REPORT OF STUDENT INDUSTRIAL WORK EXPERIENCE SCHEME (SIWES) TRAINING PROGRAMME (JANUARY 2018 – JULY 2018) AT GALANT INVESTMENT LTD. BY NNADI VICTOR CHINEDU 14CM017032 MECHANICAL ENGINEERING, MECH ENG DEPARTMENT. COVENANT UNIVERSITY BEING A REPORT SUBMITTED TO THE DEAN COLLEGE OF ENGINEERING IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR MCE 429 DEAN COE: PROF. BOLU CHRISTIAN AMAECHI JULY 2018
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REPORT OF STUDENT INDUSTRIAL WORK
EXPERIENCE SCHEME (SIWES)
TRAINING PROGRAMME
(JANUARY 2018 – JULY 2018)
AT
GALANT INVESTMENT LTD.
BY
NNADI VICTOR CHINEDU
14CM017032
MECHANICAL ENGINEERING, MECH ENG DEPARTMENT.
COVENANT UNIVERSITY
BEING A REPORT SUBMITTED TO THE DEAN
COLLEGE OF ENGINEERING IN PARTIAL FULFILMENT OF THE REQUIREMENTS
FOR
MCE 429
DEAN COE: PROF. BOLU CHRISTIAN AMAECHI
JULY 2018
1
Dedication
To God for granting me an internship placement this year, for the strength and preservation to
work for the duration of the internship.
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Acknowledgements
Firstly, I thank God for granting me an internship placement this year, for the strength and
preservation to work for 6 months. It was a pleasant experience. I thank the management of
Galant Investment LTD for accepting me as an intern and giving me the tools and permission to
work and gain experience. I thank Engr. Taiwo Ajose, the freelance generator specialist for
impacting me technically, morally and spiritually, and his wife and children for welcoming me
into their home throughout the period I worked there. I thank the management of Covenant
University for organizing the program. I thank the staff concerned for the prior 4 year theoretical
training that made the process of getting hands on training a breeze. I thank my supervisor for
taking out time to observe and carefully validate my operations at GIL. I also thank my fellow
interns for being good company to me both physically and virtually.
Chapter 6 - Challenges Observed as being faced by the SIWES Industry-based Firm ................................ 42
Related Diagrams ........................................................................................................................................ 44
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Abstract INTRODUCTION
I worked as an intern at Galant Investment Limited for 6 months from January to July 2018.
During my stay there I gained a lot of experience repairing, installing, and purchasing inverters,
solar panels, batteries and generators. The focus was on learning about combustion engines and
how it worked and learning about practical electrical and electronics engineering.
OBJECTIVE
The objectives of this report are
- To highlight my participation at GIL, and the experience I gathered.
- To highlight the challenges I encountered
- To highlight my observations and contributions to the company.
METHODOLOGY
The document starts off with an introduction of the company, GEN Galant Investment LTD,
followed by a detail-rich list of the various kinds of work I participated in. This is followed by a
chapter that highlights my experience gained at GIL, here I explain what I learnt on the field, in
lectures and through personal study inspired by the work done. Thereafter, a chapter that
highlights the challenges I faced trying to get used to the work and become a more valuable
intern, then a chapter that contains my observations and contributions, then a brief conclusion.
The report was then rounded off with the challenges I observed has been faced by the company
during the period of my attachment. All related diagrams were intelligently embedded in the
body of the document to aid a better reading experience.
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Galant Investment LTD. I started working at Galant Power Solutions LTD on January 29, 2018
Galant Power Solutions is a Nigerian energy company with a daring vision to use the power of
the sun to bring 24/7 electricity supply to Nigerian/African homes at an affordable cost, one
home at a time.
Staff Introduction
I was introduced to the concept of the business. I was given a tour around the facility and
introduced to the tools I would need. We had a sit down meeting to discuss about my industrial
training program and I was introduced to the areas of operation that I would be trained in.
We concluded that for the first three months, I would be attached with Engr. Taiwo Ajose, under
whom I would learn how to install, maintain and repair portable electrical generators of various
sizes. And for the remaining time of the program, I would come back to the head office where I
would learn practical electrical works such as household electrical wiring, electricity distribution
theory, the use of electrical engineering tools, installation, maintenance and repair of inverters,
solar panels and deep cycle batteries.
