-:INTRODUCTION:-

RF controlled starting of induction motor

Purpose: This project is a starting step towards development of a central wireless controlling scheme for industries and house hold uses. The concept is to design a controlling station (or equipment, in case of house hold use), which can completely regulate the operation of all the industrial loads (or appliances).

Advantages: This scheme would facilitate complete prevention of human electrocution, reduction in response time, saving of conductor.Not only is the expense of wiring eliminated, there are no conduits, clips or connectors required.There are no wire routing problems to solve, no need for pulling wire during installation and fewer restrictions on location and placement of switches. Wireless controlling can also reduce maintenance costs. Equipment wiring is less complex with the elimination of wired switches from the mix, simplifying troubleshooting and reducing commissioning time. Further, going wireless increases system reliability by eliminating the potential for having continuity issues with switch wiring or connectors. Switches also become simpler to replace, with no need to disconnect and re-attach wiring and no risk of incorrect wire attachment.

Conventional wired switches, present installation and maintenance challenges, especially in installations that are subject to harsh environments or involve frequent flexing in the wiring. In some cases, traditional wires can represent tripping hazards or can be compromised during normal equipment operation, thus causing expensive machine down-time.Industrial loads: Manufacturing plants and industries have different working schemes and they apply different electrical machines to control the processes, but Induction motors are the most general type of industrial load.

Induction motors are popular due to their low-cost, sturdy construction, fast pick-up , low maintenance expenditure and good efficiency. The DOL ( direct-on-line ) starters and star/delta starters used for starting and running of induction motors provide coarse type of protections against voltage fluctuations and single phasing.Induction motors are very sensitive to low voltage and single phasing during which they draw a heavy current and can burn out unless switched of within few seconds of occurrence of such conditions.

This makes the requirement of a sensitive protective device absolutely essential to avoid burning of induction motors under such conditions and hence is a suitable choice for first type of load to be controlled via RF switching.

Overall project can be divided into three major sections as follows:-

1.RF Section2.Relay Section.3. Starter Section

Radio Frequency vs. Infrared control:

γ= Gamma rays MIR= Mid infrared HF= High freq.

HX= Hard X-rays FIR= Far infrared MF= Medium freq.

SX= Soft X-rays Radio waves LF= Low freq.

EUV= Extreme ultraviolet EHF= Extremely high freq. VLF= Very low freq.

NUV= Near ultraviolet SHF= Super high freq. VF/ULF= Voice freq.

Visible light UHF= Ultra high freq. SLF= Super low freq.

NIR= Near Infrared VHF= Very high freq. ELF= Extremely low freq.

There have been previous efforts in context of wireless switching and controlling using Infrared signals. A comparative study of RF and IR signals has been done which reflect the overall advantage of RF over IR switching.

IR Advantages:

1. Low power requirements: therefore ideal for laptops, telephones, personal digital assistants.

2. High noise immunity: not as likely to have interference from signals from other devices.

IR Disadvantages:

1.Line of sight: transmitters and receivers must be almost directly aligned (i.e. able to see each other) to communicate. Blocked by common materials: people, walls, plants, etc. can block transmission.

2Short range: performance drops off with longer distances.

3.Light, weather sensitive: direct sunlight, rain, fog, dust, pollution can affect transmission.

4.Speed: data rate transmission is lower than typical wired transmission.

RF Advantages:

1. No line of sight requirement.

2.Not blocked by common materials: can penetrate most solids and pass through walls.

2. Longer range.

3. Not light sensitive.

4. Not as sensitive to weather/environmental conditions.

RF Disadvantages:1. Interference: communication devices using similar frequencies -

wireless phones, scanners, wrist radios and personal locators can interfere with transmission.

2. Higher cost than infrared.3. Licenses required for some products.

Advancements in RF technologies:

During the last decade, the telecommunications industry has made phenomenal advances toward replacing wired connectivity with wireless. As the technology evolved, it overcame both technical challenges and political barriers to deployment. A variety of fully defined and robust networking protocols emerged that function well over these wireless technologies. Government agencies worldwide settled frequency allocations and regulatory issues to allow worldwide operation of those wireless networks.

These advances in wireless telecommunications have opened the door for applications beyond telecommunications to “cut the cord” and to go wireless. For instance, one of the protocols that arose, the IEEE 802.15.4 standard, fully defines a robust wireless personal area network (PAN) that specifically targets low-power, low-bandwidth signaling from switches such as those commonly utilized in industrial monitoring and control. Further, wireless telecommunications spurred semiconductor design and manufacturing to develop highly integrated, low-power RF components for wireless communications.

