milestone 3.14 maximising circuit transfer...

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Milestone 3.14 Maximising Circuit Transfer Capacity

Milestone 3.14: Maximising Circuit Transfer Capacity

UK Power Networks (Operations) Limited. Registered in England and Wales. Registered No. 3870728. Registered Office: Newington House, 237 Southwark Bridge Road, London,

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Contents

1. Introduction ..................................................................................................... 3 2. Dynamic Rating Principles ............................................................................. 4

Background .................................................................................................... 4 Literature Review and Academic Input .......................................................... 5

3. Lab tests ......................................................................................................... 8 Overview ......................................................................................................... 8 Test arrangements ......................................................................................... 8 Initial results .................................................................................................. 11

4. Data and Analysis ........................................................................................ 12 Cyclic load test ............................................................................................. 12 Heating and cooling profiles ......................................................................... 12 Derivation of Cable Model ............................................................................ 13 Applications .................................................................................................. 15

5. Demonstration Plan and Sites ...................................................................... 18 Site selection ................................................................................................ 18 Recommended Demonstration sites ............................................................ 20

6. Summary and conclusions ........................................................................... 22 Appendix A: Small Section Cables ....................................................................... 23 Appendix B: Examples of FUN-LV Load Transfer Profiles and Asset Guarding .. 25

Transfer Profiles ........................................................................................... 25 SOP Asset Guarding .................................................................................... 26

Appendix C: Field Measurement System .............................................................. 27 Appendix D: Milestone 3.14 Scope ....................................................................... 28 References ............................................................................................................ 29

This report has been prepared by the Energy Practice of Ricardo Energy and Environment.



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1. Introduction This document details the evidence for the Ricardo-AEA milestone, on Maximising Circuit Transfer

Capacity, for Work Stream 3.14 of FUN-LV. The key deliverable is:

Documentation of the development of dynamic rating algorithms for determining the real-time

rating of transformers and cable circuits with tabulated and charted evidence of their

performance and benefits.

It should be noted that the work on deriving load profiles for transformers based on temperature sensor data

has been documented as part of SDRC9.1 (FUNLV_SP_WS1_042_Selection Criteria and

Approach_v1.00_FINAL). Revision to the coverage of this activity is summarised in Appendix D. Therefore,

this report focuses on the dynamic ratings of cable circuits.

The following sections detail work carried out in this activity:

Subsequent discussions with Peter Lang, the principles of dynamic rating are explained in

Section 2, which covers a literature review and discussions with Professor. Paul Lewin and Dr

Pilgrim from the University of Southampton;

In Section 3 the laboratory set up is described;

Section 4 presents the data analysis, including the development of a model, and comparison

between modelled and measured data;

A discussion on potential demonstrations and recommended sites is covered in Section 5; and

Finally, a summary and conclusions are given in Section 6.

Appendices provide additional information on:

Small Section Cables;

Transfer load profiles; and

Asset Guarding and Field Monitoring Systems.



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2. Dynamic Rating Principles

Background

The key functionality of the FUN-LV Power Electronics (PE) Soft Open Points (SOP) solution is the

ability to finely control power flow, to:

• provide capacity equalisation between distribution substations, irrespective of their network

impedances or sources of supply, and

• release LV circuit capacity by the control of circuit loading and unbalance to dynamic limits.

To be able to transfer power between substations it is necessary to make the maximum use of both

transformers and existing cables, without unduly compromising their integrity or asset life. The lifetime

of equipment insulation is determined by the Arrhenius theory of electrolytic dissociation:

𝐼𝑛𝑠𝑢𝑙𝑎𝑡𝑖𝑜𝑛 𝐿𝑖𝑓𝑒𝑡𝑖𝑚𝑒 ∝ 10

1

(𝐿𝑜𝑎𝑑𝑖𝑛𝑔𝑅𝑎𝑡𝑖𝑛𝑔

)⁄

Hence using equipment at even a small amount over their design rating will result in a dramatic

reduction in insulation lifetime.

The essential difference between the “Release of Transfer Capacity” (also known as “Loading to

Dynamic Limits”) and “Dynamic Rating systems” is the control over the circuit load that is provided by

Power Electronics, preventing dynamic ratings being exceeded. This means that the thermal capacity

conventionally reserved to allow for normally uncontrollable fluctuations in load currents could be

released for use.