“Modern mechanical systems hardly can do without embedded electrical systems. Hence a good
mechanical engineer should also be well grounded in Electrical and electronics systems
knowledge, to be able to safely design a complete modern mechanical system”
- Engr. Godwin Nnadi, President of Galant Power Solutions.
6
Chapter 1 – Introduction, participation and work done.
1.1 PPE DISPENSARY
I was given the following personal protective equipment
1. Hand Gloves
2. Overalls
3. Helmet
4. Safety Googles
5. Ear Mufflers
6. Safety Boots
1.2 INTRODUCTION TO BASIC MEASUREMENT TOOLS AND PRINCIPLES
I was taught how to use a tape rule, Vernier caliper, micrometer screwguage meter rule and I was
introduced to the Sounding tape used to measure the depth of liquids. I was made to understand
that other more complex tools would be revealed to me during the course of my training.
1.3 TRAINING ON THE USE OF PERSONAL PROTECTIVE EQUIPMENT
I was thought about the use of the various PPEs I was issued.
1. Hand Gloves: The workplace can create many hazards for your hands, whether from
chemicals, cuts or burns. Industrial safety work gloves are designed to reduce hand
injuries in complex work environment without hindering the user’s overall dexterity in
the field. They are useful during welding operations and when working with electricity.
2. Overalls: (also called dungarees), usually made denim or chino cloth. It is a type of
garment used as a protective clothing when working. It protects your body and garment
from harmful and harmless liquid spillages. It is also designed to not have hanging or
draping parts that can get entangled in rotating machines.
3. Helmet: This is a firm of protective gear worn to protect the head from injuries. It aids the
skull in protecting the human brain. Useful when working in an area that is prone to
fallen objects.
4. Safety Googles: Googles or Safety Glasses are forms of protective eye wear that usually
enclose or protect the area surrounding the eye in order to prevent particulates, water or
chemical from striking the eyes. In welding shaded googles are used to protect the eyes
against flares.
5. Ear mufflers: These are a style of hearing protection that fit around the external ear used
to reduce the transmission of sound from entering the ear canal. Nosie is reduced to a
safer intensity level protecting against noise-induced hearing loss. The Occupational
safety and Health Administration (OSHA) recommends the use of hearing protection
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devices HPD when an employee is exposed to an average noise intensity of 85DBA over
an 8 hour shift.
6. Safety Boots: (Also known as steel toe boot or a steel capped boot or safety shoe) is a
durable boot or shoe that has a protective reinforcement in the toe which protects the foot
from falling objects.
1.4 DETAILED TRAINING ON SAFETY
Safety was an integral and important part of operations at Galant Power Solutions. A whole
week was used to train me thoroughly on good safety practice. Here are the safety practices
that I was trained in. I was introduced to concepts such as Save Your Life, Work at height,
Firefighting, working in confined spaces and working with electricity.
1.5 WORKING WITH NEW MEASURING INSTRUMENTS
I was introduced to new measuring instruments like the AVOmeter, the Meger (for insulation
resistance testing), clip-on ammeter, and the battery tester.
1.6 PORTABLE GENERATOR REPAIRS, PURCHASE, INSTALLATION AND
MAINTENANCE.
From February 12th, I was sent to be attached with Engr. Taiwo Ajose, a Mechanical Engineer
with over 20 years of experience of working with generators of various sizes, for a period of 3
months. Throughout the period, we solved a ton of generator problems in and around FESTAC
Town, ranging from repairs, purchase assistance, installation and maintenance. We were
opportune to solve over 100 problems related to generators during my stay. Below, I have
highlighted a few of the challenges we encountered and how we diagnosed and solved them:-
Case 1; Date: February 12; Location: 2nd Avenue, FESTAC Town.
Work Nature: Preventive Maintenance (PM) and Corrective Maintenance (CM)
Generator type: GX160 Elemax
Problem as described by client: The client did not lay any complaints. He only required PM
procedures
Diagnosis: Apart from the PM that was requested, we noticed that some parts of the silencer
system were broken and they were vibrating against each other causing an abnormal operation
noise.
Solution: We carried out complete PM procedures
1. We flushed the carburetor
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2. We decarbonized the cylinder head and the piston head
3. The spark plug was cleaned
4. We drained and replaced the engine oil with Forte SAE 40 oil, as recommended for our
clime. We also welded the broken parts of the silencer and this fixed the vibrational noise
problem.
