Power quality in medium & large commercial
Contents
1. 4so 359 319 9 a w 7 UPS 3 PCload soo 755 264 a 3 3 2 UPs 4 PCload 7 00 431 552 13o s 7 4 27 fide o2 f oss o2 130 of 73 52 30l 24 0 3 18 6l 1 21 42 Laser printer Power Quality in Medium and Large Commercial Buildings PQ TechWath oS SSS The presence of even numbered harmonics is not at all typical and may indicate a malfunction of the appliance A few amps of very distorted current mixed with tens of amps of slightly distorted current should not overburden typical building wiring For single phase electronic loads the harmonic current may be higher than the fundamental current indicating a total harmonic distortion of greater than 100 Most of these machines generate odd numbered harmonics 3rd 5th 7th and so on Note that generally the higher the harmonic number the less the current produced Harmonic currents are highest when many single phase nonlinear loads such as computers are connected to a few branch circuits In fact multiple computer work stations and the like are responsible for the higher levels of current in commercial buildings As shown in the table the current drawn by single phase electronic equipment is typically rich in third harmonic The presence of even numbered harmonics is not at all typical In fact even harmonic orders indicate either a malfunction of the appliance which should be identified an2. the building automation system BAS controls all HVAC components The BAS is used to automate the air conditioning process and to increase the energy efficiency of all systems There are many different types of BAS configurations and methods of control however all types of controllers have the same basic elements BAS units are composed of a central processing unit CPU powered from either an internal or external DC power supply and all have either AC or DC I O used to interpret inputs and outputs The BAS can be protected against voltage dips and interruptions by conditioning all power to the BAS power supply and I O as shown in the figure below 230V Conditioned 230V Conditioned Building Automation System Power Conditioning Technique Building Automation System BAS eee fe a Hea a Output Module Input Module Using line to line power conditioning for building automation systems PN TechWath S gt SSS drive and affect its performance through three different areas shown in the figure below The first and typically the most sensitive to dips is the drive s control circuit The control circuit can be protected by following the centralized or discrete power conditioning technique described herein The second component of the drive sensitive to dips is its internal controller Depending on the drive s configuration when access to the internal control circuit and controller are made avail
3. use of nonlinear loads has significantly increased the load because these types of loads tend to remain turned on a high percentage of the time Additionally multi outlet power strips have made possible a significant increase in the number of loads per outlet and thus a higher average plug load Although most electronic equipment is energy efficient the power factor is typically low when all the harmonic frequencies are taken into account The resulting harmonic currents increase the amps per watt drawn by nonlinear loads An abundance of harmonic current coupled with a high demand load and heavy plug loads may consume any spare current carrying capacity designed into the building transformers and conductors In an extreme case the electrical system in a commercial building may be overburdened if it is not designed to accommodate the large number of nonlinear loads Moreover typically codes do not take into consideration design procedures to protect wiring carrying PQTechWatch o gt SSS The modern office is brimming with loads that draw nonsinusoidal currents These nonlinear plug in appliances include personal computers printers monitors fax machines and photocopiers Nonlinear equipment such as fluorescent lamps with electronic ballasts and high efficiency HVAC systems are also sources of harmonic currents in commercial buildings The table below lists the current characteristics of single phase applia
4. Quality in Medium and Large Commercial Buildings PN TechWath S gt SSS The proliferation in office use of electronic equipment and microprocessor based controls has caused electric utilities to redefine power quality in terms of the quality of voltage supply rather than availability of power INTRODUCTION Power quality has emerged as an important issue for the commercial customer segment Historically power quality issues have been the domain of electric utilities which focused on reducing or eliminating power outages However the proliferation in office use of electronic equipment and microprocessor based controls has caused electric utilities to redefine power quality in terms of the quality of voltage supply rather than availability of power In this regard IEEE Standard 1159 1995 R2001 Recommended Practice for Monitoring Electric Power Quality and its European counterpart IEC 61000 4 30 Testing and Measurement Techniques Power Quality Measurement Methods have defined a set of terminologies and their characteristics to describe the electrical environment in terms of voltage quality The table below shows the categories of power quality disturbances with spectral content typical duration and typical magnitude This document focuses on how commercial equipment is affected by power disturbances The term commercial building encompasses Categories of Power Quality Variation Typical Spectral Typ
5. SSS NOTES 1 European Commission Towards a European Strategy for the Security of Energy Supply Green Paper October 2001 p 4 available from http ec europa eu 2 EPRI Roadmap for Power Quality Mitigation Technology Demonstration Projects at Commercial Customer Sites TR 114240 Palo Alto CA EPRI 1999 3 M Stephens and C Thomas Protecting Process Water Cooling Systems Against Electrical Disturbances Power Quality for Utilities to Support Commercial and Industrial Customer Program EPRI Technical Update 1002283 2003 4 EPRI Commercial Office Wiring Nonlinear Loads Harmonic Related Heating Commentary No 1 EPRI Power Quality Testing Network TC 107163 December 1996 5 EPRI Avoiding Harmonic Related Overload of Shared Neutral Conductors Application No 6 EPRI Power Quality Testing Network TA 106576 April 1996 Power Quality in Medium and Large Commercial Buildings
6. residential and commercial building sector and the breakdown of energy usage within that sector is shown below Commercial buildings alone account for about 12 percent of EU energy use However the study doesn t show how the growth of the Internet and the proliferation of digital equipment has changed the dynamics of the electrical environment Energy End Uses in the European Residential and Commercial Sectors EU Energy Use Commercial and Residential Buildings 40 Commercial 30 Residential 70 The commercial building sector accounts for 12 of total European Union energy consumption Source European Commission Power Quality in Medium and Large Commercial Buildings PQ TechWatcth SSS Unfortunately the EU study only shows total energy use and does not differentiate electrical natural gas oil and sustainable energy users The figure below shows a breakdown of how electricity is used in commercial facilities in the United States Electrical Energy End Uses in the U S Commercial Sector Ventilation 7 Refrigeration 9 Office Equipment 18 Other 9 3 Space Heating Water Heating 1 Cooking 2 Cooling 26 Lighting 23 Source Commercial Buildings Energy Consumption Survey CBECS Energy Information Administration EIA The consequences of a disturbance may range from a minor nuisance to extensive equipment damage and loss of cri
