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1 www.megger.com ELECTRICAL TESTER - August 2016

The industry’s recognised information tool

ELECTRICALTESTER

Tesla P8

Published by Megger August 2016

Continued on page 2

Distribution network operators (DNOs) are facing

a tough challenge. They need to offer speedy

and reliable connections for a diverse range of

renewable energy sources, but at the same time

they must protect the reliability of their networks.

In the UK, the RIIO-ED1 regulation and price control

package from Ofgem, the government regulator

for the gas and electricity markets, means that if

they get it wrong they will potentially suffer severe

financial penalties.

The very nature of power generation and

distribution is changing, and this is creating a

real headache for DNOs. They have a distribution

network that was designed to accommodate

a comparatively small number of large power

stations, and are now having to adapt this to the

world of embedded generation, where a large

number of small power sources is the norm. The

changes required are by no means trivial, especially

as they must be accomplished while the network

remains fully operational, reliably delivering energy

to the DNOs’ customers.

It is clear that substantial investment may be

required, but DNOs operating in the UK are

comparatively well placed when it comes to

securing this investment. The energy market in

the UK is stable, and energy supply is a privatised

industry with established regulatory processes.

These factors make investments in energy

infrastructure an attractive proposition.

Nevertheless, DNOs will still have to demonstrate

that they can produce an attractive return on this

investment which, to put it bluntly, means that they

have to operate profitably. And their profitability is

now almost completely dependent on RIIO-ED1,

Ofgem’s regulation and price control instrument.

RIIO is an acronym for Revenue = Incentives +

Innovation + Outputs, a formula that neatly

encapsulates its intentions. In Ofgem’s own words,

these are “to drive real benefits for consumers,

by providing companies with strong incentives

to step up and meet the challenges of delivering

a low carbon, sustainable energy sector at value

for money for existing and future consumers.”

RIIO-ED1, which applies to the energy distribution

sector, came into force in April 2015, and will

remain in force for eight years.

Energy pricing is regulated by Ofgem and rises are

capped, so DNO revenue depends almost entirely

on RIIO. Innovation and outputs are measured, and

RIIO-ED1 has attractive incentives for exceeding

the targets. These are set for many aspects of

performance including customer satisfaction, safety,

network reliability and availability, environmental

impact, social obligations and connection terms.

Incentives are provided for speed of connection

and for customer engagement, factors that have

a particular relevance in relation to new energy

sources. Generating over-capacity in the UK

network in 2014 was around 6%, but a programme

of closing old environmentally damaging coal-fired

Damon Mount - Power sales manager

Between a rock and a hard place

Embedded or distributed generation schemes,

where a local generator is connected directly to the

distribution network, are becoming widespread.

The operators of these schemes face an important

challenge: how to ensure that the system behaves

safely and predictably if the local generator

becomes isolated from the network – a condition

known as islanding.

There are numerous potential hazards associated

with islanding, not the least of which is that engineers

working to restore the network connection may not

realise the system is still powered. Another hazard

is that the generator may continue to supply local

loads but, without support from the network, this

may result in it being heavily overloaded.

The solution usually adopted to address these

hazards is to immediately shut down the

islanded generator, but this can only be done if

a fast and dependable way of detecting islanding

is available. Many approaches are possible,

but one that is widely used is rate of change

of frequency (ROCOF) protection, which

has established a reputation for responding

faster and more reliably than alternative

protection techniques.

ROCOF protection relies on the fact that once a

generator is islanded, its output frequency will

no longer be locked to that of the network, but

will change rapidly to a frequency determined by

its own characteristics and those of the loads it is

still supplying. It is this change in frequency that is

detected by ROCOF protection devices.

ROCOF protection conforms to engineering

requirements such as G59/3 in the UK and

standards such as ANSI 81R in the USA. There

are strict guidelines for ROCOF settings and

unless these are optimised, the protection may

unnecessarily trip a generator when problems

Get your ROCOF right!Lennart Schottenius - Support Specialist

Niclas Wetterstrand - Program Manager

occur with the power network, and the resulting

loss of capacity may make the problems worse.

To help guard against this situation, G59/3

was revised in 2014 to require new settings for

ROCOF protection when used in conjunction with

generators connected to the UK power network.

The grace period that was granted for adoption of

the new settings in conjunction with certain classes

of equipment expires in July 2016. After this date,

ROCOF protection for all generating sites with a

capacity in excess of 5 MW that are connected to

the UK power network must comply fully with the

new requirements.

The foregoing makes it clear that a reliable method

of checking the settings and accuracy of ROCOF

protection is essential. Suitable functionality is

provided by Megger’s innovative three-phase

Sverker 900 instrument, which has been conceived

as an engineer’s multifunction test box for

protection testing.

This novel instrument does not need to be

connected to a PC and features an intuitive user

interface with a colour touchscreen. This provides

access to a wide range of pre-configured virtual test

instruments, allowing the required test function

to be selected quickly and easily. Full manual

control and configuration are also supported and,

in addition to the touchscreen, the Sverker 900

is provided with a large rotary knob that can be

configured as required to control the voltage and

current generators.

When testing ROCOF protection, the Sverker 900’s

ramping instrument is used. Because this generates

a very smooth and accurately controlled ramp, this

has proved to be an excellent and dependable tool

for these tests. The instrument is easy to configure

for ROCOF testing and, once the start and stop

criteria have been defined, it can be used to check

the operation of low and high level trips and also

to verify the trip time delay set for low and high

level operation.

Detailed guidance on ROCOF testing with

the Sverker 900, including information about

connections and instrument settings, is available

in the form of an application note. This can be

obtained free-of-charge on request from Megger,

or it can be found on the Megger website

(www.megger.com).

Rescuing refineries P6

Unfazed by 3 Phase P2

2 ELECTRICAL TESTER - August 2016 www.megger.com


ELECTRICALTESTER

Contents

‘Views expressed in Electrical Tester are not necessarily the views of Megger.’

The word ‘Megger’ is a registered trademark

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so to help you find items quickly on www.megger.com, we have

underlined key search words in blue.

The rights of the individuals attributed in Electrical Tester to be

identified as authors of their respective articles has been asserted

by them in accordance with the Copyright, Designs and Patents

Act 1988. © Copyright Megger. All rights reserved. No part

of Electrical Tester may be reproduced in a retrieval system, or

transmitted in any form or by any means, electronic, mechanical,

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permission of Megger.

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email [email protected], with a brief outline of the

reasons for your request.

All trademarks used herein are the property of their respective

owners. The use of any trademark in this text does not imply

trademark ownership rights in such trademarks, nor does use

of such trademarks imply any affiliation with or endorsement of

Electrical Tester by such owners.

