System Voltage Nos. E M Strength kN Nos. E M Strength kN 1. Thereafter, the complete hardware assembly with the conductor shall be hoisted up and fixed on the beam at this end. Sagging arrangement shall be made on the other end of the bus and the conductor shall be tensioned. The conductor shall be cut to the marked length after deducting the length of the tension hardware with insulators and fixed on the clamps of the tension hardware. The conductor along with tension hardware set shall then be again pulled up and connected to the beam.
Bus Bar Earth Wire 49 3. Spacers are not used at jumper points in case T — Spacers are used for taking jumpers from multi conductor bus bars. Thereafter, the bus bar conductor s shall be again connected with the jumper conductor s using properly curved shaped Y — conductor s and 2 nos. PG — clamps as shown in the diagram above. This shall be connected to the bus bar conductor on one side of the beam after taking into consideration the natural curve of the conductor.
The other end of the conductor shall then be taken up to the bus bar conductor on the other side and measurement of the length shall be taken. The conductor shall be cut to the appropriate length and then connected to the bus bar conductor on the other side. The length of the conductor used and its natural curve should be such that a neat and proper curve is obtained in the jumper without any kinks or bends. The clamp of the suspension hardware shall then be tightened after ensuring proportional lengths of the conductor on both the sides of the beam.
The conductor shall be passed through the clamp of the suspension hardware. The appropriate length of the conductor shall be cut and then straightened so that curves and kinks are removed. The methodology followed for system up to kV is by suitable placement of earth wire so as to provide coverage to all the station equipment.
For longer lengths, the wire drum shall be placed on a turn table or jacked up on a suitable size of steel shaft. Bus Bar Earth Wire 51 5. These shall be connected together using a PG —Clamp. The diameter of the pipes is To reduce welding work at the bus height in case longer lengths are required, a maximum of 4 to 5 lengths of aluminium pipes may be welded together on the ground using straight run couplers.
The pipe length is then lifted and erected on the post insulators. One end is fitted on the terminal connectors of the equipment. In addition, a stainless steel wire brush shall be used for cleaning the surfaces. In cases where outer diameter of sleeve does not match the inner diameter of pipe, the sleeve shall be got turned to match the inner diameter of the pipe.
The centering pin of the coupler is fitted in the hole provided for it and the pipe ends are brought together until they touch the centering pin. This flow of inert gas on joint should continue for at least 15 seconds after the welding of joint is completed.
Aluminium Pipe Bus Bar and Joints 55 4. If more layers are required at the joint, every bottom layer shall be cleaned with wire brush and checked for cracks before starting welding of the second layer.
If any crack is observed, the whole layer shall be chipped off and refilled. Unacceptable joints shall be chipped off for re — welding. The necessary arrangements for welding of joints at such heights shall be made. However, accessories such as condenser bushings, radiators, conservator, headers, pipe work and A — frame can be stored under covered sheds. A positive pressure generally 0. In case of reduction in pressure, it should be maintained by filling in gas from the cylinder on the transformer.
The weather conditions during transformer erection should be dry. The transformer tank should not be opened when it is raining. This oil is then filtered in the tank s. The vacuum pipe is generally connected to the pipeline between transformer tank and conservator.
The extent of vacuum and the time duration of its application shall be as per Manufacturer's recommendations. In case this is not specified by the Manufacturer, then vacuum of 1. The oil level can be seen in the transparent plastic pipe provided. The rate of release of vacuum should be kept very slow so that the silica gel in the breather does not get sucked into the tank. Power Transformers 59 Additional precautions prescribed by the Manufacturer for dry air and human safety during such erection activities should be followed.
This oil is filtered in the tank until the values given at para 2. The arrow marks on the oil pumps and oil flow indicators should point towards the transformer tank. Ensure that diaphragms are fitted on both ends of the vent pipe.
The arrow marks on the Buchholz relays should point towards the conservator. Where two Buchholz relays are provided, the relay near the tank is designated as Buchholz Relay — I and the relay near the conservator as Buchholz Relay — II.
Ensure that the sealing provided on the air passage of the breathers has been removed. The arrow marks on the oil surge relays should point towards the conservator.
The levelling, centering and grouting of ground mounted supports is to be got done before erection. In case these are ground mounted, then these are to be placed on the foundation, levelled, centered and then grouted. The readings of IR values shall not be taken during this process since these will be misleading due to erroneous indication of winding temperature.
After about 8 — 12 hours of circulation in this manner, the cycle is reversed, i. The test voltage of 5 kV is applied for one minute. The winding temperature is assumed to be the same as top oil temperature under steady state conditions. If there is moisture in the windings, then, the IR values at constant temperature will drop down as the moisture is removed from the insulation and gets dissolved in the oil.
The moisture in the oil is continuously removed by the filteration plant. After the moisture has been removed from the winding, the IR values will start rising as the dissolved moisture in the oil is removed.
These reach a constant value after the drying out is complete. The dehydration process is thereafter continued for a minimum of another 24 hours or until the oil values given at para 8.
In such a case, the dehydration is stopped after the time prescribed by the manufacturer. If no such time is prescribed, then the dehydration at constant temperature is carried out for a minimum of 72 hours or until the oil values given at para 8. Measure the IR values at 2 hour intervals during the cooling period.
