EHV SUB STATION

Construction – & Commissioning.

Mr. A. S. DAITHANKAR, Retd. S.E. MSETCL, Pune

In the last lecture we have seen the lay outs the positioning of various equipments in the sub stations also we have seen the equipments in the sub substations.

Your are aware of purpose of each equipment in the sub station.

In this session we will discuss mainly construction and commissioning of these equipments.

The purpose of equipments will be explained in short

1. These sub station land is initially selected and the final level to be kept for construction of sub station is decided on the basis of contour survey of the sub station land. So that the land development is carried out economically.

2. The land development is then carried out accordingly

3. The sub station equipments and gantry foundations are then cast. The control room is also constructed as per drawing.

Construction and commissioning of sub station

Construction and commissioning of sub station is a subject describing the actual execution details.

• The arrangement of 3 phase supply upto 200 KVA

• Erection of sub station columns and beams.• Stringing of various buses in the sub station.• Erection of equipment structures and

equipments

• Erection of equipment is control room• The earthing mesh and earthing electrodes

work• The equipments are connected to each other,

to bus, etc. by carrying out jumpering work as specified in the lay out .

• The clamps and connectors are used while jumpering

4. The construction of sub station includes some of following activities.

• Commissioning of breakers, isolator alignments are carried out.

• Battery charging, charger commissioning making DC supply available for testing purposes.

• Commissioning of C & R pannels relays etc.• The transformer erection filteration and testing

• Lightining in control room and switch yard.• Metal spreading • Commissioning after proper testing is carried

out.

1) Before Erection of Equipments all the civil foundations for them are already cast as per the sub Station layouts. The Foundations bolts for Equipments grouted.

2) The approach roads are made to take the crane, truck, etc near the foundations.

Erection and commissioning of Sub Station Equipments

Once above said activities are completed the actual erection of equipments Starts.

The main Equipments in any sub Station involving No. of activities during

erectioning and commissioning are.

(1) Circuit Breakers

(2) Power transformers

(1) Circuit Breakers SF6 circuit breakers are now used in EHV Substations SF6 gas is used for arc-quenching purpose, and as a dielectric material.

(a) Transportation of breaker form store yard to foundation is carried out with the help of crane and trucks.

(b) Unpacking - All the packages containing various materials of breaker should be unpacked, checked for any shortages or damages of materials.

The purpose of breaker is to isolate the faulty Equipments / Lines from Healthy system and maintain the system stable. They are operated through protective relays on the C & R pannels. The control wiring is connected between breaker and C & R Pannels. The breaker can be operated from remote pannels through operating switches on pannel or locally, electrically, manually .

(c) In case of breaker where the mechanism box serves as the base for the pole Unit assymbly, the mechanism boxes are first erected on foundations and levelled on foundations and the foundation bolts are tightened. In other cases steel structures for mounting pole assembly are first erected on the foundations, levelled and the foundation bolts are tightened.

(d) The pole Unit assymbly is then carefully lifted by crane, after properly tying it with ropes and fixed on the base structure with the help of foundation bolts.

(e) The pole unit assymbly is then connected to operating mechanism with the arrangements available for individual breaker.

These Air pipe Lines of copper of required diameter and wall thickness, are laid care fully through cable trenches with proper supports to avoid the vibrations.

The desired air pressure required for operating the breaker is then filled in these pipes from compressor.

The pipe Line is checked for any air leakage with soap water.

(f) In case of pneumatically operated breakers the air piping is connected between Air compressor operating mechanism & pole unit. Assymbly.

(g) Connection of SF6 piping

The SF6 gas pipe Lines are connected to pole Unit assymblies after checking that positive pressure of SF6 gas is maintained both in pipe lines as well in pole assymbly units.

The SF6 gas in filled in to pole assymbly units and pipelines from the gas cylinder through gas filling device to desired value for operation of breakers.

The gas leakage should be checked with the help of gas leakage detector, soap water.

(h) In Breakers slow closing and opening operations are carried out to measure contact travel, penetration of contacts, travel of mechanical Linkages in operating mechanisms.

(h) In Breakers slow closing and opening operations are carried out to measure contact travel, penetration of contacts, travel of mechanical Linkages in operating mechanisms.