The loading profiles of equalisation circuits (or “transfer profiles”) will normally be determined by a

combination of the difference between the connected substation utilisations and the load on the circuit

itself. Transfer profiles may therefore be quite different in nature to that of distribution circuits: potentially

having higher peak loads but for shorter periods than conventionally loaded circuits and often from a

lower base load condition.

Controlled loading to dynamic limits by Power Electronics should also enable increases in the maximum

sustainable short transfers able to be provided at LV to provide network support on interconnected

networks under HV fault conditions. This will reduce the risk of LV cascade tripping, whilst also not

increasing short circuit levels.

According to the FUN-LV Asset Guarding strategy, the information being collected by the SOP and the

monitoring at remote ends of circuits should also allow the conductor temperature for the next 24 hours

to be calculated based on the historic and predicted load. The forecast emergency rating can therefore

be obtained for any time within the next 24 hours (see figure 1) and recalculated in real time from the

measured data.



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Figure 1: Elements of adjusted forecast rating

Literature Review and Academic Input

A search for literature on the subject of “Release of Transfer Capacity” (also known as “Loading to

Dynamic Limits”) was performed using the Imperial College search engine (which includes papers from

the IET, IEEE, Academia and numerous journals and conference proceedings), however little significant

material was found at the time of the literature review. This was not unexpected as the FUN-LV project

is one of the first practical demonstrations of the control of LV circuits by SOPs.

A paper on Dynamic Cable Ratings for Smarter Grids [1] was identified, reviewed, and the authors

subsequently visited to discuss their learnings from the paper, and the potential application to FUN-LV.

The paper presents a Dynamic Rating system for transmission voltage underground cable circuits, and

claims that the method offers improvements on widely used current methods. Forward ratings are

determined based on both historic load data and predicted future loads. The paper shows examples of

Emergency Rating lookup tables, which take account of the previous loading level and the expected

overload time in hours, and derive a maximum rating for the different time periods (1, 6 and 24 hours).

Increases in current carrying capability by up to 1.7% (1hr), 13% (6hr) and 8% (24hr) against the against

the currently used methods are possible, suggesting that the greatest benefit of the technique is

achieved for longer term overloads.

In contrast the approach of using historic data and real-time measurements for dynamic rating

calculations is claimed by Waldorf et al. to deliver increases in cable current carrying capacity of 5-20%

[2].

Paper [1] authors, and experts in the field, Professor Lewin and Dr Pilgrim, of the University of

Southampton, were consulted to advise on the implementation of dynamic rating of LV buried cables.

In order to accurately perform dynamic rating on LV cables, three key aspects of measurement data

were identified that are required to enable the identification of the weakest "pinch points":

1. Accurate load information for the whole LV circuit;

2. An understanding of the existing phase unbalance/neutral current (as this effectively de-rates the

cable); and

3. The detailed circuit topology, including any neighbouring heat sources.

The use of a load-flow analysis package with an accurate model of a given circuits loading and topology

would reveal the current flowing on each branch. This could then be developed to incorporate a

dynamic load-flow simulation including the superposition of the proposed transfer profile (via the PED)

to inform a maximum transfer assessment.



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Accurate assessment of the dynamic rating capability of LV circuits would require detailed modelling of

each cables’ intrinsic electrical and thermal characteristics, the external environment (soil thermal

resistivity, adjacent heat sources etc.), and the detailed circuit loading.

Items 1 and 2 from the above list should be possible in due course through the development and

validation of advanced LV modelling capability of DPlan. However, the level of investigation and

monitoring required to accurately model a cables topology and external environment would make this

conventional approach impractical to achieve within the scope and timescales of the FUN-LV project

and its field trials.

Other non-invasive approaches to remotely establishing the temperature of buried cables at specific

points have been identified and have been the subject of separate preliminary and independently

funded research studies at Imperial College. However, the use of these studies are outside the current

scope of FUN-LV.

