3. Equipment Requiring both Safety and System Grounds
3.1 Power
Transformer Tanks
Power
transformer tanks shall be safety grounded at two points diagonally opposite to
each other. These connections shall be made from two different points of the
grounding grid.
A
separate system ground shall be provided for the neutral of the transformer by
means of two stranded copper wires as the ground grid conductor size.
The
neutral grounding wires shall be insulated from the transformer tank by support
insulators mounted on the tank wall and shall be connected to the grounding
grid directly.
Independently
mounted radiator bank and XLPE cable termination boxes shall be separately
grounded at two diagonally opposite locations.
3.2 Instrument
Transformers
Potential
and current transformers shall have their metal case grounded.
The
grounding terminal of the potential and current transformers shall be connected
to the grounding grid. The neutral point of the secondary connection of
potential and current transformer shall be grounded to the ground grid in the
control/relay room to reduce the transient over-voltages.
3.3 Surge
Arrestor
For
lightning arrestor with operation counter, the insulated lower end of the
lightning arrestor shall be connected to the operation counter with an
insulated coated copper conductor with cross section area not less then 50 mm2.
The surge arrestor ground terminal shall be connected to the ground grid via
two stranded copper conductors.
The
system ground conductor shall be as short as possible, free of sharp bends as
possible, and shall not be installed in metallic conduit. In addition, ground
rods shall be driven adjacent to the arrester connection to the grounding grid
to provide the lowest ground grid resistance at this point.
3.4 Station
Auxiliary Transformer
Station
auxiliary transformer tank shall be safety grounded at two locations. One
system ground shall be directly connected to the neutral bushing of wye-connected windings that are to be solidly grounded.
3.5 Shunt
Capacitors and Reactors
Shunt
capacitors and reactors are considered safety grounded when mounted on a metal
structure that is connected to the grounding grid. One system ground conductor
shall be connected to the grounding grid when the capacitors are to be
connected in a grounded star configuration.
3.6 Coupling
Capacitor Voltage Transformers (CCVTs)
CCVTs
shall be safety grounded at two locations.
4. Lightning
Protection
- The
substation shall be protected against direct lightning strokes by shield wires
or lightning masts.
- The
lightning protection system must be designed to provide a sufficiently low
impedance that the lightning energy will follow the required route.
- Lightning
masts with a suitable height shall be located on the top of the substation metal
structure to provide the required protection zones for circuits and apparatus
in the whole switchyard (i.e all structures and buildings).
- The
control building shall be protected against direct lightning strokes by
lightning masts, down conductor, driven rod, etc..
- Masts
or overhead wires (shield wires), or both, may be used. Combination of overhead
wires and lightning masts must be evaluated during the design work.
- Down
conductors shall be connected to each lightning mast/ overhead wire (shield wire)
with ground terminals (at least in two points).
- Down conductors shall be copper
240/185 mm2.
- The
lightning masts shall be copper, the overhead wires (shield wires) shall be 75
mm2 st.
5. Marking
5.1 language
All
markings shall be in Arabic and English and shall be legible and indelible.
5.2 marking on conductor drums
-
Size of conductor.
-
Exact length in meters.
-
Stranding.
-
Net weight in kg.
-
Gross weight in kg.
-
Arrow showing correct direction for rolling (which is the opposite to
the direction of unwinding) with instruction “ROLL THIS WAY”.
-
Drum number.
-
Manufacturer’s name and country of origin.
-
Year of manufacture.
-
Purchaser’s order number.
-
Purchaser’s name and address.
-
Shipping destination.
-
Stores/site destination.
In addition each end of conductor on a drum shall bear
a non-corroding tag written in English and Arabic with the first five items
listed above on it.
5.3 connectors
All
connectors and moulds for connections shall be clearly stamped with the
appropriate conductor size or sizes in the case of “tee” connectors or
crossing.
5.4 ground rods
Each
rod shall be marked with its diameter, length and manufacturer’s mark.
6.
testing and inspection
6.1 soil
resistivity test
The
soil resistivity shall be measured during summer season before the
design of the grounding system, the measuring procedure shall be submitted.
