• No results found

Construction Standard

Installation and Operation

3. Construction Standard

Firstly, the characteristics of the transformer have to be obtained from the nameplate which shall be affixed to the transformer tank as per the requirement of the relevant standards. The nameplate shall provide the necessary information for transformer energizing, installation and operation. The nameplate shall include all relevant information. Secondly, the transformers will be separated, and warehoused for future extension power distribution planning. Various recommendations will be briefly discussed, and an explanation of the other transformers will be clarified in detail, according to the utility’s construction standards.

3.1. Name Plate

a. Serial number: To identify each and every transformer manufactured by the manufacturer, the utility has to refer to this serial number when service is required. For the utility’s transformer management’s utilization, items such as: rated capacity monitoring, maintenance services, etc.

should be noted and utilized. The utility should mention in the contract that they wish to obtain another running serial number which belongs to the utility’s references.

b. kVA: To signify transformer capacity or kilovolt ampere capacity.

c. Phase: This is the phase at which transformers are designed to operate.

d. Frequency: This is the design of the transformer to meet the frequency of the electricity supply.

e. Voltage & Ampere: To signify the primary and secondary voltages, whereas the displayed ampere is the rated normal electricity current on primary and secondary side.

f. Type: This is the method of cooling system used to cool the system from the heat generated during the transformer operation.

g. Insulation class: This is the classification of the insulated materials at which the transformers can withstand either the electricity current or the temperature rise.

h. Temperature rise: This is the average of oil temperature rise and winding temperature rise above ambient temperature at the rated kVA.

i. Percentage of impedance: The real figure is obtained from testing which will affect the transformer losses.

j. Oil quantity: To signify the quantity of transformer oil to be used in each unit of the transformer.

k. The total weight (kg): This is the total weight of the complete set of transformer.

l. Winding connection diagram: This is provided to show the relevant location of bushings and internal terminals. The winding connection diagram will be designed to meet the utility’s system configuration.

m. Vector group: Follows the international standard per the specification mentioned by the utilities’ system designer.

3.2. Storage Management

It is recommended that if the transformer is not to be put into service immediately, the unit be placed in its permanent location and be filled with oil.

The foundation should include: that it be placed on a solid level foundation in the storage area (as soon as possible), it should be dry and protected from the effects of weather, or preferably stored indoors. This will contribute to keeping transformer dry and the paint in good condition.

If the event that two or more transformers are stored together, there must be sufficient space between the transformers to prevent collision on any projecting attachments and also allow space for routine visual inspection.

If the transformer is stored longer than twelve months, it should be checked before installation. Check the condition of all the safety gauges; manually turn the tap changer to all positions till smooth turning occurs. An oil sample should be taken for analysis; the result should not be lower than 30kV/2.5mm. The tests results should be verified with the original results from the factory to assure they are still within acceptable limits.

3.3. Installation Management

a. Transportation

The Transformer must be properly secured to prevent shifting and movement during transportation and handling. Jolting and vibration should be avoided. No pressure should be exerted on the radiator or corrugated fin.

The transformer must be handled in the normal upright position and lifting from the lifting lugs on the tank (if provided) or lifting on the cover in the event that no lifting lug can be utilized. Likewise, the jacking pads are to be used for jacking purposes.

Note: Do not attempt to lift/jack the transformer other than the fitting parts provided for this purpose.

The liquid immersed transformers, hermetically sealed type, are suitable for indoor and outdoor installation. It can be moved to the designated position utilizing wheels, roller, crowbar or pulley and must be levelled when installed at the designated location.

b. Indoor Installation

Transformers with natural cooling depend on the surrounding air to dissipate its heat. There must be sufficient ventilation for the transformer.

Warm air will rise to the top and cool air flows down. A good ventilation transformer room should have an opening on top to dissipate the warm air and a bottom air inlet to intake the cool air. Both must locate diagonally across the room.

As a guide, losses of 1 kW require an air flow of 5.2 m3/min, with air intake temperature at 30°C and air temperature rise of 10°C. The noise level measurement should be monitored according to the reference standards.

For the air to circulate freely around the transformer and access maintenance facilities there must be a distance of at least 0.5 meter between the transformer and the wall of partition, the same precaution must be taken should there be several transformers in a room.

c. Outdoor Installation

It is recommended that transformers to be utilized for for outdoor installation, be installed on a solid plinth. However, if plinth is not available, the base shall be strong enough to support the transformer. The weight of the transformer is stated on the transformer rating plate. The samples of the construction standards has shown the single concrete pole installation and the two concrete pole or plat-form type in Figure 18 & 19 in Figure 20 & 21 respectively.

d. Cabling

The cables connected to the transformer must be properly supported and clamped to prevent unnecessary strain on the HV bushings and LV bus bars. If the cable boxes are supplied, the cable gland plate and cable must be properly tightened.

e. Bolt Tightening Torque

• Torque Setting for various bushing and bolt sizes.

Bushing Bolt Size Tightening Torque (Nm)

1/250 M12 14

1/630 M20 24

1/1000 M30 36

1/2000 M42 70

1/3150 M48 70

• Torque Setting for various bolt sizes used in bus bar Connections - Steel

Bolt Size Tightening Torque (Nm)

M6 6-9

M8 15-22

M10 35-44

M12 70-75

M16 120-150

f. Energizing the transformer

When the voltage is first applied to the transformer, if possible, it should be brought up slowly to its full value so that any incorrect connection or other problem may be diagnosed before damage can occur. If this is not possible, then energize without load.

It is recommended, especially if the excitation is through cables or fuses, that the output voltage be measured to ensure that all three phases are energized. After full voltage has been applied, the transformer should remain energized at full voltage for a few hours without load. It should be kept under observation during this time and also during the first hours that it delivers electricity to the loads.

g. Check the transformer after energizing

The transformer should be checked after energizing to ensure that it is in normal operating condition before loading as follows:

Check the LV voltage. If the voltage is insufficient, then de-energize the transformer to reset the tap changer to the correct voltage level.

Check the phase sequence. If the phase sequence is incorrect, then de-energize the transformer to re arrange the cable connection.

Check the transformer noise. If the humming sound is abnormal, then de-energize the transformer and notify the manufacturers.

Related documents