Replacing Motor-Generator Sets with Modern Static DC Drives by Jim Papez and Mark Kobiske

Continuing Education: Elevator Drives

Although such MG systems per- Learning Objectives formed satisfactorily for years, they After reading this article, you were not without drawbacks. Some should have learned about common concerns included: N the drawbacks of motor-gener- N High power consumption: A motor ator sets. and generator working together to N the value of static DC drives. generate DC power is inefficient. N considerations when replacing Additionally, an MG set creates a con- a motor-generator set with a stant and significant power drain – digital DC drive. even at idle speed when the elevator N input power considerations. is not in motion. N N the issue of power-line distor- High routine maintenance: MG sets tion. are often specified at minimum size N sizing criteria for transformers. and cost but must rotate at relatively N output power considerations. high speeds to meet DC power re- N ripple-filter recommendations quirements. As a result, frequent and and adjustments. costly maintenance is a necessity. N N car-controller considerations in Excessive generator brush wear: a modernization with a DC drive. Brush wear is a continuing problem. N commissioning a DSD 412 DC Additionally, the large amount of car- elevator drive. bon dust generated can spread throughout the machine room and N verification of motor data and cause failure of other electrical wiring. equipment. N motor field board setup. Eventually, the cost and high main- N recording motor data and en- tenance required for MG sets rendered coder setup. these impractical – even while the N grounding considerations. rugged, low-speed DC hoist motor N power-up verification and ad- kept operating as well as the day it vanced diagnostics. Value: 1 contact hour was first installed. Static DC Drives to the Rescue At the same time, power electronics This article is part of ELEVATOR WORLD’s For many years, high-performance utilizing silicon-controlled rectifier Continuing Education program. Elevator-industry personnel required to obtain continuing-education elevator systems utilized an extremely (SCR) static switches to directly con- credits can receive one hour of credit by reading rugged, open-frame, brush-type DC vert AC line power to DC were provid- the article and completing the assessment exami- motor to power the hoist. ing new solutions to some of the MG nation questions found on page 111. The controlled DC power was set problems. This advance virtually For this article and more continuing-education generated via an AC motor operating eliminated the need to provide rotating opportunities, visit www.elevatorbooks.com from line power and driving a DC gen- and high-maintenance components

NATIONAL ASSOCIATION OF ELEVATOR CONTRACTORS ® erator – a classic motor-generator set. involved in the production of DC Approved by NAEC for CET

CERTIFIED This control configuration, known as power. ELEVATOR TECHNICIAN EDUCATION PROGRAM a Ward Leonard system, basically Additionally, conversion efficiency regulates DC power to the hoist was greatly improved, and idle losses Approved by NAESAI for QEI motor armature by controlling the were drastically reduced, resulting in generator field. much lower power consumption. Continued June 2007 | ELEVATOR WORLD | 85 Continuing Education: Elevator Drives Continued

