DATE CONSULTATIONS REVISION APPROVED · Resistance measurement ofjoints, compressed tension clamp and bolted connectors Introduction These guidelines describe requirements regarding

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UNIT, BUSINESS AREANTL, Overhead Transmission Lines, Grid Technology

OUR REFERENCETR.O5-I6E

DATE9 March 2020

CONSULTATIONSNAL, NLB, NLP TECHNICAL GUIDELINE

REVISION2

APPROVEDTD

Overhead transmission linesResistance measurement ofjoints, compressed tension clamp and bolted connectors

IntroductionThese guidelines describe requirements regarding resistance measurement of joints, and comprise measurement method and limit values for replacement of joints. The purpose is to ensure that measurements are performed in the same way, that measurement errors are minimized and that joints in bad condition are replaced

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TECHNICAL GUIDELINE 9 March 2020 TR05-16E rev 2

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Revision Notes Change notes Date

1 First issue 29 / 04 / 2015

2 Clause 4 inserted. Clause numbers revised. Clause 5.2.3, 7.3.1 and 7.3.2 revised.

09 /03 / 2020

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Content

1 References ........................................................................................................... 5

2 Scope .................................................................................................................... 5

3 Definitions ........................................................................................................... 5

4 Recommendations .............................................................................................. 7

4.1 Instruments /Apparatus for measurement-Gauging equipment 7

4.1.1 Requirements 7

4.1.2 Example of instruments that fulfil the requirements 7

4.1.3 Clamps 7

5 Performing resistance measurement ................................................................. 8

5.1 General procedure 8

5.2 Measurement of special joints 10

5.2.1 Compressed dead end connector 10

5.2.2 Screw joint 10

5.2.3 Bolted connectors 10

6 Risk for measurement errors ............................................................................ 11

6.1 Insufficient contact between conductor strands 11

6.2 Influence of temperature 11

7 Joint resistance ................................................................................................. 12

7.1 Requirement for old mid-span joint 12

7.2 Requirement for new mid-span joint 12

7.2.1 New joint on new conductor or old conductor 12

7.3 Requirements for bolted connectors 12

7.3.1 New bolted connector on new or old conductor 12

7.3.2 Old bolted connectors 12

7.4 Requirements for dead-end joints 13

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7.5 Requirements on joints on overhead earth wire 13

7.6 Limit values for old joints on face conductors 14

7.7 Limit values for old joints on overhead earth wires 16

8 Documentation ................................................................................................. 17

8.1 Requirement content 17

8.2 Example of measurement protocol 17

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1 References

TR 05-07E Svenska kraftnät Technical guidelines – Joints for conductors

TR 05-15E Svenska kraftnät Technical guidelines – Parallel groove clamps

2 Scope

These guidelines concern resistance measurement of joints. They cover how to

perform measurements, requirements on the measurement equipment and limit

values for replacement of joints.

3 Definitions

Technical terms and definitions used in this document:

Joint

Device for joining two lengths of conductor to provide mechanical and electrical

continuity. Conductor here relates to phase conductor or shield wire. A joint in a

line span (mid-span joint or dead-end joint) has also, in addition to electrical

connection, the function of maintaining the full mechanical strength of the con-

ductor.

Compression joint

A joint assembled by compression.

Detonation compressed joint

A compression joint compressed by detonation of an explosive charge wound

around the sleeve of the joint.

Hydraulic compressed joint

Compression joint compressed by a hydraulic tool.

Screw joint

A joint consisting of factory compressed sleeves on each conductor end, which are

joined by a screw sleeve.

Bolted connector (Parallel clamp)

A joint or a clamp where contact is obtained by a bolted connection.

k-value

𝑘 =Joint resistance

Resistance of the same lengt of the conductor or

Rj

Rc×Lj

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Where Rj is the resistance of the joint, Rc is the resistance of the conductor per

meter, read from datasheet, and Lj is the length of the joint in meters. The use of k-

value has the advantage of independence of conductor type and joint length.

Temperature dependency of resistance

Specified resistance values for conductors often refer to 20 ºC. The same reference

temperature is applicable for the limit values specified in this document. The

following formula gives the resistance at other temperatures, if the resistance at 20

ºC is known.

Rθ = 𝑅20 ∙ (1 + 𝛼(𝜃 − 20))

Where: R20 = the resistance at 20 ºC

Rθ = the resistance at temperature θ

θ = the actual temperature

= 0.004 for aluminum (temperature coefficient).