(i) Inter phase wiring

The Inter phase wiring is carried out as per wiring diagrams of breaker control units, The cables are laid in trenches on cable trays properly supported, the cable glands should be used, the lugs are crimped on wires and connected on terminals. The connections are then tightened properly.

Commissioning: -

(1) Check operations of Air pressure switches for alarm trip, lockouts, compressor operations at their recommended values.

Once all these tests are carried out the Insulation resistance of breaker in open and closed conditions should be measured & breaker can be put in to service.

(2) Check the above operations of gas density monitor for lockout, trip, operations of breakers.

(3) The AC DC supply should be extended to breaker and the various timings. Like closing, tripping, close trip etc. are measured by connecting the timer. It should be ensured that these are within the recommended ranges.

The power transformer is very important and costliest equipment in the sub station, it should be handled carefully and erection should be carried out systematically ensuring proper checks at every step. Following precautions should be taken before taking up the erection.

Power transformers.

1) The person going on the transformer tank should not stand on any part of Diaphragm of Diverter switch.

2) No one should be allowed on the transformer top unless he has emptied his pocket.

3) All the tools and spanners should be securely tied with cotton tape. So that there will not be dropped inside the transformer tanks

Power transformers.

4) All components are cleaned out side separately before erection.

5) Fibrous materials should not be used for cleaning. The presence of Fibrous material suspended in oil will affect the electrical properties of oil.

6) Interior of the transformer should not be exposed to atmosphers as far as possible to avoid ingress of moisture in the transformer insulating paper, windings etc. In case of sudden change in weather bringing rain, provision must be made for closing the tank quickly and pressuring it with N2 so as to preserve the insulation.

Power transformers.7) Naked Lights and flames should never be

used near the oil Filled transformers.

8) Smoking, should not be allowed when the person is on transformer top cover, when the cover plats are open & also in the vicinity oil processing plant.

1. Oil filled transformer

Transformer of 132 KV class insulation even up to 50 MVA capacity and 220KV class up to 25 mvA capacity are generally dispatched and transported with oil filled up to core level. The remaining oil required for further topping up etc is dispatched in to sealed oil barelles.

The procedure for erection and commissioning is as follows.

a) The transformer is unloaded with rollers on the rails, and should be taken into it's proper position so that the jumpers from H.V. / LV side will be easily connected to the respective bushings.

b) The transformer rollers should locked by fixing, locking clamps on rails near them.

c) The accessories of the transformer should be transported near the working place and checked as per packing list. The accessories should be checked against damage if any.

d) The operating Valves should be properly cleaned and checked for the operation many times, before fitting on transformer. This is very important because once the valves are fitted on the transformer in various piping, it should be possible to open those fully without any trouble other wise it may lead to the obstruction or even stoppage of oil flow in future and it is very difficult to remove the valves once the oil is filled. It required draining the oil

e) The T & P required for erection is mainly crane with sufficient number of slings, polypropolin ropes of varies sizes. The common T & P such as spanners pipe wrench, Hexa with blades, etc should also be available as usual.

f) The turrets should be fitted on the main tank. The turret C.T.'s should be checked, before erection for their.i) polarity ii) Continuity iii) RatioOnce the turrets are fixed the bushing should the taken of erection.

The Erection of Bushings.1) The bushings should be thoroughly cleaned from

outside & inside with cloth & with C.T.C to remove the dust.

2) It should be tested for insulation resistance, tan delta before erection.

3) The locking Pin to lock the lead coming from the winding should be checked and made available during erection on site.

4) The bushing should be properly tied with ropes and should be lifted with the help of crane and fitted on the main tank turrets. The seat of the bottom portions of bushing on the winding should also be checked through inspection cover. The lead from the winding should be taken through the middle hollow portion of the bushing and Locked on the top of bushing with lock pin. Then the clamp is fitted on the lead & Jumper is connected to this clamp.

5) Once the bushings are erected other accessories like Headers, Radiators, Conservators, piping between tank, conservator & turrets etc. Should be connected.

