DET4TC Presentation.pdf

8/20/2019 DET4TC Presentation.pdf

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New Earth Testers from Megger

Paul Swinerd


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Megger - Earth Testing Pioneer

Dr George Tagg pioneered earth testing at Megger

Designing, manufacturing and selling for well over50 years


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Days gone by


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Existing products

Direct 2 terminal & 3 terminal earth electrode testing

• DET3TA

• DET3TD

• DET3TC

• DET3/2

2 & 3 terminal and 4 terminal soil resistivity testing

• DET5/4D

• DET5/4R

• DET2/2

Stakeless testers

• DET10C-EU and DET20C-EU


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Products being replaced

DET5/4D

DET5/4R

• Last orders plan to be maximum 6 months from release ofnew products, so June 2007

• This is for sales of products – not support and repair of

the products which we plan to continue for a further five

years

Why?

• DET5/4 has been around for many years, now dated

• Although sound design, has basic user interface andfeature set


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The new family

New family to replace DET5/4D and DET5/4R

• DET4TC

– 2, 3 and 4 pole ground tester digital display

–Selective (ART) and Stakeless test capability

• DET4TCR

– As DET4TC but rechargeable

• DET4TC + KIT

–Fully kitted with ICLAMP and VCLAMP

• DET4TCR + KIT –Fully kitted with ICLAMP and VCLAMP


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DET4TC/R

Excellent user interface

Full diagnostics

New case design

(as DET3TD/TC)

Backlit display

ART

Stakeless testing


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DET4TC/R + KIT

Fully Kitted option

ICLAMP

VCLAMP

Stakeless test calibration

loop

Instrument calibration check

box Right angle adaptor kit


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Earth Testing theory


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Two Basic Test Types

Soil resistivity

• Choose location and design for earth system

Earth system resistance• Check resistance low enough


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Soil Resistivity

Theory


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Soil Resistivity

Purpose of this test:

• Find lowest possible resistance in an area

• Obtain the values needed to design the earth system Factors affecting soil resistivity

• Soil composition

• Moisture in the ground

• Temperature

Consider

• Resistivity will vary through the year

• Moisture more constant at water table

• Stable temperature below the frost line


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Soil Resistivity test methods

Purpose: Survey a site for the lowest resistance

connections for Earth.

Methods: 4-pole (Wenner method).

A A A


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Soil Resistivity test terms

Average soil resistivity, ρ = 2π AR ( cm)

Variables

• ρ is average soil resistivity to depth A in ohm-cm

• A is the distance between the spikes

• R is the resistance read from the earth tester

For example

• Planning to install 3m long electrodes?

• Then measure soil resistivity with spacing, A, betweenspikes at 3m

• The depth of test probes should be less than 3/20 =


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Soil Resistivity test terms

Soil resistivity is of interest because by rearranging the

formula and knowing its value from tables we can

calculate the resistance of the earth electrode required.

ρ = 2π AR ( cm) therefore electrode resistance R = ρ / 2π A


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Earth System Resistance

Theory


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But First

Earth system definitions

Why test?

Component parts of earth electrode resistance


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Earth system definit ions

Simple

• Generally consists of a single ground electrode driven into

the ground

Complex

• Multiple ground rods connected, mesh or grid networks

– More common in sub stations, cell sites etc


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Why test earth system?

Why a low earth resistance is required:

• Enable protective devices to operate in good time

• Reduce ground potential rises (GPR)

• Danger of shock from GPR (during fault)

– Step potential

– Touch potential

– Adjacent conductors


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Step and touch voltages

V VStep Touch


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Resistance and GPR from earth electrode

0.0

0.4

0.8

1.2

1.6

2.0

R e s i s t a n c e

( O

h m

s )

0

200

400

600

800

1000

V o

l t a g e

( V )

Resistance GPR


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Component parts of earth electrode resistance

1 – Resistance of the electrode and the

connections to it

2 – Contact resistance of the surroundingsoil to the electrode

3 – Resistance of the surrounding body

of earth around the electrode – these canbe thought of as “shells” and create a

sphere of influencesphere of influence


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Earthing System Resistance - theory

Purpose: Measure resistance of earthing system to

Earth - ascertain that prospective fault current can

be conducted safely to Earth and thus limit “touch

voltage”.