A temperature difference of 10 degrees corresponds to 4 % resistance difference for

aluminum.

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4 Recommendations

4.1 Instruments /Apparatus for measurement-Gauging equipment

4.1.1 Requirements

Requirements Comments

Four leads measurement with separate outputs

for current and separate inputs for voltage

Measure current of at least 10 A For old Chance bridges at least 5 A

Resolution 0,1 µΩ For measurement on older conductor joints can

a resolution of 1 µΩ be accepted.

Accurancy at least 1 %+1 µΩ

Automatic compensation of offset and

thermoelectric voltages

Alternatively so high current (at least

approximately 100 A) so that the offset voltages

will be neglected.

Operation temperature down to -10 oC For old Chance bridges down to 0 oC.

Impenetrability at least IP53 (dust protected and

water proof)

It shall be possible to perform measures in rain

(with extra protection if necessary)

IP53 does not allow measuring in continuous

rain.

Portable battery powered

Approved calibration less than a year ago

4.1.2 Example of instruments that fulfil the requirements

The following instruments fulfil the requirements:

Chauvin Arnoux C.A 6250

Megger DL RO 10 HD

4.1.3 Clamps

Clamps for current and measurement must have good contact force with as big

circumference of the conductor as possible. See TR05-16 clause 5.1 figure 2.

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5 Performing resistance measurement

5.1 General procedure Concerning full tension compression joints.

Three resistance values shall be measured: the whole joint R1, and the two halves

R2 and R3, where R3 is towards higher tower number.

Figure 1 Joint - resistances

Apply the clamps according to Figure 2; with the current clamps furthest out and

the measurement clamps on each side of the joint, and a measurement clamp on

the mid of the joint. The current clamps shall be placed at least 0.5 meter from the

joint. The measurement clamps on each side of the joint shall be placed 5 mm from

the joint, but must not be in contact with the joint.

Figure 2 Application of clamps, with a photo as an example.

Connect the micro-ohmmeter according to Figure 3 for measurement of R1, R2 and

R3 respectively.

R1

R3 R2

Min. 0.5 m Min. 0.5 m

Ca 5 mm Ca 5 mm

Measurement clamp

Current clamp

Towards higher tower no.

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Measurement of

R1

Measurement of

R2

Measurement of

R3

Figure 3 Connections for measurement of R1, R2 and R3.

Measurement procedure for old joint or new joint on old conductor:

Measurement:

Measure the resistance R1

Move one measurement lead to the middle of the joint and measure R2

Measure R3 in the same way

Note the measured values,

Loosen the two measurement clamps on the conductor adjacent to the joint and rotate them about 1/3 revolution,

Repeat the measurement and note the values,

Loosen the measurement clamps again and rotate them another 1/3 revolution,

Repeat the measurement and note the values.

All measurement values shall be reported. The average of the three measurements

shall be compared with the applicable limit value.

Measurement procedure for new joint on new conductor:

As above, but the measurement need not be repeated.

R1

C1 P2 C2 P1 Micro-ohmmeter

R2

Micro-ohmmeter

P2 C2 P1 C1

R3

Micro-ohmmeter

P2 C2 P1 C1

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5.2 Measurement of special joints Basic measurement principles are according to section 5.1.

5.2.1 Compressed dead end connector

For compressed dead-end connectors the resistances R1, R2 and R3, according to

Figure 4, shall be measured. For R1 and R3 the measurement procedure according

to section 4.1 is applicable, with three repetitions. For R2 the measurement need

not be repeated.

Figure 4 Compressed dead-end connector - resistances

5.2.2 Screw joint

For screw joints the resistances R1, R2, R3 and R4, according to Figure 5, shall be

measured. For R1, R2 and R4 the measurement procedure according to section

5.1shall be applied, with three repetitions. For R3 the measurement need not be

repeated.

Figure 5 Screw joint - resistances

5.2.3 Bolted connectors

For parallel groove clamps and T-clamps the resistances according to Figure 6 shall

be measured. The measurements need not be repeated.

Figure 6 Bolted connectors - resistances

R1

R2

R3

R4 R3 R2

R1

Towards higher tower no.

