What does must be specified when ordering  transformer ? Tensioning Servicing Maintenance

WHAT DOES MUST BE SPECIFIED WHEN ORDERING TRANSFORMER ?

a) Technical specifications : indicate the following

• The rate power of the transformer in kVA or in MVA
• The network frequency
• The value (values) of the primary voltage
• The value (values) of the secondary voltage and specify if it is the off-load or the in-load working value
• The vector group number and symbols (example Dyn11)
• Indicate if the neutral is either extended or not
• The number of the tap changer positions out of voltage and the percentage of variations for every position.
• The transformer filling type (hermetic, breathing)
• The type of installation (in cabin, outside, pole mounted)
• The maximal ambient temperature and the altitude of the installation site

b) Accessories

Specify the requested special accessories (see the list of all accessories above)

c) Other information

In case of imposed dimensional requirements (length, height, width) for example by measurements of an existing cabin, specify the out of all maximum measurements.

In case of installation in parallel with one or several existing transformers, indicate the following :

• The transformation ratio for all connections
• The short circuit voltages
• The coupling and hourly indications
• The rate powers

TENSIONING

Before starting the transformer, it is necessary to verify the following  :

• That the values of the voltages indicated on the name plate correspond well to those of the network
• That the tap changer is on the good position
• That the level of oil is correct
• Measure the windings continuity for every position of the tap changer
• Measure coil insulation by the mega ohmmeter
• Install the air dryer

SERVICING

The transformer living-length depends on conditions of exploitation, this life be shortened by a bad exploitation of the transformer. For a good exploitation of the transformer it is necessary to :

• For the case of indoor transformers, to assure a good circulation of air in the local.
• To avoid the prolonged overcharges and the anomalous overcharges.
• To possibly use batteries of compensation of the reactive energy.
• To assure the regular maintenance of the transformer.

Periodic operations with a lower time interval to one year

• In case of utilization of an air dehydrating breather, verify the color of active SILICAGEL grains and proceed if necessary to its regeneration by heating.
• Test the good working of control organs
• Clean the cross-over bushings
• Verify the electric adjusting tightening
• Inspect the level of oil
• Check visually the color of oil
• Retouch the paint if necessary

Periodic operations with a lower time interval to 4 years

Take a sample of oil and measure its dielectric rigidity (oil must be reprocessed if its rigidity is lower than 20 kV).

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