world education

Why Direct To Handset Satellite is a Game Changer for World Education

Direct to handset #d2d satellite technology, has the potential to transform world education.

The transformation includes allowing all children to access education.

Currently, millions of children don’t have access to education.

This lack of access disproportionately affects girls and women.

Traditional Mobile (cell) Phones work by having nearby Cell Towers.

These Cell Towers connect the user’s phone to the network, by sending and receiving radio signals between the tower and the handset.

The problem with this traditional approach is that according to satellite operator Lynk Global, only 10% of the world is served by Cell Towers.

Covering the remaining 90% of the earth’s surface, using traditional infrastructure is uneconomic.

This matters, as it’s also uneconomic to install Internet cables underground.

This means that there is still a third of the world, that is not yet connected.

Not being connected to phone calls and the Internet, means that remote communities remain isolated.

It also means that these communities are at a significant disadvantage when it comes educational opportunities.

One of the challenges facing the world is a lack of trained teachers.

This results in students underperforming, in many countries, compared to other more developed ones.

Direct-to-handset connectivity delivers worldwide coverage, of both voice and Internet data.

For more articles on this world education enablement, visit the author’s website.

Transformers – Single Phase Type

Transformers

Transformers are most commonly ‘step-down’ types.

This means that the voltage that comes out is less than the voltage going into the transformer.

The ‘transformer ratio’ of the winding’s on the input side ‘primary’ & output side ‘secondary’, determines the output voltage.

Example: 100 volts AC going in with a 10:1 (Primary / Secondary) winding ratio, would give 10 volts output.

  • single phase transformers

    Information about Single phase Transformers

There are two main types that you will come across.

Single Phase

&

Three Phase

The difference between the two types is that Single Phase have four electrical connections, whereas Three Phase have six.

In the case of a Single Phase Transformer, the four connections consist of two input connections, and two output connections.

The Three Phase types six connections, consist of three input connections, and three output connections.

Both single phase and three phase transformers will only work with Alternating Current (AC).

AC was invented by Nikola Tesla over 100 years ago, and is the dominant system used (as opposed to Direct Current (DC), for electricity transmission.

AC is the electricity that comes out of a wall socket in a house, in nearly all installations around the world.

Unlike Direct Current (DC) in which the polarity of the two connections stays constant (has a fixed + & -), AC voltage ‘Alternates’.

The ‘Alternating’ in Alternating Current (AC) means that the voltage in the two wires is constantly changing direction and level.

The picture below shows what is actually happening

AC Sine Wave

The picture above shows an AC Sine Wave.

As you can see, the ‘wiggly’ line travels both above and below the straight horizontal line.

The horizontal line represents the 0 Volts level, and below the line is minus volts, and above plus volts.

The two wires of a single phase transformer are connected in a fixed position, but the picture shows what is happening in each of the wires.

The peaks represent the peak voltage in one of the two wires, therefore if the voltage is at the peak in one wire, it is the opposite level in the other wire.

The ‘alternation’ of the voltages in the two wires happens rapidly and constantly.

The speed of change is called the Frequency, and is measured in Hertz (Hz)*.

*It is worth noting that on older pieces of British machinery such as Transformers and Induction Motors, you may find Frequency described as ‘Cycles’, rather than Hz.

In the UK and Mainland Europe the frequency of the mains electricity supply is 50Hz, whereas in countries like the USA and Japan, it is 60Hz.

This constant frequency of voltage change creates electromagnetic induction in the transformer.

Transformers rely on electromagnetic induction for their operation.

induction motor bearing tips

Marine Induction Motor Servicing Tips

Tips for Servicing Marine & Land Based Induction Motors.

These tips for marine induction motor servicing, are for education only, and should not be relied on as instructions.

Smart Manufacturing technologies can be applied to Induction Motors, to reduce servicing down time.

Wirelessly connected sensors can be used to monitor Induction motor parameters.

Such parameters include bearing vibration increases, and current in the Stator coils.

Only competent trained electrical personal should attempt to service marine induction motors.

Training Lincolnshire

Tools Required

Safety & Isolation of supply of induction motors.

Taking a casual approach to electricity can prove fatal.

This is especially true when we are talking about three-phase motors, as they operate in the UK & EU at 400 Volts Alternating Current (400 VAC).

Marine installations typically operate at an even higher 440 Volt Alternating Current (440 VAC).

Never work on a piece of three-phase machinery, such as an induction motor unless you are both qualified to do so, and have authorisation.

People able to give authorisation include senior managers, with appropriate responsibilities, in the case of onshore factory installations.

For work to be carried out aboard Ships, permission from someone such as the Chief Engineer is appropriate.

Once permission has been gained, and the appropriate paperwork issued, only then can work commence.

Certainly in the marine environment, and normally onshore as well, ‘locks and tags’ will be issued.

The lock is to ensure that once an isolator switch has been turned off, no one can switch it back on accidentally.

