories for local annunciation and alarm-sending circuits Provide remote diagnostic capability and enhanced local diagnostic information Store historical and statistical data Minimize energy usage by turning off unneeded rectifiers Dial-out capability to report alarms Dial-in polling and control capability with multi-level security features
Power Distribution The power distribution network is comprised of the circuit protection devices (fuses and circuit breakers) within the power plant, the cables that carry the power to the telecommunications equipment and any other secondary power distribution bays, cables and circuit protection devices between the power plant and the load equipment. The power distribution network must be capable of overcoming the resistance losses in the power distribution cable. The power distribution network must deliver an adequate amount of power to the load even while the battery voltage is declining due to a discharge condition. Either fuses or circuit breakers can be used within their voltage, amperage and interrupt current capacity ratings. Voltage Rating A circuit protection device must have a voltage rating equal to or greater than the normal voltage that will be seen across the device under all conditions. Ampere Rating The ampere rating of the circuit protection device is the ampere value that the device is expected to have flowing through itself without operating. Interrupt Rating The ampere interrupt rating (AIR) of the device provides for safe operation of the circuit protection device when subjected to high short circuit currents. The interrupt rating is the maximum short circuit current a device can interrupt without losing case integrity.
Function A converter is a device that utilizes a DC input of one voltage and polarity, and changes or “converts” it to the same or another DC voltage of the same or opposite polarity . The converter plant has no batteries across its output . The load is totally dependent on the output of the converters. Converter plants, therefore, are always equipped as the number of converters to satisfy the load plus 1 additional converter as a “hot” standby (N + 1). Since converters do not have reserve overload capacity, it is imperative that the N+1 configuration be maintained. In reality, all converters are operating as they share the load proportionately. Some converter applications include: Isolation of input and output Embedded converters Converter plants Isolation Converters are considered separately derived power sources since, as a converter changes the input voltage and polarity to the desired output voltage and polarity, the output becomes totally isolated from the input. Therefore, it is necessary to reestablish a ground reference on the output side of the converter to the nearest ground reference. This new ground reference will provide an isolation between the input and output of the converter.
Stability and Regulation Because the converter regulates to a constant output voltage, the input current will vary depending on the input voltage. As the input voltage decreases, the input current increases. This is an important characteristic to keep in mind. The increase in current amounts to approximately 22% from the normal float voltage of 52.08V to a typical minimum operating voltage of 42.75V. Constant Power Output Converters provide a “constant power” output to the equipment. The output voltage and amperage of the converters will remain the same even when the input voltage decreases during a battery discharge condition. Example: An equipment frame powered by embedded converters requires 10 amperes at 52.08V. If the input voltage decreases to 42.75V, the input current will increase to 12.18 amperes. Mathematically, using Ohm’s Law, (P = E x I): 52.08V x 10A = 520.8 Watts 520.8W 42.75V = 12.18A. This increase in input current is 21.8% or approximately 22%. This additional 22% drain becomes part of the power failure load and must be considered when provisioning batteries for telecommunications applications.
Embedded Converter Telecommunication equipment utilizes embedded converters to change the voltage and/or polarity supplied by the power plant into a the appropriate voltage and polarity to be used by the equipment. These are located directly within the particular equipment unit, chassis, frame or circuit pack that requires the specific output voltage. Since these converters are part of the telecommunications equipment, provisioning them is no concern to the power engineer. For more detailed information refer to Telcordia TR-TSY-001003, Generic Requirements for DC-to-DC Converters.
Converter Plants Telecommunications equipment is predominantly designed to operate on –48 volts DC. Therefore, most power plants are designed for –48 volt operation, while wireless applications operate at +24 volts. Depending on the voltage of the battery power plant there may be a need for other voltages within the facility. In wireless applications there may be a need to change the +24 volt DC battery supply to a –48 volt supply to serve transport equipment. In 48 volt applications there may be a need for a +/- 130 volt supply. Converter plants sizes usually range from 3 amperes up to 30 amperes and are generally located in the power room. They can be used for any requirements in the building.
Structures The types of equipment located in remote locations can be the same as found in a traditional large telecommunications facilities. Although this equipment may be designed to operate in extreme temperature and humidity conditions. The power equipment and batteries will also be subjected to these harsh environmental conditions. These remote structures are generally less than 350 square feet and may be customer premise locations, lease space, cabinets or huts used as wireless radio sites. Customer Premise / Leased Space A customer premise location is usually a secure room in an office or commercial building. The room will need to have sufficient floor space, adequate environment control capabilities, AC power for the DC power plant rectifiers, and a reliable grounding source. Also needed will be an AC connection for a portable engine-alternator or capacity on the building owner’s stationary engine-alternator.