Editor Jill Duplessis

E [email protected]

Megger Limited

Archcliffe Road Dover Kent CT17 9EN

T +44 (0)1304 502100

E [email protected]

www.megger.com

Between a rock and a hard place ....................p1,2

Damon Mount - Power sales manager

Get yor ROCOF right ...........................................p1

Lennart Schottenius - Support Specialist Niclas Wetterstrand, Program Manager

Three-phase support for substation test ...........p2

Matz Ohlen- Director transformer test systems

Turns ratio testing: Hand crank

versus automatic .................................................p3

Jill Duplessis - Global technical marketing

manager and Editor

Power Quality: Some Fundimentals ................p4-5

Andy Sagl - Product manager

Exhibit A: Megger hand cranked

insulation test set ................................................p5

Andrew Dodds - Group Technical Director

PD measurement saves refinery millions ........P6-7

Alexander Lüpschen - Asset Consulting Engineer, Koopmann Energie und Elektrotechnik

Wind farm cable failure averted! ........................ P7

Javier Luiz Leiva - Mexico Area Sales Manager Washington Cabrera - Regional Sales Manager, Mexico

Questions and Answers - Earth resistivity .........p8

Tesla and the Pigeon of death ...........................p8

Keith Wilson - Electrical engineer

Reminder: Knowhow delivered online .............p8

power stations and end-of-life nuclear facilities

means that the figure for 2015 was just 2.1%. The

intention is that the new small-scale generators will

fill this gap.

The RIIO-ED1 mechanism does not, however,

depend on incentives alone; there are also penalties

for DNOs who miss their targets. Performance

is reviewed retrospectively using agreed key

performance indicators (KPIs). Assessment criteria

include speed of connection, results of customer

surveys and views from stakeholders. Based on the

reviews, the Ofgem panel has the power to impose

penalties of up to 0.9% of a poorly performing

DNO’s revenue, and also to order it to make GSOP

(guaranteed standards of performance) payments

to customers for late delivery of services.

A key factor in determining the profitability of a

DNO is clearly its ability to handle new connections

quickly and efficiently without compromising

network performance. To help with this, the UK

Engineering Networks Association has produced a

series of Engineering Recommendations (ERs).

ER G81 provides a framework and guidance for

the installation and connection of commercial

and industrial loads. The applicant (that is, the

consumer) is responsible for the design, installation

and testing, along with the supply of all records

and documentation, while the DNO is responsible

for approving the design, defining the tests that

are needed, and providing the connection to

the network. ER G59/3 provides similar guidance

for the connection of distributed generation to

the network.

These ERs include examples of tests that the DNO

may require the consumer to perform before

providing a network connection, but these are very

general. ER G81, for example, states that tests must

be carried out “to verify the complete installation

has been installed correctly and is safe to energise.”

Wise applicants will, therefore, look to CIGRE

and even IEEE standards for further guidance, as

well as considering new test methods, such as

partial discharge analysis for cables, that provide

dependable results while saving time and money.

Being able to provide the DNO with comprehensive

and reliable test data will be increasingly important

since connecting an installation that does not

operate as expected may impact network

performance, leading to the imposition of financial

penalties on the DNO. With this in mind, the

DNOs can understandably be expected to take the

line that, “If you can’t prove that you’ve carried

out all of the necessary testing correctly, we won’t

connect you.”

This article has focussed for the most part on new

connections to the distribution network, but it is

important to remember that these are not the only

criteria against which the DNOs are measured,

nor are they the only factors that impact network

reliability. To ensure profitable operation, the DNOs

also need to monitor and care for key assets that

include transformers, circuit breakers and cables.

For all of these, regular testing is the key to

maximising availability and service life while

reducing as far as possible the risk of unexpected

failure. This is particularly beneficial for power

cables as poor joints and ageing insulation are

among the most common causes of failure and

downtime in power networks. However, modern

test methods can readily identify incipient problems,

allowing them to be remedied before they lead to

cable failure.

To cope with the move toward sustainable energy

from renewable resources, which means that huge

numbers of small generators are requiring new

grid connections, energy networks are currently

evolving faster than they have ever done at any

point in their history.

This presents DNOs with many challenges, but RIIO-

ED1 means that those who successfully address

these challenges have excellent opportunities

for financial reward. While it may not at first be

apparent that testing is a key element to achieving

this success, consideration of the points raised in

this article will hopefully demonstrate that testing

really does have a crucial role to play.

Engineers whose work involves testing in

substations face two important challenges. The

first is having the right equipment at hand to carry

out the wide range of tests that are often required,

and the second is carrying out those tests safely and

as quickly as possible, so as to minimise downtime

and cost. The recent appearance in the market of

versatile integrated substation test systems in the

Megger TRAX range has done much to help hard-

pressed engineers address these challenges.

These high-performance test sets have been

specifically designed to offer a convenient and

comprehensive solution for transformer and

general substation testing. They are capable of

performing more than 20 different test functions,

including measurement of winding resistance,

turns ratio, excitation current, short-circuit

impedance, tan delta / power factor, capacitance,

frequency response of stray losses, CT and VT

testing, and circuit breaker timing and motion

analysis. Clearly, when one of these novel test sets

is available, ensuring that all of the necessary test

equipment is at hand is no longer a challenge!

TRAX test sets also significantly reduce the time

taken to perform tests. They have an intuitive user

interface that offers full manual control or guided

testing using the built-in TRAX apps. Each of

these apps implements a specific test function –

for example, turns ratio measurement or winding

resistance measurement – and automatically

configures the instrument for the selected test.

All unnecessary information is removed from the

display, with only information relevant to the

test in hand remaining. This app-based approach

makes TRAX test sets safe, fast and easy to work

with as well as eliminates the need for extensive

user training.

But even the best can be made better! Until now,

one limitation of the TRAX test sets was that when

they were being used to test three-phase assets such

as transformers, it was necessary to change the test

connections after testing each of the phases.

In principle this isn’t a major issue, but in practice

it quickly becomes an annoyance, and the time

taken to change the connections soon adds up,

especially if those connections are on top of

transformer and every change means climbing up

and down a ladder!

With this in mind, Megger has introduced

the TSX130 three-phase switchbox. Available

as an optional accessory for all TRAX test

sets, this new unit allows three-phase

transformers to be conveniently tested without

the need to reconfigure the test lead connections

for each phase. An added benefit is that

switching between phases is controlled by the

test set, which means that test sequences can

be automated.

At the same time, Megger has further extended

the versatility of the TRAX system by launching

another invaluable accessory, the TDX120, which

facilitates the use of the test sets to perform tan

delta and capacitance measurements.

Despite the wide range of functions offered by

TRAX test sets, they are exceptionally light and

compact. The TRAX220, which has a maximum

AC current capability of 200 A, is the lightest test

set of its type, weighing just 32 kg in its transport

case, which means that it can be transported by air

as check-in luggage.

These innovative test sets can generate and measure

a wide range of currents and voltages with high

precision. While the TRAX220 has a maximum AC

current output capability of 200 A, the TRAX280

extends this to 800 A. The output current capability

of both units can be further extended to 2000 A

with an optional current booster.

