Running Induction Motors on frequencies other than their Design Frequency.

Induction motors use an iron core and require flux in the iron to
operate. In order to achieve the commercial goals of smallest size and
lowest price at best efficiency, induction motors are designed to
operate at a high level of flux in the iron. The flux is determined by
the turns, voltage and frequency. In a modern motor, if the flux is
increased by a small amount, the iron losses increase and the iron
tends towards saturation. At saturation, the inductance begins to fall
and the current increases further. To reduce the flux at a given
voltage and frequency, the turns on the stator are increased. This
reduces the Iron loss, but a longer length of thinner wire is used and
the copper loss increases. Design becomes a balancing act between
copper loss and iron loss and so the design is optimised for a given
voltage and frequency.

If the voltage applied to the motor is held constant
and the frequency is increased, the inductive reactance increases and
so the flux reduces. This effectively reduces the maximum torque
capacity of the motor and so the motor power rating at the higher
frequency remains the same.

If the voltage
applied to the motor is held constant and the frequency is reduced, the
current will increase and in theory, the torque will also increase. The
motor should be able to deliver the same power also, BUT the flux in
the iron is now too high resulting in excessive iron loss, and the
motor will fail prematurely. Above a very low frequency, (5 - 10Hz) the
impedance of the magentising circuit of the motor is primarily
inductive and so in order to keep the flux within limits, it is
important to keep a linear V/F ratio (Voltage to Frequency ratio). If
the frequency is reduced by 10%, the voltage must also be reduced by
10%. Because the flux in the iron remains the same, the torque capacity
remains the same and so the power rating of the motor also drops by 10%.

60Hz rated motor on 50Hz

Provided the voltage is dropped by the same proportion as the frequency, it is OK to run a 60Hz motor on 50Hz. The speed will be reduced by the reduction in frequency and the power capacity will also reduce by the ratio of the reduction in frequency.

60 Hz	50 Hz
Line Voltage	Line Voltage
480	400
460	383
440	367
230	191

 

50Hz rated motor on 60Hz

Provided the voltage is increased by the same proportion as the frequency, it is OK to run a 50Hz motor on 60Hz. The speed will be increased by the increase in frequency and the power capacity will also increase by the ratio of the increase in frequency.

50 Hz	60 Hz
Line Voltage	Line Voltage
415	498
400	480
380	456
230	276

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Know How: Electrical General

Calculation of short-circuit currents

Summary

In view of sizing an electrical installation and the required equipment, as well as determining the means required for the protection of life and property, short-circuit currents must be calculated for every point in the network.
This “Cahier Technique” reviews the calculation methods for short-circuit currents as laid down by standards such as IEC 60909. It is intended for radial and meshed low-voltage (LV) and high-voltage (HV) circuits.
The aim is to provide a further understanding of the calculation methods, essential when determining short-circuit currents, even when computerised methods are employed.

Reference

• - Author :B. de Metz-Noblat, F. Dumas, C. Poulain
• - Publication date:01/09/2005
• - Page number:32
• - ECT no:158

> Download

Power Quality

Summary

One of the properties of electricity is that some of its characteristics depend not only on the electricity producer/distributor but also on the equipment manufacturers and the customer. The large number of players combined with the use of terminology and definitions which may sometimes be
imprecise partly explain why this subject area is so complex.
This "Cahier Technique" aims to facilitate exchanges on this topic between specialists and non-specialists, as well as customers, manufacturers, installers, designers and distributors. The clear terminology used should help avoid confusion. It describes the main phenomena causing degradation in Power Quality (PQ), their origins, the consequences for equipment and the main solutions. It offers a methodology for measuring the PQ in accordance with differing aims. Illustrated with practical examples for the implementation of solutions, it shows that only by observing best practice and by applying strict methodology (diagnostics, research,solutions,implementation and preventive maintenance) can users obtain the right quality of power supply for their requirements.

Reference

• - Author :Philippe FERRACCI
• - Publication date:01/10/2001
• - Page number:36
• - ECT no:199

> Download

Source: http://www.schneider-electric.com

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What is continuity test?

Salah satu tahapan terpenting sebelum melakukan comissioining mesin yaitu continuity test. Lebih lengkap silahkan baca artikel ini.

What is continuity?

You might be asking, "What is continuity?" But don't worry, it's quite simple! Continuity means, are two things electrically connected. So if two electronic parts are connected with a wire, they are continuous. If they are connected with cotton string, they are not: while they are connected, the cotton string is not conductive.

You can always use a resistance-tester (ohmmeter) to figure out if something is connected because the resistance of wires is very small, less than 100 ohms, usually. However, continuity testers usually have a piezo buzzer which beeps. This makes them very useful when you want to poke at a circuit and need to focus on where the probes are instead of staring at the meter display.

For some basic circuits you can just look to see where the wires go to determine continuity but it's always wise to use a multimeter. Sometimes wires break or you're tired and can't easily follow all the PCB traces. I use continuity check all the time!

