Keywords: Elevator, Three-Phase Squirrel-Cage Induction Motor, Motor Design, Performance Test and Results.

Size: px

Start display at page:

Download "Keywords: Elevator, Three-Phase Squirrel-Cage Induction Motor, Motor Design, Performance Test and Results."

Austin Dalton
5 years ago
Views:

www.semargroup.org, www.ijsetr.com ISSN 2319-8885 Vol.03,Issue.

1 ISSN Vol.03,Issue.10 May-2014, Pages: Design Implementation of Three-Phase Squirrel-Cage Induction Motor used in Elevator THIDAR TUN 1, THET NAUNG WIN 2 1 Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar, newlovecreator.nyi@gmail.com. 2 Dept of Electrical Power Engineering, Mandalay Technological University, Mandalay, Myanmar, thetnaung67@gmail.com. Abstract: In most large cities, land is scarce and consequently it is very valuable. This has led to the construction of tall building which occupies only a small area of land while providing a lot of floor space where people can live or work. So, in these buildings, the elevator become useful and act in the important part to carry passengers to the required floors Every elevator must be driven by at least one motor its own and this motor must be located at the upper escalator landing. So, the major contribution of this paper is to describe the design calculation of AC three-ase squirrel-cage Induction motor of continuous power rating 11kW (15hp), 1500rpm,50 Hz and 4poles, reversible type with low starting torque, high starting current and specially designed for elevator application. In this paper, the basic designs of squirrel-cage induction motor such as sizes of stator and slots, teeth, core, rotor diameter, rotor bar area, rotor bar current efficiency, speed, and power and so on are described. Keywords: Elevator, Three-Phase Squirrel-Cage Induction Motor, Motor Design, Performance Test and Results. I. INTRODUCTION With the rapid development of city construction, the emergence of high-rise buildings and the expansion of buildings area, the use of elevator has become more important, and the quality of elevator s service is required higher and higher. Therefore, the large-scaled buildings are provided with a plurality of elevators so as to meet the transportation needs. Elevators are prevalent throughout many multi-level structures. They control the flow of foot traffic between various floors of buildings, they allow disabled persons to access upper-level floors, and they facilitate the movement of large items (such as furniture and office equipment) between various levels of the building. Several different types of motor are available for elevator, but the particular motor is chosen depending upon the supply characteristics and quality of service to be provided. In this paper, three ase squirrel cage induction motor is used to drive the escalator. Due to its simple, rugged and inexpensive construction, reduced maintenance, and excellent operating characteristics, these squirrel-cage induction motors are widely used in industrial, commercial and domestic applications. So, as a rough estimate nearly 80 % of world industrial motors are three-ase inductions motor [3] [4]. II. OVERVIEW OF ELEVATOR A. Types of Elevator s Arrangements Two main types of elevator are Hydraulic elevators and Roped elevators Hydraulic Elevator: The system includes a piston and cylinder arrangement connected to the hydraulic system. The tank is filled with hydraulic fluid and connected via, the valve to the cylinder. Roped Elevator: Roped elevator pull the elevator car using ropes or cables.one end of the steel ropes is attached to the elevator car while the other end is attached to a counterbalance.the sheave is connected to a motor that turns the sheave both clockwise and counterclockwise. When the sheave rotates in one direction the elevator car rises, when it rotates in the opposite direction the elevator car lowers.the basic components of a roped elevator are (1) control system (2)electric motors (3)sheave (4)counterweight. B. Elevator Safety Devices 1. Molded Circuit Breaker Molded Circuit Breaker (MCCB) protects the elevator control equipment from unusual voltage surges in the building power supply. 2. Over Speed Governor It locates in the machine room and engages the governor rope, causing activation of the elevator safety device, should the elevator car accelerate beyond the predetermined maximum speed in the "down" direction. Safety gear will be gripped on car guide rails to prevent free fall. 3. Safety Gear It locates beneath the elevator car, brings the car to a safe stop, should the elevator over speed in the down direction SEMAR GROUPS TECHNICAL SOCIETY. All rights reserved.

4. Safety Drive Operation When a car stops beyond DOOR (DR) zone owing to temporary failure, it prevents passenger locking in a car by AUTO-operating slow to the nearest service FLOOR (FLR). 5.

6. Door Open and Close Time Auto-control Automatically control DR open/close time according to call kind or elevator using condition in order to optimize the operation efficiency. 7.

