Harris Distribution Substation - Earthing Calculations Report - ESL0412-

ERA TECHNOLOGY TŶ CANOL CLUN AVENUE PONTYCLUN SOUTH WALES CF72 9AG Tel: +44 (0)1443 239503 Fax: +44 (0)1443 231185 Email: [email protected]

UTILITIES VENDOR DATABASE Achilles Supplier Number: 061760

RTEMP01 ISSUE 13 17/07/14

ERA Technology is a trading name of Earthing Solutions Ltd

Earthing Calculations

for

Harris 6.6kV Distribution Substation

(Norbert Dentressangle Logistics)

Report Number

ESL0412-R01

Client: ENWL

Client Contact: Paul Griffiths

Author: ______________________

David Reed

Engineer

Contact Details: [email protected]

+44 (0)1443 239503

3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation

© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page i

Approved By: ______________________

Mayur Gaglani

Principal Engineering Consultant

Revision Date Prepared Approved Notes

0 17/09/14 DR MG Original Issue

A 03/10/14 DR MG Updated fault Levels Provided

B

C

© Earthing Solutions Limited 2014

All Rights Reserved

This report and associated drawing(s) (where applicable) have been produced

by Earthing Solutions Ltd and may not be reproduced or distributed outside of the

recipient’s organisation (either in part or in full) without permission.

If received electronically, the recipient is permitted to make such copies as are

necessary to: view the document on a computer system; comply with a

reasonable corporate computer data protection and back-up policy and

produce one paper copy for personal use.

The calculations contained within this report are based on information supplied

by the client and/or measurements carried out by Earthing Solutions Ltd (unless

otherwise stated). It is the responsibility of the client to ensure that any

rectification or installation work are carried out as per recommendations

contained within this report and associated drawing(s) (where applicable), and in

compliance with the relevant Distribution Network Operator (DNO) policies and

safety documents. Earthing Solutions Ltd shall not be liable for any incidents or

costs incurred due to inaccurate information or incorrect installation.


© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page ii

Contents

Page No.

Summary of Information 1

Technical Data 1

Main Report 2

1. Introduction 2

2. Soil Resistivity 3

3. Existing Overall Earth Value 4

4. Fault Current Distribution 5

5. Earth Potential Rise (EPR) 5

6. Touch Voltages 5

7. Recommendations 6

8. Applicable Standards 7

Appendix A - Measurement Locations 8

Appendix B – FOP Measurement 2 Data 9


© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 1

Summary of Information

Technical Data Soil Resistivity Model

Layer Resistivity (Ωm) Thickness (m)

1 630 2.0

2 28 7.1

3 15 6.6

4 167 ∞

Earth Resistance

System Elements Resistance (Ω) Determination Method

Existing Overall Earthing System 0.112 Measured

Earth Fault Current

Voltage Level (kV) Total Fault Current (A) Ground Return Current (A)

6.6 1123 420

Earth Potential Rise

Voltage Level (kV) EPR (V) Status

6.6 47 COLD

Overall Classification COLD

Touch Voltages - Compliance with BS EN 50522 Limits

Voltage Level (kV) Complies with BS EN 50522 Limits

on Chippings

Complies with BS EN 50522 Limits

on Soil

6.6 YES YES



Main Report

1. Introduction

ENWL have asked for some earthing calculations at Norbert Dentressangle Logistics (SJ 79852

95974) to be carried out. This is required as part of an HSE request. The work carried out is

summarised below.

Carry out soil resistivity soundings using the Wenner Method and derive a representative soil

resistivity model.

Carry out a fall of potential (FOP) earth resistance measurement from the existing main

intake substation (Harris 6.6kV Distribution Substation).

Estimate the ground return current for phase to earth faults at the substation and calculate

the Earth Potential Rise (EPR).

Check that the touch voltages are below BS EN 50522 permitted limits.