Methods:

• 2-pole: Direct measurement.

• 3-pole: Fall of Potential – Full method

• 3-pole: Fall of Potential – short method

• 3-pole: Slope Method.

• Selective measurements: ART

• Stakeless measurements: Earth Clamp.


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2-pole: Direct measurement

Measure “coupling” between two earth points; measure

resistance of earth electrode to Earth.

C1 (E)

C2 (H)P1 (ES)

P2 (S)Imeas

Emeas

Earth electrode

under test

Second earth electrode or other

low resistance, conductiveconnection to Earth.

Measures resistance ofthe two Earth electrodes

in series.

R = Emeas/Imeas


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2-pole: Direct measurement disadvantages

A series measurement of a resistance loop.

Accuracy depends on assumption that all other

elements in loop are of low resistance. Must disconnect individual ground electrodes to

measure them.


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3-pole: Fall of Potential (full method)

Classic method for measuring resistance of a single

earthing electrode, or of a system of electrodes to

Earth.

A

B

C2 (H)P2 (S)

C1 (E)

P1 (ES)

Imeas

Emeas

Earthelectrode

under test

Auxiliary testelectrodes

R = Emeas/Imeas


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Fall of Potential - Full Method

Vary location of P2 (Potential) spike by regular

steps along a straight line between the electrode

under test and the C2 (Current) electrode.

Plot graph of resistance measurements to distance

of P

Resistance of system taken where slope is flat. Note: The C spike must be outside the sphere of

influence to achieve a viable reading

f C S f


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Fall of potential - Current Probe Sphere of

Influence

Auxiliary

CurrentProbe (C)

Auxiliary

PotentialProbe (P)

GroundElectrode

UnderTest (X)

P probe must be outside of both

spheres of influence for correct

measurement

F ll f t ti l t t d lt


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Fall of potential – test and result

CurrentProbe

Position

Distance of Potential Probe from X (dp)Ground

ElectrodePosition

X C R e s i s t a n c e i n O h m s

CurrentProbe (C)

PotentialProbe (P)

Positions

GroundElectrode

UnderTest (X)

F ll f t ti l t t d lt


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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)

PotentialProbe (P)Positions

GroundElectrode

UnderTest (X)

Fall of potential test and res lt


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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)


GroundElectrode

UnderTest (X)

Fall of potential test and result


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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition

X C R e s i s t a n c e i n O

h m s

CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)


GroundElectrode

UnderTest (X)



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CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)

Potential

Probe (P)Position

GroundElectrode

UnderTest (X)

True systemresistance

measured

here



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p

CurrentProbe

Position


ElectrodePosition


h m s

CurrentProbe (C)

Potential

Probe (P)Position

GroundElectrode

UnderTest (X)

True systemresistance

measured

here

Usually approx 62%

of X to C distance

T i l P b S i


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Typical Probe Spacing

Single electrode

• C probe 15m away

• P probe 9.5m away

Large system, several electrodes or plates

• C probe 60m away

• P probe 38m away

Above only rough guide – look up tables available

Fall of Potential Method Disadvantages


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Fall of Potential Method – Disadvantages

Extremely time consuming and labour intensive.- Temporary probes must be placed.

- Cables must be run to make connections.

Space constraints can make it hard to place remoteprobes. (probes usually many meters away)

Must disconnect individual ground electrodes to

measure them.

3 pole: Fall of Potential (short method)


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3-pole: Fall of Potential (short method)

Reduced method based on fewer measurements, saving time

Earth

electrode

under test

B

C2 (H)

P2 (S)

Emeas

C1 (E)

P1 (ES)

Imeas

0.62B

Auxiliary testelectrodes

R = Emeas/Imeas

3 pole: Fall of Potential (short method)


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3-pole: Fall of Potential (short method)

Site P2 (Potential) spike at 62% of B and take

resistance measurement.