Other key features of Megger’s new and innovative

TRAX test sets include state-of-the-art transformer

winding resistance measurements with true DC test

currents up to 100 A and up to 50 V compliance

voltage; dynamic on-load tap changer (OLTC)

measurements; and exceptional interference

suppression to secure accurate readings even in

high noise switchyards.

A wide operating frequency range of 5 to 500 Hz

(1 to 500 Hz for tan delta measurements) is also

included, as is individual temperature correction of

tan delta measurements using Megger’s patented

technology; and automatic voltage dependence

detection, which is another unique feature covered

by Megger patents.

Today’s substation engineers are under constant

pressure to work faster and more efficiently while

maintaining the highest standards of safety. The

new integrated substation test sets, of which

the Megger TRAX instruments are the leading

example, make it possible to respond positively to

this relentless pressure.

Three-phase support for substation testMatz Ohlen - Director transformer test systems

Continued from page 1.

When you have finished with this magazine please recycle it.



ELECTRICALTESTER

Figure 1. Equivalent circuit diagram for a transformer with no load

Turns Ratio Testing: Hand crank versus automaticJill Duplessis - Global technical marketing

manager and Editor

A transformer turns ratio test provides a quick

verification of the most fundamental operational

characteristic of a transformer – its ability to

transform voltage as anticipated. In doing so, the

test provides invaluable reassurance to the operator.

Open- and short-circuit conditions in transformer

main and tap windings may cause the transformer

turns ratio to change and therefore this test is at

once providing useful diagnostic information.

Engineers have noted, however, that traditional

“hand-crank” TTR instruments sometimes give

values for turns ratio that are different from those

given by modern automated TTR instruments.

Indeed, many insist that the traditional instruments

provide results that are more dependable. But is

this actually true? And why do the instruments

produce different results?

Background

To answer these questions, let’s start by considering

an ideal transformer. For such a transformer, the

ratio of the terminal voltages (that is, the field-

measured no-load voltage ratio, V1/V2) equals the

true ratio of the number of turns on each winding,

N1/N2 – the ratio of transformation. This is not true

with a real transformer. Here’s why.

The turns ratio is equal to the ratio of the voltages

induced by the resultant mutual flux (E1/E2) when

a transformer is energized. The voltage induced in

a single turn is the same irrespective of whether

it is part of the primary or part of the secondary

winding, so the total voltage induced in each of the

windings by the common flux must be proportional

to the number of turns. That is E1/E2 = N1/N2. But in

a real transformer, E1, the primary induced voltage,

does not exactly equal the applied voltage, V1. In

fact, V1 is equal to the phasor sum of E1 plus the

primary leakage reactance voltage drop due to

the exciting current plus the voltage drop due to

the resistance of the primary winding multiplied

by the exciting current (Figure 1). The ratio of

transformation is therefore only approximately

equal to the ratio of the primary and secondary

terminal voltages, e.g., the “voltage ratio” as

termed in IEEE C57.152-2013.

In all real transformers, the no-load voltage ratio

(measured in the field) is less than the transformation

ratio (i.e., the turns ratio). This is because real

transformers have losses and magnetic leakage,

and they require excitation. Consider, for example,

the ratio of primary to secondary currents. Both

currents exist together only when the transformer

is serving a load so put aside the ratio testing

concept (a no-load test) for a moment. Primary

current, i1, is the sum of an exciting component,

iex, and a load component, iL. The ratio between

the secondary current, i2, and the load component,

iL, of the primary current is given by:

N1iL = - N2i2 (1)

This can be rewritten as:

N1/N2 = - i2/iL (2)

where the turns ratio = N1/N2, iL = i1 - iex, and iL is always < i1

For an ideal transformer, N1/N2 = i2/i1 (present at

the terminals), but for a real transformer, the actual

turns ratio (given by equation 2 and which cannot

be directly measured) is greater than the ratio of

the terminal currents (voltages).

In general, where transformers have large leakage

reactance, high magnetising current, high primary

resistance or a combination of these, a higher

error will be introduced into the measurement of

the turns ratio because these factors increase the

difference between V1 and E1.

Measuring techniques

Now let’s look at turns ratio measurement

techniques. An automated TTR instrument

measures the voltage applied to the primary

winding terminals and the resulting voltage at the

secondary terminals. The instrument calculates the

ratio of these voltages and presents this as the

transformer turns ratio.

Hand-crank turns ratio instruments work in a

different way. The test set is arranged so that

the transformer to be tested and the adjustable

ratio reference transformer within the test set are

connected in parallel and excited from the same

voltage source (see diagram). This measurement

technique is called a “transformer bridge”

measurement.

Note that the instrument normally excites the

transformer under test from its secondary (low

voltage) windings. The “secondary” windings

(which, in the case of the transformer under test,

is actually the primary winding) are connected in

series opposing through a null detector.

When the ratio of the reference transformer is

adjusted so that no current flows in the secondary

circuit, as shown by the null detector, two

conditions are simultaneously fulfilled. The first

is that the voltage ratios of the two transformers

are equal and the second is that there is no load

on either transformer. The no-load voltage ratio of

the reference transformer is known, so the voltage

ratio of the transformer under test is known, and

its turns ratio is therefore also known.

The main source of error with this method is that

the primary induced voltage in the transformer

under test, EX, and the primary induced voltage

in the reference transformer, ET, are likely to be

slightly different. Although the same voltage, Vo,

(e.g., 8 V) is applied to both transformers, the

reference transformer and the transformer under

test will have different characteristics, which

means that, in general, EX and ET will not be the

same. When the reference transformer and the

transformer under test both have the same turns

ratio – that is, when the null detector senses no

current flow – the secondary voltages of the

two transformers will also differ by this same

percentage error.

Note that the difference between ET and EX,

however, will always be less than the difference

between ET or EX (whichever is the smaller) and

Vo (which represents the error with the automatic

method). Also note that in some cases the

difference may be small, in which case the error in

the measured turns ratio will also be small. In fact,

where the transformer under test has the same

characteristics as the reference transformer, the

error in the turns ratio will be zero. For this reason,

TTR reference transformers are designed to match

typical distribution and power transformers.

Why choose automated over hand crank?

Transformer manufacturers provide true turns

ratio (N1/N2 or E1/E2) on the nameplates of their

products and for some transformers, a hand

crank TTR will give a result closer to this ratio

of transformation than measuring the terminal

voltages of the windings. Note, however, that

some users claim the hand-crank model provides

limited resolution on typical transformer ratios

such as 20/1.

If a transformer core is not of an optimum quality,

as is sometimes the case, the error in the ratio

measured with an automated test set will be

greater than the error in a measurement carried

out with a hand-crank instrument. In such cases, it

is common practice to acknowledge the deficiency

of the core, or to revert to the older, hand-crank

method. Another approach, provided that the

transformer has been operating correctly, is to use

the turns ratio measured with an automated TTR

as a reference point to which future measurements

can be compared.

