Transformer
Installation - Some Best Practices
There are many problems that can be avoided during transformer
installation simply by installing the transformer in the correct environment.
Many difficulties and safety hazards can be avoided or minimized by keeping
certain factors in mind while positioning a transformer, before it is set up
and connected. Likewise, the location can have a bearing on how the transformer
should be set up, and what precautions should be taken in the future.
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| Transformer Installation |
The Standards
Installing transformers in accordance with the ANSI, NEMA, and IEEE
standards is critical to ensuring a safe electrical installation as well as a
reliable power supply system - especially for those applications where power
quality is an issue. Transformer installation is one of the most
common-yet-complicated installation practices that are cause for considerable
confusion when sizing Over Current Protection Devices (OCPDs) and bonding and
grounding conductors.
Many electrical installations can be a challenge in terms of NEC
requirements, and transformers can raise that challenge to a new level. A
properly designed installation will ensure the conductors and equipment are
properly sized, protected and also deal with the overriding issue of grounding.
Incorrect installation can lead to fires from improper protection or conductor
sizes, as well as electric shock from inadequate grounding.
This article will provide a brief overview of important considerations
to keep in mind during installation, of transformers located outdoors and
indoors, and for dry-type vs. liquid-filled transformers.
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| Transformer Installation |
Installation Best Practices Some of the particularly important
transformer installation best practices are listed below:
1. Permanent Grounding: Once the transformer is placed permanently -
before further inspection is carried out and before assembling the unit - the
tank should be permanently grounded with a correctly sized and properly
installed permanent ground.
2. Humidity: No access should be permitted to the transformer
liquid-filled compartment in conditions of excessive humidity or rain. If
humidity exceeds 70% for example, dry air should be continuously pumped into
the gas space. Liquid-filled transformers that are shipped with Nitrogen in the
gas space must be purged by pumping dry air for at least 30 minutes before
service personnel can enter the tank. Oxygen concentrations of 19.5% to 23.5%
are advised.
3. Fluid Inspection: If the insulating liquid for inspection needs to
be drawn down, make sure you have equipment for clean and dry storage of the
liquid during inspection and for filtering the liquid prior to refilling the
tank. It is very important that all associated equipment used in the handling
of the fluid (hoses, pumps, etc.) are also very clean and dry. If this
equipment was used before with a different type of fluid, clean all
contaminated items. When you remove the liquid, its level should not go below
the top of windings.
4. Pressure Maintenance: Liquid-filled transformers may be stored
outdoors upon delivery. Sufficient gas pressure must be maintained to allow a
positive pressure of 1 psi to 2 psi at all times, even at low ambient
temperature. The pressure-vacuum gauge, if supplied with the transformer, will
show pressure variations with ambient temperature. Pressure and ambient
temperature readings should be recorded regularly. The manufacturer's
instructions must be referred to for storage of accessories.
5. Inspection and filling: You should make a final inspection of the
transformer before it is energized, particularly if any work has been done
inside the tank. All electrical connections should be checked for tightness.
All bushings should be checked for tightness of gaskets, and all draw lead
connections should be checked. Electrical clearances inside the tank should be
checked. One final check should be made to ensure all tools have been removed.
6. Loading: After applying full voltage, the transformer should be kept
under observation during the first few hours of operation under load. After
several days, check the oil for oxygen content and dielectric strength. All
temperatures and pressures should be checked in the transformer tank during the
first week of operation. Except for special designs, transformers may be
operated at their rated kVA if the average ambient temperature of the cooling
air does not exceed 86'F (30'C) in any 24-hr period, and the altitude does not
exceed 3300 ft.
7. Surge arresters: When used, surge arresters must be installed and
connected to the transformer bushings/terminals with the shortest possible
leads. These arresters may be necessary to protect the equipment from line
switching surges and lightning.
When the Transformer is Under Vacuum, Never,Never...
* Apply voltage to the transformer
* Leave it unattended; a positive pressure must be applied
* Stand or walk on the transformer tank
8. Structural Considerations: Multiple transformers can be mounted on a
single pole as long as the weight is evenly distributed, and the total weight
is well within the safe limits of the pole, any cross-arms or supporting bolts.
9. Mounting: Sub-100 kVA single-phase distribution transformers are
typically mounted above the secondary mains. Platform or pad mounting are
options for transformers larger than 100 kVA.
10. Protection: Apart from self-protected transformer types, all
distribution transformers must have lighting arresters and fused cutouts
installed on the primary side.
11. Ground wires: Cover all ground wires with plastic or wood molding
to a point 8 feet above the base of the pole.
12. Guying of poles: Correctly installed guy wires can protect the pole
line from damage caused by the strain of the line conductors and pole-mounted
equipment, and minimize pole line damage caused by severe weather.So most important of Transformer Installation.
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