power plant: Wiring

 

                          Wiring

  -      Control wiring shall consist of a stranded copper conductor, not less than 1.5 mm2.  Wire insulation shall be 750 V class, thermosetting and moisture, heat, oil, and flame retardant.

   -       Color coding of all wiring shall be as per the latest codes and standards.

    -        Equipment shall be completely wired within their withdrawable unit for control and operation.

  -    Wiring requiring external connections shall be brought to terminal blocks for terminations of external leads.  Where they terminate on terminal blocks, wire shall be identified by permanent markings such as PVC sleeves. 

    -       Wire identification shall correspond to the identification used on the wiring drawings. 

. -        If the wire ends have crimped on connectors, these more likely to be pin or spade type for use in pressure plate type terminals, e.g. Klippon or Phonix.

   -     The following starter wiring points shall be brought out to separate terminal block points for external connections:

    Both sides of the control transformer secondary,

    Both sides of the seal in contact,

     Starter operating coil terminal normally connected to one side of the seal-in-contact,

    Both terminals of auxiliary contacts.

    -      All power and control cables shall enter the switchboard & MCCs assembly from the bottom.

- Compression-type terminal connectors shall be furnished for all power cables. 

   -      Suitable supports shall be provided within the switchgear/switchboard/MCC housing for the power and control cables.

-       Power cables will be solid dielectric insulated.

 

-     Terminal Blocks

    Terminal blocks shall be provided for all secondary and control wiring requiring external connections.

 Terminal blocks shall be installed in each compartment in a uniformly accessible location. 

-    Terminal blocks shall be molded composition type with separate terminals for internal and external connections. 

        Terminal shall be of pressure plate type with only a single conductor per side permitted, e.g.  Klippon, Phonix, or equivalent. 

           Terminal blocks shall have barriers between terminal points and a terminal-marking strip. 

          A minimum of 20% spare terminal points shall be provided on each terminal block.

 

 

 

     Grounding

        Each switchgear/switchboard & MCC shall be provided with a main copper ground bus not less than 50X50-mm in cross section, along the length of the switchboard/MCC. 

          The ground bus shall be furnished with a mechanical clamp-type connector at each end for ground cable connections.

 

             All framework, metal enclosures, barriers, and non-current carrying parts of equipment shall be securely grounded and grounding connections shall be brought to the ground bus. The metal framework of the assembly may form part of the internal grounding circuit, provided a solid and uninterrupted path is thereby assured; otherwise, grounding connections shall be furnished.

 

  

    Painting

    All metal sheets and framework shall be thoroughly cleaned after fabrication, treated with a phosphate coating and unless otherwise noted, given a prime coat of rust-inhibiting paint.

        A finish coat shall be applied overall (stoved enamel).

 

    Switchgear/Switchboards / MCC

     The individual unit compartments shall be such as to obtain different zones fully insulated from each other, namely:

    The switchgear compartment

    The bus bar section

    The power and control cable compartment.

            Special means shall be provided for connection of the busbar systems between transformers and boards as specified.

 

      Instrument Transformers

The completely enclosed, dry cast resin type instrument transformers shall be designed in accordance with the requirements of IEC 60185 & 60186 (latest version).

 

     Remote Indication

All electrical measuring systems with remote indications in the GT Local Control Room and/or Main Control Room shall be equipped with transducers and incorporated in the DCS.

 

        Voltage Monitoring

The following voltage monitoring relays shall be installed in the measuring section of each switchboard & MCC.

     Incoming supply voltage monitoring

    Busbar Voltage Monitoring

  Definite time delayed, two-phase Undervoltage relay (27), adjustable in steps.

 

 

        Signaling

  Each LV circuit breaker and draw-out unit shall be equipped with indication lamps or position indicators to show the following switching conditions;

    Circuit breaker or draw-out unit withdrawn

    Circuit breaker or draw-out unit in the test position

     Circuit breaker or draw-out unit in "ON" (operating position).

    Circuit breaker or draw-out unit in "OFF" position.

  In the event of failure of the control voltage on a Sub-section or in a  switchgear cabinet, a Control Voltage "OFF" signal shall be provided in the GT Unit Local Control Room and repeated in Main Control Room DCS.