Measured
procedures shall be under the supervision of the purchaser representatives. If
there is difference between the value given in the tender soil investigation
report and that measured by the contractor, the system shall be designed under
the worst one.
In
case of backfilling, measurement shall be taken to ensure that the backfilled
soil resistivity is the same as, or better than before backfilling.
6.2 ground resistance
Tests
shall be made on the effectiveness of the bonding and grounding, which will
include conductivity tests on selected joints on the main grounding system, and
at the connections to equipment and structures. Checks shall also be made on
precautions taken to avoid corrosion attach on the grounding system.
The
ground resistance shall be measured during the installation and on the
completion as follows for:
a) Each ground rods after driving.
b) The ground grid after completion
and backfilling of the trenches.
c) Each group of ground rods or test
point after completion of the connection from the test link terminal.
d) The completed installation
without any connections outside the substation.
Facilities for measuring the ground grid resistance
shall be provided from at least four points, access to these points and
connections with measuring instruments should be easy and approved by purchaser
engineers.
The tests shall be carried out by a method and with
equipment approved by the purchaser . All tests to be witnessed and the
equipment and method used recorded with the test results.
The correct functioning of all isolation links shall
also be checked.
6.3 Testing
of material
6.3.1 All
grounding materials shall be tested in accordance with the latest edition of
the referenced standards and as specified herein. Following completion of the
tests, two certified copies of the test reports shall be submitted for
approval. No grounding materials shall be shipped until the test reports have
been approved by the purchaser. The purchaser, at his discretion, may waive
type test requirements, where type tests have previously been carried out and
where acceptable type test certificates are provide by the supplier.
The
acceptance of such type test certificates shall be based on the stated
requirements for type testing contained in this specification.
6.3.2 Validity of Test Certificates
Test
certificates are considered valid if the tests have been carried out within the
last ten years on equipment identical to that on offer using test methods
outlined in this specification.
6.3.3 Location
of Tests
Routine
and/or special tests shall be carried out at the supplier’s factory.
Type
tests shall be carried out at an approved independent testing laboratory or at
the supplier’s laboratory and be witnessed by a representative of an approved
independent testing laboratory or other representative acceptable to the
purchaser.
6.4 inspection
The
purchaser may wish to witness tests or to visit the factory during manufacture
of any or all items covered by this specification. Accordingly, the supplier
shall give the purchaser adequate notice of manufacturing schedules and one
month’s notice of test schedules.
The
inspector(s) shall have free access during normal working hours to the shop and
testing laboratories in connection with the inspection and testing materials.
6.5 tests
6.5.1 Tests on
copper clad steel wire:
According to ASTM B227-70 clauses as
listed hereunder:
-
Twist test in accordance with clause 9.
-
Elongation test in accordance with clause 4.4.
-
Resistance test in accordance with ASTM method B 193.
6.5.2 Test on
Soft-Drawn Stranded Copper conductors
6.5.2.1 Before
Stranding
According
to IEC 61089 clauses as listed hereunder:
-
Tensile test in accordance with clause 11.1.
-
Elongation test in accordance with clause 11.2.
-
Wrapping test in accordance with clause 11.3.1 and 11.3.3.
-
Electrical resistance test in accordance with clause 12.
Table (9): Soft Drawn
Stranded Copper
Physical And Electrical
Properties
|
Size sq. mm. |
No. of Stranding and
diameter of wire (mm) |
Approx. overall
diameter mm |
Weight of wire kg/km |
Theoretical breaking
load KN |
|
35 |
7/2.5 |
7.5 |
310 |
13.77 |
|
50 |
19/1.8 |
9.0 |
437 |
19.38 |
|
95 |
19/2.5 |
12.5 |
845 |
37.89 |
|
150 |
37/2.25 |
15.80 |
1337 |
58.98 |
|
240 |
61/2.25 |
20.2 |
2209 |
97.23 |
- Diameter
measurement and the results compared with those in table 9. The wrapping test,
for durability, shall consist of warping the copper wire 6 times around a wire
of its own diameter, unwrapping and rewrapping without breakage of the wire.