H) Buchholtz relay -a) The inside contacts for alarm and trip operations

should be untied before erection as they are tied up during transportation to avoid the damage.

b) The Continuity of contacts for alarm and trip operations should be checked before erection.

c) The Buchholtz relay, should be fixed in the piping with it's arrow marked towards conservator.

i) The PRV :- The PRV should be tested for its operations before fixing.

j) Oil Surge relays: - There are fixed in the oil piping for Divertor switches. Contacts for Alarm and Trip should be checked before fitting.

k) The MOG :- (Magnetic Oil Gage) Showing the oil level is also checked by operating it externally. The contacts used for low oil level should be checked for continuity.

l) Once all these accessories are fitted the nut bolts should be tightened to prevent the oil leakage

m) Oil filling and Filtration of oil.

a) T & P Requirementi) Oil lank of adequate capacity.ii) Filter machine of preferably 6 KL/hr circulating

capacity and capable of achieving full vaccume of 5 torrs with main and roots vaccume pumps.

iii) The separate arrangement for evacuation of N2 Gas inside the transformer tank with simultaneous filtration of oil should be available on the filter machine.

iv) The filter papers should be cleaned and replaced if necessary

v) The heaters provided on the filter machine should be checked

vi) The LT Cable of adequate size to take the load of filter machine should be laid from ACDB with a main switch near filter machine.

vii) The rubber hoses, flanges of adequate sizes should be available to fit on the machine, storage oil tank and transformer as required.The oil storage tank, the filter machine should be properly arranged and AC supply should be connected to filter machine

viii) The oil BDV tester upto 100 Kv range should be available.

Oil filling1. Oil from the sealed barrels should be taken in the

storage tank through filter machine. 2. The oil storage tank should be cleaned from

inside before oil is taken in to it.3. Once the oil is taken in the storage tank it should

be filtered till the desired values of BDV and water content as recommended by the manufacturer are achieved.

4 Once the oil is ready it should be filled in the transfer tank from the bottom valve and the full transformer upto desired level in the conservator including headers, radiators should be filled.

The oil filtration should now be carried out by circulation of oil through filter machine. The inlet and out let pipes from machine to transformer should be changed as per requirement after certain hours.

All the floating impurities from the oil should also be removed during filtration.

5. The radiators should be flushed with the oil to remove the dust, foreign material from them if any before filling the oil.

6. The BDV of the existing oil in the main tank of the transformer should be checked before oil filling.

7. Now the oil leakage from all the joints should be check and attended by tightening the nut bolts

Oil filtration

Finally the hot oil should be sent to the transformer from the bottom so that transformer windings get heated. Filtration should be continued till in desired values of oil parameters and insulation resistance of windings are achieved.

The oil temperature in the filter machine should be maintained generally 60 to 65 Degrees Centigrade.

The diverter switch is also filled with filtered oil of desired BDV as per manufacture's directions.

Finally oil should be tested for different parameters as per IS insured that recommended values are achieved.

The IR values of windings and PI values should be checked and should be as per the recommendations of manufacture.

The driving mechanism and deverter switches are connected with connecting rods. The tap positions on the driving mechanism and diverter switch should be match.

The electrical wiring as per wiring diagram between transformer accessories and transformer mechanism box should be completed.

The wiring should be extended to control and relay panels

The neutral bushings of the transformer are separately earthed with copper strip at two separate earthing pits.

Other earthings to transformer body, fans, DM, etc. are provided with MS strip

The pre commissioning testing of the transformer is carried out. The operations of transformer breakers through protective relays are checked.

Nitrogen gas filled transformer

The activities upto checking and cleaning of the accessories, erection of transformer turrets, bushings, piping, cooling system are same as in case of oil filled transformer.

However at this point the filter machine is introduced for vaccume pulling from inside the transformer tank.

Following point are to be checked before pulling the vaccume

1. The pipes going to radiators and conservator should be blanked with blanking plates so that vaccume will not be applied to them.

2. The silica gel breather with gate valve should be fixed between the piping going to conservator to release the vaccume after oil filling

3. The diverter switch chamber and the main tank should be connected by hallow pipe so that both will be evacuated simultaneously

1) The oil should now be filled in to the transformer tank under vaccume. The vaccume pulling in the tank will avoid chances of air getting trapped or forming pockets. The oil is first filled upto core level in the main tank through filter machine.

2) This oil is filtered in storage tank before filling in the transformer. The oil is filled after the required values of BDV and water content are achieved.

Vaccume pulling

Vaccume should be pulled from the transformer tank up to the desired value recommended by manufacturer and should be maintained for atleast 24 hrs. After checking and attending the leakage's if any.

Oil filling

3) Once the oil is filled upto core level and windings and core are immersed under oil the vaccume is release through breather fitted as said above by opening the gate valve.