Three factors were considered in order to simplify the requirements:

The continuous rating of the majority of LV cable types in air is similar to those directly buried

in soil (See figure 2);

Cables in air in well loaded substations are likely to be subject to significantly higher ambient

temperatures than those directly buried in soil; and

The type of LV circuits used for FUN-LV spine circuit transfers trials are not tapered and typically

have similar effective ratings throughout (Typically 185mm2 Aluminium conductor, direct buried

or similar).

It follows that in most cases in the FUN LV project the rating of cables within the substations are

likely to be the constraining factor.

Figure 2: Sustained LV CNE AL cable ratings

It was therefore decided that the investigation should focus on:

Controlled environment lab tests to understand the effects of heating and cooling profiles in

substations on the ratings of LV cable in air; and



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A subsequent potential demonstration of the SOPs to exercise control over the cable loading

to maximise the transfer capacity without unduly compromising cable life or integrity.

The principle being that exactly the same SOP control methods can be used for the underground

sections of circuits once non-invasive approaches to remotely establishing the temperature of buried

cables along their lengths are available.



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3. Lab tests

Overview

This study aims to conduct a series of laboratory tests to provide insight into circuit short-term maximum

transfer capability, without exceeding thermal safety limits. By examining the dynamic temperature

response of LV cables subjected to large step-changes in load (replicating the transfer profiles

envisaged through the use of controllable Power Electronics) this study will generate learning in

assessing the maximum possible circuit transfers. This modelling requires knowledge of near real-time

power flows at different points on the LV network under consideration.

A test environment was built to enable development of an understanding of cable temperature response

to load changes in ambient air and single way ducts. This will be of particular use in providing insight

into the impact of the indicative transfer profiles envisaged using the Power Electronic Device (PED) for

FUN-LV Method 2 and 3 sites (2-terminal and 3-terminal SOPs respectively).

Test arrangements

A series of tests have been conducted on 185mm2 HV Cu Paper Insulated Lead Covered Steel Wire

Armoured sheath (PILCSWAS) and 185mm2 LV AL Paper Insulated Lead Covered Single Tape

Armoured Sheath (PILCSTAS) cable samples to examine the thermal response due to conventional

load profiles and indicative PED “transfer profiles” with short periods of higher load.

The trials have focussed on PILC type cable as these have a lower thermal capacity (60-65oC) than

XLPE types (up to 90oC), meaning they should represent the worst case.

Cable Construction

A. Copper or aluminium conductors – 4 x stranded sector shaped (A large range of conductor

sizes are used in practice with conductor sizes between 70 and 300mm2 and an overall cable

diameter range between 38.4 and 66.9mm);

B. Mineral oil compound impregnated paper insulation layers of thickness 1.2 to 1.6mm, between

the conductor and sheath;

C. Additional (belt) insulation layer;

D. Lead sheath, covered with bitumen coated paper and hessian layers, as a bedding for the

armour wires

E. Steel tape armour sheath

A B C D E F

Figure 3: Four Core PILCSTAS Cable



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F. Bitumen coated hessian tape serving or oversheath (This may be chalked as was the sample

supplied for test).

Note that the steel tape example shown in figure 3 has a reduced cross section neutral. The test sample has a full section neutral. LPN typically used steel wire rather than steel tape armours

Figure 4. The four core PILCSTAS cable (with full section neutral) used in the lab tests.

A test rig was developed to enable a current injection in steps of approximately 250A, 450A and 700A

per phase. These allow representation of the following conditions:

o off,

o normal (250A);

o emergency (450A);

o ultimate emergency current rating levels (700A); and

o the rapid transitions of Transfer Profiles (i.e. step changes in current as may be caused

by the use of power electronics, as opposed to the more gradual changes associated

with demand fluctuations).

As 700A per phase represents a significant overcurrent it was only applied for a maximum of 20 minutes. The following tests have been conducted:

Six permutations of heating profiles, with applied step currents of

1. 0 - 250A;

2. 0 - 450A;

3. 0 - 700A;

4. 250 - 450A;

5. 250 - 700A; and

6. 450-700A.

Six permutations of cooling profiles (the inverse of the above),

Investigation into the effects of varying the cable starting temperature, and

Determination of the resting temperature at different loading currents in a defined environment

and from a measured start.