Locate P2 ± 0.1B around the 62% point and take

additional resistance readings, Rb and Rc.

If the three readings are within an agreed accuracy

limit, the system resistance is the average

Fall of Potential Method (short method)


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Fall of Potential Method (short method)–

Disadvantages

Not as accurate as less measurements are made

Space constraints can make it hard to place remoteprobes.

Must disconnect individual ground electrodes to

measure them

3-pole: Slope Method


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Alternative method applicable for physically

constrained sites.

B

C1 (E) C2 (H)

P1 (ES)

P2 (S)

Imeas

Emeas

Earth

electrode

under test

0.4B

0.6B

0.2B

Auxiliary test

electrodes

R = Emeas/Imeas

Distance to C probe (B)

Now 2 to 3 times the

maximum dimension ofearth system.

3-Pole: slope method


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3 Pole: slope method

Distance of Potential Probe from X (dp)

R e s i s t a n c e i n O h m s

CurrentProbe (C)

PotentialProbe (P)

GroundElectrode

UnderTest (X)

No flat area



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Vary location of P2 (Potential) spike by regular

steps along a straight line between the electrode

under test and the C2 (Current) electrode

Measure resistance at each step and plot a graph

of R versus distance.

Measure resistance at 0.2B, 0.4B and 0.6B: R1,

R2 and R3.

Slope coefficient, m=(R3-R2)/(R2-R1) relates

distance B and ideal distance of the voltage spike

(P2) for measuring the resistance.



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Measure R1 at 20% distance to C2

C2 (H)

Earth

electrodeunder test

B

C1 (E)

P1 (ES)

Imeas

Emeas

0.2B

R1

C2 (H)

μ=(R3-R2)/(R2-R1)

R1= 9.3 ohm

R = Emeas/Imeasμ = (R3-R2) / (R2 – 9.3)



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C2 (H)

Earth

electrodeunder test

B

C1 (E)

P1 (ES)

Imeas

Emeas

0.4B

R2

C2 (H)

μ=(R3-R2)/(R2-R1)

R1= 9.3 ohm

R2= 16 ohm

R = Emeas/Imeasμ = (R3 – 16) / (16 – 9.3)



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C2 (H)

Earth

electrodeunder test

B

C1 (E)

P1 (ES)

Imeas

Emeas

R30.6B

C2 (H)

μ=(R3-R2)/(R2-R1)

μ = (19.2 – 16) / (16 – 9.3)

R1= 9.3 ohm

R2= 16 ohmR3= 19.2 ohm

R = Emeas/Imeas



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Calculate value of μ

C2 (H)

Earth

electrodeunder test

B

P2 (S)C1 (E)

P1 (ES)

Imeas

Emeas

0.4B

0.6B

0.2B

Auxiliary test

electrodesR3R2R1

C2 (H)C2 (H)

μ=(R3-R2)/(R2-R1)

R = Emeas/Imeasμ = (19.2 – 16) / (16 – 9.3)

=0.478



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p p

Tables of values for the co-efficient of slope

against actual P spike distance is published in the

instrument user guide.

Take calculated value of m and look up ideal

distance of the voltage spike (P2) for measuring the

electrode resistance


=0 478


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=0.478



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Measure electrode resistance at 0.632B

Earth

electrode

under test

C2 (H)

B

C1 (E)

P1 (ES)

P2 (S)

Imeas

Emeas

0.632B

Auxiliary test

electrodes

C2 (H)C2 (H)

R = Emeas/Imeas

3-pole: Slope Method - Disadvantages


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p p g

Less accurate than the full fall of potential

Requires maths

Must disconnect individual ground electrodes tomeasure them

Selective Measurements ‘ART’


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Attached Rod Technique

No need for the earth electrode to be disconnected

Uses current clamp ‘ICLAMP’ to measure currentflowing in electrode under test.

