Earthing Calculations for
Harris 6.6kV Distribution Substation (Norbert Dentressangle Logistics) Report Number
ESL0412-R01
Client: Client Contact:
ENWL Paul Griffiths
Author:
______________________ David Reed Engineer
Contact Details:
[email protected] [email protected] +44 (0)1443 239503
ERA TECHNOLOGY
TŶ CANOL CLUN AVENUE PONTYCLUN SOUTH WALES CF72 9AG Tel: +44 (0)1443 239503 Fax: +44 (0)1443 231185 Email:
[email protected]
ERA Technology is a trading name of Earthing Solutions Ltd
UTILITIES VENDOR DATABASE Achilles Supplier Number: 061760
RTEMP01 ISSUE 13 17/07/14
3 October 2014
Earthing Calculations Report
Approved By:
Harris 6.6kV Distribution Substation
______________________ 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 i
3 October 2014
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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 ii
3 October 2014
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 1
3 October 2014
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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.
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 2
3 October 2014
2.
Earthing Calculations Report
Harris 6.6kV Distribution Substation
Soil Resistivity
Four soil resistivity soundings were carried out on 10 th 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. 1000.0
) m .
100.0
Ω (
y t i v i t s i s e R t n e r a p p A
SR1 SR2 SR3 SR4 Model
10.0
1.0 1.0
10.0
100.0
Wenner Spacing (m)
Figure 2.1: Soil Resistivity Data and Model Curve SR1
SR2
SR3
SR4
Wenner Spacing (m)
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
Table 2.1: Soil Resistivity Data
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 3
3 October 2014
3.
Earthing Calculations Report
Harris 6.6kV Distribution Substation
Existing Overall Earth Value
An earth resistance measurement was carried out on 10 th 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. 0.600
0.500
0.400
) Ω
( e c n a t s i s e 0.300 R d e r u s a e M 0.200
0.100
0.000 0
10
20
30
40
50
60
70
80
90
100
Potential Probe Position (m)
Figure 3.1: Fall of Potential Curve Distance to Curr ent Probe (m): Potential Probe Position
100
Measured Resistance ( Ω)
(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
Table 3.1: Fall of Potential Measurement Data System Elements
Resistance ( Ω)
Interpretation Method
Harris Distribution Substation Overall Eart hing System
0.112
'61.8% Rule'
Table 3.2: Interpreted Measured Resistance
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 4
3 October 2014
4.
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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
5.
Total Fault Current (A)
1123
Proportion of Current following Ground Return Path (%)
<37.4
Ground Return Current (A)
<420
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 a nd Compliance with BS EN 50522 Limits Clearance Time (s) 1
Limit on Chippings (V) 298
Limit on Soil (V) 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.
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 5
3 October 2014
7.
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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 f rom 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.
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 6
3 October 2014
8.
Earthing Calculations Report
Harris 6.6kV Distribution Substation
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 Ris e of Earth Potential at Substation Sites”, 1986 (Amended 1986, 1988), published by Energy Networks Association. ENA Engineering Recommendation S36, “Procedure to Identify Substations”, 1988, published by Energy Networks Association.
and
Record ‘Hot’
BS EN 50522 “Earthing of Power Installations Exceeding 1kV A.C.”, 2010, Published by British Standards Institute.
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 7
3 October 2014
Earthing Calculations Report
Harris 6.6kV Distribution Substation
Appendix A - Measurement Locations FOP 2
SR1 FOP 1
SR3
SR4
SR2
Figure A.1: Measurement Locations
Table A.1: Measurement Location Coordinates
Latitude / Longitude *
Site
FOP 1
FOP 2
SR1
SR2
SR3
SR4
53° 27.560'N 2° 18.300'W
53° 27.655'N 2° 18.323'W
53° 27.603'N 2° 18.160'W
53° 27.613'N 2° 18.233'W
53° 27.511'N 2° 18.433'W
53° 27.510'N 2° 17.932'W
53° 27.510'N 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
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 8
3 October 2014
Earthing Calculations Report
Harris 6.6kV Distribution Substation
Appendix B – FOP Measurement 2 Data
0.500
0.450
0.400
0.350
) Ω (
e 0.300 c n a t s i s e 0.250 R d e r u s 0.200 a e M 0.150
0.100
0.050
0.000 0
10
20
30
40
50
60
70
80
90
100
Potential Probe Position (m)
Distance to Current Probe (m): Potential Probe Position
100
Measured Resistance (Ω)
(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
System Elements
Resistance ( Ω)
Interpretation Method
Hill Top Overall Earthing System
0.160
'61.8% Rule'
© Earthing Solutions Ltd
ESL0412-R01 (Rev A)
Page 9
