Ac-Dc"Circuit " Electrical engineering homework help

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A) Make yourself familiar with with the ACC-100-FT Controller. (read the first part of the hand-out) B) Carefully make the connections in Diagram No1. Let the instructor check it upon completion. Do not start the Main without permission! C) After making the connections in Diagram No.1, the main circuit breaker is turned to the “ON” position, applying a 208V – 3 phase voltage to the circuit. When the N.O. start pushbutton is depressed, coil “F” is energized and closes all four of its N.O. contacts and the pilot light is illuminated. One of the contacts of coil “F” is used as a holding contact to keep “F” energized after the start pushbutton is released. The remaining N.O. contacts of coil "F" apply a 208V – 3 phase voltage o the motor's stator and the motor starts. When the N.C. stop pushbutton is depressed, the voltage to coil “F” is interrupted, causing it to de-energize. This returns all four contacts to their N.O. condition which removes the voltage from the motor's stator, thus stopping the motor and returning the circuit to its initial condition. D) In the report: objectives measurements (line voltage measurement and RPM with 2 tachometers provided)write down the information on the Nameplate of the motor. Conclusions Bulletin 254-AC-EX ACC-100-FT Student Manual T1 A 211 22 231124 25 126 3º AC INPUT B T2 B/ IM-100 MOTOR T3 С с START STOP 4 9_110 colo 3 33 34 o " Q 27 28 F DIAGRAM NO. 1 FULL VOLTAGE STARTER FOR A SQUIRREL-CAGE MOTOR 15 Bulletin 254-AC-EX ACC-100-FT Student Manual INTRODUCTION TO THE ACC-100-FT CONTROLLER This manual contains fourteen experiments for the AC controller. These experiments cover some of the more popular control configurations, but do not exhaust all of the possible sys- tems that may be designed using the components provided. The ACC-100-FT is provided with the following: PUSHBUTTONS: 13 14 Four pushbuttons are provided, each having a set of nor- mally open (N.O.) and normally closed (N.C.) contacts. These pushbuttons are labeled STOP, START, FORWARD, and REVERSE. However, since all four are identical, each can be used for any desired function. 15 16 CIRCUIT BREAKER: A three-pole, 2.5 amp circuit breaker is provided for the incoming power line. 208-volt, 30 power is fed to the con- troller through the terminals labeled L1, L2, and L3. It is recommended that the complete control system be wired LIO and checked before power is patched to the controller. The control system can then be energized by moving the lever L20 on the circuit breaker to the left. Should an overload occur, the circuit breaker will trip, and the lever will automat- 130 ically return to the OFF position. Should this happen, al- ways be sure to remove the cause of the overload before turning the circuit breaker switch back ON. Move the lever to the right manually to de-energize the control sys- tem. Remember, however, that 208-volt AC power remains at the input until the power source is also turned OFF. FORWARD-REVERSE CONTACTOR 21 00 FORWARD-REVERSE CONTACTOR: 22 35 36 23 24 37 38 TH O 25 26 39 to 27 29 45 A reverse contactor is provided consisting of two 3-pole contactors which are mechanically interlocked. Each con- tactor has 2 N.O. and 1 N.C. auxiliary contacts. Either con- tactor may be used individually, or they may be used to- gether in any sort of control scheme requiring mechanically interlocked contactors. OOOHHORO SOUHO SO-OHO.O TOHHO: :0OHO 28 30 32 42 46 33 47 R - . 9 Bulletin 254-AC-EX ACC-100-FT Student Manual DC FIELD CONTACTOR DC FIELD CONTACTOR: 77 78 79 80 OH OHHO 81 82 83 84 OHO OHIO A DC contactor is provided for application of excitation current for synchronous motor operation The coil is rated for 115 volts DC. 85 86 FLD OVERLOAD RELAYS: OVERLOAD RELAYS 87 89 91 93 A three-pole overload relay is provided. It is manually re- set with a reset lever in the rear of the controller. Reset- ting should NOT be attempted, however, until the source of the overload is removed and the heater coil has had a chance to cool. OL1 (OL 2 OL3 88 90 92 94 VARIABLE RESISTORS: R1 R2 Six variable resistors are provided for use as starting resis- tors for squirrel-cage or wound motors, and for dynamic braking resistors. These resistors are rated for short duty only and therefore must NOT be used as speed controllers. 8 TERMINAL POINTS: Six terminals, labeled T1, T2, T3, R1, R2, and R3, are provided as convenient points for connecting external motors. Connections which are to be made to a motor's stator are first brought to terminals T1, T2, and T3. Connections which are to be made to a wound rotor are brought to terminals R1, R2, and R3. The connections to be made to the field of a synchro- nous motor are brought to check terminals R1 and R2. This permits a complete check of the wiring before the actual motor terminals are patched to these terminals. There is NOT any wiring terminating at these points within the controller housing. STATOR ROTOR T1 T2 T3 R1 R2 R3 O O RECTIFIER: RECTIFIER AC AC A full-wave bridge rectifier is provided to supply the direct current required for dynamic braking of squirrel-cage induc- tion motors. 10 Bulletin 254-AC-EX ACC-100-FT Student Manual AUTOTRANSFORMER: AUTOTRANSFORMER ATA AT5 O A three-phase open delta autotransformer is provided for reduced voltage starting of squirrel- cage induction motors. 1720 AT2 OA ATJ AT1 CONTACTORS 49 50 63 64 O KO CONTACTORS: 51 52 65 66 th o 54 67 68 53 O- HH Two independent three-pole contactors are pro- vided, each having two N.O. and one N.C. auxil. iary contacts. 57 59 69 71 ūO BOOHOO OHHOH OHOHO: O 0:00:20 FOTO: :O POROHO:20 56 60 70 74 61 62 75 76 C1 C2 TIME DELAY RELAYS: 95 96 97 103 104 105 OHHOHHO ОН НОННО 98 99 100 106 107 108 ОНКОННО Two electronically-timed, "delay-on” time delay relays are provided, each with two N.O. and two N.C. contacts. The delay time is adjustable via a thumbwheel on each relay, accessible in the rear of the Controller. The delay time, however has been factory set and is not normally changed during experimentation. OHHOHHO 101 102 109 110 TD1 TO2) PILOT LAMPS: 11 12 Two pilot lamps are provided to be used when it is desired to obtain a visual indication of the closing of a relay or contactor. To use, simply connect the lamp in series with unused set of normally open contacts between any two of the AC lines. 11
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FULL VOLTAGE STARTING FOR A SQUIRREL CAGE INDUCTION MOTOR
Introduction
Induction motors can be started easily unlike synchronous motors. Small induction motors can be
started by connecting them to power directly, a method also known as across-the-line starter
method. However, this method is not preferable for large motors because of the large current
required during starting that cause a dip of voltage in the power line. This is unacceptable in
many cases.
Current varies widely during starting of cage induction motors. This variation depends primarily
on the rated power and the rotor’s resistance during starting. Cage motors have code letters on
their nameplates that help in estimating the starting current (Chapman, 2005).
Objectives
I.

To understand the working principle of full voltage starting of a squirrel cage induction
motor.

II.
III.

To observe the drop in voltage during the starting of squirrel cage motor.
To determine speed variation during starting and normal running of the motor.

Procedure
1. Connections were made as shown in Diagram No. 1 below.

Diagram No. 1
2. The main circuit breaker was then turned on to supply a 208 V-3 phase voltage to the
circuit.
3. The N.O. start pushbutton was depressed causing coil F to be ...


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