Application of ART


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Potential Probe (P) CurrentProbe (C)

Ground

Electrodes

Building earthconnection/s

I Total

I System

Ie

1Ie 2Ie 3

Ie test Test

Ie Test > I Total

20

X

Connection

ART with 4 pole measurement


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Potential Probe (P) CurrentProbe (C)

Ground

ElectrodesUnder

Test (X)

Building earth

connection/s

I Total

I System

Ie 1 Ie 2Ie 3Ie Test

C1 and P1 connections

Effects of Earth Coupling


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X Test

point

C P P

X Test

point

C

Result – Clamp low symbol or unexpected high reading

Answer use 3 pole method – disconnect electrode

Misuses – Telecom Guy Lines


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Current CPotential P

X

Connection

We MUST fully understand the test current path

The Best Application of ART


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Field of earth / Earth Farms

Pole mounted transformers

Domestic TT (earth electrode) systems Single guy lines on towers (isolated)

Lightning protection electrodes

Measuring Earth Leakage Current


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Building earth

connection/s

System leakage current

Ie 1 Ie 2Ie 3Ie 4 leakage (mA)

DET4TC set to A range

Using ICLAMP to measure electrode leakage current

“ Stakeless” Measurements


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No need for the earth electrode to be disconnected No need for test spikes to be used

Clamp-On / Stakeless Methodology


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Inject a voltage and measure the resultant current

produced in a ground loop.

Requires a complete electrical circuit to measure.

Measures the complete resistance of the path

(loop) the signal is taking.

In a multiple ground system the circuit can be

considered a loop comprising:

- The individual ground electrode.

- A return path via all other electrodes.

- The mass of earth.



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In a multiple ground system the circuit can be

considered a loop comprising:

- The individual ground electrode.

- A return path via all other electrodes.- The mass of earth.

The single electrode will have a higher resistance

than the remainder of grounds connected inparallel.

Inject a voltage and measure the resultant current

produced in a “single turn” ground loop.



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GroundElectrode

Under

Test

Building earth

connection/s

ICLAMP

VCLAMP



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ICLAMP

VCLAMP

R testR1R2R3R4

25 Ohms 22 Ohms 19 Ohms 25 Ohms 45 Ohms

R Meas.= 50.6 Ohms

R Meas. = R test + 1 / (1/R1 + 1/R2 + 1/R3 + 1/R4)

Clamp-On/Stakeless Methodology


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For 6 similar electrodes each with a resistance of

10Ω

• Rloop = 10Ω + 2Ω = 12Ω reading on DET4TC/R

For 60 similar electrodes with a resistance of 10Ω

• Rloop = 10Ω + 0.17Ω = 10.17Ω reading on DET4TC/R

The more electrodes the more accurate the reading

Clamp-On /Stakeless Method - Advantages


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Test is quick and easy• No disconnecting the ground rod from the system.

• No probes need to be driven/cables connected.

Includes the bonding and overall connection resistance• Not available with Fall of Potential

Can measure the leakage current flowing through the

system..

Clamp-On /Stakeless Method - Disadvantages


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Effective only in situations with multiple grounds in parallel (polegrounds).

Cannot be used on isolated grounds (no return path)• Not applicable for installation checks/commissioning new sites

Cannot be used if an alternate lower resistance return exists notinvolving the soil

• Cellular towers

• Substations

Subject to influence if another part of the ground system is in“resistance area”

• Result will be lower than true resistance.

Test is carried out at a high frequency (enables the transformers

to be small)• Less representative of a fault at power frequency but easier to filter out noise

Requires a good return path

Clamp-On /Stakeless Method - Disadvantages


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Requires a good return path• Poor return path may give high readings.

Connection must be on the correct part of the loop for

the electrode under test

• Requires thorough understanding of the system

• Wrong connection can give a faulty result.

Susceptible to noise from nearby substations and

transformers (no reading). No basis for the test in standards – no objective

reference for the test results

Less effective for very “low” grounds• Extraneous elements in reading become comparatively large.

