Specifications of Substation equipments

GENERAL SPECIFICATION:

The specification for the parts of this contract mentioned below cover design, manufacture, assembly   and   testing  at  the  contractor’s  workshop  as  well  as  the  supply,  delivery, installation, testing and commissioning  of the sub-station equipment at site.

CLIMATIC CONDITIONS:

The climate is tropical and has marked Monsoon character with seasonal changes from humid, warm, rainy season , summers to cool and dry winters. Maximum temperature occurs during the period from April to May reaching approximately 43 deg. C (110 deg.F) with a relative air humidity of 60% to 70%.

The annual mean temperature is approximately 29 deg. C (84 deg.C). During the rainy monsoon month from June to September, the average relative air humidity is 80% and reaches extreme values upto saturation point during longer periods. the annual rainfall, most of which occurs from June to September is 2000mm to 2500mm.

OPERATING CONDITIONS:

The sub-station equipment will be connected to the 11KV, 3-phase, 50 Hz Bus of Power Development Board/REB/DPDC/DESCO Bangladesh.

STANDARDS:

All equipment and materials must be in conformity with the most recent relevant Bangladeshi laws, standard rules and regulation. Particular attention is to be paid to the Electrical Act 1910 and Electricity Rules 1937 (as amended in 1946). All equipment and materials to be supplied, which required any Form of approval by the Bangladesh Government or a Local Authority like PDB/DPDC/DESCO/REB or equivalent must satisfactorily pass all inspection and tests procedures imposed by them.

Otherwise, all the equipment and materials must be in conformity with the most recent international rules, regulation, standards and recommendation: IEC.

STANDARD DATA:

The following standard values for high and low voltage are standard in Bangladesh.

DISTRIBUTION BUS HIGH VOLTAGE            :  11KV, MAXIMUM SYSTEM VOLTAGE 12 KV.

LOW VOLTAGE                                                   :  415/240V LOCAL VOLTAGE

                                                                                   400/231-OPENING VOLTAGE

                                                                                   457V -MAXIMUM PERMISSIBLE

                                                                                   VOLTAGE BY PDB/DPDC/DESCO/REB

FREQUENCY:

The standard power frequency in Bangladesh will be: 50Hz.

DESIGN & CONSTRUCTION REQUIREMENTS:

All equipment are to be in accordance with the latest recognized rules of workmanship and modern engineering practice.

All parts of the equipment must be suitable in every respect for continuous operation at maximum output under the climatic conditions as specified above.

MARKING OF TERMINALS:

The terminals shall be marked in accordance with BS, IEC, VDE or equivalent standards.

PAINTING:

Protective painting shall be done in accordance with general practice and recognized methods, the paint manufacturer’s instruction and according to the present addition of DIN 55 928, CORROSION PROTECTION OF STEEL STRUCTURE’ such as to meet the tropical condition at site.

EARTHING OF EQUIPMENT:

Each electrical equipment must be provided with an earthing screw of sufficient diameter or an earthing plate.

INSULATION CO-ORDINATION:

The insulation level for load break switch, lightning arrestor and transformer are stipulated below, taking into account the maximum service voltage and the rated voltage according to IEC standard, with appropriate impose withstand test voltage and power frequency withstand test voltage values.

The insulation levels for equipment are as follows:

According to IEC rated service voltage                                           :               11KV

Maximum service voltage shall be considered                             :               12KV

The respective test voltage shall be                                                                :

Impulse withstand test voltage (BIL)                                                                :               75KV

Power frequency withstand test voltage                                         :               28 KV

For the lightning arrestor, the IEC standard voltage of 9KV is to be selected.

TECHNICAL REQUIREMENTS:

The equipment specified in the following items shall withstand the impulse levels and test voltages specified by the recommendations of IEC, as stipulated before. They must be capable of carrying the short time current for three seconds and must withstand the short circuit (Peak value) current.

The rupturing capacity of the circuit breakers is indicated in the respective items. The switchgear must be designed accordingly in order to withstand the mechanical short circuit stresses.

They must contain all technical particulars which are mentioned in the Schedule of Technical Data.

The Owner reserves the right to have routine tests carried out on each type of equipment at the manufacturer’s workshop in the presence of his representative.

HIGH TENSION SWITCHGEAR:

SCOPE:

The switchgear shall be pre-fabricated, complete and ready for erection and suitable for indoor installation.