7. ELECTRIC POWER RESEARCH INSTITUTE PQ lechWaich A product of the EPRI Power Quality Knowledge program Erel Powen Quality m Medium and Larg Commercial Buildings November 2007 CONTENTS Introduction ara ee ee 1 Major Uses of Energy in Commercial Buildings eee 1 Typical Electric Loads of Comines e ISUIICIMGS 5 cesses 7esce eee 2 Power Quality Impact on Commercial Customers 92 5 4 2 555 2 Heating Ventilation and Air Conditioning System HVAC 3 Air Conditioner Systems 3 Process Cooling Water Chillers and Water Pumps 4 Ventilation Systems ee era ree eaaa 5 Protection of HVAC Voltage Dip Sensitive COmpPoNE nts a a ee ere re ere 5 Building Automation Systems 6 Variable Speed Drives for Ventilation and Vyater PUMPS oe eae eens eee ea 7 General Recommendations for Chiller Controllers and Motor Protection Relay Settings eenaa re anaa ee oe 9 ae E E E A A A E E E ee ee 9 Types or LIgAtno e a ernest 9 Power Quality and Lighting a PIC VALONS ees ee eee ee eee 14 Harmonic Generating Loads 14 Lighting and Three Phase Loads 16 Wiring Configurations in Commercial BUIdInNgS Ves ee ee 17 Harmonic Effects on Building Wiring 18 Notes e eee eee ee ee eee era 20 Chuck Thomas Senior PQ Engineer EPRI SUMMARY According to the European Union 40 of all electric energy produced in Europe is used to power co
8. Harmonic Effects on Building Wiring The primary effect of harmonic loading on the building wiring is increased current as much as double for loads with highly distorted currents Highly distorted current also reduces the power factor and the spare current capacity of conductors Because conductor heating depends upon the square of the current building power system losses will also increase Losses in Conductors Because conductors are resistive any current flowing through them will generate heat The amount of energy lost through heat by a conductor at a particular frequency depends upon the amount of RMS current flowing through the conductor and resistance of the conductor at that frequency Harmonic currents usually add to the RMS current flowing in building wiring thus increasing the amount of energy loss For highly nonlinear loads such as personal Hj T gt T gt computers the RMS current due to harmonics could be as high as the T fundamental current 230V Loads Loads Loads Loads Loads Loads e k EA A N Loads within commercial builds often share a common neutral Losses in Transformers Nonlinear loading may increase heating in A balanced three phase system with a shared neutral conductor is also the most efficient configuration Circuit losses can be as much as 40 lower with the shared neutral configuration because the fundamental return currents cancel in the neutral conductor between office Pow
9. Lighting E Measure of allowable For motors with service There are a number of different lighting phase current 20 30 factors of L15 Or mbalance imbalance greater technologies employed in large commercial Delay time in which buildings Current imbalanced current 5 seconds Instantaneous settings Imbalance ies must be present minimum not recommended Time sec before chiller trips Incandescent Lamps Always consider auto Incandescent lamps use an electric current start features or auto Enable start up of an adjacent chiller upon the fault of the unit that is running DWP PRAM ee een eae to heat a tungsten filament to a state of Option shutdown incandescence so that it produces visible light The atmosphere around the filament is usually argon an inert gas similar in atomic Parameter not available on all chiller systems Single Cycle Detects loss of power Dropout for a single cycle Renae weight to oxygen Some premium incandescent lamps use the rarer and more Instantaneous settings expensive krypton gas atmosphere which PB Time Phase balance relay 5 seconds not recommended Power Quality in Medium and Large Commercial Buildings allows for roughly double the lamp life of a comparable argon filled lamp Operating voltage affects incandescent lamp operation As voltage increases more current passes through the filament thereby increasing lumen output efficacy and color temperature Lamp life is
10. able this circuit should be powered from a conditioned source Besides protecting all power to the BAS make sure that the CPU s battery used to maintain the program in the event of power interruption is working properly Typically the life span of these types of batteries is two years To be safe all BAS batteries should be replaced on a yearly maintenance basis Variable Speed Drives for Ventilation and Water Pumps Variable speed drives in commercial buildings are used to power ventilation fans and water pumps Voltage dips can enter the Power Quality in Medium and Large Commercial Buildings Variable Speed Drive Power Conditioning Solution 230V Conditioned Power Source Variable Speed i Pe S Sa Drive Control Circuit E aTa PWM Power conditioning for motor drives can often focus on the control circuitry only The third component of a drive sensitive to dips is the rectifier inverter circuit When the rectifier is subjected to voltage dips or interruptions the DC voltage output level is changed The DC voltage change is dependent on the magnitude and duration of the voltage dip event If the DC voltage level meets or exceeds a determined level called the undervoltage trip point the drive will stop and will need to be restarted either manually or automatically PN TechWath SSS In most cases drive manufacturers give users access to basic micropr
11. arge Commercial Buildings PTechWatch S gt SSS Discharge lamp technology is commonly applied to standard room lighting with fluorescent and metal halide lamps high powered area lighting with mercury vapor and sodium vapor lamps and art or advertising signs with neon and argon lamps The electric current that flows through the gas is called an arc because it jumps a gap between electrical contacts or electrodes at either end of the lamp The arc must be maintained at specific voltage and current or the gas pressure and temperature could escalate rapidly and cause the lamp to explode As shown in the figure below a device called a ballast is placed in the electric circuit to regulate the arc voltage and current for optimum lamp operation In order to begin the arc the gas must either be ionized by passing a very high voltage across the electrodes or heated to operating temperature This is called starting and the starting method varies with lamp type An example starter is shown in the figure on the following page Fluorescent Lamp Circuit Configuration with Ballast AC Power Source z 4 4 Phosphor PQTechWatch gt o gt SSS Arc Lamp Circuit Configuration with Starter and Ballast AC Power Source Ballast Power Quality Characteristics of Fluorescent Lights PQ Measurement Crest factor Power factor Harmonic distortion Description Crest
12. be applied to minimize shutdowns and equipment damage PQ TechWath S gt SSS About the EPRI Power Quality Knowledge program The EPRI Power Quality Knowledge program provides a wealth of resources in well designed readable and accessible formats Paramount among these resources are documents covering a wide range of PQ topics written not only for use by busy PQ professionals but also to be shared with important end use customers and internal utility managers The program s website www mypq net is the most comprehensive electronic PQ resource available providing 24 7 access to proven expertise via the PQ Hotline hundreds of PQ case studies over 200 PQ technical documents PQ standards references indexes conference presentations and a wealth of other resources For more information please visit www mypq net Copyright 2007 EPRI www epri com All rights reserved Distribution of PQ TechWatch is subject to a license agreement with EPRI No portion of this report may be reproduced or redistributed in any form including electronic copies without prior written consent from EPRI Distribution outside the licensed organization is expressly forbidden Product and company names mentioned in this document may be trademarks of their respective companies Mention of third party products is for informational purposes only and constitutes neither a recommendation nor an endorsement EPRI and the EPRI logo are trademarks of EPRI Power
