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.
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© 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
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© 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
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 2
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.
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 3
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
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 4
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
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 5
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.
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 6
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.
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 7
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.
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 8
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
3 October 2014 Earthing Calculations Report Harris 6.6kV Distribution Substation
© Earthing Solutions Ltd ESL0412-R01 (Rev A) Page 9
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