Damaged Silencer housing – It was sent for welding.
Case 2; Date: April 13; Location: 41 rd., FESTAC Town.
Work Nature: Corrective Maintenance (CM)
Generator type: SUMEC FIRMAN
Problem as described by client: Smoking Generator and other problems.
Diagnosis: We prescribed that the piston and rings be changed to achieve satisfactory working
mode.
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Solution: We had to transport the generator to our workshop.
1. We dismantled the generator set.
2. We documented and ordered the parts that needed to be replaced
3. We ground the inlet and outlet valves and valve seats, and decarbonized the entire
cylinder head.
4. We assembled the set with the new parts well installed.
5. We put in new engine oil (SAE 40) and put in new fuel and tested it to ensure that it
worked smoothly.
6. We delivered the set back to the client.
Decarbonizing the cylinder head of the SUMEC FIRMAN
Case 3; Date: March 23; Location: Ago.
Work Nature: Corrective Maintenance (CM)
Generator type: Honda
Problem as described by client: The generator operation noise was very unsatisfactory.
Diagnosis: We discovered that the ball bearing at the coil side had worn out. The balls rolling
abnormally against each other was the cause of the noise.
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Solution: We had to disassemble the generator set. We highlighted the list of parts that we
wanted to replace. Upon receiving approval from the client, we ordered the parts. We had to
detach the stator and rotor coils, in order to remove the damaged bearing since it is mated with
the rotor coil. During the operation, due to the missed strike of a hammer, some marks were
indented on the rotor coil brush sleeve. We also had to file it back into a leveled smooth surface.
Using a small sand paper to file the brush sleeve of the rotor to achieve a smooth surface.
Case 4; Date: February 23; Location: Deeper Life Church, 23 rd, FESTAC Town.
Work Nature: Corrective Maintenance (CM)
Generator type: GX160
Problem as described by client: Damaged AC socket
Diagnosis: Probably due to electricity surge, or twist and turns, the AC socket of the generator
had worn out completely and could no longer hold the plug within it.
Solution: We carried out complete CM procedures
1. We replaced the AC sockets
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My boss removing the old burnt out socket.
Case 5; Date: April 2; Location: Construction site at 24 rd., FESTAC Town.
Work Nature: Problem Inspection and Corrective maintenance.
Generator type: Honda
Problem as described by client: The set did not supply electricity.
Diagnosis: At first we thought that the problem was either with the AVR, or the coil brush.
Solution: Our first attempt of solving the problem was to purchase a new AVR. We tested this
and it didn’t remedy the problem. Interestingly, we immediately discovered that the circuit
breaker trigger switch was switched on. This meant that the generator had no issue at all, it just
needed this trigger to be deactivated.
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The new AVR we purchased when we thought that it was the problem.
13
Case 6; Date: April 5; Location: 21 rd. FESTAC Town.
Work Nature: Purchase and installation.
Generator type: Elemax GX 160
Solution: We purchased and installed a generator set for the client.
The dealer shop where we purchased the generator set.
Case 7; Date: March 16; Location: 208 rd. B close, FESTAC Town.
Work Nature: Corrective Maintenance (CM)
Generator type: Honda GX160
Problem as described by client: Oil leak from crank case during operation.
Diagnosis: The oil seal had worn out.
Solution: We disassembled mechanical assembly and removed oil seal. We ordered for a new oil
seal and reinstalled it.
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Old oil seal New oil seal installed
Case 8; Date: April 11; Location: 23 rd. I close, FESTAC Town.
Work Nature: Plant Inspection
Generator type: Diesel Generator
Solution: The client requested that we drain the diesel and check for dirt. It was clean and we simply
refilled the tank. I was also shown how to service the generator if the need arises.
15
Cross section of the diesel engine.
Due to the word limit of this document, I only highlighted a few of the interesting works I did on
generators. For the complete list, please see my logbook or the more detailed report attached
with this one.
1.7 ELECTRICAL AND ELECTRONICS TRAINING
From 14th of May, I returned to Galant Investment LTD, to continue work in the Electrical and
Electronics section. Here I participated in a series of lectures on Electrical and Electronics
engineering, we did a household electricity consumption simulation, we also practiced house
hold electrical wiring using a junction box, I assisted in the installation of inverters and solar
panels.