STANDARDS:

11KV switchgear must comply with the requirements of IEC 694,VDE0101,0670 Part-6 74(draft), 0670 Part-7 74(draft) IEC republication 298.69 Pahls recommendation No.2 and equivalent British Standard (BS 116-1952) 11KV Switch Board shall be consisting of cubicles free standing type, for indoor installation, formed by pre-fabricated factory assembled. The individual cubicles shall be made of strong sheet steel (min16SWG) at all sides with iron angles and  channels welded together.

The board shall be covered and the top shall be provided with pressure relief, flaps the bottom shall be open the allow connection of cables via and boxes, necessary holding iron and clamps are provided.

The front shall be provided with sheet steel doors with special locking devices and with viewing glasses in order to see the condition of the switches and the contact.

On the top of the cubicle a sheet steel enclosed relay, meter cabinet shall be provided.

The iron and sheet steel parts after cleaning by modern methods shall be painted in the initial layers and a final paint as such the lacquer shall be a protection against corrosion the tropical humidity. The final colour of the cubicles will be pebble grey to DIN 43656. The single busbar system shall be of copper bars to withstand the required amperage. They are to be mounted on cast resin insulators in each cubicles.

The single bars shall be marked by the colours as per IEC, VDE or BS standard.

CIRCUIT BREAKER

The circuit breaker must comply with VDE specifications 0670, Part-102, IEC Recommendations and Publication 56, IEC 695, BS 116, BS 5311 or equivalent ANS & UTE Specifications.

Technical data for circuit breaker

Nominal System voltage                                                                   :               11 KV

Rated normal current                                                                          :               630A

Number of phases                                                                              :               3

Frequency                                                                                             :               50 Hz

Rated short circuit breaking current(rms)                                       :               25KA

Rated short circuit making current duration                                   :               3 sec.

Rates short circuit making current                                                    :               50KA

D.C component of rated short circuit breaking current                :               36%

Rated lightning impulse withstand voltage                                    :               75 KV

Rated Power frequency withstand voltage (60 sec)                     :               28 KV

No. of operation cycles at the rated normal current                     :               20,000

No. of operation cycles at the rated short circuit current              :               100.

CURRENT TRANSFORMER:

Current transformer must comply with BS 3938, VDE 0414 and IEC 185.

The C.T. should be cast resin insulated with class 10P10 for protection and class 0.5 for metering. The rated over current factor and burden should be matching with operating burden of the connected equipment to prevent the instruments from being damaged, 1th = 80xIn, id=200 In.

POTENTIAL TRANSFORMER:

Potential transformer must comply IEC86,. The P.T should be cast resin insulated with appropriate accuracy class and burden minimum 50VA. The P.T. secondary shall be protected with MCB.

IDMT RELAY:

The relay for over current and earth fault protection should be of solid state (micro-computer operated) type. The complete triple pole, solid state IDMT relay with adjustable minimum setting for over current earth fault and short circuit protection including the A.C./D.C. converter.

This module can be housed in  a standard case  for assembling in cubicles. The socket which are located in either the rack or the case in which the module is plugged, should have one screw and one snap-on terminal each for the plant connections. The heavy duty current plug connector should be provided automatic shorting of the C.T. circuits whenever the module is withdrawn. A make-before-break earth contact should be there to ensure protective earthing, before the other plug connections can be made.. The relay should be suitable for d.c. shunt tripping to be operated by 110V D.C. voltage from P.T. secondary through a rectifier or 12/24V d.c. through capacitor rectifier circuit.

Wiring inside the cubicles shall be minimum 1.5mm2 area and with tinned copper conductors. Current circuits shall be made with minimum 2.5mm2 area and with tinned copper conductors.

All cubicles, frames, transformers, measuring and relay circuits shall have protective earthing. Each cubicle shall be provided with earthing bolt and earthing parts.

The busbars shall be of copper and fully insulated through their length.

The protection system shall consist of over current protection and earth fault protection.

The bidder shall enclose details of system be proposes, along with single line diagram, detailed technical specification and mode of operation of protection system, with his offer

Complete physical dimensions and electrical characteristics of the equipment offered shall be furnished along with the offer.