R2

R1

Parallel groove clamp

R1

T-clamp

R2

R1


R1

T-clamp

R2

R1


R1

T-clamp

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6 Risk for measurement errors

6.1 Insufficient contact between conductor strands The largest risk for errors in resistance measured on old joints is due to old con-

ductors often having bad contact between the strands. This makes the meas-

urement current unevenly distributed and may cause large measurement errors,

especially for joints that have an increased resistance. The deviations can be both

positive and negative.

Obtaining measurement values with good precision and repeatability would require

clamps that contact the whole circumference of the conductor and at least 2 meters

distance to the current clamps. Since this is difficult to achieve in practice, we have

chosen here a compromise, based on three repeated measurements and moving the

measurement clamps in between. The resulting average value of the three

measurements gives a reduction of the error. In addition, the difference between

the three measurements gives an indication of the degree of this problem for each

single case.

For new joints, on new conductors, this is normally not a problem, and therefore

repeated measurements are not required in this case.

Measurement of conductor resistance on old conductors is also very uncertain, for

the same reason. Therefore conductor resistance should be taken from datasheets.

6.2 Influence of temperature The temperature dependency of resistance is described in section 3.

Regarding measurements on old joints, the temperature effect is often negligible in

comparison with other error sources. For new joints the temperature may however

significantly affect the comparison with the required limit values.

The temperature can be accounted for by adjusting the limit value to the prevailing

ambient temperature. Possible solar heating may be neglected.

A special case applies for measurement of newly detonation-compressed joints,

with remaining heat from the detonation. In this case the surface temperature of

the joint needs to be measured simultaneously with the resistance measure-ment.

The use of instruments with built-in automatic temperature compensation in-

volves additional risks, e.g. due to erroneously set values of temperature coeffi-

cient or reference temperature. The requirements here applied for reporting of

measurement values mean that such automatic temperature compensation need

normally not be used.

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7 Joint resistance

The following requirements apply to resistance at the measurement occasion.

These requirements shall be applied if nothing else has been agreed on.

7.1 Requirement for old mid-span joint For old phase conductor mid-span joints, the limit values in section 7.6 apply.

Joints that show higher measured resistance than the limit value shall be re-placed.

This applies also if only one of the parts exceeds the limit value.

For a screw joint, if the problem is in the screw sleeve, this shall be corrected, after

which a new measurement is made.

7.2 Requirement for new mid-span joint

7.2.1 New joint on new conductor or old conductor

For new joint on new conductor or old conductor reference is made to TR 05 07E,

with the following additions.

The limit value shall be adjusted to the temperature of the joint; normally the

ambient temperature can be used.

For measurements of newly detonation-compressed joints, with remaining heat

from the detonation, the surface temperature of the joint must be measured by a

surface temperature probe simultaneously with the resistance measurement.

7.3 Requirements for bolted connectors

7.3.1 New bolted connector on new or old conductor

For new bolted connector on new or old conductor the resistance may not exceed

0.6 times the corresponding conductor length (k = 0.6).

For double bolted connector on old or new conductor the resistance may not exceed

0.5 times the corresponding conductor length (k= 0.5) see R1 Figure 2.

7.3.2 Old bolted connectors

If measurement of an old bolted connector shows higher resistance than the cor-

responding conductor length (k=1.0) or double bolted connector on old conductor

the resistance may not exceed 0.5 times the corresponding conductor length (k=

0.5) see R1 Figure 3, the connector shall be opened; brushed by a wire brush, coated

by contact paste, brushed again and reassembled, after which a new measurement

is made.

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7.4 Requirements for dead-end joints For dead-end joints, the limit values in section 7.6 apply for the compressions

joints on line span conductor and on jumper conductor. For the bolted jumper

connection, the requirement according to section 7.3 applies.

The dead-end joint shall be replaced if any of the compression joints exceed the

limit value. If the bolted jumper connection exceeds the limit value, then it shall be

corrected (see 7.3.3) after which a new measurement is made.

7.5 Requirements on joints on overhead earth wire For new joints on overhead earth wires, the requirements according to section 7.2

apply.

An old joint in a overhead earth wire shall be replaced if the measured resistance

exceeds the limit value in section 7.7.

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7.6 Limit values for old joints on face conductors TR05-16 Table 1 lists limit values in the form of k-values as a function of the

highest continuous operating temperature of the line. Joints constitute a higher

risk, and age faster, at higher current load. Therefore the limit values are stricter

for lines operated at higher temperatures.

The limit values are for the reference temperature 20 oC, however, adjustment for

the temperature at measurement need not be made for measurements on old

joints.