Static components produced re- manufacturers to exit the MG busi- switch to another. The result is a har- markable savings on maintenance, ness, resulting in a severe shortage monic distortion on the power line. making MG set brush wear and carbon of replacement parts for existing MG Potentially harmful effects are generally dust contamination things of the past. set installations. eliminated by use of an input isolation Crowded machine rooms also bene- Thus, more and more MG sets are transformer with good secondary fited from the comparatively small size being replaced with all-digital DC reactance. of the static drive. drives as part of modernization pro- SCR Switching (commutation): Two Today’s Advanced, All-Digital Static grams or simply to reduce mainte- conditions must be met to provide DC Drives nance costs. proper operation: 1) the AC voltage Incorporation of modern, micro- Application Considerations must be equal to or greater than the processor-based controllers into today’s Three major considerations must be DC voltage, and 2) at least 2-4% re- all-digital elevator drives provides: met when replacing a MG set with a actance on the input is needed. Both N Minimum installation and operat- digital DC drive. Those considerations of these conditions can be met with ing cost. are: an input transformer. N High reliability. N Input power; Transformer Sizing Criteria: N N Exceptional performance to help N Output power; and Input primary voltage must match reduce passenger waiting times and N Car control interface. the line voltage. N floor-to-floor times. Input Power Considerations Output secondary voltage must N All-digital control to ensure re- Power Feed: Since it converts AC equal or exceed DC armature volt- peatability over time and consistent to DC directly, the DC drive will draw age. If there is a potential for the line operation of all elevators in a group. approximately 30% more amps from voltage to drop, then a 10-20% in- Digital DC drives have virtually the line during car acceleration. crease in secondary voltage is rec- eliminated problems experienced Also, the requirement for peak accel- ommended as a safety factor. N 5% voltage taps are recom- with the earlier analog versions. eration amps is immediate, rather mended to allow for unforeseen field Analog DC drive problems included than built up gradually as with the conditions, such as line voltage drop difficult adjustments caused by nu- MG set. The power line must be able or the need to more closely match ar- merous potentiometer settings that to support these conditions without mature voltage for power factor or were sensitive, often interactive and excessive voltage drop affecting performance. could not be replicated successfully equipment on the same feeder. N Continuous (rated) secondary on another car; component drift with Input Voltage: MG sets convert line amps should equal or exceed 1.05 X age and environmental changes that volts to armature volts via rotating 0.82 X full-load DC armature amps. affected car performance; and high components. Static DC drives do the N Continuous (rated) KVA rating is part count with many more electrical AC to DC conversion directly via secondary amps X secondary volts X connections that negatively im- three-phase rectification. If the DC 1.732. pacted reliability. voltage required by a hoist motor is N The transformer must not saturate Today’s DC elevator drives are de- significantly lower than the line when acceleration amps are substituted signed and field-qualified specifically input voltage, the drive will lower for full-load amps in the above formula. for elevator applications. They have the input power factor. A low power N The secondary reactance should the high lift capacity demanded for factor means a higher KVA require- be at least 2-4%. minimum floor-to-floor times and can ment that needs to be supported by Output Power Considerations withstand the rigorous duty cycle as- the power distribution equipment These are somewhat more empir- sociated with high-speed elevators. and wiring. Older buildings may not ical, as they depend on both motor In addition, modern software incor- have this capability, and thus, an input and hoistway conditions. Thus, some porates unique control algorithms to transformer is recommended to make degree of application experience must provide optimum performance and a the voltage input to the drive compara- be taken into consideration. broad spectrum of input/output capa- ble to motor armature voltage. As will DC Motor Armature: Elevator mo- bilities for car control interface. be seen, there are other good reasons tors almost always have armatures DC Drives as MG Set Replacements for using this transformer. designed to minimize torque ripple Since the introduction of DC static Power Line Distortion: Static switch- and provide for a smooth ride. This is drives, MG sets have essentially disap- ing draws square-wave current from also the best motor for operation peared from use in new installations. the line and creates a notch when from a static DC drive. In the rare This, in turn, has caused some current is commutated from one older hoist motor that may not have

86 | WWW.ELEVATOR WORLD | June 2007 this armature design, torque ripple armature inductance and resistance. conjunction with the recommended may be accentuated by the static DC N Adjustable capacitance and damp- ripple filter will achieve more than drive. If that results in a performance ing resistance should be included with adequately quiet operation. Many issue, such as car vibration, then the basic design criteria of roll-off times – almost always for geared greater care in adjustment is needed. starting at approximately 300 Hz and machines – the addition of inductance An increase in the size of the DC rip- a tuned peak of approximately 100 Hz alone will achieve the desired results. ple filter may also be necessary to further (Q of 1.2-1.5). If it does, then the capacitors are per- reduce drive-generated voltage ripple. N The filter should be rated for con- forming no useful function and may DC Drive Output Voltage Ripple: tinuous operation at full-load arma- be disconnected from the filter. Doing Three-phase rectification produces a ture current and not saturate at accel- so now removes an unnecessary com- 360-Hz ripple on DC voltage. This eration current. Inductance needs to ponent from the power circuit, which ripple can excite the hoist motor and be constant from very low armature in turn, improves reliability and re- produce acoustical noise in the motor current through maximum accelera- duces future maintenance of the filter and mounting structure. That noise, in tion current. circuit. In the rare circumstance that turn, is transmitted to the hoistway. N The supplier of this filter must unacceptable noise is still present Thus, some type of ripple filter in the be familiar with its application. after the filter and drive are properly DC line is normally desirable. Ripple Filter Adjustment: Most adjusted, mechanical dampening of Ripple Filter Recommendations quality manufacturers provide appli- hoistway components is required. A ripple filter added in the DC line cation notes advising on how to Practical Experience: Experience from the static drive to the DC motor is measure the actual value of the filter within the industry has shown that a normally recommended. The general and how to properly set up the DC ripple filter consisting of a 5mh induc- criteria are: drive with the filter. tor with sufficient range of adjustment N Filter inductance and resistance Acoustical Noise Abatement: in the capacitors and damping resist- should be approximately equal to motor Typically, a static DC drive used in ance is broadly effective. However, Continued