The ‘tag’ details who has isolated the supply, and is working on that circuit.

Only the person who has been issued with the lock and tag set, can remove them.

Double check that circuit is dead.

Another marine induction motor servicing tip is don’t assume that just because you have locked and tagged the appropriate electrical isolator, that you are safe to work on a circuit.

The isolator may be incorrectly labeled, or even worse, you have taken someone else’s word for it.

Before you stick your fingers in, and potentially kill yourself, you need to use an appropriate device to check that the circuit is safe to work on.

induction motor bearing tips

Induction Motor

There are three possible devices that can be used:

  1. Test Bulb
  2. Multimeter / Voltmeter
  3. Line Tester

Firstly lets look at the test bulb as an option.

A test bulb with appropriate leads and clips attached, can provide indication of a live circuit, but has a flaw.

If the bulb filament breaks, then you could falsely assume that the circuit is safe to work on, with possibly fatal outcomes.

The second option is the Multimeter / Voltmeter which these days will probably be a ‘solid state’ digital type, rather than the older analogue types, which are commonly referred to as ‘AVO’s’ in the UK.

The Multimeter / Voltmeter being ‘solid state’ is more likely to be a bit more reliable than, a filament bulb tester. However it still may be broken, and you would not necessarily know. An example being the test probe wires may be ‘Open Circuit’.

The third option, the ‘Line Tester’, will provide the most reliable indication of whether a circuit is safe. Therefore this is the preferred option.

The reason that a line tester is safer is because it contains four separate Neon bulbs (some modern ones are LED).

The bulbs light up according to how high the voltage is, for example a 400 VAC supply would light not only the 400VAC light, but the lower voltage indicator lights as well.

So imagine that the 400VAC indicator bulb has broken.

The lower voltage indicator bulbs will still light up, for example the 230VAC and 110VAC indicator bulbs.

Therefore the engineer will still have an indication that there is voltage in the circuit, and can investigate further.

Before using a Line Tester you should use a ‘proving unit’. A proving unit is a small hand-held device capable of producing a voltage such as 250 Volts.

The Line tester can thus be tested using the proving unit, prior to testing a real live circuit.

To test the Line Tester the two probes are pushed against the Proving Unit which then produces a voltage.

This will be indicated by an indicator LED lighting up on the proving unit itself.

The Neon or Led indicator lamps of the Line Tester should also light up at the same time, to indicate the voltage being supplied.

Tips when changing bearings on Induction Motors

Importance of identification code facing outwards.

When refitting bearings to an induction motor you will notice that the bearing itself has a code written on the one side of it.

This code is the product identification code, and is what you need to quote in order to order the correct replacement bearing.

Once the correct replacement bearing has been obtained, and is ready for fitting, ensure the following.

Firstly, that the bearing identification code is facing away from the Stator, and outwards towards the end of the motor shaft.

This will help you in the future, if you ever have to replace the bearings again.

The reason for this is that you can just remove the end plate of the induction motor, and read the bearing code easily, provided it has been fitted with the code facing outwards.

If the bearing code was facing inwards, then it is harder to read the bearing code, and might mean that the motor shaft has to be disconnected from its mechanical load.

This adds to the motor downtime, and hence has financial and productivity implications.

Ways to remove bearings from induction motor shaft.

The ideal way to remove an old bearing from the induction motor rotor shaft is to use a bearing puller tool.

Removal is then just a matter of fitting, the tool into position, and winding in the screw thread in a clockwise direction.

As this happens, the bearing is slowly pulled up and off the shaft.

If however you don’t have a puller, other methods, such as  using a metal bar to leverage between the bearing and the end of the shaft can be tried.

However this is not the way I recommend, and you do it at you own risk of injury and damage to the motor shaft.

Methods for fitting a new induction motor bearing when marine induction motor servicing.

Ideally you will have a hydraulic bench press, that you can use to put massive pressure down onto the bearing to ‘press it’ onto the shaft, in the correct position.

When using such a press, a number of precautions should be observed.

Firstly, ensure that you are fully competent to use the hydraulic press. Even fairly cheap versions are capable of exerting many tons of pressure, which can be dangerous to human health.

Secondly, ensure that the tube or sleeve that you fit over the shaft of the motor is only just wide enough.

The reason for this is that a wide metal tube (or sleeve) put over the motor shaft in order to push against the bearing, can damage it.

This is because too wide a tube will make contact with the plastic middle of the bearing, or the outer metal edge.

Both of these two scenarios are bad, because pressure applied to anywhere but the centre metal part of the bearing, will cause damage.

This damage can result in the replacement bearing being ruined, which defeats the object of replacing it.

Using a hydraulic press is the method that we would recommend, however this option is sometimes not available.

In particular to engineers working at sea in a marine environment, such as a cargo ship.

If you find yourself in this situation, then there are other ways to re-fit a replacement bearing to an induction motor.

One method is to take advantage of the fact that metals contract and expand due to cold and heat.