6.5.2.2 Tests on Copper Wires After Stranding
These
tests which are the same as those listed in item 6.5.2.1 shall be carried out
on samples of the finished conductor.
6.5.2.3
Tests on Complete Conductor
These tests shall consist of:
Measurement of lay ratio of each
layer.
Tensile
strength calculated from the results of the individual wire tests as in IEC
61089.
Measurement of weight.
Measurement of resistance.
6.5.3
Tests on Connectors
Proof
of current rating and mechanical pull-out strength shall be provided by the
manufacturer for each type of connector offered.
6.5.4 Test on Copper Ground Rods
6.5.4.1 Testing of Bond Between Copper And
Steel.
A 150
mm length of rod with one end cut to 45 degree point shall be driven between
two steel clamping jaws of a vice set at mm less than the diameter of the rod
so as to shear off sufficient metal to expose the joint between the jacket and
the rod.
6.5.4.2
Bending
There
shall be no evidence of cracking of the copper jacket if at room temperature a
length of the rod is rigidly held in a vice and the free end bent by applying
force normal to the rod at a distance from the clamping device equal to 40
times the diameter of the rod. The magnitude of the force and the direction of
application shall be such that the rod is permanently bent through a 30 degree
angle.
7.
sampling
7.1 tests on wires before stranding
According
to IEC 61089.
Tests
shall be carried out on samples of individual wires taken from not less than
10% of the individual lengths or wire which will be included in any one
consignment. Each sample shall be of sufficient length to provide one test
specimen for each or the appropriate tests.
7.2 acceptance tests on wires after stranding
According
to IEC 61089.
Tests
shall be carried out on wires from samples of finished conductor taken from not
less than 10% of the drums included in any one consignment. Each sample shall
be of sufficient length to provide, for each wire of the conductor, one test
specimen for each of the appropriate tests.
7.3 acceptance tests on complete conductor
According
to IEC 61089.
Tests
shall be carried out on samples of finished conductor taken from not less than
10% of the drums included in any one consignment. Each sample shall be of
sufficient length to provide one test specimen for each of the appropriate
tests.
7.4 acceptance tests on flexible leads
Tests
shall be carried out on samples selected according to test schedules mentioned
later.
7.5 copper-clad steel wire
In
accordance with ASTM B227-70 clause 4.
8.
method of test
- All
tests shall be carried out in accordance with the aforementioned
specifications as outlined previously.
The
attached test schedules specify the relevant clauses.
9.
acceptance and rejection
9.1 general
- The
supplier shall forward to the purchaser , three (3) copies of certificates
proving that all the required tests have been carried out and that the
materials and construction comply with the specified requirements in the attached
test schedule. No deliveries of grounding materials shall be made prior to
approval by the purchaser of the test certificates.
9.2 grounding conductors
If ,
on testing a sample from any drum, the results do not conform to the
requirements, two additional samples shall be taken from the same drum and
tested. Both of these samples shall conform to the requirements, otherwise the
drum shall be rejected. Samples shall then be taken from all drums comprising
the consignment, and tested. If a sample from any drum does not conform to the
requirements, then that drum shall be rejected.
If
the number of drums rejected exceeds 20% of the the complete number of drums in
the consignment, the complete consignment shall be rejected.
10.
delivery
10.1 Packing
and shipment :
10.1.1 Conductors
10.1.1.1 All conductors shall be wound on strong,
non-returnable wooden drums suitably treated for outdoor storage and capable of
withstanding all normal transportation and handling. All nails and metallic
parts on the inner surface must be countersunk so that they cannot damage the
conductor. All old nails remaining from previous use of the drum shall be
removed. Drums shall not be treated with chemicals injurious to the conductors.
A round spindle hold of minimum diameter 80 mm is required at the center of all
wooden drums.
10.1.1.2 Each drum shall be clearly marked with the
supplier’s name, purchaser order no., conductor size and length, drum serial
no., and gross weight.
10.1.1.3 The drums shall be close lagged after
filling. Wooden battens shall be nailed at each end to the drum flange and also
secured by two steel straps.