Vintage motor generator

June 2007 | ELEVATOR WORLD | 87 Continuing Education: Elevator Drives Continued some motors have very high armature However, since both elevators and inductance and, thus, may require a buildings vary greatly in the details, an larger reactor, typically equivalent to the experienced elevator application engi- armature inductance, to obtain desired neer should be responsible for ensuring acoustical results. The elevator appli- proper design and installation. cation engineer relies on his experience to make these judgement deci- sions initially. However, since noise is usually subjective, it may be necessary Commissioning to have the building owner pass final of the Magnetek judgement on acceptability. DSD 412 DC Car Controller Considerations Elevator Drive

In total modernization projects, a new The Magnetek DSD 412 is one of the Pre-power checks car controller that includes the drive is world’s most widely used DC elevator from ground. Verify that it is installed usually provided. All interfaces with the drives. Its applications range from low- in the correct terminal and that the drive are then either handled or specified speed geared to high-speed gearless terminal is tight (3.5-in.-lb. maxi- by the car controller manufacturer. If such as the Sky View observation deck mum). All low-power, low-voltage simply replacing the MG set while reat the Sears Tower. Whether fast or wiring should be run separate from taining the existing car controller, slow, geared or gearless, it is crucial to 120 VAC, three-phase AC, DC arma- then several issues must be considered: follow proper guidelines that will en- ture and field wires. These include: N An electrical schematic, wiring sure years of trouble-free operation. Encoder wiring diagram and operational sequence Verify Wiring Speed reference wiring chart should be generated to ensure Wire sizes are required to comply Pre-torque reference wiring proper installation and operation. with National Electrical Code (NEC), 24-VDC logic inputs N The compatibility of all signal and Underwriters Laboratories Inc. (UL), Open collector outputs power supply ratings requires verifica- Canadian Standards Association To avoid noise pickup, shielded tion. In particular, low-level electronic (CSA) and other applicable codes for cable should always be used for these signals interfacing with relays must be power-distribution safety. signals. N controlled via appropriately rated con- Verify Wiring: The wiring between N Control Wire: The control wiring tacts. the DSD 412 and the motor should be located on the power supply (A4) N Older-style controls may not have checked to determine that no insula- TB3-1 through TB3-8 should be had to consider the susceptibility to tion has been damaged during the in- checked to verify that connections electrical noise of today’s processor stallation. This check should be done are correct and tight. controls. Relay coil switching and con- at the drive end of the power wires. Verify Motor Data tact arcing are significant noise gener- Disconnect the shunt field wires F1 N Field Coil Checks: Prior to reat- ators that must be isolated from the and F2 from the field interface taching the F1 and F2 wires to A3 electronics. board (A3) terminal TB4. Attach the TB4-F2(-) and TB4-F1(+), record the N A digital drive also generates electri- field wires temporarily to the load resistance of the field coil. In most cal noise that must be isolated from side of the armature contactor A1 cases, the motor nameplate states existing electronic controls. Physical and A2. Remove the wires from the the full field voltage or full field cur- separation of products and wiring is the armature interface board A2TB5-1 rent. A quick calculation can verify first step in successfully achieving that. and A2TB5-2 and isolate them from which AC voltage must be applied to Conclusion the ground. With the power wiring the field interface board (A3) to Today’s all-digital static DC drives now isolated from the drive, “meg- achieve full field current. The calcula- offer both the installer and building ger” from the load side of the arma- tion below will provide the minimum owner many benefits over older analog ture contactor to ground. If a prob- acceptable level; however, typically DC drives and Ward Leonard MG set lem is detected, the source of the the level could be in the range of 1.5 controls. To realize these fully, espe- ground fault must be determined and to 2.5 times VAC(min). VAC(min) = cially when replacing MG sets, several resolved prior to proceeding further. VDC10.9 or (Full Field Current X Field factors beyond simple rating criteria N Signal Wire: Each signal wire Resistance)/0.9. If the actual value for must be considered. A general discus- located on the main control board VAC drops below this point during sion of those has been presented here. TB1 must be checked for isolation the operation of the elevator motor,