Applications – Service Entrance/Meter


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Ground

Rods

ServiceBox

Pole-Mounted

Transformer

Service

Meter

Applications – Lightning Protection


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Removable links

(Jug handles)

Link removed for

2 pole measurement

Lightning protection tape

Normal 2 Pole method

Applications – Lightning Protection


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Removable links

(Jug handles)

ICLAMP and VCLAMP

Lightning protection tape

Using ‘Stakeless’ method no need to remove link

Grounded

Misuses – Substations


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Substation PerimeterFence

E

Clamp-On

Ground

Tester

Substation

Ground

System

Test

Current

Misuses – Lightning ProtectionTest current flowing around loop


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Of lighting protection tape.

Lightning protection

tape

The Best Application of “ Stakeless”

Testing


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g

Field of earth / earth farms

Pole Mounted transformer electrodes

Pole mounted transformer guy line when connectedto earth system

Earthing in Sub-station cable cellars

• It is often impossible to drive in test spikes so this is an

ideal application for stakeless measurements

Single guy lines on towers

Lightning protection electrodes

DET4TC/R


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New product common philosophy


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Intuitive to use

One button operation

Automatic checking to avoid mistakes and poor

connections, indicated on display

Complete and ready to start testing kit, including

calibration certificate

Competitively priced to sell, including distribution

Combination of features, benefits and price makes

these ground testers the most attractive on the

market

New product common features


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Like DET3TD, based on building wiring housing

Delivered in plastic carry case

Includes stake and wire kit with each model

High quality large and easy to read backlit LCD

Includes batteries

Has quick start guide on the lid

Easy to use wearing gloves

Comes with calibration certificate as standard

Three year warranty

Avoids language variants for easy stock holding

Basic specification – DET4TC/R

2 terminal test, no links required


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3 terminal earth electrode test, no link required

4 terminal Resistivity test to 20k Ohms

ART (Attached Rod Technique)

‘Stakeless’ measurements Earth voltage measurement

Earth leakage current measurement (with ICLAMP)

Automatic checking of

• Current spike resistance

• Voltage spike resistance

• Earth noise voltage

• Blown fuse

• Battery status

Rechargeable batteries on DET4TCR

DET4TC/R specifications - electrical


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Resistance range (2,3 & 4 pole): 0.01 to 20kΩ Maximum P & C spike resistance: 100kΩ (50V output)

ART range: 0.01 to 20kΩ

Stakeless range: 0.01 to 200Ω

Earth voltage range: 0 – 100V

Earth current range (DET4TC/R + ICLAMP): 0.5mA to 19.9A

Test frequency: 128 Hz

Test voltage: 25V or 50V selectable (Factory set 50V) Earth noise rejection: 40V peak to peak

Battery type: 8 off AA cells or rechargeable

Approximate battery life: 700 consecutive tests

Safety: EN61010-1 CATIV 100V

EMC: EN61326-1:1998 heavy industrial

Common specifications - Mechanical


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IP54

Terminals: 4mm plug type

Dimensions: 203 x 148 x 78mm

Weight: 1kg

Operating temperature range: -15 to 55°C

Storage temperature range: -40 to 70°C

Humidity: 95% RH non-condensing at 40°C

DET4TC/R Accessories

St d d


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Standard• Hard carry case

• Stake and wire kit (15m, 10m, 10m, and 3m)

• External AC/DC adaptor – interchangeable plugs

Optional

• ICLAMP

• VCLAMP (includes calibration check pcb)• Calibration check box – 6220-824

• Right angled terminal adaptor set – 6220-803

• Black crocodile clip - 6220-850• Vehicle 12V charger lead – 6280-375

DET4TC/R + KIT Accessories

St d d


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Standard• Hard carry case

• Stake and wire kit (15m, 10m, 10m, and 3m)

• External AC/DC adaptor – interchangeable plugs• ICLAMP

• VCLAMP (includes calibration check pcb)

• Calibration check box – 6220-824• Right angled terminal adaptor set – 6220-803

Optional

• Black crocodile clip - 6220-850• Vehicle 12V charger lead –

Accessories – terminal adaptor set


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DET4TC/R Competitors

4620/30 / CA 6460/2

• Disadvantages DET4TC/R

AEMC / Chauvin Arnoux


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• Disadvantages

– 42V output only

– P and C high ind. combined

– No cal. Cert. – IP50

– No leads or case etc. std.