What is it good for?

Continuity is one of the most important tests. Here are some things it is good for

• Determine if your soldering is good. If your solder joint it is a cold solder connection it will appear connected but in actually it is not! This can be really frustrating if you are not experienced in visually detecting cold solder joints
• Determine if a wire is broken in the middle. Power cords and headphone cables are notorious for breaking inside the shielding, it appears as if the cable is fine but inside the wires have been bent so much they eventually broke.
• Making sure something isn't connected. Sometimes a solder joint will short two connections. Or maybe your PCB has mistakes on it and some traces were shorted by accident.
• Reverse-engineering or verifying a design back to a schematic

Remember!

You can only test continuity when the device you're testing is not powered. Continuity works by poking a little voltage into the circuit and seeing how much current flows, its perfectly safe for your device but if its powered there is already voltage in the circuit, and you will get incorrect readings

Always test to make sure your meter is working before starting the test by brushing the two tips together, and verifying you hear the beep. Maybe the battery is low or its not in the right mode.

Continuity is non-directional, you can switch probes and it will be the same.

If you are testing two points in a circuit and there is a (big) capacitor between those points you may hear a quick beep and then quiet. That's because the voltage the meter is applying to the circuit is charging up the capacitor and during that time the meter 'thinks' its continuous (essentially)

Small resistors (under 100 ohms or so) and also all inductors will seem like short circuits to a multimeter because they are very much like wires.

Likewise, continuity doesn't mean "short" it just means very very low resistance. For example, if you have a circuit that draws an Amp from a 5V supply, it will appear to be a 5Ω resistor. If you measure that with your meter it will think its a short circuit, but really its just a high-drain circuit.

Get into the mode

First step is to get your multimeter into the correct mode. Look for the icon that looks sort of like a 'sound wave'

Here are three examples. Note that sometimes the mode is "dual" (or possibly more) usage,

Turn the multimeter knob so that it points to this symbol

Touch and go

For a majority of multimeters, you're ready to go, just touch the tips of the probes together so that they make a beeping sound!

Here's a video demonstration

If you can't view embedded videos, click here to download an mp4

Here are some examples covering a couple of different multimeters

Example 1

This meter is very simple. When the probes are not touching, the display shows "1"

When you touch the tips together, the display changes to a three digit mode (it's displaying resistance, which we will cover later) It also emits a beep

Example 2

This meter is dual-mode but still very easy to use. Turn the dial to the symbol. When the probes are not touching the display shows "OL" which stands for Open Loop. (Open loop is another way of saying there is no continuity)

When you touch the probes, the soundwave icon shows up in the display (upper right) and it also shows a number. The number is not the resistance, actually...its the voltage (look for the V in the right hand side for Volts). This is because this mode is also a Diode Test (which will be discussed later)

Example 3

This meter is triple-mode and requires an extra step to get to the continuity function. Click on the image to get a closer view of the triple-mode. After you dial to this mode you must press the Mode button, the wave icon will then appear in the display.

You can see the wave icon in the top right as expected. This meter also displays OL (I've noticed that nicer meters do this)

Unlike the other meter, this one displays Ohms (see the symbol on the right of the display). The resistance is low (4.7Ohms) but not 0 (the ideal value) because the probes and wires act as resistors. Usually with these sorts of meters they will beep whenever resistance is under 100 ohms or so.

Probing a PCB

Here is an example of testing a PCB for continuity.The first test shows that the two points are not connected.

The second test shows that these two points are connected

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Handbook of Electrical Safety

This is contents on this book.