There are very good reasons why hand

crank instruments are now being used less

frequently. These include:

1. Their use is considered dangerous because:

a. High voltages up to 1,000 V AC can be produced

at instrument terminals. Since the transformer

is tested from the LV side, a high voltage is

produced on the HV side. If the transformer

ratio is greater than 130:1, this voltage will be

in excess of 1,000 V.

b. The test leads must be short, which often means

that the user of the instrument has to stand on

the transformer during testing.

2. Using hand crank TTRs is inefficient because:

a. Only one phase at a time can be tested

b. The instrument requires manual balancing

c. The instrument must be cranked and balanced

at the same time

d. Leads must be changed for each phase tested

e. Results have to be recorded manually then

transferred manually to the test reports

f. Manual calculation is needed to determine the

percentage error

g. Total test time is approximately three to four

times longer than with an automatic TTR if the

time taken to complete the report is included

3. Hand-crank instruments have limited

capability when testing instrument

transformers. (They are designed to measure

accurately turns ratios of no more than 130/1).

4. Hand-crank instruments excite the

transformer under test from the LV winding.

Some transformers draw excessive magnetising

current and the instrument’s output may be

insufficient to excite them from the low voltage

winding – for example, network transformers of

the 15000/115 V class and some voltage regulators.

Conclusion

There are a few instances where hand crank TTR test

sets will give a result that’s closer to the nameplate

turns ratio than a modern automated TTR test

set. This apparent benefit is, however, more than

offset by the many disadvantages of hand crank

TTRs, which include time-consuming operation

and safety concerns. For these reasons, automated

TTRs are replacing their hand-crank counterparts,

and this is a trend that will undoubtedly continue.



ELECTRICALTESTER

In our last issue, we reported that power quality

issues are a growing concern all over the world,

and we noted in particular that the adoption

of the smart grid would do little to address this

concern. The primary function of the smart grid is

to increase the reliability of power delivery – any

positive impact it may have on power quality is

no more than incidental. With these thoughts in

mind, in this issue we are going to look at some

of the fundamentals of power quality, and in

particular at the most common types of power

quality problems and why they occur.

Under-voltage

Under-voltage is a decrease in rms voltage to less

than 0.9 pu for a duration longer than one minute.

Typical values encountered in practice are between

0.8 and 0.9 pu. Under-voltages are most often

caused by the switching of loads and capacitor

banks and may persist until the voltage regulation

equipment on the system has time to react

and bring the voltage back within acceptable

tolerance. Overloaded circuits can also cause

under-voltages.

It is worth noting that the term “brownout” is

sometimes used to describe periods when the

supply voltage has been deliberately reduced as

a strategy for reducing power delivery. The type

of supply disturbance caused by a brownout is

essentially the same as an under-voltage, but

the term brownout has no formal definition

and, to avoid possible confusion, its use should

be avoided.

Over-voltage

Over-voltage is an increase in rms voltage to

more than 1.1 pu for a duration longer than

one minute. Typical values are between 1.1 and

1.2 pu. Over-voltages typically result from load

switching, particularly when large loads like

motors are switched off; variations in reactive

compensation, usually the switching of capacitor

banks; poor system voltage regulation capabilities;

and incorrect tap settings on transformers.

Voltage sags and swells

Voltage sags (also called dips) and swells are two

of the most common power quality problems.

They are impossible to eliminate completely; as

impedances change over the course of a day,

the system voltage will also momentarily change.

This is unfortunate, as even short duration sags

can lead to process shutdowns that take many

hours to re-start. Voltage swells are one of the

most frequent causes of circuit breaker nuisance

tripping. In short, sags and swells can cause

major financial losses, particularly in the

manufacturing sector.

Voltage sags are often caused by sudden increases

in load, such as short circuits or faults, motors

starting or electric heaters turning on. They can

also be the result of sudden increases in the source

impedance of the supply, typically caused by a

loose connection. Voltage swells are almost always

caused by sudden decrease in the load on a circuit

that has a poor or damaged voltage regulator,

although they can also be caused by loose or

damaged neutral connections.

For Class A sag detection on single-phase systems,

a voltage sag event begins when the Urms(1/2)

voltage (the rms voltage of the supply calculated

over a half cycle) falls below the sag threshold. The

event ends when the Urms(1/2) is equal to or greater

than the sag threshold plus the hysteresis voltage.

On poly-phase systems, the sag begins when the

Urms(1/2) voltage of one or more channels is below

the sag threshold and ends when the Urms(1/2)

voltage on all channels is equal to or greater than

the sag threshold plus the hysteresis voltage.

For Class A swell detection on single-phase

systems, a swell is defined as beginning when the

Urms(1/2) voltage rises above the swell threshold,

and finishing when the Urms(1/2) voltage is equal

to or less than the swell threshold minus the

hysteresis voltage. On poly-phase systems, the

swell begins when Urms(1/2) on one or more

channels rises above the swell threshold and

finishes when Urms(1/2) on all of the measured

channels is equal to or less than the swell threshold

minus the hysteresis voltage.

Transients

There are two main types of transients over

voltages. Low-frequency oscillatory transients

have frequency components in the hundreds-of-

hertz range. Low frequency oscillatory transients

are typically caused by capacitor switching.High-

frequency or impulsive transients have frequency

components in the hundreds-of-kilohertz range.

High frequency impulse transients are typically

caused by lightning or the switching of inductive

loads.

Transient over voltages can lead to dielectric

degradation or failure in all classes of equipment.

Large magnitude transients with a fast rise time

contribute to insulation breakdown in equipment

such as switchgear, transformers and motors, while

repeated exposure to lower amplitude transients

can cause slow degradation of insulation, leading

to eventual failure and reducing mean time

between failures (MTBF).

The mechanism by which transients damage

insulation can be understood by considering

cables and other forms of insulated electronics

as capacitors, with the insulation acting as the

dielectric of the capacitor. The capacitance of the

system provides a path for the transient pulse.

If the transient pulse has sufficient energy, it will

damage the insulation.

Lightning is a major source of transients. Lightning

strikes, which can be more than 8 km long and

reach temperatures in excess of 20,000 ºC, and

the electromagnetic fields produced by such

strikes, can induce voltage and current transients

in power lines and communication lines. These

transients are typically unidirectional.

The switching of capacitor banks is another

common source of transients. When a capacitor

bank is switched, there is an initial inrush of

current, which produces a low-frequency transient

that has an oscillatory ringing characteristic. Such

oscillatory transients can cause equipment to trip

out as well as malfunctions in uninterruptible

power supply (UPS) installations.

Less frequently encountered are extremely fast

transients (EFTs) that have rise and fall times in the

nanosecond region. These are caused by arcing

faults, such as bad brushes in motors, and are

rapidly damped by even a few metres of distribution

wiring. Standard line filters, which are included in

almost all electronic equipment, are very effective

at removing EFTs, but EFTs may still cause problems

in installations with very short cable runs, such as

those found on off-shore platforms.