13. d removed or replaced or the use of a half wave rectifier such as an electric hand tool The relative power consumption of the electronic appliance and the percentage of THD determine how much the electronic equipment contributes harmonic current to the building wiring system While some office loads may have a high percentage of distortion the actual amount of harmonic current they contribute to the building wiring may be insignificant For example the personal computer with 150 current THD draws less than 1 amp of harmonic current In contrast the microwave oven with only 45 current THD draws almost 4 amps of harmonic current Many small equipment such as computers may contribute very little to the total harmonic current in a wiring system A few amps of very distorted current mixed with tens of amps of slightly distorted current should not overburden typical building wiring The power circuit design of an electronic appliance determines its current distortion characteristics For example each of the four UPSs in the table has a different front end rectifier design Consequently the current harmonic distortion of each UPS ranges from 8 to 130 The typical computer monitor printer and fax machine all staples of the modern workplace use switch mode power supplies SMPSs which draw current as shown in the figure below Current Waveform of a Typical Switch Mode Power Supply Computer equipment and pe
14. e which contributes to resistance and thus heating In summary the results of harmonics created by office equipment are overloaded undersized neutral conductors inadequate filtering caused by undersized transformers and energy losses through the neutral conductor and transformers By installing neutral conductors sized one gauge larger than the phase conductors building designers and engineers can adequately mitigate the effect of harmonic currents on shared neutral conductors Additionally a rating system for sizing transformers in a world of harmonic currents has been in place for several years and has been effective in measuring and reducing the potential for overloading transformers In the end the total energy losses caused by harmonic currents tend to go unnoticed in the power bill because of the increased energy efficiency of many harmonic generating loads Office equipment manufacturers have not been idle With every new generation of office equipment they have an opportunity to improve their products For example manufacturers are beginning to incorporate power factor correction circuits into their power supplies Therefore future generations of energy efficient electronic appliances may generate such low levels of harmonic current that even buildings with modestly sized neutral conductors and transformers would be able to carry the currents drawn by office appliances PQTechWatch gt o gt
15. e in harmonic distortion which is mostly 5th and 7th harmonic with little if any 3rd harmonic Typical loads for a commercial building include office equipment conveyance lighting and building heating and cooling Power Quality in Medium and Large Commercial Buildings Large three phase loads such as HVAC are served from motor control centers or main power panels at 400 V Lighting is often served from its own panel at single phase 230 V office plug loads derived phase to neutral connections Although much of the harmonic current flowing from office equipment to the utility system will eventually cancel harmonic current flowing in the branch circuits serving nonlinear loads may actually add in neutral conductors The plug loads in commercial office buildings are typically single phase and connected from line to neutral which can be either a separate neutral conductor ora neutral conductor shared by other loads in the circuit The most common wiring configuration in Europe is a four wire circuit with a shared neutral conductor see figure below Single Phase Branch Circuits with a Shared Neutral Conductor PQTechWatch o gt SSS equipment However harmonic currents in this type of configuration may overload the neutral conductor particularly if the conductor is undersized Until recently electric codes required neutral conductors to be one size smaller than the phase conductors
16. e objective is to maintain as close as possible the desired output voltage for operating the moter and load Controlled When the drive senses a DC link undervoltage condition the drive Deceleration and begins to decelerate the motor at a user defined rate When the Acceleration undervoltage condition ends the drive reaccelerates the motor back to the desired operating point This feature is often used in processes with multiple drives operating in succession where all drives are expected to operate in unison to maintain process quality This feature works well for common DC bus drive systems Phase Loss and DC Link Undervoltage Functions Parameter Parameter Description Input Phase Loss The input phase loss detection circuit monitors either the input phases or DC bus current ripple and activates when one of the input phases is lost In some drives an inpul phase loss alarm will be generated if the duration of the phase loss is greater than the input Phase Loss Delay setting Input Phase Loss This parameter controls the delay time in which an input phase loss must Delay be present before a fault is generated If the input phase returns to nominal before the delay time a fault will not be generated DC Bus Some drive manufacturers allow users to change the DC bus Undervoltage Limit undervoltage trip point By lowering the trip point drives and processes or Undervoltage may ride through longer and deeper voltage sags without interrupti
17. eing exposed to voltage dips and interruptions Control circuits can be protected by powering all control circuits from a conditioned power source The two most common techniques to provide conditioned power to all control circuits are Central power conditioning m Discrete power conditioning Central Power Conditioning Technique If there are a number of control circuits requiring conditioning a centralized power conditioner can be used to condition all control circuits as shown in the figure on the top of the next page Due to the high maintenance needs of many small battery based power conditioners they are not recommended for critical process systems However when a centralized conditioner can be used a battery based conditioner such as a UPS is recommended since maintenance for only one unit is required If this option is applied safety needs to be considered because the equipment will be powered by a separate power source Be sure to follow all local codes for external power SOUrCES Centralized Power Conditioner Solution for Individual Control Circuits Unconditioned 400V Lt L2 Es G Process Cooling Water Control Circuits 400V Three phase Uninterruptible Power Supply Conditioned 400V eee Compressor Starter Controls L1 _ Pump Starters AAAS 230V Control Circuits A typical process cooling water control circuit Discrete Power Conditioni
18. er Quality in Medium and Large Commercial Buildings transformers because the RMS current is usually higher per watt with nonlinear loads Additionally the higher frequencies in nonsinusoidal current will heat transformer components more than an equivalent amount of sinusoidal current Step down transformers connected in a delta wye configuration and serving single phase nonlinear loads can act as a filter protecting PN TechWath S gt SSS The results of harmonics created by office equipment are overloaded undersized neutral conductors inadequate filtering caused by undersized transformers and energy losses through the neutral conductor and transformers the upstream part of the building wiring Load losses due to harmonics are usually significant These losses are related to current in both the primary and secondary windings Load loss is the sum of all current related losses including copper losses IR c and eddy current losses Copper losses depend upon the load current and AC resistance of the windings DC skin effect and proximity effect resistances When the currents flowing in the windings of a transformer are rich in harmonics the induced eddy current losses in the windings increase significantly and may be many times higher than the eddy current loss due to 60 cycle current The table below shows the load losses for a typical delta wye transformer The total losses nearly triple for n
