MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007 EMD-SOP-000 7
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
1 of 6
HSEQ Dept. CCPP
Page
Issuing Department
Authorization: Name
Designation Designatio n
Prepared by:
M. Laiq Ahmed
DM Electrical
Reviewed by:
Nowshad Alam
GM Maintenance
Approved by:
Shabber Imam Rizvi
Director CCPP
Signature
Distribution list: 1. 2. 3. 4. 5. 6. 7. 8.
Director, 220 MW CCPP GM Maintenance, 220 MW CCPP DGM Operation, 220 MW CCPP DGM HSEQ, Performance & Planning DGM Maintenance Mechanical DGM E&I DM Electrical Manager I&C
Edition
Version no.
Page Amended
Issue Date
Effective Date
MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
2 of 6
HSEQ Dept. CCPP
Page
Issuing Department
TABLE OF CONTENTS:
1.0) 2.0) 3.0) 4.0) 5.0)
PURPOSE SCOPE REFERENCES/DEFINITIONS RESPONSIBILITIES PROCEDURE
3 3 3 3 3
5.1)
INTRODUCTION ROUTINE TESTING AND INSPECTION BELOW GROUND ROUTINE TESTING AND INSPECTION ABOVE GROUND
3 4
5.2) 5.3) 5.4) 6.0)
RESULT OF TEST RELATED DOCUMENTS
5 6 6
MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
3 of 6
HSEQ Dept. CCPP
Page
Issuing Department
(1.0) PURPOSE: This document lays out the procedure for effective testing and maintenance of Power Station Main Earthing System (MES).
(2.0) SCOPE: This applies to Earthing System installed at 220MW CCPP, KESC Station.
(3.0) REFERENCES/DEFINITIONS: 1) MET-110701-ER-EP-DW-00-096_1-B (Earthing System Plant Area) 2) MET-110701-ER-EP-DW-00-096_2-B (Earthing System Fuel Tank Area) 3) MET-110701-ER-EP-DW-02-099-B (Earthing System of RO, FGC and GRS)
(4.0) RESPONSIBILITIES: It is the responsibility of Electrical Section Manager to ensure that the Earthing System is tested and maintained in accordance with this procedure.
(5.0) PROCEDURE: (5.1) Introduction For the safety of personnel and plant, it is essential that the earthing system at the power station should remain effective. The Main Earthing System (MES) has two main functions: 1) To safely discharge the designed value of primary system earth fault current into the ground in all conditions, without change in resistance. 2) To provide sufficiently low impedance path into the ground for the designed earth fault current, so as to limit the resultant rise of value of primary system earth potential to an unacceptable level. The possible rise in potential between the station earth system and the general body of earth should be as low as economically possible.
MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
4 of 6
HSEQ Dept. CCPP
Page
Issuing Department
When electrical fault occurs, the failure of the earth system can result in damage of catastrophic proportions. Planned routine maintenance, detailed inspection and recording of results can ensure the safe operation of the earthing system at the Power Station site. Therefore, a system of routine electrical testing and some visual inspection is necessary to achieve continued reliable performance.
(5.2) Routine Testing and Inspection of Below Ground Earthing (5.2.1) Inspection The accessibility to earthing electrodes and the associated connections varies from station to station and also within station. Electrodes pits/mesh often has been buried. It is important that accurate records and drawings of all electrode pits/mesh should be available in station documentation system. The location of buried or built over pits is often undeterminable, the only indication to their existence being the conductor from the electrode to the earthing system as it enters the station buildings at basement, subbasement or cable tunnel level. These electrode mesh/pits are examined for the condition of the conductor connections to the electrodes, corrosion of fixings/fastenings, and the general condition of the civil work and covers. The most common form of deterioration takes place at the joint between the copper conductor and the steel pile or cast iron pipe, where corrosion increases the joint resistance. These joints should be protected by the application of a proprietary anti corrosion system. The visual inspection of these pits and joint resistance measurement is being done at a regular frequency of one year.
(5.2.2) Testing The grounding system shall be tested at intervals of not more than one year.
(5.2.3) Individual Electrodes At CCPP Power Station, for MES the conductor coming from electrode/Mesh is connected to the marshalling bar. However, electrodes that have been buried or built over should be tested from the point of connection where the
MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
5 of 6
HSEQ Dept. CCPP
Page
Issuing Department
conductor from the electrode joins the MES, if this point is accessible. b) The individual electrodes should be tested by comparison. The test procedure should use a low resistance Ohmmeter. Individual electrode resistances should be less than 10 ohms. c) When testing, only one group of rods or a plate should be isolated at a time, such that the remaining electrodes are capable of discharging the prevailing earth fault current. d) Disconnection and testing should not be undertaken at times of lightning risk. e) Prior to disconnecting an electrode, a check is to be carried out to confirm that the system terminating at the point is fully interconnected to other adjacent earth electrodes via the MES. f) If any doubt about connection to the MES exists, the MES side of the termination point should be connected to the MES with temporary conductors of a cross section equivalent to the termination conductor. g) Following the tests, the bolted link connections should be cleaned, remade and checked for continuity. h) Results of the tests will be recorded on the sheets as shown in attachment #1.
(5.3) Routine Testing and Inspection of Above Ground Earthing Above ground earthing is subject to mechanical damage, theft and manual Interference, thus all the following items will be visually inspected at regular one year intervals. 1) Earth link connections between buried electrodes and the rest of the MES. 2) Connections at buried earth electrode to the adjacent MES.
MAINTENANCE AND TESTING OF STATION EARTHING SYSTEM EMD-SOP-0007
IR
Document no.
Revision
Title 11 Aug 2011 Date of Issuance th
6 of 6
HSEQ Dept. CCPP
Page
Issuing Department
3) Link connections between various sections of the MES. 4) Main earthing conductor runs. 5) Transformer neutral connections to the MES. 6) Alternator earthing systems including associated earthing resistors/transformers and the connections of the latter items to the MES. 7) The connections between - switchboard earth conductors, alternator casings, phase isolated bus bar casings, steel support structures for outdoor high voltage overhead conductors, station structural steelwork and the MES. 8) Connections from lightning protection to the MES. 9) Connections between fuel oil storage tanks and driven rod electrodes. 10) Earthing connections and systems associated with flammable gas storage compounds. 11) In addition to the above, portable earthing leads
(5.4) Result of Test Electrode resistance depends on various factors, such as electrode dimension, soil type and ground conditions etc. Reliance on absolute values should not be made; changes in value should be noted and a judgment made on trends, modified by local conditions such as prolonged dry weather. Values for electrode resistance measured before commissioning and subsequent results should be available. Seasonal variations should not account for more than a 25% change in results. If variations are greater than this then consideration should be given to excavating or replacing the electrode in question.
(6.0) RELATED DOCUMENTS: 1. Check sheet of inspection and checking of earthing resistance