C. Classifications of Elevator s Sizes, Capacity TABLE I: ELECTRICAL DESIGN GUIDE FOR SPEED 200 FT/MIN THIDAR TUN, THET NAUNG WIN Figure1. Electric Traction Geared Elevator. D. Model Elevator Figure 2 shows model elevator.

2 4. Safety Drive Operation When a car stops beyond DOOR (DR) zone owing to temporary failure, it prevents passenger locking in a car by AUTO-operating slow to the nearest service FLOOR (FLR). 5. Miscall Cancel Function When the going floor is much more than the passengers, this function cancels the entire going floor registered after performing bottom service, to avoid unnecessary operation. 6. Door Open and Close Time Auto-control Automatically control DR open/close time according to call kind or elevator using condition in order to optimize the operation efficiency. 7. Overload Detection When the rated load of car exceeds 110%, prevents an overload operation by opening the door and ringing buzzer. The following figure 1 shows the Electric Traction Geared Elevator. C. Classifications of Elevator s Sizes, Capacity TABLE I: ELECTRICAL DESIGN GUIDE FOR SPEED 200 FT/MIN THIDAR TUN, THET NAUNG WIN Figure1. Electric Traction Geared Elevator. D. Model Elevator Figure 2 shows model elevator. It is constructed with four floors. The car, cable, elevator motor (stepper motor), control equipment, counterweight, hoist way, rails, limit switch (ototransistor) and seven-segment display unit make up the principle parts of this elevator project installation. The car and the car load are suspended on a roped connected to the Figure2. Elevator s Arrangements.

Design Implementation of Three-Phase Squirrel-Cage Induction Motor Used in Elevator counterweight by means of a friction sheave which the motor drives.

The motor load is at a maximum with a fully loaded up traveling car or empty down traveling car.

3 Design Implementation of Three-Phase Squirrel-Cage Induction Motor Used in Elevator counterweight by means of a friction sheave which the motor drives. The size of the counterweight is equal to the total weight of the car and half of the car load. Thus the smallest possible load differences are achieved. The motor load is at a maximum with a fully loaded up traveling car or empty down traveling car. Due to the friction present, no load running occurs with approximately a ¼ loaded car traveling up or a ¾ loaded car traveling down. In this paper, the elevator design is (carrying load of 1500lb and car speed of 200 ft/min (1m/s)) used in 150ft high building (9 stories). Over head (OH) = 132 in (11ft) Pit depth (P) = 48 in (4ft) Machine room high (MH) = 87 in(7.25ft) Therefore, the total travel for elevator is TL = 150-OH-P = = 135 ft For 10 passenger (1500lb), car speed of 200ft/ min and 400V of main lines Motor capacity =15hp (11kW) Power supply capacity = 9kVA (12hp) Lead- in wire size = in 2 Earth wire size = in 2 In order to drive this elevator, rating 11kW (15hp), 1500rpm,50 Hz and 4 poles, reversible type AC three-ase squirrel-cage induction motor is chosen according from table 1.Therefore, the details design calculation for this squirrelcage induction motor is described with the next sections. III. CONSTRUCTION OF THREE-PHASE SQUIRREL CAGE INDUCTION MOTOR A three-ase squirrel cage induction motor consists of two main parts: stator and rotor (see fig 3). A. Stator This is the fixed part of the motor. A cast iron or light alloy frame surrounds a ring of thin laminations (around0.5 mm thick) made of silicon steel. The laminations are insulated from one another by oxidation or an insulating varnish. The "lamination" of the magnetic circuit reduces losses via hysteresis and eddy currents. The laminations have slots in them for holding the stator windings that produce the rotating field (three windings for a 3-ase motor). B. Rotor This is the moving part of the motor. Like the magnetic circuit of the stator, it is made up of a stack of thin laminations insulated from one another, forming a keyed cylinder on the motor shaft. Two different technologies can be used for this part, which separate asynchronous motors into two distinct families: those with a squirrel-cage rotor and those with a wound rotor which are referred to as slipring. But in my thesis, a squirrel-cage rotor is used (see fig 4). [4] Figure3. Detail construction of three-ase squirrel-cage induction motor [4]. Figure4. Typical squirrel-cage rotor. C. Advantages of Squirrel-Cage Rotor over Wound Rotor There are several advantages of squirrel-cage over wound rotor induction motor. They are rugged in construction,no slip rings, brush gears, etc, minimum maintenance, trouble free performance, cheaper, better cooling conditions, better pullout torque and overload capacity. D. Four Types of Squirrel-Cage Rotor There are several types of squirrel-cage rotor. They are Resistive squirrel-cage rotor Single squirrel-cage rotor Double squirrel-cage rotor Rotor with deep slots Among them by using the double squirrel-cage rotor and deep bars rotor, the low starting torque of a squirrel- cage induction motor can be changed to get the high starting torque condition. [5]

