DESIGN
Outdoor transformers shall be separated
from each other by fireproof walls.
To prevent or reduce fire in case of an oil
spill, transformer oil collection pits shall be provided.
The outdoor transformer station shall be equipped with efficient fire detection and extinguishing system.
Fire detection System
-
The transformer station shall be
equipped with an efficient fire fighting, complete with a pressurized water tank
sufficient for one 125 MVA or one 25MVA transformer but not less than 40m3
, 20m3 respectively.
-
Time required for extinguishing
fire of one transformer 25MVA shall not exceed 2 minutes.
-
Duration of water sprinkling
shall be 5 minutes.
-
The detection systems in any
transformers shall instantaneously come into action in case of a fire isolating
the transformer by tripping the transformers circuit breakers from both sides
and put a fire extinguishing system into action.
- A number of detectors shall be
suitable for the transformer and mounted at the cover level of the transformer. The
detectors shall detect any amount of abnormal temperature rise generated by a
fire on the transformer tank, or the terminals, or even on the transformer's bed.
-
The detectors shall be designed
and equalized such that they do not operate at slow temperature rise which may
occur due to variation of load, ventilation, solar effect…etc and shall ensure
complete security such that it will not be operated due to any reason except
fire.
-
The detectors shall be connected
in series by a fire-resistance cable which is connected to detection unit and
the detectors shall be simple, study inspects vibration proof and moisture acid
resistant construction.
- A double detection system shall be
designed in order to prevent the activation of the extinguishing system due to
false indication.
-
In order to prevent the
activation of the system due to false indication, the detection system is
doubled with one piping system pressurized by air and with thermo activated
nozzle and with one electric differential thermal activated system the water the spray system is activated only when a fire detection signal is given from the two
detection system at the same time. The activated system shall be indicated in a
control unit and activate in the area fire alarm signal.
-
Provision shall be made for a
guard current flowing through the detectors. Interruption of the guard current
due to the breaking of the elements series connecting cable or load terminal shall
activate an audible and visible alarm signal at the detection unit of the
equipment indicating interruption of guard current. This alarm signal must not
activate the extinguishing system and the signal can be used for blocking the extinguishing system if needed.
Fire Extinguishing System for Outdoor Power
Transformers
- In order to extinguish a fire in the shortest possible time, the transformer shall be provided with a high-velocity water spray system. The water spray system shall be provided as a conventional system with pressurized water in the tubes and crown, pressure, and closed spray nozzles or as an empty system with an open spray nozzle. Any provided system shall fulfill the regulations in the following:-
·
High-velocity water spray system
for transformer system design and installation instructions (automatic
sprinkler corps of America).
·
NEPA15 water spray fixed systems
for fire protection association inc./ USA)
-
This system consists of two
cages of tubes surrounding the periphery of the transformer at suitable
distance apart.
-
The cages shall be supported and
held in place by a re-fixed pipe arrangement, and the part of the cage at the
side of the running rail shall be disconnectable.
-
One of the two cages shall be
fixed at the height of the transformer cover and the other at a height straight
above the transformer bed.
-
The cages shall consist of
prefabricated parts which are hot-dip galvanized after forming and mounting on
spot without damaging the galvanization.
-
Each cage shall be equipped with judiciously directed spray
nozzles having sufficient number to ensure complete flooding and coverage of
the transformer by means of sprayed water. The nozzles shall be protected with caps arranged to blow off when nozzles
operate.
-
This system consists of tubes,
pipes and nozzles, when a fire is detected a deluge valve are opened and the whole system with its open spray nozzles is activated.
-
Automatic deluge valve assembly
should be complete with pressure switches, pressure gauge, drain and test
valve, site drainage system, etc. The site drainage system should be designed to
clear the water discharged from the drain and test valve during periodic tests. An automatic deluge valve simply should be protected from adverse
environmental conditions.
Function
Power
transformers water spray fire extinguishing system shall comprise as in a schematic
diagram an air pressure water tank has an insulating air cushion in
order to protect the transformer in case of fire without electric energy. As
temperature control, melting nozzles are installed inside the pressure
activator line on the transformer. In case that the temperature limit is
exceeded, the melting nozzles break and the air in the activator line escapes.
Due to this sudden pressure drop, the valve station (deluge valve) opens
immediately.
The insulating The water tank pushes the water out of the air pressure water tank through the deluge
valve into the spraying cage. Which is assembled on the transformer.