1. House hold electricity consumption: We imagined a typical bungalow in Lagos state and
tried to deduce n estimate of its power consumption.
16
2. Lectures on how electricity is distributed in the home – the Distribution Board.
3. Household electrical wiring practice using a junction box
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4. Inverter and solar panel installation: I assisted in the installation of inverter, solar panels,
solar charge controller and batteries for one of GIL’s clients.
These and other related activities were carried out in this section.
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Chapter 2 – New Experience gained.
2.1 DIVERSE TYPES OF CHALLENGES ENCOUNTERED RELATED TO PORTABLE
GENERATORS.
I was privileged to work on diverse problems as opposed to routine ones, therefore I was able to
encounter, diagnose and solve different kinds of problems related to portable generators.
2.2 EXPOSURE TO NEW CONCEPTS LIKE STROBOSCOPY
STROBOSCOPY
Stroboscopy is an effect in which a cyclically rotating object is made to appear stationary. When
working with rotating machineries in a workshop. It is a good safety measure to avoid
stroboscopy as it would be very dangerous to come in contact with a rotating machine without
prior awareness. A good practice is to use an incandescent bulb as against a fluorescent light in
the work shop.
If you have to use fluorescent bulbs, they should all be connected in different phases.
2.3 HOUSEHOLD WIRING
We used a junction box to practice the most native form of electrical wiring.
2.4 HOW ELECTRICITY TRANSMISSION WORKS
I was exposed in details to the way electricity is generated and transmitted to homes, offices and
industries.
2.5 LOCK AND TAG
Lockout-tagout (LOTO) or lock and tag is a safety procedure which is used in industry and
research settings to ensure that dangerous machines are properly shut off and not able to be
started up again prior to the completion of maintenance or repair work. It requires that hazardous
energy sources be "isolated and rendered inoperative" before work is started on the equipment in
question. The isolated power sources are then locked and a tag is placed on the lock identifying
the worker who placed it. The worker then holds the key for the lock ensuring that only he or she
can remove the lock and start the machine. This prevents accidental startup of a machine while it
is in a hazardous state or while a worker is in direct contact with it.
Lockout-tagout is used across industries as a safe method of working on hazardous equipment
and is mandated by law in some countries.
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2.6 BATTERY TESTING
I was trained on how to use a battery tester to know the health of battery.
2.7 INVERTER INSTALLATION
I was theoretically trained on how inverters are installed and how they are wired such that they
select only the loads of the premises that they can bear.
2.8 LAYING OF SOLAR PANELS
I assisted in the laying of solar panels for a client of ours. I got to understand the different
precautions that needed to be observed to have a successful installation (e.g, avoiding direct
contact of the positive and negative terminals, the adequate exposure of the panels to the sun,
required direction or bearing of lay, Etc.)
2.9 SOLAR CHARGE CONTROLLER CONFIGURATION
I learnt how to connect and configure the solar charge controller which helps to monitor and
control the charge of the batteries for the inverter.
2.10 TRADE STRATEGIES, TRICKS, AND PRICING.
Since it was a small organization, we also had to handle the business aspects ourselves. I was
thought about the pricing system, the strategies that are used to succeed in the trade, the
importance of relationships and how to build and keep them and the tricks and shortcuts that are
used by masters of the trades.
2.11 NEW MEASURING INSRUMENTS
I was also exposed to new measuring instruments that I had never worked with before.
AVOMETER
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AVOmeter is a British trademark for a line of multimeters and electrical measuring instruments;
the brand is now owned by the Megger Group Limited. The first Avometer was made by the
Automatic Coil Winder and Electrical Equipment Co. in 1923, and measured direct voltage,
direct current and resistance. Possibly the best known multimeter of the range was the Model 8,
which was produced in various versions from May 1951 until 2008; the last version was the
Mark 7.
The multimeter is often called simply an AVO, because the company logo carries the first letters
of 'amps', 'volts' and 'ohms'. The design concept is due to the Post Office engineer Donald
Macadie, who at the time of the introduction of the original AVOmeter in 1923 was a senior
officer in the Post Office Factories Department in London.
Megger | Working Principle, Types, Uses of Megger
What is Megger?