10.1.1.4 All drums shall be fitted with steel hubs
having a minimum inside diameter of 80 mm. The ratio of the diameter of the
inside barrel and the diameter of the flange must not be less than 0.48.
10.1.1.5 The timber to be used shall be new, dry,
properly seasoned and suitably treated to stand changes in temperature and
humidity without deterioration or shrinking.
The
timber shall be sufficiently hard and compact to hold the nails and must be
treated with a fungicidal and germicidal termite and white ant proof
preservative prior to painting.
All
drums shall be painted inside and outside with aluminum paint.
10.1.1.6 Nails shall be fitted with proper care to
avoid any contact with the conductor. Nailing shall be executed from the inside
toward the outside. The nail heads shall be embedded into the flange for
approximately 6 mm, while their points shall be sufficiently long to allow a proper
riveting of about 15 mm. The spacing of the nails shall be approximately 70 mm.
10.1.1.7 The inner wrapping of the drum shall be made
with a double layer of waterproof paper and another layer shall be placed over
the conductor under the lagging.
One
layer of waterproof paper must be inserted underneath the last layer of
conductor on the drum to avoid sliding against the inner layer. Moreover the
conductor shall be tied, at the beginning of the last outer turn, back to one
flange with a suitable string and the outer end stapled to the other flange to
avoid the conductor moving from the correct position.
10.1.1.8 A piece of conductor 45 cm long shall be left
sticking out of the flange hole.
The
extreme end of the conductor shall be tied, then 25 cm left free and then the
remaining 15 to 20 cm shall be tied and taped and covered with cloth (no jute
allowed).
The
untied section shall be bent as much as possible towards the center of the drum
and nailed. Four staples strong enough to withstand transport stresses shall be
used; the two outside must clamp the whole conductor, whilst the two inside are
fixed through the conductor in order to prevent it sliding.
10.1.2 Connectors,
ground rods, tools and dies.
All
of above items other than copper conductor shall be packed in strong
non-returnable cases. The sides and top of each case shall be clearly marked
with the supplier’s name, purchaser no., contents, case serial no. and gross
weight and shall be accompanied by a detailed packing note in Arabic and
English.
10.2 delivery
10.2.1 The
tender shall include a guaranteed delivery time from the date of receipt of the
official order to arrival designated store.
10.2.2 Equipment
supplied from outside A.R.E shall be delivered CIF to the designated port of
entry.
10.2.3 Equipment supplied from within A.R.E shall be
delivered to designated stores in A.R.E.
11.
guarantee
The supplier guarantee the delivered equipment against
manufacturing, design and material defects for a period as given in the tender
documents.
12 submittals
12.1 Submittals
Required With Tender:
Submittals required with tender are, three copies each of:
Tender schedules fully completed.
A guaranteed ex-works delivery date and the estimated
time required for transport from to the designated stores or site in the A.R.E
shall be given.
The supplier’s quality assurance program or manual
together with a list of international/ national standard specifications
covering raw materials, components, processes, tolerances, test procedures,
etc. and a list of tests normally carried out one raw materials with a
description of test equipment.
A
short description of the manufacturing processes and equipment employed in
grounding material production shall be provided.
In
addition to the specified three copies one set of reproducible drawings showing
grounding materials shall be provided.
Detailed
drawings of each type of drum that will be used for packing conductors
including the constituent material and the method of manufacture shall be
supplied.
12.2 submittals required following award of
contract
Submit
drawing, calculations, test reports and literature pertaining to the specified
items, submittals shall include but not be limited to the following:-
-
Soil resistivity measuring procedure.
-
Resistivity measurement of the surface material used.
-
Calculations of touch and step voltages, station gourd potential rise,
and the total calculation of substation grounding system design.
-
Layout drawings of the ground grid.
-
Detailed drawings showing the connections between all equipment and the
ground grid.
-
Layout drawings and design calculations of shielding system.
-
Detailed description of shielding system materials.
-
Detailed description of various connectors and connecting processes
used to the ground grid.
-
Test reports.
No work shall proceed until these calculations
and drawings have been approved.