The air
pressure and the water level inside the water tank are continuously controlled and
automatically filled up by appropriate devices.
The manual
operation is carried out with an excitation valve in the valve station causing
the same action achieved by the separate excitation air pipeline in the
automatic operation. Push buttons for manual operation shall be completely
secured against the unauthorized operation and accidental system operation.
Automatic deluge valve assembly shall be complete with pressure switches,
pressure gauges, drain and test valve, site drainage system… etc. Site the drainage system should be designed to clear the water discharged from the drain
and test valve during periodic tests, and the automatic deluge valve assembly shall also be protected from adverse environmental conditions.
Air Pressure Water Tank
-
The water supply shall consist
of storage vessel put under pressure by pressurized air.
-
The water storage vessel shall
be externally and internally galvanized
with an anti-corrosion coat approved by a qualified organization and
tested at a pressure not less than 150% of the operating pressure.
-
The storage vessel shall be
equipped with filling, inlet, discharge outlet, discharge pipe in the direction of the pressure of the spraying cage, and a pipe in direction of compressed air.
-
The water pressure shall be
sufficient to charge the water vessel to the specified pressure within a time
not more than 3 hours.
-
The capacity of the storage of the vessel shall be sufficient to maintain flooding of the biggest transformer for
a time not less than stated in standards and regulations.
-
The water pressure system shall
be a dual system one in operation and the other is standby. Each one should have
its own control, protection supply, etc., and will be adjusted on operation mode
or standby mode by a selector switch.
-
Push buttons for manual
operation shall be completed secured against an unauthorized operation and the accidental system, technical specification for systems components, and mounting
as stated in the regulations should be submitted with tender standby, system
should comprise the following:-
·
Air, compressor complete with
driving units.
·
Pump complete with driving unit.
The water
pressure shall meet the requirements of
efficient operation of spraying nozzles.
Spraying Cage for Transformers
The cage is
self-supporting and shall not be fixed on transformers, the cage can easily be
opened. The water spray system will be released automatically by bursting one of the glass bulb sprinklers which causes a pressure loss in the pneumatic
incitation pipe, together with a signal from the electrical detection system.
By these two actions, the deluge valve concerned will be opened and the water
can flow towards the nozzles installed in the spray cage to flood the transformer.
Electrical / Control For Automatic
Process
The control
cabinet shall be with a degree of protection IP54, the signal from automatic fire
detection system shall be received by the fire alarm control panel, heat
dissipated shall be controlled by a thermostat. CPU and the control shall include
air pressure, water refill, and run dry safety device of the filling pump.
TESTING
If the supplier
has carried out type tests on the offered equipment in the last ten years
according to the relevant standard then the supplier shall provide type test
certificates for the approval of the owner, otherwise type tests have to be
carried out in the presence of the owner.
ACCEPTANCE AND REJECTION
The supplier
shall forward to the purchaser, three copies of certificates proving that all
tests required have been carried out and also samples & catalogs of the
equipment.
SPARE PARTS
List of manufacturer’s recommended
spare parts shall be included in addition to spare parts requested by the purchaser
if required.
GUARANTEE
The supplier shall guarantee fire
fighting equipment against design, material, and manufacturing defects for a
period as given in tender documents.
SUBMITTALS
Required
Submittals:-
- The number of documents required under this clause shall be three (3) in all cases.
-
The supplier shall complete and return on
three (3) copies of all schedules are attached to this specification.
-
A list of international /
national codes and standards specification covering raw material, components,
test procedures, etc and a list of tests normally carried out on material and a
description of test equipment used shall be supplied.
-
A short description of
manufacturing processes and equipment employed for production shall be
provided.
-
Detailed physical,
characteristics and electrical drawings.
-
Dimensioned drawings of complete
equipment and its detailed components with a brief description of erection and
maintenance requirements.
-
Fully detailed type test
reports.
-
Details of routine tests to
which all units will be tested before dispatch.
-
Supplier’s recommended training
requirements for purchaser’s staff.
DELIVERY
The manufacture shall be responsible for and shall repair or
replace at his own expense any and all damaged equipment where damage was due
to improper preparation for supply.
REFERENCE LIST
The tenderer shall submit a reference the list that the proposed equipment has been in successful operation in an integrated system on three different substations of same or higher capacity outside country of the manufacturer and/or in EEHC network for a period not less then three years during the last ten years.
No comments:
Post a Comment