88 | WWW.ELEVATOR WORLD | June 2007 torque may be affected, which will N Setup of Alternate AC Voltage to pated DC armature voltage at rated result in higher-than-expected arma- the Motor Field Board (Optional): If the car speed. The control transformer, if ture current. three-phase voltage fails to meet the used, should be checked to verify it is N Motor Field Board Setup: The criteria defined above, it will be nec- wired to provide 120 VAC on the sec- DSD 412 can operate motor fields in essary to supply an alternate AC ondary when the power is turned on. the range 0.2 to 40.0 ADC as stan- voltage. This is done by using a sin- N Encoder Considerations: The pre- dard. Connection on the field inter- gle-phase transformer. The DSD 412 ferred method of mounting the face board for the motor field is TB4. factory wire should be moved from encoder is inline with the motor Common connection point is F2(-). AC1 to L1A on TB1. Connect H1 on armature; precision alignment is The maximum range of the motor the transformer to L1A on TB1. Move crucial to stability of the DSD 412 field current determines which termi- the factory wire on AC2 to L2A on speed regulator. The body and shaft nal F1(+) should be connected. For TB1. Connect H2 on the transformer of the encoder should be electri- the drive to recognize the selected to L2A on TB1. This will provide volt- cally isolated from the motor frame current range, “S1” must be set cor- age to the primary side of the trans- to prevent electrical noise from rectly. The figure below identifies the former. Connect X1 on the trans- causing interference. Digital encoders terminal locations and proper switch former to AC1 of TB1. Connect X2 on that operate with this product will positions for “S1.” In some models of the transformer to AC2 of TB1. This require a shielded cable with three the DSD 412, switch “S1” is a rocker completes the wiring of the alternate twisted pairs. The pairs should be type. A rocker switch is closed when single-phase transformer. Install made up of A and A-, B and B-, +5 VDC it is pushed “in” on the top, and a semiconductor fuses between second- and common. The shield should be rocker switch is open when it is ary of the transformer (X1, 2) and the insulated from the encoder case and pushed “in” on the bottom. Newer TB1 (AC1, 2). only connected at the drive end. The models of the DSD 412 will be slide Recording Motor Data maximum frequency of the encoder type (see figure below). Move the slide N Record the Remaining Information at rated car speed should not exceed actuator of “S1” or press the rocker from the Nameplate of the Motor: Rated 300 kHZ. switch actuator in as indicated to co- motor amps, rated armature voltage, Grounding ordinate the position of “S1” with the rated motor RPM, full field current and N Grounding Considerations: Ground ampere range connected at TB4. The weak field current. Record encoder bonding wire sizes are required to AC voltage is the next consideration pulses per revolution and rated car comply with NEC, UL, CSA and other when approaching this part of the speed. These numbers will need to applicable codes for safety. Provide setup. Typically, the DSD 412 comes be entered into the DSD 412 drive as ground bonding wires as indicated. wired from the factory with the AC volt- parameters later in the startup. Do not rely on metal conduit or age derived from the L1 and L2. If the N Input Isolation Transformer/ building steel connections to per- three-phase voltage fails to meet the Control Transformer: Transformer taps form this function. Drive enclosures criteria defined above, it will be neces- need to be set so the secondary volt- should have an electrically bonded sary to supply an alternate AC voltage. age is equal to or exceeds the antici- ground stud or bus bar contained Continued