4) The pressure equalising pipe between diverted switch and main tank is removed. Then oil is filled in the remaining part of the transformer. The oil filteration is carried out after the oil filling is completed till the desired results of oil and IR values of transformer are achieved. The testing of the transformer is then carried out as in case of oil filled transformer. The transformer is ready for commissioning. The air venting should be carried out before commissioning

Conservatior with air cell

Now a days the conservators with air cell are used instead of conventional ones.

The contact between the atmospheric air and the transformer oil is prevented by air cell made of synthetic rubber component.

The principal of such system is that when the oil level in the conservator tank falls or rises due to contraction or expansion of oil. The breathing takes place through silica gel breather and the air cell.

1) WEB - used when the particular equipments is to be earthed. Normally up to 220 KV Sub Station these isolators are used on line side to earth the line when under shutdown for any work to be carried out.

2) Not operated on load; they are operated when they are disconnected from load side and source of supply and current may be only due to capacitive / charging currents of transformers and lines

3) To ensure that the isolators are not operated on load it is necessary that they are suitably interlocked with connected breakers. The isolators should be operated only when breaker is in open position.

Isolators two types

4) For construction purpose they are grouped as

A) Three post, centre post rotating double break isolates.

B) Two post (rotating) single break isolator.

A) The center post carries moving contact arm with contacts assembled at the extrem ends. The moving contacts engage the fixed contacts mounted on other post insulators on either side.

The rotating center post insulators of all the three phases are connected with the operating rods so that the simultaneous movement of each contact arm is ensured.

Rotation of center post insulator is effected through a lever at the base of each of it. these 3 leaves are connected to by operating rods and are driven from one post by these operating rods through a driver rod connected between operating mechanism (fitted on isolator structure) and driving post insulators. They can be hand or motor operated.

B) Single break isolators operated where in both the post insulators rotate causing movement of contact arm. The contact arm is devided in two parts, One caring male and the other female contacts. These are rotated through a down rod between operating mechanism on structure and operating mechanism between two post insulators.

Only one phase isolator can be operated mechanically at a time. However for simultaneous operation electrical operation is necessary or can be achieved mechanically as in case of double break isolators.

Earth Switch

5) Earth switch usually comparies of a vertical break switch arm with the contact at the extrem end and engages with fixed contact fixed on the post insulator on the line side. They have saperate operating box and operating system. Mechanical interlock is provided between main and earth swithches so that earth switch can be operated only when main isolator is off and vice versa.

b) These isolatos are operated form local as well from remote ends (i.e. pannels) The control wiring is to be connected accordingly between pannels and the operating mechanisms of isolators

c) The ON & OFF indications of isolators can be brought on the panels through aux. switches provided in operating mechanisms which operates while operation of the isolators.

6. Arcing Horns :-These are provided for insulation co-ordination. The use of arcing horns is avoided where the insulation strength between poles (i.e. phases) and between two poles of same phases when the isolator is open, is higher than that between live points of poles to earth.

7. Construction and commissioning a) The structure is assemble according to the

drawing provided and levelled properly.

b) The isolator base chaises are mounted on this levelled structure and fixed with nut bolts. The chassis are also levelled so that top plates of chassis where the post insulators are fixed are at the same level.

c) The post insulators are then mounted with on top plates of chasis with fixed contact and connecting arms (isolator blades), fitted on them.

d) The operating mechanisms are then fixed on the structurs and the operating roads fixed between three phases.

e) The isolator alignment is carried out first on each phase saperately and commonly for three phases through the operating mechanisms.

f) This alignment is first carried out for manual operations and then for electrical operations through motors locally.

g) The position of limits switches are adjusted to mach the travel of isolator blades while closing and opening. This is when the operation is through electrical motors.

h) The oilling greasing of gear boxes and moving parts on the mechanism is carried out where ever necessary.

i) The petroleum jelly is applied to contacts for easy operations and protection against corrosion .

j) The jumpers are then connected to the isolators and final operations are checked from local as well from remote end.

k) It is also checked as to whether the proper ON - OFF indications appear on the pannel.

l) The megger values between phase and earth as well between phase are measured.

m) Some times contact resistance is also measured. The isolators can now be taken in to service.