19. ervers personal computers uninterruptible power supplies and network and telecommunication equipment Critical facility loads are those loads that are vital to the operation of the building Types of equipment that fall into the critical facility group include air conditioning systems process cooling water chillers and water pumps and ventilation systems Air Conditioner Systems Split or packaged air conditioning systems are common in commercial buildings with multiple zones The split air systems are composed of two major components the outdoor compressor fan and the indoor furnace ventilation units In the split air conditioner configuration one HVAC unit is used to control the environment of one Lighting control Unit damage Brightness or dimness in lights Flickering of lights Transients voltage variation Source EPRI TR 114240 zone as shown in the figure below Voltage variations such as dips interruptions and under and overvoltages both long term and short term have the greatest impact on commercial sector equipment Only the impact of voltage dips is not as critical as it is in the industrial sector The main reason is that mission critical equipment such as data processing centers are in most cases protected by uninterruptible power supplies UPSs and backup generators In industrial processes minor voltage dips can cause product loss operational delays and possibly loss of custome
20. ests have shown that voltage dips and interruptions cause transients that damage control cards Voltage dips cause the controller s power supply to drop out The table at top left lists general recommendations for power quality events that could either damage or cause the elevator to stop To prevent damage caused by overheating it s important to keep the elevator control room below 85 F Power Quality in Medium and Large Commercial Buildings Common Power Quality Events Affecting Elevator Operations Install metal oxide varistors MOVs with sufficient clamping voltage to protect the control cards while not clamping every transient If the device were subjected to all of the transients associated with the normal elevator operation its life would be shortened If the problem persists after the MOV installation another solution can be investigated If cards are frequently damaged check with the elevator manufacturer for transient protection solutions Internal transients Condition the AC power to the main controller This will significantly reduce the number of trips requiring a manual reset Voltage dips and interruptions HARNMONIC GENERATING LOADS The increasingly abundant use of nonlinear loads is changing the design requirements for building wiring This change is especially true in large commercial buildings where three phase circuits serve multiple single phase nonlinear loads Today the increased
21. etermine the motor speed Once the speed is recognized the drive reaccelerates the motor to the desired operating point The odds of the motor and load experiencing extreme current and torque transients are greatly reduced A drive s programming parameters associated with reducing the effect of voltage dips are seldom described in one section of the user manual The table below lists some common programming parameters that when enabled disabled or changed may improve the drive s performance to voltage dips The parameter names in the tables may differ from those used by manufacturers so each table includes a functional description Automatic restart and reset parameters control the starting and stopping behavior of the drive and can be adjusted to prevent nuisance tripping of a drive and the subsequent shutdown of a process Motor Load Control Functions Flying Restart Parameter Parameter Description Kinetic Buffering When the drive senses a DC link low voltage condition the drive uses the combined motor load inertial energy to maintain a factory programmed DC link voltage inside the drive by applying a braking force to the motor This feature does not create a potential for extreme current or torque transients Motor Voltage Compensation When the drive senses a DC link low voltage condition the drive s controller changes the inverter firing timing sequences to compensate for a reduced DC link voltage Th
22. factor is related to the shape of the power wave delivered to the lamp by the ballast High crest factors the ratio of voltage peak to voltage mean can reduce lamp life Ballasts with crest factors below 1 7 are considered good Power factor is the ratio of watts to volt amperes of a ballast This value measures how effectively the ballast converts input power into actual usable power Some ballasts are equipped with a high power factor designation meaning they are equipped with a power factor of at least 0 90 A low or normal power factor ballast will have a power factor of less than 0 90 usually between 0 25 and 0 70 Harmonic distortion of the 60 Hz fundamental power waveform Is an ongoing topic of concern and research Lamp ballasts having total harmonic distortion below 20 are preferred below 10 is considered excellent Power Quality in Medium and Large Commercial Buildings Fluorescent Lamps Fluorescent lamps are by far the most common type of discharge lamp They use a low pressure argon mercury vapor atmosphere and a fluorescent mineral phosphor coating on the bulb wall to produce light The sheer predominance of fluorescent lamps in commercial buildings demands the consideration of this load on the overall electrical environment Power Quality and Lighting Power quality issues first gained prominence in the early 1980s with the first large scale use of electronic ballasts for fluorescent lamps Power quality
23. ic products Dimming systems and dimmable electronic ballasts can also reduce power factors due to line harmonics created by dimming Engineers can avoid power factor problems by minimizing the use of low power factor Power Quality in Medium and Large Commercial Buildings loads a small portion of a building load can be low power factor without concern In addition they should carefully evaluate the power quality and harmonics impact see below of high power control systems such as very large solid state dimming systems variable speed drives for mechanical HVAC systems mainframe computers and other high power devices employing switching devices in power supplies or controls Harmonic Distortion Harmonic frequencies are higher multiples of the fundamental frequency 60 Hz in 120 VAC systems superimposed on the sinusoidal waveform For example frequencies generated at 180 Hz are referred to as third harmonics The sum of these multiple frequencies is referred to as total harmonic distortion THD THD caused by electronic fluorescent lighting ballasts has evolved into a major concern among members of the lighting community Electronic ballasts increase lamp efficacy by converting 60 Hz power into high frequency 20 to 40 kHz alternating current Unfortunately this action can introduce harmonic distortion in a building s power line It seems unfair perhaps that electronic ballasts have been singled out f
24. ical Typical voltage Categories Content Duration Magnitudes 1 0 Transients Pr Pe 1 1 1 Nanosecond 1 1 2 Microsecond 1 1 3 Millisecond 1 2 Oscillatory ooo lt 5kHz 1 2 1 Low Frequency lt 5 kHz 1 2 2 Medium Frequence 5 500 kHz 1 Impulsive 2 3 1 Interruption ges 3 3 Overvoltages 4 0 Voltage imbalance 5 0 Waveform Distortion 6 0 Voltage fluctuations 1 2 3 High Frequenc 0 5 5 MHz 2 0 Short duration variations S 0 1 0 9 pu Ls aes Panera 0 100th H Ci Steady state 0 1 0 1 Pp E ooo E a Pp Pp E Pp E po es Po min lt 0 pu i Pp E _ Pp E po Oooo Pp E E PS 0 100thH_ 7 0 Power frequency variations Po 108 O Source IEEE Std 1159 1995 all buildings other than industrial buildings and private dwellings It includes office and apartment buildings hotels schools churches steamship piers air railway and bus terminals department stores retail shops government buildings hospitals nursing homes mental health and correctional facilities theaters sports arenas and other buildings serving the public directly Major Uses of Energy in Commercial Buildings Each principal building activity has its own set of characteristics energy sources equipment number of workers hours of operation that contribute to total energy use European research shows that 40 of the total energy used in the European Union EU is used in the