Further trials with other sizes and types using the same approach are possible but are outside the scope

of this initial investigation.



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A number of temperature sensors were placed on different parts of the cable. The following diagram

(Figure 5) shows the test arrangement and position of the temperature sensors on a 185mm2 AL

PILSWA cable. Temperatures and currents were logged on data logging computers.

Figure 5. Test Rig Arrangement

Figure 6. Temperature measurement points on cable

Top Core

Bottom Core Bottom sheath

Top Sheath

Top Core

Bottom Core

Bottom sheath

Top Sheath

3phase

generator

Remote control switches

Temperature logger

Current logger Options for external heating and

cooling cable sheaths and

operation of cables in close

proximity are also possible

Water

Pump

Heat

source



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Initial results

Some results from a single test period at 700A per phase for 20 minutes on the PLICSTAS cable can

be seen in figure 7. The heating and cooling curves appear reasonable, in that:

Similar top and lower sheath temperatures are recorded as would be expected.

The duct temperature is similar to the top sheath temperature, but cools faster.

The bottom core temperature, which is affected by adjacent bolted cable lug terminations, is

hotter than the top core temperature.

The top core temperature aligns with operational experience.

Figure 7. Initial results from lab test set-up

Lab Doors

closed

Hot connections nearby affecting

bottom core results –

needs attention

Top –Lower ambient

Top –Lower sheath

Duct temp is similar to top sheath

but cools faster

Top core looks good



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4. Data and Analysis

Cyclic load test

A set of tests were run applying a fixed 500A current, alternating on and off, over a 12-hour period to explore the heating and cooling profiles of the 185mm2 LV PILCSTAS cable sample. Temperature profiles (in Degrees Centigrade) for the bottom core, lead covering, sheath and top core were recorded.

Figure 8 below shows the results of this test and the consistency of temperature response in each

element of the cable due to the applied current.

As expected the top core temperature maximum is more than that for the bottom core, lead and sheath.

Also the rate of heating and cooling is faster for the cores in comparison to sheath and lead, due to the

higher thermal conductivity of the material. Similar results were found from tests using different current

levels.

Figure 8: Cyclic load test results

Heating and cooling profiles

Some examples of heating and cooling profiles for the Bottom core, Lead, Sheath and Top Core are

shown in Figure 9.

The heating or cooling rate of cable components is a function of the temperature difference between

the component and its surroundings. This is dependent on the ambient temperature, cable loading and

the ability of the surrounding environment to transfer heat (thermal conductivity).

In practice the cooling or heating rate of cables will also be affected by unbalanced loads along the

length of cable, and external environment heating or cooling factors such as adjacent cables.

Heating

intervals

Cooling

intervals 500 A load

(not to

scale)



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Figure 9: Measured cable component heating and cooling profiles (Load applied/removed at 00:00:00)

Derivation of Cable Model

Once a number of tests had been run, a “curve fitting tool” was developed, using the test results to

model the time-temperature relationship, based on the following “Newton's Law of Cooling” equation:

𝑌 = 𝐶 + 𝐴(1 − 𝑒−𝑘𝑡)

Where:

Y = Temperature (Degrees Centigrade)

t = Time (Seconds)

C, A and k are parameters related to the cable and its environment

The model can be run for repeated loading/unloaded cycles, and the results summarised, as shown in

the following figure.



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Figure 10: Cable temperature curve fitting tool

In order to demonstrate the difference between the modelled and measured temperature profiles, the heating and cooling profiles were both analysed using the curve fitting tool. The detailed output of the model is presented in Figure 11.