Unbalance

Unbalance is a condition in a poly-phase system

where the values of the fundamental component

of the line voltages, or the phase angles between

consecutive line voltages are not equal, as

defined by IEEE 1159 and IEC 61000-4-7. Voltage

unbalance is most commonly seen in relation to

individual customer loads with an imbalance of

the loads on the phases, especially where large

single-phase loads, such as arc furnaces, are in

use. It is important to note that a small unbalance

in the phase voltages can produce a much larger

unbalance in the phase currents.

Unbalanced voltages can adversely affect many

types of equipment including induction motors

and variable speed drives. In addition, unbalanced

voltages can cause heating in transformers and

neutral conductors.

Flicker

Flicker is a very specific problem related to human

perception of the light output of incandescent

light bulbs. It is not a general term for voltage

fluctuations. The human eye is very sensitive to the

light flicker that is produced by voltage variations.

Because of this, flicker is almost always the limiting

criterion for controlling small voltage fluctuations.

If the sensitivity of the human eye to flicker

is assessed by considering the eye’s response

to flicker from a 60-watt incandescent bulb

for rectangular voltage variations at various rates,

it is found that that the sensitivity is a function

of the rate of fluctuations and is also to

some extent dependent on the voltage of the

lighting supply.

In general, flicker is measured using the method

defined in IEC 61000-4-15. This method takes

the instantaneous voltage and compares it with

a rolling average voltage. The deviation between

these two is multiplied by a value taken from a

weighted curve based on the sensitivity to flicker of

the human eye to incandescent bulbs operating at

either 120 V 60 Hz or 230 V 50 Hz. The result – the

percentile unit – is subjected to further statistical

analysis in order to calculate two values, Pst and Plt.

Pst, or short-term flicker is calculated from the

percentile unit and is based on behaviour over

a 10-minute interval. Plt, or long-term flicker is

calculated from Pst and is based on a two-hour

interval. The criteria for evaluating the results are

straightforward. If Pst is less than 1.0, the flicker

levels are good but if Pst is greater than 1.0, the

flicker levels may be high enough to be annoying.

All of this applies only to incandescent lighting

Power Quality: some fundamentalsAndy Sagl - Product manager



ELECTRICALTESTER

Power Quality: some fundamentals

Megger’s test instruments are well known for their

reliability and versatility – and the many decades

of reliable service they’ve provided in the electrical

industry can certainly testify to that. However, it is

this versatility that has landed a 1950s version of

the popular insulation test set … in court!

The test set in question, which is at present

exhibited in New Scotland Yard’s Black Museum, is

a nicely dovetailed, wooden cased, 1950s Series 1

Megger - a 500V hand cranked insulation test set.

Unfortunately, the series of events that landed this

instrument in court, and subsequently in a crime

museum are quite gruesome – so read on at your

own risk!

It all started in the 60s in London, when gangsters

like the Krays and the Richardsons ruled the back

streets. Murder, extortion, torture and everything

in between were everyday activities for these

perpetrators.

Charlie and Eddie Richardson, crime gang leaders

from Camberwell in South East London, were

running a series of unsavoury businesses behind the

camouflage of a respectable (and thriving) scrap

metal merchant and a fruit machine dealership. In

reality, the brothers were involved in racketeering,

illegal drugs, extortion, money laundering, robbery,

prostitution and when necessary, contract killing.

The Richardson gang were also known as the

Torture Gang given their reputation for intimidating

their victims with sadistic methods of persuasion.

These included but were not limited to severe

beatings, nailing feet to the floor, cutting off toes

and fingers, extracting teeth and electrocution!

A public turf war and shoot-outs with rival firm

the Krays in the 1960’s, along with increasing

pressure on the police from the gangsters’ victims

led to the Richardsons’ capture. Key evidence was

provided by Lawrence “Johnny” Bradbury, who

was convicted for the murder of Tom Waldeck, a

mineral prospector and business partner of Charlie

Richardson in the Perlite Mining Company which

– other types of lighting cannot be evaluated in

this way. In addition, the weighting curves apply

only to lighting that operates at 120 V 60 Hz or

230 V 50 Hz.

Harmonics

Harmonics are sinusoidal periodic waves with

frequencies that are integer multiples of the

fundamental frequency. Harmonics can cause

many problems, including excessive heating in

neutral conductors, overheating of motors and

transformers, and failure of electronic equipment.

IEEE 519 defines a harmonic as a component of

order greater than one of the Fourier series of

a periodic quantity. IEC 61000-4-30 defines a

harmonic frequency as a frequency which is an

integer multiple of the fundamental frequency,

and defines a harmonic component as any of the

components having a harmonic frequency.

Linear loads such as incandescent lights and

heating elements draw current equally at every

point of the supply waveform. These loads do not

generate harmonics. However, non-linear loads

such as switching power supplies and variable

speed drives usually draw current only at the peaks

of the supply waveform. It is these non-linear

loads that cause harmonics. Typically, current

harmonics do not propagate through a system,

but voltage harmonics will propagate as they can

pass through transformers. Voltage Harmonics

occur when current harmonics are great enough

to start clipping the voltage in various locations

throughout the waveform.

Harmonics can be characterised by their order –

which is equal to their multiple of the fundamental

frequency. Thus a 180 Hz harmonic in a 60 Hz

supply system is a third order harmonic. Odd

harmonics are harmonics with odd order numbers

and even harmonics are those with even order

numbers.

Even harmonics are often produced by faulty

rectifiers and produce waveform distortion that

is non-symmetrical. Triplens are harmonics with

orders that are multiples of three. These do not

cancel out in three-phase systems and, as a result,

they give rise to high neutral currents.

Harmonics can also be characterised by sequence,

based on the direction of rotation of the magnetic

field they produce. Positive sequence harmonics

create a magnetic field in the direction of rotation

of the fundamental. Indeed, the fundamental can

be considered to be a positive sequence harmonic.

Negative sequence harmonics produce magnetic

fields that rotate in the opposite direction, which

reduces torque in motors and increases the current

required to drive a given load. Zero sequence

harmonics do not produce a rotating magnetic

field. Zero sequence harmonics can be in phase.

This can lead to high neutral currents, high neutral

to ground voltages, transformer losses as well as

equipment overheating.

Positive, negative and zero sequence harmonics

run in sequential order – positive, negative and

then zero. Since the fundamental frequency is

a positive sequence harmonic, the second order

harmonic is a negative sequence harmonic and the

third order harmonic is a zero sequence harmonic.

In balanced three-phase systems, the fundamental

currents cancel each other out, so that there is no

current in the neutral. Zero sequence harmonics

however, such as the third harmonic, add together,

resulting in high neutral currents.