This method involves carefully wrapping up the Stator part of the induction motor in a polythene bag, and putting it in the freezer overnight.

This will very slightly shrink the size diameter of the bearing shaft.

The second part to the operation involves gently heating up a pan of engine oil, so that it is warm.

Obviously extreme care needs to be taken, so that either a fire is not caused by the oil igniting, or the engineer receiving burns while trying to handle the hot bearing.

Once the bearing is warm, the Stator can be removed from the freezer, and the warm oiled bearing should slip fairly easily onto the shaft.

The oil can then be wiped off the bearing with a non fluffy cloth, and motor reassembly can begin.

For more tips on marine induction motor servicing, why not check out the authors (and our founders)  personal website at www.craigmiles.co.uk/blog

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Training

Technology Training by Experienced Marine Engineering Trainer

Marine Engineering Electrical Maintenance Training

Our experienced marine engineering trainer can offer your organisation experienced trainers, specialising in Marine electrical and radio engineering systems.

Our professional skillset encompasses marine electrical installation, fault finding, and servicing.

Our trainer is formally a lecturer of South Shields Marine School, where he taught practical workshop and theoretical classroom courses.

Highly experienced in working with international marine engineers, and trainees.

Of course, our trainer is also highly experienced in radio communications systems, having earned a degree in the subject, and starting in the industry in 1990.

Installation Training

Star Delta Starter Training

handheld walkie talkie

Schools radio audit

Radio communications is often used by schools to communicate between the office and the playground, but does it need a free audit ?

Many systems in use can be easily eavesdropped on by strangers, which has possible safeguarding issues.

We are offering schools a free onsite audit of their two-way radio equipment.

To register email:     schools [at] yesway.co.uk

Note: replace the [at] with the @ symbol. We do this to prevent spam bots on the internet.

Induction Motor

Star-Delta Starter

Star-Delta (or Wye-Delta)  starter is used in electrical engineering to start larger three phase motors, typically over 4 KW (5 HP).

The Star-Delta starter is chosen, rather than the cheaper D.O.L (Direct On Line) for larger motors, because when a motor is started a surge current is generated for a short initial period. This surge current is typically 5 – 7  times greater than  the normal operating current of the motor, and can cause problems due to the fact that suddenly a large load is appearing on the electrical circuit of your ship or building.

If you started a large induction motor, rated at 50 Amps, then the surge current being between 5 – 7 times that figure, would mean a current appearing on your electrical system of between 250 – 350 Amps. This surge current could potentially cause a ‘blackout’ on board a ship, or at least put strain on the generator.

Even on land, large surge currents are undesirable, and many countries require Star (Wye) – Delta starters to be used to start motors rated above 5 HP or 4 KW.

Operation

The Star-Delta Starter basically consists of three contactors, a timer, and an OCR (Over Current Relay).

When the Star- Delta is first switched on, the electromagnetic coils in the ‘Line’ & ‘Star’ contactors are energised. The magnetic field produced by the coils (in conjunction with the metal cores fitted) closes the contacts of both contactors. This allows voltage to flow through the line contactor into one side of each of the three (three phase) windings.

The Star contactor is also initially closed, and this creates a ‘star’ winding configuration, by shorting the other side of each of the three windings together.

Having the motor windings connected in Star means that surge current is reduced when the motor initially starts up.

At motor startup, a timer is also started.  To be continued………………..

(c) 2013 Craig Miles, all rights reserved.

Comparison of True Versus Reactive Power

 Comparison of True Versus Reactive Power

When a  resistive load is connected, no phase shift is occurs between the voltage and current.

The Power that is the  result of the resistive load  performs work in the circuit. This is      known as “true” power, and is measured in watts.

By  comparison, an inductive load causes a 90-degree phase shift between voltage and current.

To calculate the power that results from an inductive load, multiply voltage by current. When either voltage or current is zero, the power is zero. This type of power is known as  “reactive” power. It counteracts the true power in an electrical circuit. It is measured in reactive volt-amperes.
© 2013 Craig Miles, all rights reserved

Induction Motor

Inductive Loads

 

Inductive loads are loads from electrical equipment.  Electricity circulates through coiled or wound  wire. An inductor is a component which produces a magnetic field, when a current is passed through it.

Examples  include relays, motors, solenoids, & transformers.

As a general rule, if an electrical load involves movement, it is classed as being an inductive load..

Inductive loads can cause ‘blowback’ and must be protected by diodes. Diodes allow the current to flow in one direction only.

Blowback is caused by a surge in voltage. This is caused when the magnetic field in the inductor collapses.

(c) 2013 Craig Miles, all rights reserved

single phase as sine wave picture

Resistive Loads

Resistive Loads

Resistive loads are most often are found  in circuits where electricity  produces heat, light, or both forms of energy, Resistive loads do not produce movement.

Examples of resistive loads include Kettles, Incandescent Bulbs, and Heaters.

(c) 2013 Craig Miles