Rat

e o

f T

chan

ge (

TºC

/30

s)

Data A k C x^2

Top core On (2) 57.53 100.645353349 -4.639 28.63402497

T-Tamb

43 Top core Y=C+A(l-exp(-kt))

Row Labels Seconds 2 2pred Error^2

00:00:00 0 -0.73 -4.6

00:00:30 30 -0.62 -2.7

00:01:00 60 -0.03 -0.8

00:01:30 90 1.01 1.1

00:02:00 120 2.4 2.9

00:02:30 150 3.92 4.6

00:03:00 180 5.51 6.2 Only use data after N seconds

00:03:30 210 7.13 7.8 0.5 200

00:04:00 240 8.53 9.4 0.7

00:04:30 270 10.25 10.9 0.4

00:05:00 300 11.87 12.3 0.2

00:05:30 330 13.14 13.7 0.3

00:06:00 360 14.71 15.1 0.1

00:06:30 390 16.07 16.4 0.1

00:07:00 420 17.42 17.6 0.0

00:07:30 450 18.8 18.8 0.0

00:08:00 480 20.06 20.0 0.0

-10

0

10

20

30

40

50

60

0 1000 2000 3000 4000 5000 6000

Ra

te o

f T

cha

nge

(Tº

C/3

0s)

Top core

Print coefficients to "Equations" sheet

Data A k C Ʃ squares

Core On (3) 38.17 0.00149 0.818 14.038

Core On (4) 33.34 0.00151 7.789 13.423

Core On (5) 38.16 0.00162 1.450 9.799

Core On (6) 38.46 0.00152 1.057 15.233

Core On (7) 38.62 0.00146 1.796 20.485

Lead On (3) 33.20 0.00036 0.644 15.545

Lead On (4) 33.11 0.00016 13.081 16.906

Lead On (5) 50.68 0.00017 5.958 10.083

Lead On (6) 32.63 0.00031 4.014 14.682

Lead On (7) 29.77 0.00033 5.388 18.052

Sheath On (3) 80.61 0.00006 2.498 10.140

Sheath On (4) 41.84 0.00007 13.262 11.917

The constants C, A and

k are automatically

calculated based on

measured results



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Figure 11: Temperature simulation and comparison with measured data (from PLICSTAS cable)

It can be seen from Figure 11 that the overall shape of the modelled temperature profile, calculated using the derived values for the constants C, A and k, is similar to the measured profile for all tests. The average values of C, A and k (independently calculated for heating and cooling cycles) are used to model the heating and cooling temperature profiles. The results show that:

1. The parameter A is related to the cable heating and cooling rates and is dependent on the

resistivity of the conductor material. Absolute values of A for heating and cooling are

reasonably similar. A is positive for heating and negative for cooling.

2. The constant “k” influences the curvature of the temperature profile. The same value of k can

be used for heating or cooling profiles with reasonable level of accuracy (about 5°C).

3. C is dependent upon the temperature at the end of last period, which can be used instead of

average C.

Applications

Typical temperature responses to a load step change have been investigated (Figure 8). Using the

methodology described above, the following recommendations are made in order to predict the real-

time temperature of underground cables.

Heating

Cooling

Adopted A, k

and C Max 5˚C

Inaccuracy

Sum of squares

are calculated

from least

square

methodology.

Excel Solver

minimises the

sum of the

squares of the

errors made in

the results of

every single

equation.



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1. Carry out studies to obtain A and k values for a variety of cable types, in various heights

and layouts, using different heating and cooling sources, and ground type;

2. Derive the loading along LV circuits from CGI network analysis tool; and

3. Use the results to create algorithms that can be incorporated in the SOP control

algorithm based upon:

a. Real-time (as opposed to historic) Load conditions;

b. The cables characteristics

c. The cables position and elevation

d. The cable surrounding environment

e. Recent weather conditions

Using a lookup table or specific parameter calculations, an iterative process could be followed to

calculate temperatures for each load step change:

Figure 12: Real-Time temperature determination process

An example of real-time cable temperature rating tool is shown in figure 13.

Additional research questions that should be considered in a future project are:

How to model the thermal storage of the ground?

How to measure and model ground conditions and variability?

How to account for small sections of distributed loaded circuits (with and without generation)?

How results be validated against field trials?

Calculate or estimate the substation

transfer profile

Obtain value of C from previous

days data or the result of the

previous interval

Divide the transfer

profile into 15 minute

intervals

Obtain values of A & k from look

up tables

Calculate the simulated

temperature using the model for the interval

Calculate cable temperatures

using a moving average

Compare the calculated

temperature against limits and identify

constraints.