Cabinets A cabinet is a relatively small weatherproof structure designed to hold a variety of telecommunications equipment and the necessary power plant and batteries. This cabinet can house two or three “bays” of equipment with each “bay” being approximately 4 feet high. The cabinet may not be environmentally controlled and will subject the power equipment to extreme temperature conditions. Therefore, the battery service life can be significantly less due to the high temperatures.
Huts A hut is a fully assembled, transportable structure, capable of housing telecommunications equipment. The basic function of a hut is to provide protection from the elements and vandalism, and to discourage access by unauthorized persons. The pre-assembled structure is environmentally controlled, therefore equipment that is used does not need to be designed to operate in extreme temperature conditions. Because this structure is environmentally controlled the service life of the batteries will be more in line with published data. The huts provides for: Entry of wireless antenna cables into the building Entry of telephone cables into the building Grounding of equipment Air conditioning and heating AC panelboard for electrical distribution Connection for a portable engine-alternator. A typical hut is about 11’ x 15’ and can hold approximately 15 bays of equipment.
DC Power Plants This figure shows a block diagram for a typical DC power plant used in a remote location. It is very similar to larger DC power plants. DC power at a remote location is generally provided through the following: Bulk Power - A single plant is provisioned to power all of the equipment in that structure. This power plant can vary from 50A to 600A or greater. Note: This power plant contains a low voltage disconnect/reconnect device (LVD/R). A LVD/R can be used to disconnect the battery strings when the voltage reaches a preset level to protect both the batteries from excessive discharge and the equipment from too low a voltage.
Plant Capabilities As with the power plants used in large telecommunications facilities, the capacity of the power plant must be selected to match the present and future needs of the equipment at that location. The capacities can vary from a few amperes to several hundred amperes. The power plant capacities will be determined by the amount of telecommunication equipment deployed, with consideration for any future equipment additions as well.
Rectifier The rectifiers provisioned most commonly at a remote location are of the switchmode, plug-in variety. They vary in capacity from 3 amperes up to 50 amperes each. When provisioning rectifiers in remote locations, there are: Maintenance spare requirements Recharge requirements The recharge requirements at remote locations are different from larger applications, in that the recharge requirement at a remote location is up to 40% of the normal busy hour DC load (busy-hour x 1.40). This recharge requirement is greater because most remote locations have an 8 hour battery reserve time. Since the batteries could sustain a deep discharge, the extra capacity is to ensure recharge to 95% of capacity within 24 hours.
Requirements The primary responsibility of the power planner is to select and engineer power plant equipment. The planner may also have a secondary responsibility for locating this equipment within the building. Some of these requirements include: Ceiling Height Floor loading Floor support Cabling & lighting Standard floor plans These and other requirements are addressed in the CORE-GR63, which establishes the industry standards. GR63-CORE Telcordia has established environmental requirements for Network Equipment Buildings Systems (NEBS) in CORE-GR63. This document is a comprehensive review of the environmental requirements for not only the equipment, but also the structure in which the equipment is located. It addresses spatial requirements within vertical and horizontal space allocations and floor loading limits, as well as environmental criteria for temperature, humidity, fire and earthquake. GR63-CORE addresses telephone company requirements as well as suppliers’ requirements, even down to the level of packaging to prevent damage during shipment.
Floor Plans Many things must be considered when laying out a floor plan for a power plant: Weight of the equipment - especially batteries Adequate space for hauling and hoisting apparatus Minimizing conductor lengths Adequate bending radius for power cables Most power plant manufacturers have developed standard layouts for their equipment taking into consideration the above information. However, many telecommunications buildings will not accommodate these ideal arrangements.
Ceiling Height Generally, DC power equipment shall have a maximum height of 10 feet as shown in the above figure. This height includes all superstructure and overhead facilities such as cable, cable racks, and bus bars. It also includes the headroom necessary for installation, operation, and maintenance.
Power Plant Selection When selecting a power plant to fit an application, several general and site-specific issues must be considered. More detailed information may be obtained from Telcordia GR-63-CORE and ANSI T1.311-1991. Some of these considerations include: Environmental Rectifiers and batteries are designed to operate within a specific temperature and humidity range. When provisioning rectifiers and batteries in outside applications, such as cabinets, it is important to consider the effects of extreme temperatures and humidity. In controlled environments adequate ventilation must be provided. Space / Floor Loading SCR and ferroresonant rectifiers require more physical space and are considerably heavier than switchmode rectifiers. VRLA batteries are more energy dense than flooded batteries. The facility must be suitable to accommodate the initial spatial and floor loading requirements and future growth. The longer battery reserve times require more batteries. Adequate working space for proper operation, installation and maintenance must be provided. DC Output The rectifier output voltage must be operational across the voltage limits of the telecommunication equipment served (48 volt rectifiers for 48 volt applications, 24 volt rectifiers for 24 volt applications, etc.). AC Input Power The input voltage of the rectifier should match the voltage available from the utility and the standby generator, where applicable. Rectifier input voltages can range from 120 volt, AC, single phase, to 208/240 volt, AC, single phase for small applications such as cabinets, customer premise, huts, cell sites, etc. In larger applications the rectifiers may require 208 volt, AC, three phase or even 480 volt, AC, three phase service.