RFsection:-

ISM Bands: The industrial, scientific and medical (ISM) radio bands are radio bands (portions of the radio spectrum) reserved internationally for the use of radio frequency (RF) energy for industrial, scientific and medical purposes other than communications.

(i)Receiver- Transmitter unit: Selection of Rx-Tx unit is based upon the following requirements:

1. Allowed ISM band (here 433 MHz).

2. It should also have appropriate operating range suitable to be controlled remotely (about 55-60 metres).

3. The output voltage and current should be able to drive commercially available relays.

4. Suitable encoding of RF signal, so that other RF signals ( close to 433 MHz) are not able to interfere.

5. Working temperature should be such that it withstands industrial ambient temperature.

Based on the above requirements, model: RKI-1014 has been selected.

It has following major components:

TRANSMITTER MODULE

433.92 Mhz RF Transmitter SAW Resonator ASK

The MO-SAWR is an ASK transmitter module .The result is excellent performance in a simple-to-use .The MO-SAWR is designed specifically for remote-control.wireless mouse and car alarm system operating at 433.92 MHz.

Applications Automation systemRemote switching operation.

Product Identification433.92MHz MO-SAWR-AS434M

Parameter Rating Units

Supply Voltage 1.5 to 12 V dc

Operating Temperature

-20 to +85 ℃

Make Holy stone Enterprise Co. Ltd.

RCEIVER MODULE:RX3400 Low Power ASK Receiver IC

DescriptionThe RX3400 is a low power ASK receiver IC ( Himark) which is suitable for use in a variety of low power radio applications. The RX3400 is based on a super-heterodyne receiver architecture for precise local oscillator generation.FeaturesExtremely low power operationReceiver input frequency: 290 – 460 MHzIntegrated IF and data filtersApplicationsRemote controllerHousehold control systems

Encoder:HT 12-E Encoder (18 Pin DIP)

General Description:

The 212 encoders are a series of CMOS LSIs for remote control system applications. They are capable of encoding information which consistsof N address bits and 12 N data bits. Each address/data input can be set to one of the two logic states. The programmed addresses/data are transmitted via RF transmission.

Decoder:

General DescriptionThe 212 decoders are a series of CMOS LSIs for remote control system applications. They are paired with 212

Holtek’s series of encoders. For proper operation, a pair of encoder/decoder with the same number of addresses and data format should be chosen.

Overall specification of RF section:

Frequency 433.92MHz Working voltage

5v dc- 12v dc

Max. O/P Volt. 12 v dc Channels 256 ( 4 Operating at a time)

Max O/P Current

2 amp Input voltage used

9v dc

Range 55-60 meters Make Robokits india

2.Relay Section:

RELAYS :-

A relay is an electrically operated switch. Many relays use an electromagnet to operate a switching mechanism mechanically, but other operating principles are also used. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal.

All relays are classified as :i. Electromagnetic.ii. Moving-coil.iii. Inductive.iv. Electronic

According to power of control signal, electric relay sub-divided into :i) Low power ( less than 1 W )ii) Medium-power (from l to W )iii) High-power ( 10 W )

Design of Relay unit:Relay unit has been designed to operate in accordance with the switching signal and controlled quantity.

Following are the points upon which relay has been selected:

1. Operating voltage- Should lie between 5v - 9v2. Low loss 3. Instantaneous operation.4. Compact size5. Equipped with NO an NC contacts.

By going through different commercially available relays we finally choose GOODSKY (RWH-SH-106D) Attracted armature type relay.

Fig: Actual picture of attracted armature type relay.

Main features:1. RWH Series Relay covers switching capacity by 10A in spite of

miniature size to comply with wide selection.2. RWH is approved by vvarious safety standards.3. The employment of suitable plastic materils is applied under

high temperature condition.

4. Complete protective construction is designed from dust and soldering flux. It is completely sealed so that it is also protected from moisture.

Reference Data:-

3.Starter section:

For starting purpose star delta type starter is designed because it is the most widely used starting method for starting 3-ph induction motor above 3 HP. Also, it can be used to start Synchronus motors.

Starting Current An induction motor draws a very large starting current, of the order of 6 to 8 times the full-load current if started direct-on-line. The amplitude of the starting current may be comparable to fault current. Therefore, the over-current protection provided to the motor must be able to discriminate between a genuine fault and an

over-current due to starting of the motor. Hence, coordination between the starting characteristic of the motor and the over-current relay is required Figure 2 shows the starting current superimposed on the thermal capability curve of the motor, and the characteristic of an over-current relay, which might be used for protection of the motor. It can be seen from Figure 2 that the OC relay characteristic must be above the starting characteristics but below the thermal characteristics of the motor. This will ensure that the protective relay does not operate during starting phase the motor but will positively operate when the load exceeds the motor's thermal capability.