25. igital scale Unit damage Transients EMI RFI Digital thermostat Lack of control Transients EMI RFI Unit damage Energy management Loss of control Transients EMI RFI Fax machine Unit damage Transients EMI RFI No or poor communication Fire security system False alarms Transients EMI RFI voltage Unit damage variations Increased service calls Compressor failure Increased service calls computerized Data loss data error Voltage variation system ECG EKG machine Component damage Voltage variation transients Erroneous reading Elevators Component damage Voltage variation Increased service call Data loss data error Power Problem Symptoms HVAC equipment Voltage variation Patient database Computerized reservation system Simplex clock Incorrect time EMI RFI system ATM machine Processing unit damage Transients Incorrect data Unit damage Voltage variation Gamma counter Check approval Unit damage system Increased service call Bar code scanner Scanner damage EMI RFI transients Wrong scanning EEG EKG machine Unit damage Transients voltage variation Data processing Data loss corruption Voltage variation Voltage variations transients Voltage variation transients CONDITIONING SYSTEM HVAC The largest commercial building load is the HVAC system In addition to environmental controls for personal comfort levels an HVAC system plays a vital role for buildings with data centers which contain s
26. manifestations caused by fluorescent light ballasts are listed in the table on the left Power factor and harmonic distortion are the most relevant for commercial buildings Power Factor Power factor the ratio of watts consumed by an electrical component to the root mean square RMS volt amperes delivered to it is an important characteristic of any electric device or equipment Power factor affects current which in turn affects the overall efficiency of the generation transmission and distribution of power from plant to customer In lighting power factor problems are usually associated with the ballasts used on fluorescent and high intensity discharge HID lamps Traditional electromagnetic ballasts require internal power factor correction so that the total load ballast and lamp has a power factor of 0 9 to 1 0 Normal power factor NPF ballasts commonly found on compact fluorescent and low wattage high pressure sodium HPS lamps traditionally have had power factors of 0 2 to 0 45 without correction This means that a significant percentage of the current being drawn by the ballast is unused as opposed to being used by the P TechWatcth gt SSS A growing awareness on the part of the lighting community of the desirability of higher power factors has encouraged manufacturers to make available high power factor ballasts lamps or lost in the ballast For example although a 13 watt twin tube lamp balla
27. mercial Customers Power quality variations as described in the table on page 1 affect all categories of commercial customers However depending on the criticality of the equipment affected the consequence of the disturbance may range from a minor nuisance to extensive equipment damage and loss of critical data For example a momentary voltage dip may impact the operation of an elevator and may cause it to stop at a floor where it wasn t supposed to In most cases this is nothing more than a nuisance However the same voltage dip might instead cause an elevator controller to fail and may require a service call during which the elevator would be PQTechWatch o gt SSS unavailable The table below shows the list of generic equipment used in the commercial sector and the associated power quality symptoms and the primary power disturbances in both the commercial and industrial sites must be considered when designing a building or purchasing and operating equipment quality disturbances affecting the equipment HEATING VENTILATION AND AIR Impact of Power Quality Disturbances on Commercial Sector Electrical Equipment Electrical Primary Power Quality Equipment Disturbance Category Air conditioning Premature compressor failure Voltage variation Computerized Unit damage Transients cooking equpment Imersased semie cats CSS Copy machine Touchpad damage Transients Increased service calls D
28. mmercial and residential buildings Commercial buildings include nonresidential nonindustrial buildings such as hospitals office and apartment buildings hotels schools churches stores theaters and sports arenas Within those buildings HVAC units PCs fax machines copiers and printers are now sharing the building wiring system with electronic fluorescent lighting adjustable speed heat pumps and various electronic communications equipment While electronic based commercial equipment increases productivity this type of equipment can often be adversely affected by poor power quality Today the quality of electric power generation transmission and distribution systems is very high With the exception of conditions associated with brownouts most utilities deliver well regulated power to all but the most extremely remote customers However power dips and surges are still of concern largely because of the potential impact for electronics damage and interference with computer operations Another power quality issue that must be kept in mind is the production of harmonic currents by nonlinear equipment such as office equipment lighting and some HVAC systems This PQ TechWatch takes an in depth look at some of the larger components of commercial operations including HVAC lighting office equipment and elevators The intent of this document is to show how power quality impacts commercial equipment and what mitigation techniques can
29. nces found in a typical commercial office building harmonic rich current Current Characteristics of Single Phase Equipment Found in Typical Office Buildings Total Total eal Harmonic Harmonic Distortion Component C A Operating Current urrent Current Distortion State A A EN Iae 0 251 ote 020 130 sa 6s Printing 375 374 022 6 00 8 s8 67 486 IBM comp PC 93 80 PentiumPc Jon oe9 oss oss f z s 2 amp l MacintoshPc Jon 10 oeo oso 13 z sof 32 Laptop PC On oe oof ot of 2f 78 sof 40 PF correctedPC Jon ozs oz os 9 asf a ef 2 13 inch monitor on os7 osof os too s 3 Phone switch Jon o42 onj coos go sa tz 7 4 Photocopier lide 1o0o oso osf of s z nf 3 wr eS VCR Video system fon o oeo ozn 12 sa e 42 2 Coffeemaker ide os oss oos 3 2 s 4f o3 Po Brewing S nof neoj os s 2 s 1 o5 Microwaveoven Cooking 9 00 821 seoj 45 asf 12 af 22 Water cooler Cooling 44se 4a5 o2 es 4o 2 1 o6 Pencilsharpener___ ide oo3 0o02 oo of 3 a n n Pd Sharpening ozs ozs oo7 tof of 4af 1l fuowsct fon owl o oo a ef wl 2 fluorescent On 0 12 0 08 120 85 64 40 22 Electronic eer las ael an o al al al ael a factor corrected On 0 13 00 13 00 0 02 15 3 3 7 3 1 O o a s 2 o8 Magnetic fluorescent Deskfan On oo oo ooo n wf 3 oof o1 UPs dT PCload 44o 439 35 s 7 2 3 o4 UPS 2 PCload
30. ng Detection Level production This feature may be standard or may require a drive software upgrade from the manufacturer DC Bus This parameter allows the user to set a time delay fora DC bus Undervoltage Delay undervoltage fault If the duration of the undervoltage exceeds the delay time the drive faults Otherwise the drive continues normal operation Parameters that Affect Recovery Parameter Parameter Description Acceleration These parameters are especially important after a sag ends and the Deceleration drive attempts to recover Inappropriate settings may cause the dive to Current Limit and trip or may not allow the process to recover Torque Limit Power Quality in Medium and Large Commercial Buildings PAQ TechWath S gt SSS However automatic restart operations may only be used as outlined in NFPA 79 Equipment damage and or personal injury may result if the automatic restart function is used in an inappropriate application Motor load control uses the motor s inertia or controlled acceleration deceleration to ride through voltage dips Detecting a loss of phase enables a drive to delay a fault condition and ride through the loss of phase The DC link undervoltage trip point can be adjusted to enable a drive to ride through dips After a voltage dip has occurred rate of acceleration rate of deceleration current limit and torque limit are parameters that affect the way a drive attempts to recover Rec