1.0

10.0

100.0

1000.0

1.0 10.0 100.0

Ap

pa

ren

t R

es

isti

vit

y (Ω.m

)

Wenner Spacing (m)

SR1

SR2

SR3

SR4

Model

Measured

Resistance

(Ω)

Apparent

Resistivity

(Ωm)

Measured

Resistance

(Ω)

Apparent

Resistivity

(Ωm)

Measured

Resistance

(Ω)

Apparent

Resistivity

(Ωm)

Measured

Resistance

(Ω)

Apparent

Resistivity

(Ωm)

1.0 19.900 125.04 127.500 801.11 7.480 47.00 7.220 45.36

1.5 14.430 136.00 81.700 770.00 4.640 43.73 3.620 34.12

2.0 9.840 123.65 51.800 650.94 2.520 31.67 2.550 32.04

3.0 5.670 106.88 17.720 334.01 1.329 25.05 1.273 24.00

4.5 3.500 98.96 7.290 206.12 1.057 29.89 0.921 26.04

6.0 1.950 73.51 3.200 120.64 0.837 31.55 0.710 26.77

9.0 0.610 34.49 0.543 30.71 0.525 29.69 0.491 27.77

13.5 0.270 22.90 0.226 19.17 0.352 29.86 0.361 30.62

18.0 - - 0.253 28.61 0.280 31.67 0.281 31.78

27.0 0.080 13.57 - - 0.208 35.29 0.196 33.25

36.0 - - - - 0.194 43.88 0.161 36.42

54.0 - - - - 0.288 97.72 0.202 68.54

Wenner

Spacing (m)

SR3SR1 SR2 SR4

2. Soil Resistivity

Four soil resistivity soundings were carried out on 10th September 2014 using the Wenner Method

and a Megger DET 2/2 instrument. The measurement locations are shown in Appendix A. The

measurement data are shown in Figure 2.1 and Table 2.1 below. The soil resistivity model derived

is shown on the Summary of Information page.

Figure 2.1: Soil Resistivity Data and Model Curve

Table 2.1: Soil Resistivity Data



0.000

0.100

0.200

0.300

0.400

0.500

0.600

0 10 20 30 40 50 60 70 80 90 100

Me

as

ure

d R

esis

tan

ce (Ω)

Potential Probe Position (m)

100

(m)(% of Distance to

Current Probe)

90 90.0 0.487

80 80.0 0.180

70 70.0 0.129

60 60.0 0.109

50 50.0 0.098

40 40.0 0.085

30 30.0 0.062

20 20.0 0.062

10 10.0 0.052

Distance to Current Probe (m):

Potential Probe PositionMeasured

Resistance (Ω)

System Elements Resistance (Ω) Interpretation Method

Harris Distribution Substation

Overall Earthing System'61.8% Rule'0.112

3. Existing Overall Earth Value

An earth resistance measurement was carried out on 10th September 2014 using the fall of

potential method and a Megger DET 2/2 instrument with the remote current electrode located

100m away was carried out from the main intake substation. Due to the short traverse of the test,

a second test was carried out along a different route to verify the results. The measurement data

for the first FOP test route is shown in Figure 3.1 and Table 3.1 below, along with the interpreted

earth resistance in Table 3.2. The measurement data for the second FOP test route is shown in

Appendix B. The measurement routes are shown in Appendix A.

Figure 3.1: Fall of Potential Curve

Table 3.1: Fall of Potential Measurement Data

Table 3.2: Interpreted Measured Resistance



4. Fault Current Distribution

4.1 Fault Current

The earth fault level and fault clearance time is 1.123kA and 1s respectively. Based upon this fault

clearance time, the 430V ITU threshold limit is applicable.

The 6.6kV supply arrangement from the source Primary 33/6.6kV substation (Chester Road) is via a

continuous underground cable. For earth faults at the main intake substation, there will be a path

back to source, via the supply cable sheaths and earth electrode connections. Current, which

returns using a metallic route such as the cable sheath, will not contribute significantly to the

consequential EPR at the site. Only the component, which returns through the soil, will do this. The

split of current between the ground and cable sheaths has been calculated using industry

standard routines and the methodology described ENA ER S34.