Total harmonic distortion

Total harmonic distortion (THD) is a measure

of the sum of the harmonic components in a

distorted waveform, and it can be calculated for

either current or voltage. THD is the rms sum of

the harmonics, divided either by the rms value

of the fundamental or the rms value of the

total waveform. Most often, THD is quoted as a

percentage of the fundamental.

THD values can be misleading, especially when

used in relation to current. The THD value is

typically calculated with reference to the amplitude

of the fundamental. With voltage calculations, this

voltage fundamental will always be present, but

the amplitude of the current fundamental changes

according to the load – as the load decreases,

so does the fundamental current amplitude. If

the current drawn by the load is low – close to

zero – the THD value will, therefore, appear to be

very high.

For example, if the total harmonic current in a

circuit is 0.2 A and the fundamental current is

200 A, the THD is 3.16%, but if the fundamental

current being drawn by the load drops to 0.2

A, and the harmonic current remains the same,

the THD is now 100%! This is deceptive as THD

appears to be very high, but the only reason for

this is that the load is drawing so little current at

the fundamental frequency.

To avoid this problem, total demand distortion

(TDD) measurements should be used for current

harmonic measurements. TDD references the total

root-sum-square harmonic current distortion to

the maximum average demand current recorded

during the test interval. The reference value is,

therefore, the same throughout the test interval,

ensuring that the TDD result obtained is valid.

TDD is calculated in accordance with the IEEE

519 document, “Recommended Practices and

Requirements for Harmonic Control in Electrical

Power Systems.”

In summary, the power quality industry has

developed certain index values that can be

used to assess the waveform distortion caused

by the presence of harmonics. The two values

most frequently encountered are THD and TDD.

Individual harmonic values are also indexed in

various specifications, such as the North American

IEEE 519 document and the European EN 50160

standard issued by CENELEC.

Conclusion

This article has introduced some of the most

important concepts relating to power quality, and

future articles in this series will build on these.

The next article will look at Class A recording and

this will be followed by an article examining the

impact of transients and harmonics on motors

and transformers.

Exhibit A: Megger hand cranked insulation test set

controlled a mineral claim in the Ghost Mountains

of the Transvaal.

The murder, it later transpired, was the result of

misunderstandings and voting rights amongst

the mine shareholders. When sentenced to hang,

Bradbury offered to turn Queens evidence and

informed on the Richardson gang of which he was

part, in exchange for a pardon and immunity.

The Richardson brothers were found guilty of

fraud, extortion, assault and grievous bodily harm.

Charlie Richardson was sentenced to twenty-five

years in prison, and Eddie had ten years added

to his existing five year sentence for affray. Roy

Hall got ten years for his acts of torture with an

electrical generator.

The “Torture Trial” convened at the Old Bailey in

April 1967 and amongst the evidence and exhibits

was a Megger insulation tester – the “electrical

generator” –which was operated by gang member

Roy Hall to inflict pain on torture victims.

Stories in the press describe the so-called ‘black

box of torture’, with claims that the generator

came from an army field telephone or from a

WWII bomber. A keen electrician however will be

able to spot the fact that the item on display at

New Scotland Yards Black Museum is not a death

box, but rather a 500 V hand cranked insulation

test set which was built with the absolute opposite

intentions – to make equipment and buildings safe

for users!

The history of the Megger insulation testers is

interesting and without a doubt exciting to follow.

Yet the use of this particular instrument will go

down in history for all the wrong reasons!

Andrew Dodds - Group Technical Director



ELECTRICALTESTER

With a Megger Centrix cable test van, Koopmann Energie und Elektrotechnik, a service company that specialises in handling emergencies in the energy supply sector, was able to prevent losses amounting to millions of Euros at an oil refinery in Germany. The emergency arose when a medium-voltage cable failed, causing a circuit breaker to trip and stopping the oil transport pumps. Not only did this halt production, but if the situation had not been remedied rapidly, very costly damage to the plant would have resulted.

Background Network operators responsible for supply reliability usually want cable test vans that are perfectly tailored to suit their own infrastructure. Before a test van is purchased however, the question often arises whether it should be used exclusively to deal with urgent incidents, or whether it would be more beneficial to use its diagnostic systems for status-oriented servicing to help ensure that cable faults do not occur in the first place.

Today, many sophisticated cable diagnostic techniques are available, including tan delta measurements as well as PD measurements using VLF test voltages with 50 Hz slope technology or damped AC (DAC) voltages, which can be used to test underground cables in a gentle, non-destructive manner. These methods have become widely known and accepted.

What is less well known is that these tried-and-tested techniques also significantly improve the ability to respond effectively to emergencies, as well as making it much easier to determine the location of a cable fault. This means that from the perspective of a service company like Koopmann, the question of whether or not a cable test van should incorporate diagnostic tools is completely redundant. The answer, unequivocally, has to be yes.

In fact, status-oriented servicing is now well established as the best and most efficient servicing strategy for network operators. This is the only servicing strategy that Koopmann recommends to its customers, as it demonstrably offers the best balance between economic efficiency and supply reliability.

This is because the network operator only needs to take action if the cable diagnostic tests indicate that problems exist, rather than acting purely on suspicion by replacing cables for no better reason than their age or, even worse, waiting until cable faults occur and cause damage, meaning that costly rectification work is carried out far too late. Of all available servicing strategies, this last one – waiting until a fault occurs – is the most expensive and the least efficient, but unfortunately it is still the strategy most frequently adopted.

This can have serious consequences, as is clearly shown by the following report, which describes a situation where, by using Megger DAC diagnostic systems, Koopmann saved an oil refinery from the threat of millions of Euros worth of damage.

It is worth mentioning, however, that had the diagnostic tests been carried out earlier, even the limited damage that did occur could have been avoided.

The incident The Koopmann 24-hour service team was called to an incident in an oil refinery. A 20 kV medium voltage cable had appeared to fail suddenly, with the result that the circuit breaker supplying power to a high-pressure tank had tripped. For the refinery, the consequence was devastating – all of the pumps failed. Operations came to a complete standstill because the oil being supplied via the pipelines could no longer be processed. The refinery was facing enormously costly damage that would be almost impossible to rectify, and the immediate challenge was to contain this damage within tolerable limits.

Insulation measurement The first action taken by the emergency team was to switch the power supply to another cable to put at least some of the pumps back into operation. But where was the original fault? As a first step to answering this question, the team used its Centrix cable test van to carry out a standard DC insulation measurement at 1000 V, along with capacitance measurements on the 20 kV cable. This preliminary insulation measurement usually determines whether the fault is solely the result of a short circuit, whether it is a high impedance fault or indeed whether there is any fault at all. Comparing the insulation resistances and capacitance values of all phases often gives an indication of the type of cable fault. This was not the case here, however. There was no short circuit and no significant differences in the insulation resistances of the phases.

Reflection measurement The service team then carried out a traditional reflection measurement using a Megger Teleflex VX test set. It proved very easy to recognise the end of the cable, thanks to the length-dependent amplitude compensation. There were no significant variations between the phases, which reliably indicated that there were no particular issues anywhere between the measuring point and the end of the cable. Neither was any problem found at the end of the cable.