 

     Space Compartments

Each Switchgear/switchboard section and MCC shall be provided with at least 10 % or a minimum of one (1) empty compartments of each type completely wired as space.

 

     Spare Feeders

Each switchgear/switchboard section / MCC shall contain 10 % or minimum of one fully equipped and functional spare outgoing feeder of each type.

 

     Terminal Boxes and Subsidiary Distributions

Field-installed intermediate or collective terminal boxes as well as subsidiary distributions comprising collective power and control circuits, such as  for electrically operated dampers, valves, etc.  it shall be of the cast iron, clad type, consisting of individual and standardized cast iron cases, of IP-55 protection class according to IEC Standards.

 

       Interlocks

          Electrical ON/OFF interlocks of incoming feeders, transformer feeders, and coupling feeders shall be realized in the relevant boards.

            Electrical interlocks of motors and valve feeders involved in the main process functions of the units shall be effected in relay cubicles.

      The basic interlocking principles for the power supply systems are listed below:

      All incoming feeders of a switchgear/switchboard or a section of such board shall be interlocked against each other and against the bus coupler/interconnector, so that each distribution board or section thereof shall be fed only by one power source.

     Paralleling of in feeds and overlapped switching shall not be possible.

      Tripping of a protection device in one of two feeder circuits of any double fed switchboard (for example tripping by 13.8kV transformer feeder protection, transformer Buchholz or oil temperature protection, but not the LV incomer protection) shall automatically trip the faulty circuit and close the second feeder circuit (provided its feeding breaker is closed) via the second LV incoming breaker or the bus sectionalize, whatever is applicable. The automatic change over shall be controlled by an under-voltage function. A manual change over initiation shall be realized for switching back.

     Operational switching-off of any infeed shall not actuate the second infeed. Manual changeover initiation shall be realized by a separate changeover switch.

   Each transformer feeder shall be interlocked such that the LV the circuit breaker cannot be closed unless the MV circuit breaker is closed, and if the latter is tripped manually or automatically, the former shall also be tripped automatically.

 

      L.V. Transfer/Change Over Devices and Scheme

                             Transfer/change-over devices and scheme shall be provided for all L.V. boards equipped with two independent in feeds.

          In case of fault on the transformer, the Buchholz or overcurrent relay, etc. shall trip the transformer’s 13.8kV & 480V circuit breakers.

               On the LV side, an Undervoltage the relay shall switch over the normal source to the other source by closing the tie-breaker or second incoming breaker, by fast transfer, so as no tripping occurs. The fast transfer is required to ensure the unit is selected to this board, does not trip.

             Manually or process initiated change-over between two feeding sources shall be provided without voltage interruption.

 

   TESTS AND INSPECTIONS

        The Low Voltage Switchgears and MCC shall be subject to inspection and tests by the COMPANY Engineer should they so require, during manufacture, erection, and after completion. The CONTRACTOR shall give three weeks in advance notice of scheduled tests.

        The inspection and tests shall include but not be limited to the requirements of Technical Specifications in this bid document.

           Each completed low voltage switchgear, motor control center and individual circuit breakers and motor starters shall be tested in accordance with IEC recommendations.

          Five copies of certified test reports shall be furnished.

        Type test reports for the equipment offered shall be submitted with the tenders. 

    Tests at Manufacturer’s Works

                            Specific tests required by the various items of the plant, parts, materials, and equipment shall be performed in accordance with the applicable Codes & Standards.

    The CONTRACTOR

 shall, at the appropriate time, prove that his material and/or equipment complies with all the requirements of this Section, such proof being the successful completion of tests and inspections witnessed by the COMPANY Engineer.

          Certified routine test and type test certificates shall be submitted for each item of equipment, where applicable.

             At least the following tests shall be performed in the manufacturer's workshop on the individual apparatus and on the complete installation, respectively, all in accordance with IEC standards:

    Visual inspection

    Power frequency H.V. tests at the main circuit

     Dielectric tests of the auxiliary circuits

    Functional test of the control circuits

    Check of the operational sequence

    Check of the denominations.

        The COMPANY Engineer reserves the right to witness these tests.

 The CONTRACTOR shall give three weeks in advance notice of scheduled tests.

     Five copies of certified test reports shall be furnished.

      Type test report for the equipment offered shall be submitted with the Manufacturer/Vendor qualification documents.