PP&B <ul><li>Partial support for this curriculum material was provided by the National Science Foundation's Course, Curriculum, and Laboratory Improvement Program under grant DUE-9972380 and Advanced Technological Education Program under grant DUE‑9950039. </li></ul><ul><li>GWEC EDUCATION PARTNERS: This material is subject to the legal License Agreement signed by your institution. Please refer to this License Agreement for restrictions of use. </li></ul>
Overview <ul><li>This module will address the following topics: </li></ul><ul><li>Power Sources </li></ul><ul><li>Power Plants </li></ul><ul><li>Power supplies </li></ul><ul><li>Rectifiers </li></ul><ul><li>Converters </li></ul><ul><li>Batteries </li></ul>
Learning Objectives <ul><li>At the end of this module, participants will be able to: </li></ul><ul><li>Describe the typical power sources found at a cell site. </li></ul><ul><li>Differentiate between a power plant and a power supply. </li></ul><ul><li>Explain the technologies, discharge cycle, and life expectancy of various battery sources. </li></ul><ul><li>Explain the theory and design principles of a power plant in a telephony network. </li></ul>
Power Plant Function <ul><li>Change AC to DC at the required voltage and polarity </li></ul><ul><li>Store energy in the event of AC failure </li></ul><ul><li>Distribute the DC to the equipment loads </li></ul>
Power Plant Components Rectifiers Power Board (PBd) Batteries
Main Battery Only Plant Charge Bus Load Bus Return Bus C.O. Ground Batteries Rectifier Rectifier Equipment Loads A + - + - Equipment Loads
Rectifier Features <ul><li>Each company’s product selection group reviews the features of rectifiers being considered for purchase. </li></ul><ul><li>Based on this review, a list of approved products is published </li></ul>
Battery Reserve Time <ul><li>Standby AC Plant </li></ul><ul><ul><li>On-site </li></ul></ul><ul><ul><li>Portable </li></ul></ul><ul><li>Office – attended or unattended </li></ul><ul><li>Reliable utility AC at location </li></ul><ul><li>Travel time </li></ul><ul><li>Company policy </li></ul><ul><li>Regulatory requirements </li></ul>
Battery Strings in Parallel Cells in Series- Voltage Adds Batteries in Parallel – Current Adds . . . . . . . . . Loads
Discharge Curves 52 50 48 46 44 Float Time Hours Reserve Time with two strings Battery Voltage Reserve Time with one string Lower voltage limit of served equipment Float Voltage = 52.08V
Effects of Aging and Replacement Criteria 120 100 80 60 40 20 % Capacity 0 10 20 30 40 50 60 70 80 90 100 % of Rated Battery Life
Hut Equipment Bays Equipment Bays Bulk Power Bay A/C and Heater Unit Communications Cable Entrance Electric Service Panel
DC Power Plants Rectifier Rectifier Battery Battery Charge Bus Battery Bus LVD/R Ammeter Shunt DC Loads Power Board Alarm Monitoring Center Dial-up Status and Polling Status, Alarm, Data Acquisition, and Reporting Return Bus Dischg. Bus
Power Plant Capabilities Small Single-Bay Power Plant Medium and Large Two-Bay Power Plant Distribution Fusing, Control, Monitoring, & Alarm Panel Rectifiers Batteries Batteries DC to DC Converters Rectifiers Monitoring, Alarm, and Control Panel Distribution Fusing
Floor Plans 20 - 0 20 - 0 String A String E String D String C Battery Strands with Spill Containment Trays String E + + + AC PDBC + Rectifiers DC-DC Conv., Inv., etc Cont & Dist’n Fut.
Ceiling Height 12’ 6” Bus bar or Cabling Power Cabinet 10 Foot Max. (Including Equipment Cable and Clearance) Air Duct Batteries
Power Plant Selection <ul><li>Environmental </li></ul><ul><li>Space/Floor Loading </li></ul><ul><li>DC Output </li></ul><ul><li>AC Input Power </li></ul>
Industry Contributors <ul><li>The following companies provided materials and resource support for this module: </li></ul><ul><li>Telcordia Technologies, Inc (www.telcordia.com) </li></ul>
Individual Contributors <ul><li>The following individuals and their industry or educational institutions provided materials, resources, and development input for this module: </li></ul><ul><li>Branislav Rosul </li></ul><ul><ul><li>College of DuPage </li></ul></ul><ul><ul><li>http://www.cod.edu/ </li></ul></ul><ul><li>Philip DiPiazza </li></ul><ul><ul><li>Florida Institute of Technology </li></ul></ul><ul><ul><li>http://www.fit.edu/ </li></ul></ul>