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Figure 13: Real-Time temperature demonstration tool



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5. Demonstration Plan and Sites

An activity to demonstrate the real-time application of the Maximising Circuit Transfer Capacity process

in real LPN &/or SPN networks could be implemented as part of a future study.

The trial design would demonstrate the ability of the SOP to calculate the temperature of the connected

LV cables. The calculated temperatures would then be validated against the measured temperatures,

and then used in the SOP control system to determine the maximum circuit currents permissible in

order to maximise the network support available without exceeding the cables’ defined thermal limits or

acceptable “Use of Life” rate. Suitable systems for measuring electrical power and asset temperatures

have been developed during 2016 as part of the Electricity North West Celsius NIC project are

described in Appendix c: Field Measurement Systems.

The essential process steps that should be demonstrated are:

1. The calculation of transfer profile currents of cables in real time. This will require significant

further work, outside of the scope of the FUN-LV project, to achieve, as:

The real time application of dynamic power flow systems (e.g. DPlan) are not within

the current FUN-LV scope.

Transfer profiles calculated using customer metered data and standard load profiles

has not been considered to be sufficiently accurate for use. Hence real-time measured

load data would need to be used instead of calculated data, which in practice will only

be available at circuit ends and SOP terminals.

2. Simple algorithms based on measured data, suitable for deployment in the SOP but not

requiring regular downloading of tabular files, but requiring additional memory in the SOP

controller from a system upgrade.

Site selection

The demonstration activity should focus on the following key thermal constraint pinch points:

• Ducted cables;

• Multiple cables in clusters;

• Vertical cables; and

• Cables in an environment with a high ambient temperature;

Thermal constraints caused by small section underground cables are important, but are not expected to be major issues within the selected FUN-LV trial sites. Their issues are therefore not prioritised for demonstration, but are discussed in Appendix A.

The 2-Port SOP has a lower rating than the 3-port Sops, 240kW as oppose to 400kW. It is therefore

less likely than the 3-Port SOP to encounter thermal transfer constraints. In addition, as the 2-Port

SOPs are installed as street furniture, they are not well positioned for the installation of thermal logging

equipment when it is likely that key thermal constraints are most likely to occur inside or in the immediate

vicinity of substations. 3-Port SOPs, which are installed within substations, are therefore considered to

offer a greater opportunity to investigate this subject.

To explore the full range of key thermal constraints it is recommended to select 3-Port sites that have

cables in one or more of the following conditions:

in air;

in close proximity to each other;

in higher ambient temperature conditions;



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in vertical orientation;

with access to externally ducted cables.

This narrows the selection of target sites to those with:

well loaded existing transformers,

vertical and ceiling mounted cables, and

ducted incoming cables.

These criteria exclude LV only substations (with no transformer), those housed in separate GRP

enclosures and those without high level cable runs.

Table 1 below identifies those Method 3 sites that could be considered for the trial. It is proposed that

only one or two sites are considered for demonstration.

ID Substation Comment Suitable

for trial?

LPN Interconnected

3.1i 24410 - Shaftesbury Ave 125 Yes

3.2i 34179 - Bulstrode St Clifton Ford Htl Yes

3.3i 30107 - Nutford Pl Holiday Inn (G) Yes

3.4i 36223 - 36 Pall Mall LV only in footway vault No

LPN Radial

3.2r 30123 - Ellwood Ct Shirland Rd LV only No

3.3r 08070 - Bushey Rd West LV only No

3.4r 90260 - Loughborough Rd Newark Hse LV only No

3.5r 34819 – Alfred Rd Oversley Hse North Ground floor of tower block of flats Yes

SPN Radial

3.1 523637 - Prudential North Street [ T1] Freestanding No

3.2 523280 - Robert Street [T1] Freestanding No

3.3 523036 - Church Street [N2] Basement of large building Yes

3.4 523025 - Kings Road [T1+T2] Under promenade / road Yes Table 1. FUN-LV method 3 sites

It is proposed that the required temperature measurements could be made using the Klik-Fit Griffin

units that were used in the initial FUN-LV site selection process. Alternatively, new equipment could be

used.



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Recommended Demonstration sites

All of the following sites have Transformers, LV cables at high level with some vertical rise and access

to external ducts.