A typical indicative drying out curve is shown below: Power Transformers 61 8. Insulation resistance varies inversely with the temperature. If the specified IR values are achieved, the transformer can be charged. However, in case of transformers within guarantee period, the manufacturer is to be contacted. The process at d is mostly adopted and is described at para 8. After maximum top oil temperature is attained, the hot oil circulation is continued for 2 — 3 volumes of the transformer oil.
The IR values and the temperature are noted. The precautions, as given earlier, for application of vacuum para 2. Start hot oil circulation and continue for 2 — 3 volumes of the transformer oil after maximum top oil temperature is attained. If there is improvement in the IR values, then the above process as given at para 8.
If still there is no change, then the drying out process is stopped, otherwise it is continued till two consecutive readings are same. These are compared with the reference values. If the previous IR values are achieved, the transformer can be charged. This can be checked by ensuring that there is no oil in the Buchholz relay s. Connect the air filling device, which is provided with a pressure gauge and a filling pipe in which a non return valve is fitted, to the breather pipe.
Any valves in the breather pipe should be kept open. Power Transformers 63 9. Close the air release valve such that the flow of oil will be very slow. Where air release plugs are provided, they should be fitted but not fully tightened. Oil mixed with air bubbles shall start coming out. The prismatic oil level gauge, if provided on the conservator, will indicate full oil level.
The oil is allowed to come out until there are no air bubbles in the oil. This oil is filtered in the OLTC diverter switch chamber s until the values given at para 8. Condenser type Bushings. When connecting the operating shaft s , ensure that the tap position indicated in the OLTC drive mechanism and at the head of OLTC diverter switch es are the same.
Lock the bolts nuts of the coupling brackets of the operating shaft s , if provided. Prior to putting the transformer into service, attention should be paid to the checks and tests given in the following paras. Problems arising out of peculiar situations are to be assessed and solved on case to case basis.
Power Transformers 65 If found necessary, re — tighten the bolts. Close these after the above check has been carried out. Power Transformers 67 protection, Transformer Differential protection relays, associated Master Trip relays, alarm annunciations, etc. This may be checked for operation of each Master Trip Relay for 2 or 3 protective relays. There should be no electrical operation of the OLTC with handle inserted.
Never start this OLTC operation from extreme tap positions. LV winding is kept open — circuited. There should not Power Transformers 69 be any break in the current during tap change which is indicated by the sudden deflection in the multi — meter reading. The 60 second value shall be taken as the reference value for future comparison. The top oil temperature is to be recorded.
The following tests are generally desired to be got carried out on transformer oil as per IS : — Code of Practice for Electrical Maintenance and Supervision of Mineral Insulating Oil in Equipment.
The limits for unused mineral oil filled in New Power Transformer as recommended in Table — 1 of the above Indian Standard are given below. Highest Voltage of Equipment kV S.
Property of Oil Appearance Clear; free from sediments and suspended matter 2. Density at Water Content ppm , Max. Breakdown Voltage kV , Min. Dissolved Gas Analysis For Reference 9. The limits as recommended in Table — 1 of IS are also given below.
During this period observe the temperature rise of the oil winding. Tap position same voltage ratio should also match with the transformer already in service in case of parallel operation. Total views 5, On Slideshare 0. From embeds 0. Number of embeds 7. Downloads Shares 0. Comments 0. Likes 5. You just clipped your first slide! Clipping is a handy way to collect important slides you want to go back to later. Now customize the name of a clipboard to store your clips.
This process typically consists of a series of stringent visual and physical inspections and actions carried out according to a set schedule.
All inspection and actions during substation maintenance should be accurately documented and stored for further reference. Substations are the most critical part of any electrical supply grid.
Substation care is one of the most important parts of any electrical department's preventative maintenance schedule. These schedules generally consist of a tiered plan of minor and major maintenance events. Minor maintenance will seldom require any sort of power shut down although major events typically requiring short intervals of supply interruption.
Figure 10 — One circuit breaker and a half configuration Figure 11 — Triple busbar configuration. It is used in substation where the division of bays between the two busbars and the possibility to change bays to one busbar to the other are operations that allow increasing the continuity and the reliability of power supply , minimizing the number of bays out of service when the breaker failure protection actuates as shown in fig With this configuration , if there is a bus coupling bay and the line and transformers bays have a bypass isolator is possible to keep the continuity of power supply when there is a fault in the circuit breaker or it is breaker maintenance operations are necessary.
This configuration is more expensive than the double busbar configuration and requires a more complex protection system , but maintenance costs are reduced. With triple busbar configuration it is possible to execute maintenance operations on a complete bay , which is totally placed in bypass mode. One circuit breaker and a half and triple busbar configurations are only used in EHV installations.
Figure 12 — Schematic layout of earthing system. This system , which functions are performed by a set of equipments and sub-systems , has a topology architecture usually with 4 levels and is designated as DCS Distributed Control System , as shown in Figure Figure 14 — Schematic typical architecture of substation control, monitoring and protection system. Under normal conditions local control is only possible with the authorization of the person in charge of the operation of the substation that must release this function to the assigned local operator.
The control of circuit breaker and isolators is made according to the defined interlocking programme. The system usually performs the following control and monitoring actions:. For safety reasons the actuation of protection units is done directly to the tripping coils of the circuit breakers and should not be done through the PLC.
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