Insulation resistance IR quality of an electrical system degrades with time, environment
condition, i.e., temperature, humidity, moisture and dust particles. It also gets impacted
negatively due to the presence of electrical and mechanical stress, so it’s become very necessary
to check the IR (Insulation resistance) of equipment at a constant regular interval to avoid any
measure fatal or electrical shock.
Uses of Megger
The device enable us to measure electrical leakage in wire, results are very reliable as we shall be
passing electric current through device while we are testing. The equipment basically uses for
verifying the electrical insulation level of any device such as motors, cables, generators,
windings, etc. This is a very popular test being carried out since very long back. Not necessary it
shows us exact area of electrical puncture but shows the amount of leakage current and level of
moisture within electrical equipment/winding/system.
Types of Megger
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This can be separated into mainly two categories:-
1. Electronic Type (Battery Operated)
2. Manual Type (Hand Operated)
But there is another types of megger which is motor operated type which does not use battery to
produce voltage it requires external source to rotate a electrical motor which in turn rotates the
generator of the megger.
Electronic Type Megger
Important parts:-
1. Digital Display: - A digital display to show IR value in digital form.
2. Wire Leads: - Two no’s of wire leads for connecting megger with electrical external
system to be tested.
3. Selection Switches: - Switches use to select electrical parameters ranges.
4. Indicators: - To indicates various parameters status i.e. On-Off. For Example Power,
hold, Warning, etc.
Note: - Above construction is not similar for every megger, it difference appears
manufacture to manufacture but basic construction and operation are same for all.
Advantages of Electronic Type Megger
Level of accuracy is very high.
IR value is digital type, easy to read.
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One person can operate very easily.
Works perfectly even at very congested space.
Very handy and safe to use.
Disadvantages of Electronic Type Megger
Require an external source of energy to energies i.e. Dry cell.
Costlier in market.
Hand Operated Megger
Important parts: - Analog display: - Analog display provided on front face of tester for IR
value recording. Hand Crank: - Hand crank used to rotate helps to achieve desired RPM
required generate voltage which runs through electrical system. Wire Leads: - Used same as in
electronic tester i.e. for connecting tester with electrical system.
Advantages of Hand Operated Megger
1. Still keeps important in such high-tech world as it’s an oldest method for IR value
determination.
2. No external source required to operate.
3. Cheaper available in market.
Disadvantages of Hand Operated Megger
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1. At least 2 person required to operate i.e. one for rotation of crank other to connect megger
with electrical system to be tested.
2. Accuracy is not up to the level as it’s varies with rotation of crank.
3. Require very stable placement for operation which is a little hard to find at working sites.
4. Unstable placement of tester may impact the result of tester.
5. Provides an analog display result.
6. Require very high care and safety during use of the same.
Construction of Megger
Circuit Construction features:-
1. Deflecting and Control coil: Connected parallel to the generator, mounted at right angle
to each other and maintain polarities in such a way to produced torque in opposite
direction.
2. Permanent Magnets: Produce magnetic field to deflect pointer with North-South pole
magnet.
3. Pointer: One end of the pointer connected with coil another end deflects on scale from
infinity to zero.
4. Scale: A scale is provided in front-top of the megger from range ‘zero’ to ‘infinity’,
enable us to read the value.
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5. D.C generator or Battery connection: Testing voltage is produced by hand operated
DC generator for manual operated Megger. Battery / electronic voltage charger is
provided for automatic type Megger for same purpose.
6. Pressure Coil Resistance and Current Coil Resistance: Protect instrument from any
damage because of low external electrical resistance under test.
Working Principle of Megger
Voltage for testing produced by hand operated megger by rotation of crank in case of
hand operated type, a battery is used for electronic tester.
500 Volt DC is sufficient for performing test on equipment range up to 440 Volts.
1000 V to 5000 V is used for testing for high voltage electrical systems.
Deflecting coil or current coil connected in series and allows flowing the electric current
taken by the circuit being tested.
The control coil also known as pressure coil is connected across the circuit.
Current limiting resistor (CCR and PCR) connected in series with control and deflecting
coil to protect damage in case of very low resistance in external circuit.
In hand operated megger electromagnetic induction effect is used to produce the test
voltage i.e. armature arranges to move in permanent magnetic field or vice versa.
Where as in electronic type megger battery are used to produce the testing voltage.
As the voltage increases in external circuit the deflection of pointer increases and
deflection of pointer decreases with a increases of current.