Final
approval of the grounding grid system shall be after site test measurement of
the grounding grid resistance.
Details
of manufacturing, test and shipping schedules.
Certificates
covering raw materials used in the manufacture of conductors.
Certificates
covering sample tests carried out on wires before the stranding of conductors.
Certificates
covering the routine tests carried out one wires after stranding and on
complete conductors before shaping of conductors.
A
list giving per drum, the drum number, the size of conductor, the exact length,
the net weight, the gross weight, the number of any joints made during
stranding and their distance from the outer end.
13. reference list
Tenderer shall submit a reference list that the
proposed equipment have been in successful operation in an integrated system
for a period of three years minimum on three different substations of same or
higher capacity outside the country of the manufacturer and/or in EEHC network for a
period not less than three years during the last ten years
The experience of the manufacturer and its
sub-manufacturers shall be evaluated on the above basis.
Test
schedules
Test
schedule I
Grounding materials for substations
Tests on copper clad steel wire according
to astm b227-70
|
Test |
Method |
Conditions for Acceptance |
|
Twist test |
Clauses 9.1 , 9.2
|
The wire
shall withstand without fracture, not less than 20 twists. |
|
Elongation
test
|
Clause 4.4 |
Elongation
shall be not less than 1.5 per cent. |
|
Resistance
test
|
ASTM method – B193 |
Resistance
conforms to standard value.
|
Test
schedule II
Grounding materials for substations
Tests on soft drawn stranded copper
Conductors according to
IEC 61089 (except where stated)
(Before and after
stranding)
|
Test |
Method |
Conditions for Acceptance |
|
Tensile
test
|
Clause 6.5.3 |
The tensile values obtained shall comply with the
standard requirements of tables 3 and 5 of BS 125. |
|
Elongation
test |
Clause 11.2 |
The values obtained shall comply with the
appropriate requirements of table 5 in BS 125. |
|
Wrapping
test
|
Clause 11.3.1 and 11.3.3 |
The
conductor shall not break. |
|
Electrical
resistance test |
Clause 12 |
The values obtained, after correcting to the
reference temperature of 20° C, shall not exceed the appropriate minimum
values in tables 3 and 6. |
|
Diameter measurement and wrapping tests |
Clause 6.5.2.1 of this
specification |
The diameter is within 2% of than specified in table 9.
Wire shall not break on completion of wrapping test. |
Test
schedule III
Grounding materials for substations
Tests on soft drawn stranded copper
conductors
According to IEC 61089 (complete
conductor)
|
Test |
Method |
Conditions for Acceptance |
|
Measurement of lay ratio |
Clause 6.5.2.3 |
Lay ratio
shall lie within limits given in table 1. |
|
Tensile
strength (calculated) |
Clause 6.5.2.2 |
Values calculated according to table 2 shall be
recorded. |
|
Measurement
of weight |
Conductor weight
calculated from weight of sample in accordance with table10 |
Conductor weight shall be equal to that specified in
table 9 of this specification. |
|
Measurement of resistance |
Conductor resistance calculated from resistance of
samples in accordance with table 10. |
Conductor resistance calculated shall be recorded. |
Test
schedule IV
Grounding materials for substations
Test on copper ground rods
|
Test |
Method |
Conditions for Acceptance |
|
Bond between copper and steel |
Clause 6.5.4.1 of this
specification |
No evidence of separation of the copper jacket from
the steel core (peeling of the jacket by the jaws of the vice is acceptable) |
|
Bending |
Clause 6.5.4.2 of this
specification
|
No evidence of cracking of the copper jacket |
Test
schedule V
Grounding materials for substations
Connectors
|
Test |
Method |
Conditions for Acceptance |
|
Current rating
Mechanical pull-out strength |
Manufacturer
Manufacturer |
Manufacturer to provide evidence of: (a) Current rating of each
connector. (b) Mechanical pull-out strength
for each connector |
inquiry
schedules
Inquiry schedule
(To be Completed by
Purchaser)
Grounding Materials For
Substation
1. Bare Soft Drawn Stranded Copper
(a) 240 sq.mm …………… Length
…………………………..km
(b) 185 sq.mm …………… Length
…………………………..km
(c) 150 sq.mm …………… Length
…………………………..km
(d) 120 sq.mm …………… Length
…………………………..km
2. Insulated Soft Drawn Stranded Copper
(a) 150 sq.mm …………… Length
…………………………..km
(b) 95 sq.mm …………… Length
…………………………..km
(c) 50 sq.mm …………… Length …………………………..km
3. Ground rod equipment
(a) Ground rods with connectors for No .
