Three Phase Induction Motor

UNDER EDITING

Students should be able to perform the following:

A- explain the construction of the ac induction motor.
B- explain the concept of rotating field and how it is created.
C- explain the working of the rotor
D- calculate the speed of rotating field .
E- calculate slip speed ans speed of the rotor


Many of my students find it difficult to understand the AC induction motors.

It does not matter whether it is 3 phases or 2 phase motor, because the principle is the same.

It needs the understanding of 2 concepts:

- the rotating magnetic field
- the rotor

It is the interaction of the rotating field and the rotor will cause the rotor to rotate.

B. Creation Of Rotating Field
This is better explained by video used by this video

DC Generator Overhaul

UNDER  EDITING




Testing The Armature
There are 2 basic test:
- Using meter
- Using Growler

1. Test Using Gowler
Growler is like the primary winding of a transformer. When the armature is positioned on the growler, the armature is acting like the secondary of the transformer. However, please take note that the secondary winding of the armature is open circuit, so no current flows in the armature windings but there are the induced voltage

a. Check for short circuit.

DC Generators and Motors

I had chosen an old film produced by US Department of Defense in 1961. I like it because the video was made with the specific purpose, that was to train the staff. Please view the video below...

 The following topics were discussed...

1. The theory of .. Generation of EMF through the movement of a conductor in a field of magnetic flux.

2. A simple generator with a single loop.

3. The formula of the instantaneous EMF, e= BlV Sin The angle.

4. The operation of an armature.

5. Converting the AC within the armature to DC output.

6. Making the DC output smoother by adding additional poles and loops.

7. Prevention of sparking by positioning the brushes in the neutral plain.

8. The Armature Reaction and its effects.

9. Creation of magnetic fields and different methods to excite the field, separately excited and self excited.

10. The different way the fields are connected, series, parallel and compund.

Transformer Module 3:15

The Part 66 document list the content of the syllabus.

The contents can be summarized as follws:

Module 5.14 Electromagnetic Environment

I am consolidating the modules in one blog. This is done to enable easier searching by readers...

I had prepare 18 slides for the topic shared below:

MODULE 5  SLIDES

CHAPTER 12 – ELECTROMAGNETIC ENVIRONMENT

Slide 1 - Syllabus as Per Part 66

Electromagnetic Environment Syllabus (part 66) (Level – L2)   

Influence of the following phenomena on maintenance practices for electronic system:

EMC-Electromagnetic Compatibility

EMI-Electromagnetic Interference

HIRF-High Intensity Radiated Field

Lightning/lightning protection  

Slide 2 WHY THE INCREASED CONCERN IN RECENT YEARS?  BECAUSE:

- Greater dependence on electrical and electronic systems for continued safe flight.

- Reduced electromagnetic shielding due greater use of composite materials.

- Increased susceptibility of electrical and electronic systems to HIRF due to increased data bus and processor operating speeds, higher density integrated circuits and cards, and greater sensitivities of electronic equipment;

- Expanded frequency usage, especially above 1 gigahertz (GHz);

Increased severity of the HIRF environment because of an increase in the number and radiated power of radio frequency (RF) transmitters; and

- Adverse effects experienced by some aircraft when exposed to HIRF.

Slide 3. ADVERSED EXPERIENCES

The experiences had proven the need consider the threat seriously.
Gross navigation error in a passenger aircraft in USA (from Newark to San Maarten) caused by a portable tv set used by a passenger.

Lap top used by a passenger affected the navigation equipment during aircraft take-off and landing.

4. ELECTROMAGNETIC ENVIRONMENT

Caused by transmission of electrical energy in space, e.g from radar, radio or TV.

Like current flowing in a wire, magnetic fields are created.

EMC – Electromagnetic Compatibility

Electromagnetic compatibility, or EMC means that a device is compatible with (i.e., no interference is caused by its electromagnetic (EM) environment and it does not emit levels of EM energy that cause electromagnetic interference (EMI) in other devices in the vicinity.

All electric devices or installations influence each other when interconnected or close to each other. Eg your TV set, your GSM handset, your radio and nearby washing machine or electrical power lines.

5. The purpose of electromagnetic compatibility (EMC) is to keep all those side effects under reasonable control

Electromagnetic interference or EMI, also called radio frequency  interference or RFI. It is the disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source.

If avionics equipments are left unprotected, may cause serious flight safety issues.

6. EMI SOURCES (electromagnetic interference)

EMI IN AIRCRAFT

SOURCES OF EXTERNAL INTERFERENCES (note P168)

Two forms of interference

Conducted interference

Radiated interference

Sources of interferences

External Electrical Systems  e.g brushes, switches

Engines system – ignition system

 Inadequate bonding

Faulty static discharger/wicks

7. CONTROLLING THE INTERFERENCE

Well Located aerials – the interference to the comm/nav systems like ADF and VHF

Electronic equipment to be grounded and the related wires to be shielded and grounded.

 The lighting current flows through the outer skin and discharge to the extremity.

Bonding – all equipments to be bonded together, min R = 0.05 ohms.

Static Discharger – provide the low resistance path to the admosphere.

8. WHAT IS HIRF

It is High Intensity  Radiated Fields (electromagnetic energy)  external to the aircraft, of a strength sufficient to  have adverse affect on aircraft safety.

Note: The source of energy is external, exclude onboard system and static sources.

9. LIGHTNING

The high energy and high voltage can affect the aircraft hardware as well as the data.

The high transient discharge current can damage the skin of the aircraft and the bonding wires.

10. PROTECTION AGAINST LIGHTNING

Aircraft skin

Voltage and current protector at the equipment

Wire shielding

11 PERSONAL ELECTRONIC DEVICES (PED)

Personal Electronic equipments can produce signals that affect electronic equipments.

However there was no definitive proof of individual cases. Symptoms and failures went off when passengers were asked to switch PED.

12. The cautions were founded as some of the sensitive electronic wires run in close proximity to passengers.  

EXAMPLE OF HIRF CHECK

TYPICAL INSPECTION (P166)

13 REVIEW and QUESTIONING