Vol 2 - 4.6- Neutral earthing equipment by nuhman10

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									                                                           MHEW, Sultanate of Oman
Tender Documents                                     Power line connection between Oman     Volume 2
                                                       (Al Wasit) and U.A.E. (Al Ain) and   Section 4
                                                            associated substations




                           4.6.               33 kV NEUTRAL EARTHING EQUIPMENT
                           4.6.1.             GENERAL
                           4.6.2.             RESISTOR ELEMENTS
                           4.6.3.             ENCLOSURE
                           4.6.4.             TERMINAL CONNECTIONS




Doc: ICON f96ed47b-5fdb-43f7-9691-b1b3df86569d.doc   FICHTNER - ENERGOPROJEKT ENTEL           Date: April 11
                                                         MHEW, Sultanate of Oman            Volume         2
Tender Documents                                   Power line connection between Oman       Section        4
                                                     (Al Wasit) and U.A.E. (Al Ain) and     Subsection     4.6
                                                          associated substations            Page           1




                           4.6.         33 kV NEUTRAL EARTHING EQUIPMENT
4.6.1.            GENERAL

                  The 33 kV neutral earthing arrangement shall be as shown on single line diagram
                  drawing. The 33 kV system neutral earthing equipment for each 220/132 kV, 500 MVA
                  autotransformer shall comprise:

                   One earthing Resistor 19.0 , 1000 A for 30 sec
                   Two earthing Isolators
                   Three neutral current transformers.

                  The equipment shall be so arranged to permit safe working during maintenance and to
                  enable neutral point of the transformer to be isolated, solidly earthed or earthed
                  through earthing resistor.

4.6.2.            RESISTOR ELEMENTS

                  The resistors shall be non-inductive, of cast grid. The cast grid resistor elements shall
                  be stainless steel type.

                  The grids shall be securely supported at sufficient number of points so that no damage
                  is caused to the grids due to vibrations and no mechanical stresses are developed.
                  The resistor elements shall be insulated from supporting bars by mica tubes. The grid
                  elements shall be given a protective coat of a suitable heat resistant paint.

                  The insulating material used in the construction shall be heat resistant such as mica.

                  The Tenderer shall clearly indicate the maximum temperature rise permissible for the
                  type of resistor to be supplied without exceeding safe temperature for the insulation.

                  All the resistor elements comprising one stack shall be internally connected and end
                  terminals shall be brought out of tank enclosure in the terminal boxes. If resistor taps
                  are specified all taps shall also be brought out of the tank enclosure in the form of
                  bushings.

4.6.3.            ENCLOSURE

                  The grid resistor elements shall be enclosed in a tank type enclosure degree of
                  protection IP55. The enclosure shall be made of one-piece welded construction rigid
                  frame fabricated from steel angels. The frame shall be adequately protected from
                  rusting and deterioration due to exposed conditions by antirust coating and final
                  aluminium paint. The frame shall be fitted with removable louvered aluminium covers
                  on all sides, top and bottom. The enclosure shall be completely weatherproof for
                  outdoor application. The louvered openings shall be provided with fine galvanised wire
                  mesh.

                  Cap and pin type, stand insulators shall be provided for supporting the enclosure and
                  isolating it from ground. Insulators shall be complete with the required hardware for
                  supporting resistor enclosure and fixing to the mounting structure.




Doc: f96ed47b-5fdb-43f7-9691-b1b3df86569d.doc GC     FICHTNER - ENERGOPROJEKT ENTEL             Print Date: April 11
                                                         MHEW, Sultanate of Oman          Volume         2
Tender Documents                                   Power line connection between Oman     Section        4
                                                     (Al Wasit) and U.A.E. (Al Ain) and   Subsection     4.6
                                                          associated substations          Page           2




4.6.4.            TERMINAL CONNECTIONS

                  Terminal connections arrangement shall be provided on the enclosure for the incoming
                  and outgoing conductors. All terminals shall be insulated from ground as well as the
                  body of the resistor.

                  For the incoming and outgoing connections to the resistor, the end terminal shall be
                  brought to a terminal box mounted on the side of the enclosure, degree of protection
                  IP55. The terminal box shall be complete with necessary cable glands.




Doc: f96ed47b-5fdb-43f7-9691-b1b3df86569d.doc GC     FICHTNER - ENERGOPROJEKT ENTEL           Print Date: April 11

								
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