– Only 2kΩ range

– Links required• Advantages

– However many lead kit

options

• Advantages

– Superior noise rejection

– CATIV 100V

– Much lighter – ART and Selective

capability

– Earth leakage current

range – Earth voltage range

– Superior diagnostics

AEMC / Chauvin Arnoux

6470

• Advantages

DET4TC/R

• Advantages


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• Advantages

– 2 & 4 pole DC bond check

– 0 – 100kΩ range

– 16 or 32V output

– Auto frequency control – 50Hz earth resistance test

– Wenner method rho calc.

– Schlumburger method rhocalc.

– Memory for 512 tests – Software supplied

• Disadvantages

– IP54 but only with lid closed

– Rechargeable only

• Advantages

– ART & Stakeless

capability

– 25 or 50V output

– 128Hz only

– Much lighter

– Easy to use

– Hard carry case

Fluke

1623 (Saturn Geo Plus)

• advantages

DET4TC/R

Ad t


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• advantages

– Battery life 3000 tests

– 125 or 128Hz

– 2 years warranty

– ART noise current

rejection better at 3A

– Stakeless noise current

rejection better at 10A


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1625 (Saturn Geo X)• Advantages

– ART noise currentrejection better at 3A

– Stakeless noise currentrejection better at 10A


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• Advantages

– 2 pole DC bond check

– Wenner method rho

calc. – 125 or 128Hz

– Result memory

– Output to PC

• Disadvantages – Large 30cm required

between clamps

– Many accuracies not

specified

• Advantages

– Better quality

– Accuracy

– 25 and 50V output – Back lit display

– Superior noise rejection

– Superior temp specs.

– Ground voltage range

Features and Benefits

Tough rubber armoured IP54 rated instrument case


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Tough rubber armoured IP54 rated instrument case• Instrument will last a long time, and will be ready to test

when required

Supplied in tough blow moulded carry case• Helps prevent loss of accessories, also makes ideal ‘tray’

to put the instrument on when testing. Saves having to lay

the instrument directly onto muddy ground.

Supplied with calibration certificate, test leads and

spike kit

• Saves time having to source separate leads and spikes.

No waiting for calibration to be carried out. No hiddencosts. Convenient.


‘Attached Rod Technique’ capability ART


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Attached Rod Technique capability, ART• Saves both time and aggravation having to undo rusted

connections. No need to shut down supply to ensuresafety

‘Stakeless’ testing capability• Allows testing in areas when driving test spike is

impossible. E.g. Sub station cable cellars, or when testinglightning protection in concreted locations

One button operation with automatic noise checkand automatic P and C spike resistance check

• Little time required learning operation, and time saved not

having to spend considerable time troubleshooting poorconnections etc.


User selectable output voltage – 25V or 50V


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User selectable output voltage 25V or 50V• The ability to test in agricultural locations as per

IEC61557-5. 25V will not harm livestock

40V Pk to Pk Noise rejection• Can be used in most locations with ground noise such as

sub-stations, near transformers etc.

Back light

• Easier to operate when not having to use a torch to be

able to read the display

Potential Customers

Existing DET5/4 customers


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Existing DET5/4 customers

Petro-chemical companies

Utilities, Maintenance

Railways

Repair Organisations (Industrials),

Telecoms and Datacoms installers Specialist grounding/earthing companies and

consultants

Service providers

Insurance companies

Available?

New family in stock Dover from January Launch


100/100

100

New family in stock Dover from January Launch

DET5/4

• Declare intention to be made obsolete June 2007

• Last orders accepted June 2007

• Repaired and calibrated for a further 5 years.

DET4TC Presentation.pdf

Documents

Transcript of DET4TC Presentation.pdf