Hence, resultant torque is directly proportional to voltage and inversely proportional to
current.
When electrical circuit being tested is open, torque due to voltage coil will be maximum
and pointer shows ‘infinity’ means no shorting throughout the circuit and has maximum
resistance within the circuit under test.
If there is short circuit pointer shows ‘zero’, which means ‘NO’ resistance within circuit
being tested.
Work philosophy based on ohm-meter or ratio-meter. The deflection torque is produced with
megger tester due to the magnetic field produced by voltage and current, similarly like ‘Ohm's
Law’. The torque of the megger varies in a ration with V/I, (Ohm's Law:- V = IR or R = V/I).
Electrical resistance to be measured is connected across the generator and in series with
deflecting coil. Produced torque shall be in opposite direction if current supplied to the coil.
1. High Resistance = No Current: - No current shall flow through deflecting coil, if
resistance is very high i.e. infinity position of pointer.
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2. Small Resistance = High Current :- If circuit measures small resistance allows a high
electric current to pass through deflecting coil, i.e. produced torque make the pointer to
set at ‘ZERO’.
3. Intermediate Resistance = Varied Current: - If measured resistance is intermediate,
produced torque align or set the pointer between the range of ‘ZERO to INIFINITY’.
Connection Diagram of Megger for Testing
TACHOMETER
A tachometer (revolution-counter, tach, rev-counter, RPM gauge) is an instrument measuring the
rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the
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revolutions per minute (RPM) on a calibrated analogue dial, but digital displays are increasingly
common. The word comes from Greek ταχος (tachos "speed") and metron ("measure").
Essentially the words tachometer and speedometer have identical meaning: a device that
measures speed. It is by arbitrary convention that in the automotive world one is used for engine
and the other for vehicle speed. In formal engineering nomenclature, more precise terms are used
to distinguish the two.
ELECTRICTY METER
An electricity meter, electric meter, electrical meter, or energy meter is a device that measures
the amount of electric energy consumed by a residence, a business, or an electrically powered
device.
Electric utilities use electric meters installed at customers' premises for billing purposes. They
are typically calibrated in billing units, the most common one being the kilowatt hour (kWh).
They are usually read once each billing period.
When energy savings during certain periods are desired, some meters may measure demand, the
maximum use of power in some interval. "Time of day" metering allows electric rates to be
changed during a day, to record usage during peak high-cost periods and off-peak, lower-cost,
periods. Also, in some areas meters have relays for demand response load shedding during peak
load periods.
CLIP-ON AMMETER
In electrical and electronic engineering, a current clamp or current probe is an electrical
device with jaws which open to allow clamping around an electrical conductor. This allows
measurement of the current in a conductor without the need to make physical contact with it, or
to disconnect it for insertion through the probe. Current clamps are typically used to read the
27
magnitude of alternating current (AC) and, with additional instrumentation,
the phase and waveform can also be measured. Some clamps meters can measure currents of
1000 A and more. Hall Effect and vane type clamps can also measure direct current (DC).
Types of current clamp
Current transformer
A common form of current clamp comprises a split ring made of ferrite or soft iron. A wire coil
is wound round one or both halves, forming one winding of a current transformer. The conductor
it is clamped around forms the other winding. Like any transformer this type works only with
AC or pulse waveforms, with some examples extending into the megahertz range.
When measuring current, the subject conductor forms the primary winding and the coil forms the
secondary.
This type may also be used in reverse, to inject current into the conductor, for example in
electromagnetic compatibility susceptibility testing to induce an interference current. Usually,
the injection probe is specifically designed for this purpose. In this mode, the coil forms the
primary and the test conductor the secondary.
Iron vane
In the iron vane type, the magnetic flux in the core directly affects a moving iron vane, allowing
both AC and DC to be measured, and gives a true root mean square (RMS) value for non-
sinusoidal AC waveforms. Due to its physical size it is generally limited to power transmission
frequencies up to around 100 Hz.
28
An electrical meter with integral AC current clamp is known as a clamp meter, clamp-on
ammeter or tong tester.
A clamp meter measures the vector sum of the currents flowing in all the conductors passing
through the probe, which depends on the phase relationship of the currents. Only one conductor
is normally passed through the probe. In particular if the clamp is closed around a two-conductor
cable carrying power to equipment, the same current flows down one conductor and up the other;
the meter correctly reads a net current of zero. As electrical cables for equipment have both
insulated conductors (and possibly an earth wire) bonded together, clamp meters are often used
with what is essentially a short extension cord with the two conductors separated, so that the
clamp can be placed around only one conductor of this extension.