ID Substation Photo Comment

LPN Interconnected

3.1i 24410 - Shaftesbury

Ave 125

Site has LV cables at

high level with some

vertical rise and

access to external

ducts.

3.2i 34179 - Bulstrode St

Clifton Ford Htl

Site has LV cables

running at high level

over a Transformer

with some vertical

rise and access to

external ducts.

3.3i 30107 - Nutford Pl

Holiday Inn (G)

Site has LV cables


over a Transformer

with some vertical

rise and access to

external ducts.



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ID Substation Photo Comment

SPN Radial

3.1 523637 - Prudential

North Street [ T1]

Site has LV cables


over a Transformer

with some vertical

rise and access to

external ducts.

3.3 523036 - Church

Street [N2]

Site has LV cables

with vertical rise, but

the transformer and

LV board are located

on the floor above.

The transformer is

well away from LV

cables.

3.4 523025 - Kings Road

[T1+T2]

Site has LV cables


over a Transformer

with a vertical rise

bank.

Table 2. Recommended demonstration sites



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6. Summary and conclusions

Background research indicates that dynamic ratings have potential to deliver increases of between 5

and 20% in cable current carrying capacity using historic and real-time data [2]. The key inputs in

determining dynamic ratings are day-ahead load and temperature prediction, and factors associated

with the cables and surrounding environment. Lookup tables have been developed and used by the

University of Southampton based on laboratory tests [1]. However, this approach is not well suited to

Maximising Circuit Transfer Capacity and the scale of work required to develop a similar approach for

FUN-LV is both outside of the project scope and would require large scale monitoring / validation of

distributed buried cable temperatures.

In order to demonstrate the concept of real-time temperature prediction and dynamic rating a test rig

has been built to enable a current injection in steps of approximately 250A, 450A and 700A per phase.

The results indicated that the concept of real-time temperature prediction and dynamic rating can be

demonstrated using a time-temperature relationship; which was validated by comparing experimental

results against a model. An example tool has been developed and the steps required to validate the

tool have been detailed. The key parameters in the real-time temperature equation used in the model,

A, C and k, can be determined from trials.

A site selection activity was carried out in order to identify candidate FUN-LV sites for a potential future

dynamic rating demonstration. The recommended sites are:

LPN

24410 - Shaftesbury Ave 125

34179 - Bulstrode St Clifton Ford Htl

30107 - Nutford Pl Holiday Inn (G)

SPN

523637 - Prudential North Street [ T1 ]

523036 - Church Street [ N2 ]

523025 - Kings Road [T1+T2]

Whilst all the sites are suitable those in bold are prioritised as the most appropriate for initial trials.

These sites have the highest potential for demonstrating the impact of heat on high level LV cables and

consequentially the greatest potential for using the SOP to maximise the capacity of these LV circuits

to within thermal limits.



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Appendix A: Small Section Cables

Although not identified in the FUN-LV demonstration circuits, there are credible small section circuit

constraint scenarios, both with and without generation connected. In the following examples the arrows

represent units of loading and the thickness of the lines represent the rating of circuits. Small section

constraints are ringed in red.

Figure 14. Examples of small section circuit constraints

For the FUN-LV demonstration networks no significant small section constraints were identified, as the

Spine circuits in these networks are of uniform equivalent section, and the generation connected to the

distribution cables is at present too small to have a significant impact on ratings. Larger generation is

generally being connected direct to the LV board via dedicated separate cables.



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The rating of a cable section could be artificially constrained, to simulate a small section for

demonstration purposes. However:

The temperature of buried cable sections in the field trials cannot be easily measured to validate

the results; and

The measurement would be of the actual installed cable, and not of the small section simulation,

so validation would not be possible.



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Appendix B: Examples of FUN-LV Load Transfer Profiles and Asset Guarding

Transfer Profiles

The transfer profile created by SOPs is a function of the difference between the transformer load profiles

and utilisations, the spine circuit loading and length and any utilisation bandwidth threshold or asset

guarding settings on the SOP.

In practice the transfers vary widely including:

Those that comprise occasional short bursts, equalising demand peaks;

Those that vary over the course of a day in a similar manner to a conventional load profile; and

Those that operate almost continuously.