Table 1 Limit values for old joints, represented by k-value.

Highest continuous

conductor temperature (C) k-value

50 1.5

60 1.4

65 1.3

70 1.2

80 1.1

85 1.0

Limit values in micro-ohms can be obtained as:

𝑅 = Rc × k × L

Where Rc = conductor resistance in µ/m (see Table 2)

k = k-value

L = the length over which the resistance is measured.

Table 2 contains listed values in micro-ohm/meter, i.e. Rc×k, for joints on common

conductors.

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Table 2 Limit values in micro-ohm/meter joints on common conductors, for different values of highest continuous conductor temperature.

Conductor type, area

Conductor resistance 1)

(µ/m)

Limit value for joint, in resistance per meter (µ/m), at highest continuous conductor temperature:

50 °C 60 °C 65 °C 70 °C 80 °C 85 °C

Dove, 329 102 153 143 133 122 112 102

Condor, 454 72 108 101 94 86 79 72

Curlew, 593 55 83 77 72 66 61 55

Morkulla, 593 51 77 71 66 61 56 51

Martin, 772 42 63 59 55 50 46 42

Ripa, 774 39 59 55 51 47 43 39

Falcon, 910 36 54 50 47 43 40 36

Orre, 910 33 50 46 43 40 36 33

454Al59 65 98 91 85 78 72 65

774Al59 38 57 53 49 46 42 38

910Al59 33 50 46 43 40 36 33

593AlMgSi-B 52 78 73 68 62 57 52

774AlMgSi-B 40 60 56 52 48 44 40

910AlMgSi-B 34 51 48 44 41 37 34

1) DC resistance at 20 °C, from datasheet, rounded to integer values. Example of how to use Table 2:

For a joint on a Curlew-conductor, with measured length 0.81 m, and a highest

continuous operating temperature of 50 C, the limit value is obtained as follows.

The distance between the measurement clamps, when measuring R1, is 1 cm longer than the joint. This gives L = 0.82 m. Table 2 gives the limit value 83 µΩ/m. This multiplied by L gives 0.82×83 = 68 µΩ. For R2 and R3, the length is L/2 and the limit value half the value applied for R1. The limit values to be applied are:

R1: 68 µΩ

R2, R3: 34 µΩ.

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7.7 Limit values for old joints on overhead earth wires The following limit value, in the form of k-value, applies for old joints on shield

wires:

k= 2.0

Table 3 contains listed values in micro-ohms/meter. The table is used as de-scribed

in section 7.6.

Table 3 Limit values in micro-ohms/meter for joints on shield wires, for common types of shield wires.

Conductor type, area

Conductor resistance 1)

Limit value for joint, in resistance per meter

(µ/m) (µ/m)

Dotterel, 142 323 646

Ibis, 234 143 286

Atle, 241 190 380

Ymer, 319 115 230

1) DC-resistance at 20 °C, from datasheet, rounded to integer values.

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8 Documentation

8.1 Requirement content Measurement protocols shall be delivered in Excel-format and contain at least the

following information:

Measurement performed by: Company and person

Date when the measurement was performed

Identification of measurement instrument: type and id-number

Identification of measurement object:

Line

Line designation

Conductor type

Highest continuous operating temperature

Joint type (hydraulic compressed, detonation compressed, screw joint etc.)

Length of the joint

Ambient temperature

Limit value applied

Identification of joint individual: Span no, Conductor no

All measurement values. Values larger than 10 may be rounded to integers

Average values of repeated measurements

Commentary field: any action taken, visual observations etc.

8.2 Example of measurement protocol Figure gives an example of measurement protocol for old joints.

Measurement protocol templates are provided by Svk.

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Figure 7 Example of measurement protocol for resistance measurement of old joints.

Performed date

Line designat. Highest cont. cond. temperature ( °C)

Cond. resistance (µ/m vid 20 °C) Type of joint Length of joint

Ambient temperature Applied limit value

°C R1 µ

R2 µ

R3 µ

Span no. Cond. no. Comment

Meas. no. R1 R2 R3

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

1

2

3

Average

Resistance measurement - JointsCompany Performed by

Measurement instrument type Measurement instrument id-number

Line Conductor type

Measured resistance (µ)

R1

R3R2Towards higher tower no.

Documents

DATE CONSULTATIONS REVISION APPROVED · Resistance measurement ofjoints, compressed tension clamp and bolted connectors Introduction These guidelines describe requirements regarding