Star- Delta starterThe circuit of an automatic starter, incorporating theimportant features given below, is described here.

1. Under-voltage and over-current cut-out.

2. Single phasing prevention.

3. Specially suited for remote operation of induction motor.

CONTROLLING CIRCUIT OF R.F CONTROLLED I.M. STARTER

Power circuit of Y-Δ induction motor starter:

WORKING

When switch S1 is closed STAR contactor coil is energized through (NC) RELAY 1, NC push button (STOP), (NC) RELAY 3 and NC (DELTA). When we give signal to (NO) RELAY 2 it gets closed and main contactor coil is energized through RELAY 1 and RELAY 2. In this configuration induction motor starts running in Star connected mode. Since STAR contactor is energized NC contact of the STAR contactor gets opened and prevents the starting of motor in DELTA mode. RELAY 2 is given a short time signal sufficient only to start the motor in STAR configuration. When the signal is removed supply to the circuit is continued through HOLD (M) contact.

After a predetermined time delay (determined from the current time graph) we switch it from STAR to DELTA this is done by giving signal to RELAY 3 which opens after receiving the signal and breaks the supply line going to STAR contactor coil.

As soon as STAR coil is de-energized the NC contact of STAR contactor gets closed which in turn completes the supply line to DELTA contactor coil and the motor starts running in DELTA mode.

Now, since the DELTA contactor is energized NC contact of DELTA contactor becomes open and thereby breaking the supply line of STAR contactor coil. This mechanism works as an electrical interlock which prevents DELTA and STAR contactor from being energized at the same time.

To switch off the motor we give signal to RELAY 1which opens after receiving the signal and thus breaking the supply to the whole circuit including HOLD (M). All the states are being shown by indicators.

The START , STOP and Y-Δ changeover function can be accomplished using manual PUSH buttons also, in case, RF switching fails to operate.

Components used in Y-Δ starter:

1.

Fig: Contactor (Top view) Fig: Contactor coil

Specifications:

Max current through main contacts

9 amps

Coil voltage 220-240 v ac

Power rating 4kw

No. of poles 3

NO contacts 1

Make Havells

2.NO-NC Contacts

Specifications:

No. of NO Contacts 2

No. of NC Contacts 2

Type of Mounting Front mount

Type of coupling Mechanical

Make Havells

WORKING OVERVIEW (STARTING AND Y- Δ SWITCHING OF I.M. MOTOR THROUGH REMOTE):-

The circuit module comprises of receiver module planted on hardwood ply board, connected to three electromagnetic relays.The relays are connected to contactor (actually star –delta starter) units. One of the contactors is made star by shorting all the three

terminals of it . The other contactor is connected in delta with the 3rd. One. The main power line 3-phase terminals are connected to the contactors terminals through MCB.

The other three terminals of the contactor is connected to induction motor terminal . The transmitter and receiver sets are energised by a 5-12 volt battery. Now, when the remote switch is operated to control the relay from a distance of about 55-60 meters by switching on , the transmitter sends a signal to receiver unit and in return receiver signals to the one of the electromagnetic relay connected through it ,to send switching command to complete the current path by closing contacts for one of the contactor coil.

The motor thus starts running in star configuration as it is set initially. Again, after a particular time settings (of about 4-6 sec)The switch over signal is sent through the remote ,to the receiver module. Which, in turn makes electromagnetic relay close to send signal to delta contactor .The star contactor is relieved from the circuit and delta configuration is switched over by operating relays through RF circuit. The motor is thus connected to delta configuration through contactors. As the motor on and switch over is attained, the display bulbs show this .

CIRCUIT LAYOUT (OVER VIEW)

CONCLUSIONS AND RESULTS

1. The project –kit was tested for its operation.

2. The test was performed in electrical lab. On a squirrel cage induction motor.

3. When connected properly with the motor and power supply , the project kit performed well.

4. The starting and star delta transformation was successfully done by wireless transmitter switch well with in the range of 55-60 meters.

5. The induction motor showed satisfactory results of response when controlled by remote operated switch.

Future planned modifications and speed control

As the project is only a starting step towards developing a complete controller, it does not have the facility to control the speed of induction motor.

We have planned to take this thing in the major project. Moreover we have thought of an idea in which we will try to couple an ammeter or a speedometer thorough RF, right there on the control panel so that we are able to take complete control of Y-Δ changeover (even if there is a fault).

References:1. www.eetimes.com

2.Wikipedia 3. www.goodsky.co.uk 4. www.alldatasheet.com 5. www.holtek.com