The transfer profiles are dynamic and can change rapidly in response to changes in loading conditions,

as well as during network support following an HV or LV circuit fault.

Figure 15. Examples of SOP Transfer profiles

There is therefore no simple rule that can be generically applied to estabish what would be reasonable loading limits for transfer profiles in the way that has been historically applied to conventional load profiles. It is also notable that the transfers demonstrated in the field trials were limited so as to not have a detrimental effect on any asset life.



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SOP Asset Guarding

SOPs use a range of Asst Guarding features that can be used to control the circuit loading as shown in Fig 16.

Figure 16. Example of SOP Asset Guarding limits

Although the 2-port SOP device rating is 240 kVA, the evening transfer in shown in figure 16 clearly shows limiting at 150 kW on consecutive days. This reduced export limit was set during the initial trial period of this device to validate control of export to a predefined limited such as would be presented by an LV circuit with a restricted rating. This limit could equally be set by a dynamic maximum power transfer algorithm. During commissioning tests on the 3 port SOP at Prudential North in Brighton the operation of the Asset guarding function was validated for a very short period of loading to the fully rated 400kW capacity of the SOP at which point the Asset Guarding operated. SOP Asset guarding settings are presently set to reflect standard ratings based on typical conventional load profile ratings, and LV network voltages.

Test 150kW limit



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Appendix C: Field Measurement System In order to validate the developed algorithms for estimating cable temperature in optional field conditions suitable sensors are required to measure the temperature of:

HV and LV cable surfaces; Transformer and switchgear external surfaces; and Ambient air.

Also required are suitable commissioning, communication and backend systems to provide data that can be integrated with SOP Port data for performance analysis and tuning. The KeLVN Power and Temperature wireless monitoring system has been developed during 2016 as part of the ENW Celsius NIC project. Installations in ENW and UKPN have demonstrated the simplicity of installation and the suitability of the system for undertaking the trial set out in section 5 of this document in a future project.

Figure 17. The KeLVN Power and Temperature wireless monitoring system



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Appendix D: Milestone 3.14 Scope

A meeting was held between Ricardo Energy & Environment and the FUN-LV Technical Lead on 20th

April 2014 to discuss the scope of the Maximising Circuit Transfer Capacity activity.

The scope of the activity has changed since the inception of the milestone descriptions for a number of

reasons. These include:

• The original aim of the activity was to predict and use real-time transfer profiles. However, neither

GE nor CGI have resources or scope to incorporate this functionality. Further the FUN-LV

demonstrations indicate that the thermal constraints appear to be at circuit ends in substations.

• While there is potential to incorporate the outcomes into the SOP control algorithm using real-time

data, there are potential constraints around the amount of working memory available in the devices.

This could be alleviated to some extent by upgrading the Programmable Logic Controller. However,

this would not be possible within the project timescales.

• Setting up and running the lab tests to obtain data for an algorithmic approach was more complex

than anticipated, and the project budget and timescales precluded further expenditure.

It was therefore agreed that the revised aim of the activity would be to complete the laboratory tests in

order to provide insight into short-term maximum transfers. It was proposed that the scope for this

activity would be restricted to:

• Completion of the final lab tests

• Finalise the algorithms that model thermal heating and cooling paths against circuit loading

• Document the concepts for tracking and predicting circuit temperatures from real time loading

measurements

• Document the milestone activity and results so far, including learning points from the field trials such

as the impact of transfer profiles on assets and the effect of asset guarding limits.

• Make recommendations for the next steps required for development of the concept and a limited

field demonstration trial on one or two 3-port sites once they are fully operational



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References

[1] Dynamic Cable Ratings for Smarter Grids; R. Huang, J. A. Pilgrim and P. L. Lewin; 2013 4th IEEE

PES Innovative Smart Grid Technologies Europe (ISGT Europe), October 6-9, Copenhagen

[2] The use of real-time monitoring and dynamic ratings for power delivery systems and the Implications

for dielectric materials; S. Walldorf, J. Englehardt and F. Hoppe; IEEE Electrical Insulation Magazine,

Volume 15, pp 28-33; 1999

milestone 3.14 maximising circuit transfer...

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