VLF test Next, the team enhanced protection and connected its VLF system. A voltage of 3 x Vo 36 kV was used, with the intention of causing a breakdown. As a service provider, Koopmann

needs to be prepared for all possible incidents that can occur on site. That’s why the company relies on the most powerful VLF testing systems with cosine-square technology from Megger, which are integrated into all of its test vans.

These systems are the only way of testing extremely long cable routes in a way that complies with the applicable standards, a feature that the Koopmann engineers find particularly valuable. Contrary to expectations, however, no breakdown occurred; the cable at the refinery withstood this high stress without any problems. Apart from slightly increased leakage current, yet again no abnormalities were discovered. The cable fault, which certainly seemed to exist, was proving elusive!

An air of tension admittedly started to spread slowly among the members of the experienced Koopmann team. All of the standard methods that had always been so successful did not seem to be yielding results this time.

The circuit breaker For safety reasons, it was then decided to check contact resistances at the circuit breaker, as the pumps would stop only if this breaker tripped. The Koopmann team routinely carries a Megger MOM2 micro-ohmmeter in its emergency kit for situations of this type. Its compact dimensions and convenient weight of just 1 kg means that it is easily stored in any test van and, despite its small size, the MOM2 provides a test current of 200 A.

But even the contact resistance measurements at the circuit breaker did not yield any explanation. In fact, all of the tests performed indicated that the supply network was essentially in tip-top condition. The decision was therefore taken that it was safe to re-energise the cable. When this was done, everything worked perfectly; the problem appeared to have been resolved. The refinery was once again running at full output, much to the satisfaction of the client. But still no one knew why the problem had occurred.

The second event Three days later, Koopmann received another call from the refinery. The section had tripped again. Once again, the standard tests described above were carried out without success, raising suspicions that this was a periodically occurring fault that would continue to elude all traditional fault location methods, unless someone happened to be testing the cable section at exactly the right time.

PD measurement saves refinery millions

Alexander Lüpschen - Asset Consulting Engineer,

Koopmann Energie und Elektrotechnik

The Koopmann 24-hour deployment team was quickly on site



ELECTRICALTESTER

PD measurement saves refinery millions

Mexico already has over 3 GW of installed wind power capacity and plans are in place to increase this to more than 9.5 GW by the end of 2018. This ambitious target can only be achieved if the installation and commissioning of a new plant proceeds smoothly and the plant proves reliable in operation.

To help achieve the necessary high levels of reliability, partial discharge (PD) analysis is routinely carried out on newly installed cables and has proved invaluable in detecting poor workmanship and splice defects. This was amply confirmed by a recent experience with a 6.3 km XLPE cable.

The cable was tested with a Megger TDS NT 60 kV test set using standards-compliant VLF cosine-rectangular test technology operating at a frequency of 0.1 Hz. This test technology is ideally suited to testing the long cables often encountered in wind farm applications, as these

are difficult or impossible to charge with VLF sine-

wave equipment unless the frequency is reduced

below 0.1 Hz, which then makes the testing non-

compliant with IEEE 400.3.

For the cable at the Mexican wind farm however,

the test set was configured to operate at 20

kV. Partial discharge activity was immediately

detected on all three phases at the near ends

of the cables, and at 1.8 km on phases L1 and

L2. The near-end activity was of little concern,

because the connection between the test set

and the cables is rarely PD free. The PD activity at

1.8 km was much more puzzling as the cable

operator had no knowledge of any cable feature

at this distance.

Despite this, the indication provided by the TDS NT

test set was clear and unequivocal, as is shown by

the screen capture in Figure 1. With this in mind,

the cable operator checked the documentation for

the installation and discovered that this had been

updated. The new version revealed that there was

a joint in the cable at 1.8 km, in exactly the location

where unexpected PD activity had been detected.

The splices were removed and opened, and a

visual inspection revealed that no sealing mastic

had been used in the mechanical connector screw

housings on the L1 and L2 phases. (See Figure

2). This shortcoming was quickly remedied and,

on retesting, the cable was found to be free of

PD activity.

This exercise in preventive and predictive

maintenance revealed a problem that was possible

to address relatively easily and inexpensively. Had

the lack of mastic remained undetected and

the cable been put in service, however, it would

almost certainly have failed in a relative short time,

causing costly disruption and damage.

With modern test equipment that uses cosine-

rectangular waveform technology, experience

on Mexican wind farms has clearly shown that

PD analysis, even on long cables, is a convenient

and cost-effective form of insurance against

premature failure.

Luckily for the refinery, the Koopmann team on

site that day had a Megger Centrix 1 80 PD partial

discharge analysis system, which incorporates

sophisticated diagnostic functions for DAC testing.

The team recommended to the refinery that a

partial discharge (PD) measurement be carried out.

Koopmann has been using DAC test equipment

from Megger for PD measurements for years, as

it is still to this day the only non-destructive PD

measurement device on the market. When this

equipment is used, even critical cables can be put

back into service following PD diagnostics.

The fault is found!

It was precisely this test that ended up paying

off in this situation, as it revealed increased PD

levels at a coupling, which were indicative of a

serious abnormality.

The accompanying image clearly shows partial

discharges at a coupling 120 metres away (the

x-axis is the cable length, the y-axis the PD level).

In Koopmann’s experience, it is the PD frequency

rather than its level that is the decisive factor in

intermittent faults. As there was only this one PD

weak point in this particular case, it was easy to

work out what had caused this intermittent fault.

Using the refinery’s exemplary documentation,

the Koopmann team was immediately able to

work out exactly where the faulty coupling was

located, and what type of coupling it was – an oil-

filled coupling sleeve. Without further delay, the

team found and replaced the coupling. A repeated

VLF test, as prescribed by VDE Standard 0726 (HD

XY) and additional PD measurements showed no

further abnormalities. The partial discharges at the

coupling were no longer there. Full operation was

immediately resumed, and the cable section has

not failed since.

Summary

A cable fault location system with a non-destructive

PD measurement function, as is currently offered

only by Megger’s DAC technology, is undoubtedly

the best cable fault location system. Without this

technology or with another cable fault location

system from other manufacturers, the Koopmann

team would not have been able to finally locate

this elusive cable fault. The refinery’s exemplary

documentation also played an important role, as it

allowed the correct coupling to be located quickly

and accurately.The central Centrix control unit means that tests can be carried out in quick succession

Mapping for V <= Vmax (L1, L2, and L3)

Javier Luiz Leiva - Mexico Area Sales Manager

Washington Cabrera - Regional Sales Manager, Mexico

Figure 1. PD activity showed by the TDS NT software in circuit 7 of the wind farmFigure 2. Circuit 7, L1 joint without seal mastic in the mechanical connector screw house

Wind farm cable failure averted!



