EXPERIMENT : STAR DELTA STARTER 1. Aim To provided knowledge in Star Delta Starter 2. Objectives To familiarize the student with : i. Control circuit and main circuit for Star Delta Starter ii. Operation in stating AC motor with Star Delta Starter iii. Control equipment for electrical motor control 3. Equipment list i. 3 phase contactor ii. Thermal overload relay (TOR) iii. Push button start iv. Push button stop v. Miniature circuit breaker (MCB) vi. Molded case circuit breaker (MCCB) vii. Pilot lamp viii. 3 phase AC motor ix. Timer (TDR) x. Cables 4. Theory Three phase star-delta motors are constructed similarly to a direct online single ph ase motor, but the terminals for each winding are not t erminated within the motor, instead they are brought out of the motor for control wiring to connect to.Three phase star-delta star-delta motors are used for maximum talk, where the motor will try to start under a heavy load. A star-delta motor starts in two stages, controlled by equipment connected to it. Stage one The motor is required to start. To provide the maximum available torque, the motor is started in ‘star’, which provides a supply of 230v olts to each of the windings (providing high current to each winding). Once the motor is running, it is running in an inefficient mode, due to the use of a high current supply, which will (if left) cause the motor to ove rheat. Stage two Once the motor is running, it no longer needs a high torque supply, so to save energy and prevent the motor from destruction, the motor must change into a ‘delta’ configuration. By changing the configuration of the motor supply cables at the control equipment, the motor can be run in delta mode (running each winding at 400volts rather than 230v, which uses less current)
5. Experiment procedures : EXERCISE 1 : CONTROL CIRCUIT i. The control unit connected as shown in figure 1 (a) or 1 (b). ii. This circuit become to single phase. Take the incoming supply from 1 to 3 phase line. iii. The circuit line connected to the neutral (N) using black cable. iv. The circuit tested using power supply to make operation of controlling circuit.
EXERCISE 2 : MAIN CIRCUIT i. The main circuit connected as shown in figure 2. ii. Incoming supply for this circuit is from 3 phase line 415V (R.Y.B and N). iii. The Earth connected to the phase motor ground by using green.
6. Result
7. Discussion The operation of Star Delta Starter :
The ON push button starts the circuit by initially energizing Star Contactor Coil (KM1) of star circuit and Timer Coil (KT) circuit. When Star Contactor Coil (KM1) energized, Star Main and Auxiliary contactor change its position from NO to NC. When Star Auxiliary Contactor (1)( which is placed on Main Contactor coil circuit )became NO to NC it’s complete The Circuit of Main contactor Coil (KM3) so Main Contactor Coil energized and Main Contactor’s Main and Auxiliary Contactor Change its Position from NO To NC. This sequence happens in a friction of time. After pushing the ON push button switch, the auxiliary contact of the main contactor coil (2) which is connected in parallel across the ON push button will become NO to NC, thereby providing a latch to hold the main contactor coil activated which eventually maintains the control circuit active even after releasing the ON p ush button switch. When Star Main Contactor (KM1) close its connect Motor conn ects on STAR and it’s connected in STAR until Time Delay Auxiliary contact KT (3) become NC to NO. Once the time delay is reached its specified Time, the timer’s auxiliary contacts (KT)(3) in Star Coil circuit will change its position from NC to NO and at the Same Time Auxiliary contactor (KT) in Delta Coil Circuit(4) change its Position from NO To NC so Delta coil energized and Delta Main Contactor becomes NO To NC. Now Motor terminal connection change from star to delta connection. A normally close auxiliary contact from both star and delta contactors (5&6)are also placed opposite of both star and delta contactor coils, these interlock contacts serves as safety switches to prevent simultaneous activation of both star and delta contactor coils, so that one cannot be activated without the other deactivated first. Thus, the delta contactor coil cannot be active when the star contactor coil is active, and similarly, the star contactor coil cannot also be active while the delta contactor coil is active. The control circuit above also provides two interrupting contacts to shutdown the motor. The OFF push button switch break the control circuit and the motor when necessary. The thermal overload contact is a protective device which automatically opens the STOP Control circuit in case when motor overload current is detected by the thermal overload relay, this is to prevent burning of the motor in case of excessive load beyond the rated capacity of the motor is detected by the thermal overload relay. At some point during starting it is necessary to change from a star connected winding to a delta connected winding. Power and control circuits can be arranged to this in one of two ways – open transition or closed transition. Function of equipment list:
Equipment
Function
1. Contactor
Mainly used to control machinery which uses electric motor
2. On-off push button
Push buttons can be functional - as in the case of an on/off switch for a conve yer belt or other piece of electrical equipment, or safety-oriented - as in the case of an emergency stop for a dangerous hydraulic press.
3. Miniature Circuit Breaker
to protect cables and conductors against overloads and short circuits, and electrical equipment from overheating.
4. Molded Case Circuit Breaker (MCCB)
used to interrupt heavy currents as in an industry. The mccb can handle very high fault currents ranging from 16KA or more.
5. Pilot Lamp
used in a wide variety of settings and in some cases are required by law for safety reasons.
6. Thermal Overload Relay (TOR)
to prevent burnout and to ensure maximum operating life.
7. 3 phase AC motor
AC electric motor in which the electric current in the rotor needed to produce torque is induced by electromagnetic induction from the magnetic field of the stator winding
8. CONCLUSION : As a conclusion, the experiment was function good and correctly. According to the experiment, voltage reduction during star-delta starting is achieved by physically reconfiguring the motor windings as illustrated in the figure below. During starting the motor windings are connected in star configuration and this reduces the voltage across each winding 3. This also reduces the torque by a factor of three. After a period of time the winding are reconfigured as delta and the motor runs normally. This is all because the star delta starter is the reduced voltage starting method. They are used in an attempt to reduce the start current applied to the motor during start as a means of reducing the disturbances and interference on the electrical supply. The Star/Delta starter is manufactured from three contactors, a timer and a thermal overload. The contactors are smaller than the single contactor used in a Direct on Line starter as they are controlling winding currents only. There are two contactors that are close during run, often referred to as the main contractor and the delta contactor. The third contactor is the star contactor and that only carries star current while the motor is connected in star.