DSD 412 field interface board

June 2007 | ELEVATOR WORLD | 89 Continuing Education: Elevator Drives Continued within their construction. The fol- removed. The first of these tests is called car speed to 100%. Make multi-floor lowing items should be connected “drive diagnostics” F998: this routine runs. Monitor the armature voltage to the enclosure ground point, each will verify the power components within feedback on parameter #610. This with its own bonding wire: DSD 412 the drive and some of the critical wiring. number should be equal to or less drive ground lug, the sub panel (to The second routine is called “self tune” than the AC line voltage feeding the which the DSD 412 is mounted), motor F997: this step calculates critical motor drive. If the armature voltage is frame, isolation transformer frame parameters that are required for greater than the line voltage drive, and inductor frame of the armature proper speed regulation. If either of then the motor needs to have less ripple filter (if used). The secondary these tests fail, the problem must be field current at top speed. This is done of the isolation transformer should resolved prior to proceeding further. by a technique referred to as field remain ungrounded. The building N Verifying Field Current: The weakening. ground should be tied to the enclo- most critical step once the startup sure ground point. On the DSD 412 has reached this point is to verify Jim Papez, now retired, was a service consultant drive, the low-voltage circuit common functions to ensure that the con- with the Elevator Products Division of Magnetek. He is a graduate of the University of Wisconsin- should be grounded by connecting troller is performing as expected. Milwaukee. A1TB1-44 to A1TB11. The motor field control on the con- Power Up troller can be easily verified to deter- Mark Kobiske is a senior application engineer N Apply the Control and Three- mine proper setup. Set up the ele- with the Elevator Products Division of Magnetek. Phase Power: Verify that the control vator to run at zero speed. Do not A graduate of the Milwaukee School of Engineering, he started his career with Magnetek in 1990. voltage is between 103 VAC and 126 lift the brake on the drive monitor VAC. Check for balanced VAC from function #612 (field current feed- each phase to ground. Measure the back). With an external monitoring voltage line to line. Verify that the device, such as an amp probe, voltage is in the range that was de- measure the actual field current. termined previously. Enter into the Verify that these two readings DSD 412 the motor parameters, line match. If the only tool available is a voltage and other specific parame- digital volt-ohm meter, measure ters that will allow the elevator to the voltage and calculate the actual operate as it was designed. field current: I = V shunt field/R N Advanced Diagnostics: Prior to shunt field (recorded previously). operating the motor, the DSD 412 has N Operating the Motor: Set the ex- two automatic routines which need to pected car speed to 5% of rated speed, be performed. To perform these tests, it run the drive, and verify that the ele- is crucial that the DSD 412 has control vator is moving in the correct direction of the armature contactor. Placing a and at the correct speed. Repeat the jumper from TB3-3 to TB3-6 on the check for the opposite direction. DSD 412 typically does this. Once these The Rated Car Speed can be moni- tests are complete, the jumper must be tored on function #600. Set the rated

Learning-Reinforcement Questions Use the below learning-reinforcement questions to study for the Continuing Education Assessment Exam available online at www.elevatorbooks.com or on page 111 of this issue.

N What are the three main drawbacks of motor-generator sets? N What are the four main values received when replacing motor-generator sets with DC drives? N What are the most important things to consider when replacing motor-generator sets with DC drives? N What is a ripple filter? N How is the encoder mounted in a DSD 422 installation? N Ground bonding wire must comply with which applicable codes? N How is a jumper used in advanced diagnostics on the DSD 412?