Table 4.1: Fault Current

6.6kV Fault

Total Fault Current (A) 1123

Proportion of Current following

Ground Return Path (%) <37.4

Ground Return Current (A) <420

5. Earth Potential Rise (EPR)

Table 5.1: Calculated EPR

6.6kV Fault

Ground Return Current (A) 420

Earth Resistance (Ω) 0.112

Earth Potential Rise (V) 47

ITU Voltage Limit (V) 430

Site Classification COLD

ENWL have confirmed that Chester Road substation is classified as a ‘cold’ site, so there will be no

transfer potential hazard and therefore Harris Distribution substation will be classified as ‘cold’.

6. Touch Voltages Assuming that the fault clearance time is 1s, the allowable Touch Voltage limits in accordance

with BS EN 50522 are shown in Table 6.1:

Table 6.1 Maximum Touch Voltages and Compliance with BS EN 50522 Limits

Clearance

Time (s)

Limit on Chippings

(V)

Limit on Soil

(V)

1 298 233

As the maximum calculated EPR (47V) is below the permitted touch voltage limits (233V on soil,

298V on stone chippings), then the distribution substation and the rest of the site can be deemed

safe.



7. Recommendations

Action

It is not known if the low earth value at the site is due to the in ground copper installed or the

contribution from the site network. It is recommended that the earthing system of each

distribution substation is reviewed to comply with modern standards in case any of the

substations are inadvertently disconnected from the network, i.e. each substation’s earthing

system in isolation should provide touch voltage control.

Carry out periodic testing to ensure the low overall earth value is maintained into the future.



8. Applicable Standards

ENA Technical Specification 41-24, “Guidelines for the Design, Installation, Testing and

Maintenance of Main Earthing Systems in Substations”, Issue 1, 1992 (Amended 1999),

published by Energy Networks Association.

ENA Engineering Recommendation S34, “A Guide for Assessing the Rise of Earth Potential at

Substation Sites”, 1986 (Amended 1986, 1988), published by Energy Networks Association.

ENA Engineering Recommendation S36, “Procedure to Identify and Record ‘Hot’

Substations”, 1988, published by Energy Networks Association.

BS EN 50522 “Earthing of Power Installations Exceeding 1kV A.C.”, 2010, Published by British

Standards Institute.



Appendix A - Measurement Locations

Figure A.1: Measurement Locations

Table A.1: Measurement Location Coordinates

Site FOP 1 FOP 2 SR1 SR2 SR3 SR4

Latitude /

Longitude *

53°

27.560'N

53°

27.655'N

53°

27.603'N

53°

27.613'N

53°

27.511'N

53°

27.510'N

53°

27.510'N

2°

18.300'W

2°

18.323'W

2°

18.160'W

2°

18.233'W

2°

18.433'W

2°

17.932'W

2°

17.932'W

Note:

* Refers to main entrance (Site), current probe location (FOP measurement) or centre of traverse (SR

measurement)

Site personnel: Amy Pears, Louise Christopher

SR1

SR2

FOP 1

FOP 2

SR3

SR4



0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

0.500

0 10 20 30 40 50 60 70 80 90 100

Me

as

ure

d R

esis

tan

ce (Ω)

Potential Probe Position (m)

100

(m)(% of Distance to

Current Probe)

90 90.0 0.461

80 80.0 0.224

70 70.0 0.185

60 60.0 0.154

50 50.0 0.125

40 40.0 0.098

30 30.0 0.090

20 20.0 0.091

10 10.0 0.079

Distance to Current Probe (m):

Potential Probe PositionMeasured

Resistance (Ω)

System Elements Resistance (Ω) Interpretation Method

Hill Top Overall Earthing

System'61.8% Rule'0.160

Appendix B – FOP Measurement 2 Data

Documents

Harris Distribution Substation - Earthing Calculations Report - ESL0412-