31. ng Technique When critical process machine control circuits are powered by control power transformers CPTs the CPT can be replaced with a constant voltage transformer or a single phase batteryless power conditioner can be added to the secondary between the load and the transformer The two circuits in the figure on top right show both CPT options If the control circuits are powered by a line to neutral L N connection all line to line control circuits must be identified and conditioned by a power conditioner The line to line control circuit in the figure on bottom right is protected by a single phase batteryless power conditioner installed between the circuit breaker and the control circuit Power Quality in Medium and Large Commercial Buildings PQTechWatch oS gt S Power Conditioning Solutions for Control Circuits Powered by Constant Voltage Transformers Unconditioned Power Circuit Breaker Circuit Breaker Control Power Constant Transformer Voltage Transformer 230V Batteryless Power Conditioner Conditioned Load Constant voltage transformers can condition power for control circuits Line to line L L Control Circuit Power Conditioning Solution Lil G N G A vn CLL 230V Batteryless Power Conditioner Power conditioning can be configured line to line Building Automation Systems In large commercial buildings
32. ocessor program parameters to configure it for a particular application A low cost or perhaps no cost method of reducing trips caused by undervoltage faults is through software configuration setting changes This technique applies to AC and DC drives The vast majority of drives in use today have rectifiers that convert AC power to DC Some drives use inverters to create a variable voltage variable frequency AC waveform to control AC motors Others use the DC power directly to control motors in DC servo and DC drive systems These types of drives are similar in that they have a microprocessor program that governs the AC to DC conversion processes and motor control circuits In most cases drive manufacturers give users access to basic microprocessor program parameters so that the drive can be configured to work in the user s particular application Programming Parameters That Can Improve a Drive s Tolerance of Voltage Dips Automatic Reset and Restart Functions Parameter Automatic Reset Automatic Restart Automatic Restart Attempts Automatic Restart Interval Automatic Restart Time Delay Restart at User Defined Frequency Setting Flying Restart Parameter Description This parameter allows the drive to automatically reset some fault conditions such as DC link undervoltage or overvoltage without the need for operator user intervention This feature is used in conjunction with Automatic Restar
33. ommended Settings for Chiller Controller and or Motor Protection Relay for Optimal Power Quality Performance General Recommendations for Chiller Controllers and Motor Protection Relay Settings Voltage dips not only affect the electromechanical components like relays and contactors they can also have an impact on the chiller s compressor motor protection relay MPR The MPR is used to protect the large compressor motor from damage caused by steady state voltage or current unbalance conditions The MPR can be a separate discrete component or the MPR functions can be built into the chiller s controller Depending on the type configuration and software setting of the MPR a voltage dip could be interpreted as a steady state condition thus causing the MPR to shut down the compressor motor To prevent nuisance trips the table on the left includes recommended settings for different MPR configurations Recommended Parameter Function Setting for Best Note PQ Performance LIGHTING KO ANo 1 SO A variety of lighting fixtures can be found in visage Measure of allowable of the electric supply oo unbalance within the 0 3 0 power quality characteristics vary from one Meee ea aCe ange lighting technology to another is fundamental Delay time in which to ensuring sound up front design Voltage unbalanced voltage 5 seconds Instantaneous settings Unbalance ae must be present minimum not recommended Time sec n before chiller trips Types of
34. onlinear loads with the same real power watts Circuit Breaker and Connector Heating Harmonic currents affect circuit breakers and connectors in subtle ways Generally harmonic currents heat circuit breakers and related connectors Peak harmonic current and vibrations induced by harmonic currents can also heat connectors and contacts Additionally voltage distortion resulting from current distortion can heat the coils of a circuit breaker When circuit breakers are subjected to continuous nonlinear load current near their rated thermal trip a transient or small increase in Typical Transformer Losses with Linear and Nonlinear Loads Type of Load Loss Copper Loss 2 D Rac Eddy Current Loss Pec hac Total Load Loss Pi IFR Pec Linear Load PF 1 0 ITHD 0 Losses Watts Nonlinear Load PF 0 64 ITHD 100 1500 2986 Is 1336 57s 4322 Assumptions Three phase delta wye transformer is rated at 112 kVA load is 60 kW Power Quality in Medium and Large Commercial Buildings loading may trip them When reset they are likely to be cooler so the cycle may begin again Consequently some overload problems go unnoticed for a long time until more definite symptoms appear Loose connectors may cycle between hot and cold as the load changes state for example as equipment is turned on or the heater elements of printers and copiers cycle on and off This cycling loosens the connectors even mor
35. or so much attention during current debates on the harmonics issue Similar harmonic distortion can be introduced by any electronic rectifying system or high speed switching device see Power Quality Impact on Commercial Customers section THD is also produced by magnetic ballasts THD is significant because when any combination of harmonics generating devices composes a significant portion of a building or system load the following undesirable effects may occur imbalance and or overloading of transformers and neutrals in three phase distribution systems caused by additive triplen 3rd 9th etc currents power surges PoTechWatcA gt SSS Utilities are primarily concerned that there is a positive correlation between total harmonic distortion and power factor and spikes due to circuit resonance or interference with electrical communications Distortion of the input voltage at the service location also results in reduced power factor In an office building for example fluorescent lighting can constitute 35 to 50 of the electric load in the building If all fluorescent lighting had electronic ballasts with 40 THD the whole building s THD would likely fall between 5 and 8 Power factor would be reduced and problems with computers and other systems could result In extreme conditions high neutral currents caused by additive triplen currents could cause transformer damage and overheating in neutral conducto