4 IV. DESIGN PROCEDURE OF THREE-PHASE INDUCTION MOTOR The specifications of three- ase induction motor are: Rated output power : 11 kw Rated voltage : 400 V Speed : 1500 rpm Numbers of pole : 4 poles Numbers of ase : 3 ase Frequency : 50 Hz Connection of stator winding : Star Types of rotor : Squirrel-cage rotor A. Motor Output The output equation relates the output of the induction motor with the main dimensions of the stator and is the basic tool to initiate the design. Output of three-ase induction motor is given by, THIDAR TUN, THET NAUNG WIN Sectional area of rotor bar, I b A (17) b Equivalent rotor resistance, ' Rotor copper losses rr (18) ' 2 3 Ir D. Calculation of Performance No load current per ase, I I 2 I 2 0 m mμ (19) I No load power factor, μ cos φ (20) 0 V Magnetizing reactance, Xm Im (21) Total reactance, X = Xs+ Xh+ Xo+ Xz (22) Total equivalent impedance, 2 2 Z R + X (23) I 0 b Output in kw, Q = Co D 2 Lns (1) Input to three-ase Induction motor = 3V Icosφ 10-3 kw (2) Output coefficient, Co = 11Bav q cosφηkw10-3 (3) B. Detail Design of Stator In this paper, to obtain the best power factor in an induction motor, the following equation is used. Number of turns per ase, Hence, internal diameter of stator, D = 0.135P L (4) Induced e.m.f per ase, E= 4.44 fϕtkw (5) E Thus, turns per ase, T (6) 4.44fφk w Sectional area of the stator conductor, Is as (7) s Stator current per ase, Q/ Is (8) 3V cos Size of the stator slot = b s h s (9) Stator winding resistance per ase, L T mts rs (10) a s Mean flux density in stator teeth, ' I B s t s (11) Total stator copper losses = 3I 2 s r s (12) Depth of stator core, Acs ds L (13) i C. Detail Design of Rotor Number of rotor slot is selected based on the following equation. Length of air-gap, L g = DL mm (14) Outer diameter of rotor, Dr= D 2 L g (15) Bar current, I b K K ws wr r ' r Ss Z s ' Z ' r S Z (16) E Short circuit current per ase, Isc (24) Z Short circuit power factor, R cos sc Z (25) Total losses at full load=stator losses + no load losses (26) Efficiency at full load, Output % Output totallosses (27) Full load efficiency for small size motor should be between0.82 to 0.85, for medium size between 0.85 to 0.88 and for large machine between 0.88 to Starting torque = [I sc I r]2 slip full load torque (28) Percentage slips at full load, rotor copper losses S (29) rotor input Maximum output = I - I 0 V sc KW 2(1 Cos ) sc (30) The maximum output developed by three-ase induction motor normally lies between 2 to 2.5 times its full load ratings. E. Result Design Data Sheet According to the design procedure, firstly the design specifications of three ase induction motor are mentioned with the following Table II. TABLEII: Specifications of Three-Phase Induction Motor Specification Symbol Unit Design Value Full Load output - kw 11 Line voltage V Volts 400 Frequency F Hz 50 Number of pole P - 4 Number of ase Rotor types - - Squirrel-cage rotor

Design Implementation of Three-Phase Squirrel-Cage Induction Motor Used in Elevator By using the above equations 1 to 13 the following details design data for stator shows in Table III.