1.0 INTRODUCTION1-1
1.1 PURPOSE
1.2 SCOPE
1.3 AUTHORITY HAVING JURISDICTION (AHJ)
2.0 GENERAL REQUIREMENTS
2.1 ELECTRICAL MAINTENANCE OR REPAIRS
2.1.1 WORK ON ENERGIZED/DEENERGIZED
ELECTRICAL EQUIPMENT
2.1.2 CONSIDERATIONS FOR WORKING ON
ENERGIZED SYSTEMS AND EQUIPMENT
2.1.3. SAFETY WATCH RESPONSIBILITIES
AND QUALIFICATIONS
2.2 BASIC SAFEGUARDS
2.3 RESPONSIBILITIES
2.3.1 MANAGEMENT RESPONSIBILITIES
2.3.2 EMPLOYEE RESPONSIBILITIES
2.4 REVIEWS/INSPECTIONS
2.5 APPROVAL OF ELECTRICAL EQUIPMENT
2.6 CODES, STANDARDS, AND REGULATIONS
2.7 GROUND FAULT CIRCUIT INTERRUPTERS
2.7.1 HOW A GFCI WORKS
2.7.2 USES
2.8 TRAINING AND QUALIFICATIONS OF QUALIFIED WORKERS
2.8.1 FORMAL TRAINING AND QUALIFICATIONS
2.8.2 TRAINING OF SAFETY PERSONNEL
2.9 WORKING SPACE AROUND ELECTRICAL EQUIPMENT
2.9.1 ELECTRICAL EQUIPMENT RATED AT 600 VOLTS OR LESS
2.9.2 ELECTRICAL EQUIPMENT RATED OVER 600 VOLTS
2.10 IDENTIFICATION OF DISCONNECTION MEANS
2.10.1 DISCONNECTING MEANS
2.10.2 PANELBOARD CIRCUIT DIRECTORIES
2.10.3 ENCLOSURE LABELING
2.10.4 LOAD LABELING
2.10.5 SOURCE LABELING
2.11 WORK INSTRUCTIONS
2.11.1 SAFE WORK INSTRUCTIONS AND SUPERVISION
2.11.2 WORK INSTRUCTIONS
2.11.3 WORK PLANNING
2.12 ELECTRICAL PERSONAL PROTECTIVE EQUIPMENT (PPE)
2.12.1 MANAGEMENT’S RESPONSIBILITIES
2.12.2 INSPECTING PPE
2.12.3 CLEANING AND ELECTRICAL TESTING OF PPE
2.12.3.1 TESTING
2.12.3.2 TESTING APPARATUS
2.12.3.3 RETESTED PPE
2.12.4 LIVE-LINE TOOLS
2.12.4.1 FIBERGLASS-HANDLED TOOLS
2.12.4.2 WOODEN-HANDLED TOOLS
2.12.5 MAXIMUM USAGE VOLTAGE
2.12.6 MAXIMUM USAGE VOLTAGE FOR LIVE-LINE TOOLS
2.12.7 RUBBER-INSULATED GLOVES
2.12.8 STORAGE
2.12.9 SAFETY SHOES, HATS, AND GLASSES
2.13 WORK PRACTICES
2.13.1 TRAINING
2.13.1.1 LIVE PARTS
2.13.1.2 SAFE PROCEDURE
2.13.1.3 CIRCUITS AND EQUIPMENT
2.13.1.4 STORED ELECTRICAL ENERGY
2.13.1.5 STORED NONELECTRICAL ENERGY
2.13.1.6 LOCKOUT/TAGOUT PROCEDURE
2.13.2 VERIFICATION OF DEENERGIZED CONDITION
2.13.2.1 VOLTAGE VERIFICATION TEST
2.13.2.2 APPLICATION OF GROUNDS
2.13.3 REENERGIZING EQUIPMENT
2.13.3.1 TESTS AND VISUAL INSPECTIONS
2.13.3.2 WARNING EMPLOYEES
2.13.3.3 REMOVING LOCK AND TAG
2.13.4 SAFE ENERGIZED WORK (HOT WORK)
2.13.4.1 APPROACH DISTANCE
2.13.4.2 TWO WORKERS
2.13.4.3 ELECTRICAL SAFETY RULES
2.13.4.4 UNEXPECTED ELECTRICAL HAZARDS
2.13.4.5 ILLUMINATION
2.13.4.6 SYSTEMS UNDER LOAD
2.13.4.7 WORKING WITH TEST INSTRUMENTS
AND EQUIPMENT
2.13.4.7.1 QUALIFIED EMPLOYEES
2.13.4.7.2 VISUAL INSPECTIONS
2.13.4.7.3 RATING INSTRUMENTS AND
EQUIPMENT
2.13.4.7.4 CALIBRATION OF
ELECTRICAL INSTRUMENTS

Download : pdf1 (Please right click and Save As..)

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Buku Untuk ELECTRICAL ENGINEERING

Most books on transmission and distribution electrical engineering are student texts that focus on theory, brief overviews, or specialised monographs. Colin Bayliss and Brian Hardy have produced a unique and comprehensive handbook aimed squarely at the engineers and planners involved in all aspects of getting electricity from the power plant to the user via the power grid. The unique scope of this book embraces power systems, substations, cabling, switchgear, power systems protection, overhead lines, project management, planning, regulations, and more... The third edition include a new chapter on power quality, a thoroughly updated section on earthing and bonding, coverage of the integration embedded generation and renewables in modern power systems, and has been fully updated in line with the latest IEC and European standards. The resulting book is an essential read, and a hard-working reference for all engineers, technicians, managers and planners involved in electricity utilities, and related areas such as generation, and industrial electricity usage. 1. A reference handbook written by engineers for engineers 2. Unrivalled in its scope, covering systems, substations, cabling, switchgear, power systems protection, overhead lines, project management, planning, regulations, and more... 3. The third edition includes expanded sections on power quality, a thoroughly updated section on earthing and bonding, and coverage of the integration embedded generation and renewables in modern power systems

Rincian lebih lanjut

Transmission And Distribution Electrical Engineering: Electrical Engineering

Oleh C. R. Bayliss, B. J. Hardy

Kontributor C. R. Bayliss, B. J. Hardy

Diterbitkan oleh Newnes, 2006

ISBN 0750666730, 9780750666732

1010 halaman

BACA ? Klik Disini!

-------------------------------------

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