36. ower Quality in Medium and Large Commercial Buildings PN TechWath S SSS The tolerance of HVAC systems can be greatly improved by protecting all control circuits from being exposed to voltage dips and interruptions The voltage dip sensitive components of a chilled water system are the chilled controller C control relays and contactors motor starters and the motor protection relay Ventilation Systems The function of ventilation systems is to move conditioned air Volume requirements set by ventilation standards dictate the size and number of motors required for a given space Ventilation fans are either driven by a constant speed or variable speed motor A variable speed fan is more energy efficient than a constant speed fan Both types of fan configurations are shown in the single line diagram below Components of the ventilation system sensitive to voltage dips are highlighted in red Variable and Constant Speed Ventilation Fan Configurations Building Automation System BAS Ventilation Systems i Variable Speed Constant Speed Air Handling Air Handling Unit S Unit S Components sensitive to voltage dips such as the adjustable speed drive ASD are highlighted in red Power Quality in Medium and Large Commercial Buildings Protection of HVAC Voltage Dip Sensitive Components The tolerance of HVAC systems can be greatly improved by protecting all control circuits from b
37. r confidence However power Power Quality in Medium and Large Commercial Buildings Split Air HVAC Configuration Make up Air Compressor One HVAC system controls one zone in commercial buildings with multiple zones The power quality events that most adversely affect this type of conditioner system are voltage dips and interruptions Voltage dips can cause any or all contactors and relays to change state and can also cause misoperations of controls A single line diagram of a typical split air conditioning system is shown below Components Sensitive to Voltage Dips on a Split Air Conditioning System Air Handling and Furnace Indoor Compressor Outdoor 400V Thres phase Fone 3 f T Q O Q Ventilation Compressor Fan Fan Components sensitive to voltage dips are highlighted in red Chilled Water Process Loop Secondary Sr cM fs eg m apen mm ae ate m apee Pe ae m ae 7 Cooling Tower Pu PCW Loop Punpa DAE mpa to Procass ET Loads P oe i Compressor lo a nen O nEn peamisi mney j g Refrigeration Heat Chilled 5 F Loop Rejection Water 5 Loop Bm ye Loop s 7 5 8 e l l l Three Way Modular Valve From Process Leads Capacity Control Valve 2 or 3 Way Chilled water systems are used to cool equipment and products in commercial manufacturing processes Process Cooling Water Chillers and Water Pumps B
38. reduced however Conversely as voltage is reduced lamp life increases while output efficacy and color temperature decrease Tungsten Halogen Lamps Tungsten halogen lamps are incandescent lamps that are specially treated by the addition of a halogen material iodine chlorine bromine or fluorine to the lamp atmosphere The halogen material causes tungsten that evaporates from the filament during lamp operation to redeposit on the filament This halogen cycle increases lamp life by decreasing lamp depreciation Tungsten halogen lamps also have a higher color temperature and efficacy The halogen cycle requires very high lamp temperature inside a fairly small bulb Consequently most tungsten halogen lamps use fused quartz glass bulbs that can withstand high operating temperatures This gives rise to the common name quartz lamps Discharge Lamps In discharge lamps an electric current is passed through a gas filled tube ionizing the gas so that electrons are released Reabsorption of these electrons releases energy at very specific wavelengths In some lamps this energy is within the visible range while in other cases a phosphor coating in the lamp is energized by the discharged energy The phosphors react to the energy by glowing or fluorescing thus creating visible light Lamp color characteristics depend on gas type pressure and on the properties of the lamp s phosphor coating Power Quality in Medium and L
39. rent Waveform for HVAC Systems earlier levels are significantly lower than i 30 current THD and a power factor greater distortion can s _ than 0 9 The figure below shows the current be significantly waveform of a typical electronic ballast with y higher _ a THD of 22 Although compact fluorescent lamps are as efficient as 4 ft lighting systems their current distortion can be significantly higher Each phase of an HVAC system driven by an adjustable speed drive produces this two pulse waveform Electronic Ballast Current Waveform for Fluorescent Lighting Wiring Configurations in Commercial Buildings The effect of harmonic currents on the building wiring depends heavily upon the configuration of the wiring The figure below is a typical wiring schematic fora commercial building Typical Commercial Building Power l er Distribution Single Line This waveform reflects the typical results of a ballast with a total harmonic distortion of 22 HVAC loads are usually three phase loads ae operating at either 230 or 400 V and have predominantly motor type inductive 400 230 V loading characteristics Some of the newer HVAC systems incorporate adjustable speed drives ASDs whose input power supplies are basically three phase diode bridge rectifiers which inject harmonic currents back into the power distribution system For three phase loads an unbalanced voltage will cause an increas
40. ripherals all use switch mode power supplies The waveform of SMPS current tends to be very peaked and contains mostly third harmonic The current harmonic distortion of one personal computer shown in the table is less than 20 because its power supply employs power factor correction and harmonic elimination circuitry a design that was probably influenced by International Electro technical Commission standards Low harmonic designs are expected to be used extensively in the near future Lighting and Three Phase Loads In most cases lighting and HVAC systems are connected to individual branch circuits separating them from other loads in the building Lighting in a modern office Power Quality in Medium and Large Commercial Buildings PQTechWatch gt o gt SSS Although building provides a wide range of current The current drawn by each phase of an ASD compact waveforms and harmonic distortion Energy driven HVAC system has the characteristic efficient fluorescent lighting is beginning to two pulse waveform shown in the figure fluorescent dominate all other types of lighting in below lamps are aS commercial buildings Both magnetic and efficient as electronic ballasts serving 4 ft fixtures can 4 ft lighting systems the typical computer Industry standards for their current 4 ft fluorescent lighting require less than generate harmonic currents but as seen Electronic Ballast Cur
41. rrent distortion produced by other devices such as magnetic ballasts and motors can introduce a phase shift between the voltage and current also leading to reduced power factor However as long as there are no voltage current phase shift contributions to the power factor the THD of a given electronic ballast may be as high as 48 and still maintain a power factor greater than 0 90 THD in Recent Electronic Ballast Products In order to minimize THD in electronic ballasts to generally acceptable levels the National Electrical Manufacturer s Association NEMA and the American National Standards Institute ANSI have proposed limits of 33 for total harmonic distortion and 27 for triplens Some utilities have independently established lower THD limits that electronic ballasts must meet in order to be eligible for rebate programs Using the latest technology electronic ballasts have been designed with less than 10 THD These products have been costly in the past but increased competition among manufacturers has contributed to lower prices Current electronic ballast products include models with THD as low as 5 with little or no cost increase over competing 20 THD products PQTechWatch o gt SSS Elevators are susceptible to voltage fluctuations and interruptions and are exposed to internal transients caused by a highly inductive field winding ELEVATORS The elevators are po