5 Design Implementation of Three-Phase Squirrel-Cage Induction Motor Used in Elevator By using the above equations 1 to 13 the following details design data for stator shows in Table III. The parameters of performance tests are showed as the following Table V by using the above equations 18 to 30. TABLE III: Detail Design Stator Sheet Specification Symb Design Unit ol Value Specific magnetic loading B av Tesla 0.46 Specific electric loading q Ampcond/m Internal diameter of stator D m 0.19 Gross core length L m 0.13 Turns per ase T Numbers of slots Conductors per slots Full load current I s A 21.1 Cross-sectional area of conductor a s mm Width of slot b s mm Height of slot h s mm Flux density in stator teeth Resistance of stator winding Copper losses in stator winding B' t Tesla r s Ω W 534 Depth of stator core d cs m TABLE V: Parameters Of Performance Tests Specification Symbol Unit Design Value Total iron losses - W 507 Friction and windage losses - W 110 No load current I o A No load power factor cos o Short circuit current I sc A Total losses at full load Short circuit power factor - W 1528 cosφ sc Total copper losses - W 911 Efficiency at full load η % 88 Slip at full load S % 3.3 Ratio of starting torque to full load torque Maximum output - kw V. MOTOR PERFORMANCE In this paper, we point out that the variation of slip can change output torque of the motor by using the following equations from (31) to (33). The output torque reaches 161Nm which is the highest in the case of slip at 0.2 and shows in Fig7. Further using Eq.33, total output torque developed may TABLE IV: Detail Design Rotor Sheet Specification Symbol Unit Design Value Length of air gap L g mm Diameter of rotor D r m Number of rotor slots Bar current I r A Bar area a r mm Width of slot b r mm 4.5 Height of slot h r mm 12.5 Resistance of rotor bar r b Ω Rotor copper losses - W 289 Equivalent resistance of rotor r' r Ω 0.4 Figure5. General torque-slip characteristics of induction motor. be represented as a function of operating slip by changing the four angular frequency values such as 94.25, , , rad/sec is shown in Fig7. However, this escalator motor is running with the output torque at rad/sec as

6 this machine is only needed this torque. Figure 5 shows the general three different torque-slip curves due to different rotor resistance at possible maximum slip. So, the rotor resistance of motor in this paper is low as the maximum torque which occur the value of slip at 0.2. TABLE VI: Required Parameters for Performance Calculation Stator resistance (r1) 0.4Ω Stator reactance(x1) Ω Rotor resistance(r2) 0.4 Ω Rotor reactance(x2) Magnetizing reactance( xm) Ω Ω THIDAR TUN, THET NAUNG WIN + V - r 1 jx 1 jx 2 V th jx m r 2 /s Figure6. Equivalent Circuit Diagram of an Induction Motor. jx m V th = Vth V (31) r1 jx 1 jx m (r1 jx1)(jx m) Z th = (32) r1 jx1 jx m The output torque can be calculated with the following equation, Figure8. Characteristics of Output Torque-Speed Curves. Both the figures 6 and 8 show the Equivalent Circuit Diagram of an Induction Motor and Characteristics of Output Torque-Speed Curves. VI. CONCLUSION Elevator is a moving up and down case-a conveyor transport device for carrying people between floors of building. The motor used in elevator is AC three-ase squirrel-cage induction motor of continuous power rating 11kW(15hp),1500rpm,50Hz and 4 pole, reversible type with low starting torque, high starting current and specially designed for elevator application. Although it s starting torque is 57.8% N-m and its maximum output torque is 161 N-m. Due to its simple, rugged and inexpensive construction, reduced maintenance, and excellent operating characteristics, these squirrel-cage induction motors are widely used in industrial, commercial and domestic application. Although it has low starting, the running performance is excellent. So, squirrel-cage induction motors are very appropriate for driving elevator. VII. ACKNOWLEDGMENT The author would like to express her gratitude to Dr Khin Thu Zar Soe, Associated Professor and Head of Electrical Power Engineering Department, Mandalay Technological University and U Thet Naung Win, Lecturer, Department of Electrical Power Engineering, Mandalay Technological for her encouragement and helpful suggestion and supervision. The author wishes to thanks all my teachers. Thanks are also extended to her dear parents and friends for their support. Figure7. Torque-Slip Curves of an Induction Motor. T out = (33) VIII. REFERENCES [1] Hoboken: John Wiley & Sons, 2006, Mechanical and Electrical Equipmentfor buildings. [2] [3] Annett F.A, 1935, Electric Elevators, Second Edition, Printed by McGraw-Hill Book Company,Inc. [4] Hubert Charles I., 1991, Electrical Machine(Theory, Operation, Applications, Adjustment and Control). [5] MittleDr,V.N. and MitalArvind, 1996, Design of Electrical Machine,Fourth Edition.

ESO 210 Introduction to Electrical Engineering

ESO 210 Introduction to Electrical Engineering Lectures-37 Polyphase (3-phase) Induction Motor 2 Determination of Induction Machine Parameters Three tests are needed to determine the parameters in an induction