GENERAL SPECIFICATION OF 11KV SWITCHGEAR:

Nominal System Voltage                                                                   KV                           11

Highest Voltage for Equipment                                                        KV                           12

Type of Switchgear                                                                             LBS/VCB/SF₆

Class of Switchgear                                                                            Indoor Metal clad

Number of Phases                                                                              3

Frequency (Supply)                                                                            Hz                           50

Busbars                                                                                                Three Phase

Rated short circuit capacity

a)            Symmetrical Breaking Current                                         kApms                   25

b)            Making Current                                                                    kApms                   50

Short Time Current                                                             kApms                   20

Short Time Current Duration                                             Seconds                3

System Neutral Earthing                                                    Effective

Rated Current                                                                                    

a)            Busbars                                                                                 Amperes               Min 800

b)            Vacuum Circuit Breaker                                                     Amperes               Min 630

Rated Insulation Level

a)            Impulse Withstand Voltage to Earth                                                KV                           75

b)            Impulse Withstand Voltage between Phases                                KV                           75

c)             Minimum Dry Power Frequency Withstand Voltage    KV rms                   28

Voltage Transformer

a)            Rated Primary Voltage                                                       KV                           11

b)            Rated Secondary Voltage                                                  V                             110

c)             Rated Output/Phase                                                            VA                           50

d)            Accuracy Class                                                                                                   0.5

THREE PHASE POWER TRANSFORMER:

The Transformer shall comply with IEC726, VDE 0532 etc. and the general specifications will be as follows:

Oil immersed Indoor/Outdoor Type Power Transformer:

a.             Rated capacity                                     :               As per Schedule KVA  

b.             Rated frequency                                  :               50 Hz

c.             Rated primary voltage                        :               11 KV

d.             Rated secondary voltage                   :               0.415KV

e.             Tap changing ( off load)                    :               ±  2.5%, ± 5%, ± 7.5%

f.              Phase connection                                :               DYN 11.

g.             L.V. neutral                                           :               Brought out

h.             BIL level (H.T. side)                             :               75KV (H.T. side)

i.              Maximum system voltage                 :               12KV (H.T. side), 0.5 KV (L.T. side)

j.              Cooling                                                  :               as per schedule.

The Tenderer shall furnish following data at 75 deg. C.

a.             Iron loss at rated voltage and frequency

b.             Copper loss (including supplementary eddy current loss ) at continuous rated current (50 c/s) and for winding at 40 deg.C ambient temperature with the changer in middle position.

c.             Impedance voltage with tap changer at middle position.

d.             Voltage drop referred to rated voltage at rated load with tap changer in middle position and at unit p.f.

e.             Permissible maximum symmetric three phase short circuit current referred to rated current.

f.              Rated no load current (RMS value referred to rated current).

g.             Type of windings with conductor materials.

h.             Class of insulation material.

i.              Voltage regulation.

j.              Temperature after continuous rated load at 40 deg. C ambient temperature.

                In windings

                Core

k.             one minute double power frequency induced tests voltage applied to:

                H.V. line terminal

                L.V. line terminal

                L.V.  Neutral.

l.              Impulse test voltage 1.2/50 micro  second fully wave positive and negative polarity applied to:

                H.V. line terminal

                L.V. line terminal

                L.V. Neutral

m.           Weight of:

                Iron core

                Copper

The transformer shall be designed and manufactured in accordance with the requirement of B.S. 171: 1970 equivalent.

LOW TENSION SWITCHGEAR:

The Low Tension Switchgear shall be pre-wired, free standing and Type conforming to IEC 439-1.

SWITCHGEAR DESIGN:

The switchgear shall be pre-fabricated, complete and ready for erection on the site.

The switchgear shall be totally enclosed. All line parts shall be adequately and efficiently protected against accidental touching.

The switchgear cubicles shall conform to relevant provisions of BS/IEC and shall be adequate in all respect to accommodate the cables, switchgears, meters, cable terminations and inter connection as indicated in the schedule/specification/drawings and be with provided lockable doors. All apparatus and other components shall be easily accessible from the front as required for inspection, replacement and repair. The switch gear shall be of tropical design.

The Switchgear shall conform to the specifications

Operating Voltage                                                               :               0.415KV, 3-phase at 50 Hz.

Voltage system                                                                    :               Direct earth

Number of bus bar                                                              :               5 (L1, L2, L3, N & E)

Rated current of bus bars                                                  :                As per schedule

Bus bar materials                                                                                :               Copper

Degree of protection of busbar chamber                       :               Enclosed

Maximum protective current

(cos Q = 0.2, t=0.1 sec) of busbar                                    :               80KA

Maximum short time withstand current of busbar        :               63KA

Maximum protective peak current of busbar                 :               150 KA.

All parts of the switchgear including apparatus shall be designed to withstand without being damaged, the mechanical and thermal, strain of this current or, where protected by circuit breaker, the interrupting current of the circuit breaker.

Outgoing cables shall be arranged in separate specious cable spaces.

Protective screens shall, as far as possible, be arranged between main busbars and cable space.

Terminals for power cables shall be protected against accidental touching.

Interior control wiring shall be accommodated in plastic conduits.

Wiring inside the cubicles shall be made with minimum 0.75mm2 area and with tinned copper conductors.