90 | WWW.ELEVATOR WORLD | June 2007 Continuing Education: Elevator Drives

ELEVATOR WORLD Continuing Education Assessment Examination Questions Instructions: N Read the article “Replacing Motor-Generator Sets with Modern Static DC Drives,” (page 85) including the sidebar “Commissioning of the Magnetek DSD 412 DC Elevator Drive” and study the learning-reinforcement questions. N To receive one hour of continuing-education credit, answer the assessment examination questions found below online at www.elevatorbooks.com or fill out the ELEVATOR WORLD Continuing Education Reporting Form found over- leaf and submit by mail with payment. N Approved for Continuing Education by NAEC for CET and NAESAI for QEI.

1. The Ward-Leonard system is a control configuration 6. When replacing the MG set while retaining the existing that generates: car controller, the following should be generated to a. Controlled DC power via a DC motor operating from ensure proper installation and operation: line power and driving a DC generator. a. An electrical schematic. b. Controlled DC power via an AC motor operating b. A wiring diagram. from line power and driving a DC generator. c. An operational sequence chart. c. AC power via a DC motor operating from an AC d. All of the above. generator. d. DC power via a DC motor operating from line power. 7. The wiring between the DSD 412 and the motor should be checked to determine that no insulation has been 2. The following is a major drawback of MG systems: damaged during the installation. This check should be a. High power consumption. done at the: b. High routine maintenance. a. Motor end of the power wires. c. Excessive generator brush wear. b. Drive end of the power wires. d. All of the above. c. Midsection of the power wires. d. Exposed area of the power wires. 3. Since the introduction of DC static drives, MG sets have essentially disappeared from use in new installations. 8. Encoder wiring, speed reference wiring, pre-torque ref- This, in turn, has caused: erence wiring, 24 VDC login inputs and open collector a. A severe shortage of replacement parts for existing outputs should be run _____ 120 VAC, three-phase AC, MG sets. DC armature and field wires. b. An overage of replacement parts for existing MG sets. a. Together with c. A manufacturing boom for replacement MG sets. b. Separate from d. None of the above. c. Directly underneath d. None of the above 4. Since it converts AC to DC directly, the DC drive will draw approximately _____ more amps from the line 9. In most cases, the _____ states the Full Field Voltage of during car acceleration. Full Field Current. a. 0% a. Motor nameplate b. 10% b. Safety Handbook c. 30% c. Main control board d. 90% d. DC drive

5. A _____ is added to the DC line from the static drive to 10. The preferred method of mounting the encoder is the DC motor to reduce acoustical noise in the motor ______the motor armature. and mounting structure. a. Perpendicular to a. Noise filter b. Below b. Ripple filter c. In line with c. Output filter d. Above d. Capacitor filter

June 2007 | ELEVATOR WORLD | 111 Continuing Education: Elevator Drives Continued

ELEVATOR WORLD Circle correct answer Continuing Education Reporting Form 1. a b c d 6. a b c d 2. a b c d 7. a b c d Article title: “Replacing 3. a b c d 8. a b c d Motor-Generator Sets with Modern Static DC Drives” 4. a b c d 9. a b c d (EW, June 2007, page 85). 5. a b c d 10. a b c d Continuing-education credit: This article will earn you one contact hour of elevator-industry Signature: ______continuing-education credit. Payment options: Directions: Select one answer Check one: J $30.00 – Non-subscriber course fee for each question in the exam. Completely circle the ap- J $25.50 – ELEVATOR WORLD propriate letter. A minimum score of 80% is required to subscriber course fee earn credit. You can also take this test online at website: Subscriber #: ______www.elevatorbooks.com. (Six-digit number on your print label or in your digital confirmation) Last name:

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E-mail: Signature: ______This article, “Replacing Motor-Generator Sets with Modern Static DC Drives,” is rated for one contact hour of To receive your certificate of completion using the continuing-education credit. Certification regulations mail-in option: Send the completed form with questions require that actual study time is verified with all program answered and payment information included to: Elevator participants. Please answer the below question. World, Inc., P.O. Box 6507, Mobile, AL 36660. How many hours did you spend reading the article and To receive your certificate of completion online, visit studying the learning-reinforcement questions? website: www.elevatorbooks.com and follow the instruc- hours minutes tions provided for online testing.

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