ELECTRICALTESTER

Q&AQ: When I’m measuring the resistance

of an earth electrode or system, how far away

from it should I place my test spikes?

A: As far away as possible – and ideally at

least 6 to 10 times the maximum dimensions of

the earth system. To provide some rough rules of

thumb, for a single earth electrode, the current

reference spike C can usually be placed 15 m

from the electrode under test, with the potential

reference spike P placed about 9.3 m (62% of the

distance to C) away. With a small grid of two earth

electrodes, C can usually be placed about 30 to 40

m from the electrode under test; P correspondingly

can be placed about 18.6 to 24.8 m away. If the

earth electrode system is large, consisting of

several rods or plates in parallel, for example, the

distance for C must be increased to possibly 60 m,

and for P to some 37 m. You’ll need even greater

distances for complex electrode systems that

consist of a large number of rods or plates and

other metallic structures bonded together.

Q: My earth system is very large, so

to make measurements in the usual way I

would need very long leads. This simply isn’t

practical. What’s the alternative?

A: You can work with the test spikes at

shorter distances from the earth system if you use

the slope test technique. With this technique, the

current spike is inserted at a distance of about 2

to 3 times the maximum dimension of the earth

system. Measurements are then made with the

voltage spike at 20%, 40% and 60% of the

distance to the current spike. By using various

criteria to evaluate the results obtained from these

three tests and, if necessary performing further

tests, a reliable value for the resistance of the

earthing system can be obtained. There’s no space

here for the full details, but they can be found in

Megger’s invaluable publication, “Getting Down

to Earth”, which can be downloaded free of

charge from the Megger website.

Q: I’ve used the ‘stakeless’ technique to

measure the resistance of an earth electrode

and the result is very obviously too low.

What’s going on?

A: The most likely answer is that you’re actually

reading a metallic loop in the earth system. This

is a very common problem as most equipment is

bonded to ground, and this bonding frequently

creates earth loops. Unfortunately, you may not

be able to use the stakeless technique in your

application.

Q: What are the applications that

require high-resolution measurements of

earth resistance?

A: While in most cases it is only necessary

to show that the earth electrode resistance is

below some specified maximum acceptable

value, there are certain applications where high-

resolution measurements are necessary. These

include the determination of earth resistance

using the slope technique mentioned in an earlier

question, and the evaluation of earth resistivity

over large areas. High-resolution instruments,

such as the Megger DET2/2 automatic earth

tester, typically use the four-terminal method of

measurement and include additional features

such as variable test frequency, that help users to

obtain good results even in difficult conditions. As

well as earth electrode resistance measurements,

these instruments are ideally suited for soil

resistivity measurements, which can be used

to establish the optimum electrode design and

location, as well as for performing archaeological

and geological investigations.

Not long ago, the need to measure earth resistivity or the resistance of an earth electrode was, for most engineers, a rare occurrence. With the advent of small generating schemes and, in particular, solar and wind energy schemes, this situation has changed. Most of these schemes have their own earthing systems and, to ensure safe operation, these need to be checked. This has led to a large increase in the number of questions our helpline receives about earth testing; here is a selection of the most common.

Nikola Tesla’s name is synonymous with pioneering

electrical developments, and he is accepted as

the originator of many devices – not the least of

which is the AC induction motor – which we now

take for granted. His inventions form the basis

of much of the technology we currently use and

although controversial, his life is now celebrated

by engineers and history pundits alike.

However, this was not always the case and during

his lifetime, Tesla rarely received the recognition he

deserved for his work. Ironically, when in 1917 the

American Institute of Electrical Engineers finally

decided to award him a medal for his contribution

to technology, it was the Edison Medal. This was

indeed bittersweet recognition, as the accolade

was set up by Thomas Edison’s supporters – the

same Thomas Edison who took Tesla’s patents and

made a fortune out of them without crediting him.

The award meeting took place at the Engineering

Society Building in New York on May 18. Modestly,

the 60-year-old Tesla graciously accepted the award

for his lifetime achievements, and then proceeded

to hold an extremely lengthy acceptance speech

that went on for hours, much to the desperation

of his captive audience.

Keith Wilson - Electrical engineer

In the February issue of ET, special note was

made of Megger’s series of live monthly

webinars that make it easier for busy power

engineers to keep up to date with the latest

testing techniques and technology. These have

been formulated by the company’s experts,

who have consulted widely with customers

to identify the topics that are of the most

immediate interest. Register today at http://

us.megger.com/company/media-centre/events/

for an upcoming webinar, including:

� Friday, August 19th 2016 – Improving the

efficiency of transformer commissioning

� Friday, September 23rd, 2016 – An

approach to CT testing in the field

� Friday, October 21st, 2016 – Testing

complex relays

All of the webinars start at 10:00 United States

Central Time. For the benefit of anyone who

finds these times and dates inconvenient,

the seminars are being recorded and will be

available to view online on the Megger website

(www.megger.com) within a few days of being

presented.

Reminder: Knowhow delivered online!

Tesla and the pigeon of deathThis event was proof, once again, that despite his

outstanding intellect, Tesla lacked social skills and

refused to observe societal norms, considering that

only science is ever of any use to human beings.

All other things were considered to be trivial and

non-important in the greatness of the universe he

was hoping to build.

Unfortunately, as he aged, Tesla started showing

signs of obsessive-compulsive disorder, and was

potentially a high-functioning autistic.

He gradually withdrew from public life and his

quirks slowly took over. He became obsessed with

hygiene and when he shook people’s hands he

felt compelled to wash his hands three times. The

fixation on number three and its multiples was

affecting every area of his life – for instance he

had to have 18 napkins at the dinner table and

he would count the steps he walked during a day.

Tesla also claimed to have an abnormal sensitivity

to sounds, as well as an acute sense of sight. By his

own admission, he had “a violent aversion against

the earrings of women,” and “the sight of a pearl

would almost give me a fit” – he even sent his

secretary home one day upon seeing her choice

of accessories!

As Tesla’s world became more and more contorted,

he found solace in observing and feeding pigeons.

Having remained a bachelor his entire life, his

twilight years were spent fixating on a specific

white female pigeon, which he claimed to love

almost as one would love a human being.

Allegedly, the white pigeon visited Tesla one night.

The bird flew in his hotel room though an open

window. He believed the bird had come to tell him

she was dying. Tesla apparently saw “two powerful

beams of light” in the bird’s eyes: “Yes, it was a

real light, a powerful, dazzling, blinding light, a

light more intense than I had ever produced by the

most powerful lamps in my laboratory.”

The white pigeon died in the inventor’s arms,

which made a profound impact on his already

anguished psyche. He believed that the

pigeon’s death symbolized his own mortality and

that he had now accomplished all that he was

supposed to.

Nikola Tesla died in 1943, in debt, at his apartment

in the New Yorker hotel. His passing was at the

time unremarkable and only decades later was his

reputation restored as one of the greatest thinkers

of the twentieth century.

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