……………………..
240/185 sq. mm copper
(b) Ground rod steel tips No. ……………………….
(c) Ground rods driving heads No. ……………………….
4. Connectors
(a) Compression
‘Tee’ or parallel connectors
(as required)
(b) Bimetallic
connectors
Description
…………………………………………………….
Inquiry
schedule
(To be Completed by
Purchaser)
Grounding Materials For
Substations
(c) Compression
lug connectors
Single lug 240 sq.mm. No. ……………………
Single lug 185 sq.mm. No. ……………………
Single lug 150 sq.mm. No. ……………………
Single lug 120 sq.mm. No. ……………………
Single lug 95 sq.mm. No. ……………………
Single lug 50 sq.mm. No. ……………………
Double lug 95 sq.mm. No. ……………………
5. Copper ground rods No.
……………………
Additional Requirements
………………………………………………..
……………………………………………………………………………
……………………………………………………………………………
……………………………………………………………………………
6. Material destination stores/site
…………………………………………
tender
schedules
tender
schedule
(To be Completed by
Tenderer)
Grounding Material For
Substations
|
Ref |
Description |
Units |
|
Offered |
|
1. |
Bare Soft
Drawn Stranded Copper |
…………. |
|
………….. |
|
|
Manufacturer
|
…………. |
|
………….. |
|
|
240
sq.mm. Length per drum No. of
drums |
…………. |
|
………….. |
|
|
185
sq.mm. Length per drum No. of
drums |
…………. |
|
………….. |
|
|
150
sq.mm. Length per drum No. of
drums |
…………. |
|
………….. |
|
|
120
sq.mm. Length per drum No. of
drums |
…………. |
|
………….. |
|
|
|
…………. |
|
………….. |
|
2. |
Insulated
Soft Drawn Stranded Copper |
…………. |
|
………….. |
|
|
Manufacturer
|
…………. |
|
………….. |
|
|
150
sq.mm. Length per drum No. of
drums |
…………. |
|
………….. |
|
|
Thickness of insulation |
…………. |
|
………….. |
|
|
95 sq.mm
Length per drum |
…………. |
|
………….. |
|
|
No. of drums |
…………. |
|
………….. |
|
|
Thickness
of insulation |
…………. |
|
………….. |
|
|
50 sq.mm
Length per drum |
…………. |
|
………….. |
|
|
No. of
drum |
…………. |
|
………….. |
|
|
Thickness
of insulation |
…………. |
|
………….. |
|
|
|
…………. |
|
………….. |
tender
schedule (Cont.)
(To be Completed by
Tenderer)
Grounding Material For
Substations
|
Ref |
Description |
Units |
|
Offered |
|
|
|
…………. |
|
………….. |
|
3. |
Ground rods, steel tip and driving head |
…………. |
|
………….. |
|
|
Manufacturer
|
…………. |
|
………….. |
|
|
Material of rods |
…………. |
|
………….. |
|
|
Length of
rods |
m |
|
………….. |
|
|
No. of
steel tips |
…………. |
|
………….. |
|
|
No. of
driving heads |
…………. |
|
………….. |
|
|
|
…………. |
|
………….. |
|
4. |
Compression
lug connector |
…………. |
|
………….. |
|
|
Manufacturer
|
…………. |
|
………….. |
|
|
Type
single/double |
…………. |
|
………….. |
|
|
Conductor
size |
…………. |
|
………….. |
Singed :
……………………………………
Company :
……………………………….
Position in
Company : ………………….
Date :
……………………….. ……………………
Company Stamp
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