42. rs The table below lists the expected THDs for various lighting technologies In comparison personal computers have a typical THD between 100 and 150 while variable speed drives are greater than 100 Typical Total Harmonic Distortion for Different Lighting Technologies Lighting Equipment Magnetic energy saving ballast 2 F40 Magnetic energy saving ballast 2 F96 Screw in electronic ballast compact fluorescent Industry standard electronic ballast 2 FO32 Low harmonic electronic ballast 2 FO32 Dimming magnetic ballast Solid state dimming of magnetic standard ballast Solid state dimming of incandescent lamps Diode operation of incandescent lamps Typical THD 1572075 255076 125 175 20 or less 10 or less 40 maximum over dimming range 100 maximum or greater over dimming range 100 maximum over dimming range 100 8 alf a parallel lamp with opposite diode polarity is used the THD drops to 0 Source Power Quality Laboratory Niagara Mohawk Lighting Research Laboratories Rennsalaer Polytechnic Institute Power Quality in Medium and Large Commercial Buildings THD and Power Factor Utilities are primarily concerned that there is a positive correlation between THD and power factor Harmonic currents generated by electronic ballasts and other electronic devices reduce power factor by distorting the sinusoidal wave shape of the current By contrast the electric cu
43. st combination uses only 17 watts it actually draws 34 VA if it has a power factor of 0 50 The utility must deliver this amount of apparent power regardless of how much of it is used to light the lamp Buildings with low power factors require electrical distribution systems that are able to handle larger currents Branch circuiting and overcurrent protection must be sized accordingly Furthermore low power factor can cause voltage drop and in extreme cases voltage dip This may cause lights to dim fuses to blow and computers to crash Fortunately a growing awareness on the part of the lighting community of the desirability of higher power factors has encouraged luminaire manufacturers to make available high power factor HPF ballasts for most of their compact fluorescent and HID equipment HPF ballasts are sometimes offered as standard luminaire components More often however they are available only as an option and must be specified High power factor generally is the rule rather than the exception for incandescent lamps and for magnetically ballasted full size fluorescent and HID lamp ballast systems However electronic ballasts for full size fluorescent lamps often have low power factors and may also generate high levels of current harmonic distortion see the following section Compact fluorescent lamp ballast systems are also associated with low power factors This is particularly true of the self ballasted electron
44. t This parameter defines the method in which the drive automatically restarts after a fault condition is over Automatic Restart operations may only be used as outlined in NFPA 79 Equipment damage and or personal injury may result if the Automatic Restart parameter is used in an inappropriate application This parameter allows the user to program the number of times that the drive attempts to restart the motor after an undervoltage or other fault condition This parameter is a user specified time delay between the automatic restart attempts and the end of the fault condition This parameter is a user specified time delay between the end of the fault condition and an automatic restart When the drive senses a DC link undervoltage condition the drive shuts down the inverter allowing the motor to coast The motor is allowed to coast until the undervoltage condition ends The drive then restarts the motor at a user defined frequency setting If the restart frequency is significantly higher or lower than the frequency of the motor large inrush currents torque and speed transients could be induced on the motor and load The restart frequency setting the acceleration rate deceleration rate current limit and torque limit should be considered when using this feature This parameter is similar to the parameter above with one major exception Rather than restarting at a pre defined frequency setting the drive uses a search algorithm to d
45. tical data Typical Electric Loads of Commercial Buildings The systems equipment and facilities used to satisfy functional requirements of large commercial buildings will vary with the type of commercial building but will generally include some or all of the following Interior and exterior lighting both utilitarian and decorative Communications systems such as telephone telegraph computer link radio closed circuit television code call public address paging electronic intercommunication pneumatic tube doctors and nurses call and a variety of other signal systems Fire pumps and sprinkler fire detection and alarm systems Power Quality in Medium and Large Commercial Buildings m Elevators moving stairways dumbwaiters and moving sidewalks Heating ventilation and air conditioning m Garbage and rubbish storage and removal incinerators and sewage handling Hot and cold water systems and water treatment facilities Security watchmen and burglar alarms electronic access systems Business machines such as computers calculating machines and duplicating machines Refrigeration equipment Food handling and preparation facilities Building maintenance facilities Lightning protection Automated building control systems Entertainment facilities and specialized audiovisual and lighting systems Medical facilities Power Quality Impact on Com
46. uildings requiring between 50 and 5000 tons of energy utilize chillers to provide process cooling water to air handling units throughout the building The two basic refrigeration system methods are chilled water or direct expansion DX In the chilled water system the cooling media that interfaces to the airside heat transfer coil is chilled water In a direct expansion system the evaporator coil interfaces directly to the refrigeration system loop eliminating the use of chilled water In commercial buildings that support manufacturing processes cooling water plays a vital role in cooling equipment and products The process loop shown in the figure at bottom left is a general representation of a process cooling water system Similar to both the split air conditioner and ventilation systems the electrical components of a chilled water process are also sensitive to voltage dips and interruptions An example single line diagram is shown below Components Sensitive to Voltage Dips on a Process Cooling Water System Located in Motor Control Center MCC or Stand Alone 400V Three phase Chiller Panel Disconnect Chiller cB1 cB2 cBa CB4 CBS Controller CPT2 msz M3 M34 Mss Oil Building Chilled Condenser Cooling Caaling a4 totor Pump Automation Pumps Tower Fans Tower Pump _ oe eee eee umps Communication to BAS System BAS Components sensitive to voltage dips are highlighted in red P
47. wered by a delta connected DC generator mechanically coupled to an AC motor shaft The generator s field voltage is controlled producing a variable DC output The variable DC is necessary to control the speed of the large DC motor that drives the elevator car Elevators are susceptible to voltage fluctuations and interruptions and are exposed to internal transients caused by a highly inductive field winding which can carry significant current depending on elevator loading and can produce a high energy voltage transient if the current is interrupted Under controlled stop conditions the field can be deenergized very quickly by diverting the energy through a surge suppressor connected across the field winding The surge suppressor s function is to protect the control card from the regularly occurring transients that are associated with the operation of an elevator When the elevator is at rest for shorter than 17 seconds as when loading and unloading passengers the DC motor acts as a brake and holds the car If the car is at rest for longer than 17 seconds such as when the last passenger leaves the car a mechanical brake activates relieving the DC motor of its load This sudden change in current through the inductive field winding causes a transient voltage to appear which can be sufficient to destroy the control card An elevator s surge suppressor is designed to protect the exciter control card from these transients T
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