A relatively recent development was a multi-conductor clamp meter with several sensor coils
around the jaws of the clamp. This could be clamped around standard two- or three-conductor
single-phase cables to provide a readout of the current flowing through the load, with no need to
separate the conductors.
The reading produced by a conductor carrying a very low current can be increased by winding
the conductor around the clamp several times; the meter reading divided by the number of turns
is the current, with some loss of accuracy due to inductive effects.
Clamp meters are used by electricians, sometimes with the clamp incorporated into a general
purpose multimeter.
It is simple to measure very high currents (hundreds of amperes) with the appropriate current
transformer. Accurate measurement of low currents (a few milliamperes) with a current
transformer clamp is more difficult. The range of any given meter can be extended by passing
the conductor through the jaw multiple times. For example a 0–200 A meter can be turned into a
0–20 A meter by winding the conductor 10 times around the jaw's core.
The vane is usually fixed directly to the display mechanism of an analogue (moving pointer)
clamp meter.
Hall Effect
The Hall Effect type is more sensitive and is able to measure both DC and AC, in some examples
up to the kilohertz (thousands of hertz) range. This type was often used with oscilloscopes, and
with high-end computerized digital multimeters, however, they are becoming common place for
more general use.
Rogowski coil
Resembling a current clamp in appearance and function is the Rogowski coil current sensor. This
coreless transformer is used in clamp meters and power monitoring loggers. It has the advantage
of better linearity, having no core to saturate, it can be made flexible, and does not require any
magnetic or electrical contact at the opening end. The Rogowski coil gives a voltage proportional
to the rate of change of current in the primary cable, so more signal processing is needed before
the sensed values can be displayed.
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An electrical meter with integral AC current clamp is known as a clamp meter, clamp-on
ammeter or tong tester.
CLAMP METER
A clamp meter measures the vector sum of the currents flowing in all the conductors passing
through the probe, which depends on the phase relationship of the currents. Only one conductor
is normally passed through the probe. In particular if the clamp is closed around a two-conductor
cable carrying power to equipment, the same current flows down one conductor and up the other;
the meter correctly reads a net current of zero. As electrical cables for equipment have both
insulated conductors (and possibly an earth wire) bonded together, clamp meters are often used
with what is essentially a short extension cord with the two conductors separated, so that the
clamp can be placed around only one conductor of this extension.
A relatively recent development was a multi-conductor clamp meter with several sensor coils
around the jaws of the clamp. This could be clamped around standard two- or three-conductor
single-phase cables to provide a readout of the current flowing through the load, with no need to
separate the conductors.
The reading produced by a conductor carrying a very low current can be increased by winding
the conductor around the clamp several times; the meter reading divided by the number of turns
is the current,] with some loss of accuracy due to inductive effects.
Clamp meters are used by electricians, sometimes with the clamp incorporated into a general
purpose multimeter.
It is simple to measure very high currents (hundreds of amperes) with the appropriate current
transformer. Accurate measurement of low currents (a few milliamperes) with a current
transformer clamp is more difficult. The range of any given meter can be extended by passing
the conductor through the jaw multiple times. For example a 0–200 A meter can be turned into a
0–20 A meter by winding the conductor 10 times around the jaw's core.
Less-expensive clamp meters use a rectifier circuit which actually reads mean current, but is
calibrated to display the RMS current corresponding to the measured mean, giving a correct
RMS reading only if the current is a sine wave. For other waveforms readings will be incorrect;
when these simpler meters are used with non-sinusoidal loads such as the ballasts used with
fluorescent lamps or high-intensity discharge lamps or most modern computer and electronic
equipment, readings can be quite inaccurate. Meters which respond to true RMS rather than
mean current are described as "true RMS".
Typical hand-held Hall effect units can read currents as low as 200 mA, and units that can read
down to 1 mA are available.
The Columbia tong test ammeter (illustrated) is an example of the iron vane type, used for
measuring large AC currents up to 1000 amperes. The iron jaws of the meter direct the magnetic
field surrounding the conductor to an iron vane that is attached to the needle of the meter. The