The Switchgear shall be suitable for busbar entry from the top, if required as per schedule.

APPARATUS:

The switchgear shall be arranged in accordance with the attached principle drawing.

The switchgear shall be of modular type design. The apparatus of each functional group shall be assembled on a common base.

Coils for contractors must be of open type to be repairable.

CUBICLE CONSTRUCTION:

The distribution sections shall be of carcase construction and the carcase shall be augmented with various cladding plates as required.

The top plate, bottom plate and side plates shall be polled for easy removal.

The door shall be IP23 for distribution sections and IP54 for bottom plate respectively. Creep age and clearance paths shall conform to VDE 0110 insulation group C or UL508 cable 18.1 and BS 162 table 4.

The electrical equipment inside the panel shall be finger proof. The cubical shall be dust vermin proof.

CABLE ENTRIES AND TERMINATIONS:

The distribution board shall be so designed that the cable are fed in and connected in the base. The bottom plate shall be split and removable type to facilitate cable entry having cable grommet.

All cable socket for incoming and outgoing cable are to be provided.

CURRENT TRANSFORMERS:

All current transformers shall comply with IEC 185 /BS 3938 and shall be of suitable class, rating and accuracy depending on the duty.

INDICATING LAMPS:

Panels shall have indicating lamps as specified.

AIR-CIRCUIT BREAKERS / MCCB:

The air-circuit breakers / MCCBs shall comply with IEC 947, 157 BS 4752.

The breaker shall have spring assisted manual closing mechanism with, breaker closing speed independent of operator. There shall be breaker closed opened position indicator manual tripping shall be by push button and it shall not be possible to trip the breaker by means of the closing mechanism. Over load release shall trip the breaker by means of the closing mechanism. Over load release shall trip the breaker on over current or short circuit. The time lag for these released and the current setting shall be adjustable.

CIRCUIT BREAKERS:

The MCB/MCCB’s shall be quick-make, quick-break, trip free, indicating type and shall have inverse time limit characteristics with adjustable overload, adjustable short circuit (the maximum adjustable limit should be as per schedule) and instantaneous magnetic trip elements functioning on overloads above the normal operating range. All circuit breakers shall be in accordance with schedule. All lugs must be of the solder less above the normal operating range. The MCB must comply with IEC 157-1, IEC 898 rated voltage 240/415V, A.C. 50 Hz. interrupting capacities minimum 6 KA current limiting class 3, finger proof, protection through Thermal and Magnetic Trip sections respectively, temperature rating 40 deg.C preferably tropicalized (moisture fungus corrosion treated), with contacts of silver alloy, terminal capability as per requirement. The MCCB must comply with IEC 947, 157-1 having rated voltage 600V A.C. 50 Hz with thermal overload and instantaneous magnetic tripping action, temperature rating 40 deg.C preferably tropicalized (moisture-fungus-corrosion treated), terminal capability as per requirement. The bidder may offer MCCB instead of MCB to meet requirement of the specifications.

AUTOMATIC REACTIVE POWER CONTROL EQUIPMENT WITH CAPACITOR BANK:

The Power Factor Improvement Plant shall be sheet steel clad dust and vermin proof free standing, floor mounting indoor type. The centrally controlled automatic PFI Plant will be of compact design and will be suitable for operation in 12 steps in the system for automatic control of the reactive power. The PFI plant shall be consisting of  required capacity KVAR, 415V,  50 Hz, self healing non-PCB, capacitor bank with disconnecting switch  with fuses of proper rating, discharge resistors required nos. suitably rated air-breaker contractors and associated control unit. The contractors shall have special non-welding contacts which can control inrush current of upto 180 times the rated current. When the contractors drops out the resistors shall be switched on the capacitor by means of two break contact. The control  unit shall be an integral part of the PFI Plant and will be comprised of  C.T. of adequate rating automatic power factor correction relay to keep the automatic power indicating lamp ON/OFF switches, switching step indicator etc. PFI panel shall be of a type conforming to IEC 439-1 from manufacturer having ISO 9001. The automatic control must be non-responsive in a certain range to element hunting.

BUSBAR TRUNKING SYSTEM (OPTIONAL):

The low impedance prefabricated sand witch type main busbar trunking system shall conform to IEC 439/1-2, tested Siesmic standard shall be suitable for use in installation conforming to IEC 364.

The busbar trunking system shall be comprising of (i) two piece aluminium enclousure (ii) Straight length (iii) Fixing brackets (iv) Elbows (v) Bends  (vi) closed type transformer connection unit (vii) distribution board connection unit (viii) tap-off boxes with MCCB etc.