1. Voltage transformers

1. Voltage transformer step down the system voltage to sufficiently low values for

a) indication of voltage conditions b) Metering of exchange of energyc) Relaying d) Synchronizing

2. The indicating instruments, meters, relays are designed for voltages as obtainable from secondary sides of the voltage transformers.

3. The calibration of these instruments is however according to primary voltages of voltage transformer.

4. Construction and commessing 1. Supporting structurs assemble as per drawing2. They are fixed on the foundation and levelled

properly.3. The voltage transformer mounted on the structure

by fixing with the nut bolts.4. The meggare values checked5. The polarity and ratio checked6. The earthing is checked especially the second

terminal of primary winding is earthed.7. The oil level in the voltage transformer is checked8. If every thing is correct the voltage transformer

can be commissioned after connecting the jumpers.

5. Current transformers

Measurement of the current is one of the most frequent operations for following reasons

a. Indicating ammeters b. KWH & KW meters c. protective relaysd. telemetering

If current exceding several 100 of amps. are circulating through the equipments continuously the best solution is to obtain replica of these currents in primary circuits. This is achieved by means of current transformers

The current transformers are connected in series in network and is intended normally to operate with rated current in primary circuits

The secondary winding of CTs connected to measuring instruments and relays supply the current to them proportionate and in phase with the primary currents flowing in the network.

The Construction method is same as that of voltage transformers

5. Before commissioning ratio, polarity and the currents in the secondary circuits are checked, the oil level is checked, meggar values are checked. The CTs can be commissioned after connecting the jumpers.

6. Lightning Arrestors 1. The LAs are provided on lines and for

transformers.2. These are connected directly to line or bus

connected to transformer.3. The purpose is to earth the lightning surges to

earth and save the sub station equipment's and the transformers from the over voltages causing due to lightning.

4. The Lightning Arrestors should be effectively earth separately

5. Construction - The supporting structures are first fixed on foundation and leveled properly. and then Lightning Arrestors are fixed on the structures. The search counter provided should be connected.

6. Surge counter counts the surges passed through the Lightning Arrestors as well monitor the leakage current under normal conditions.

7. C & R PannelsThe C & R Pannels are mounted in control room the main functions are

a. To control the operations of breakers under normal and abnormal conditions of system

b. Provide indications of status of equipment's in the switch yards.

c. To indicate the current in the system, bus voltage, line voltage, temperature of transformer windings, oil etc.

d. Measurement of energy through energy meters

e. The annunciation of the fault in the sub station or any abnormal conditions is seen on the annunciator facia, alarm for trip and non trip signal are given

2. The C & R Pannels are mounted on the floor in control room near cable trenches so that cables can be taken in conveniently

3. The C & R Pannels are arranged in rows in the sequence according to that in switch yard.

4. Earthing is provided for each C & R Pannel5. Various relays are provided on this pannels for

protection of equipment's like transformers and lines etc. The appropriate protective relays are provided on the pannels for protection.

6. The relays are tested with testing kits and their characteristics are checked. The various functions of relays are also checked.

7. Once the testing is completed the settings are set on the relays according to proper protection co- ordination in the system as per requirement.

8. The operation of breakers, isolators are checked from the control switches provided on the pannels.

9. The indicating and measuring instruments like ammeters, voltmeters, energy meters are calibrated. It is also checked by primary injuction as to whether the indicate the proper values.

10. It is checked as to whether the status of equipments in this switch yard is shown correctly on the pannel.

11. The lighting in pannels should be checked, heater should be ON

12. After these checks the pannels can be commissioned and put into service.

a. The DC supply is required in the sub station for signaling remote position control, remote indications and similar purposes. The AC supply is not always reliable hence in no case of absence of AC supply the important purpose of control of CB in event of fault in sub stations, on EHV lines should be affected.

b. Fixed storage batteries can be used for these purpose.

They are lead acid cells Complete DC equipment's for sub station may be divided in to following parts.

a) Storage batteries and accessoriesb) Charging equipment'sc) DC DBs

DC Supply

The ratings of the batteries used is as follows

1. 132 KV sub station - 110 V (55 Cells), 200 Amp Hrs.

2. 220 KV sub station - 220 V (110 Cells), 300 Amp Hrs.

3. 400 KV sub station - 220 V (110 Cells), 500 Amp Hrs.

5. The stationary batteries under normal conditions do not deliver the energy but provide the same as and when required hence should always be in readiness

DC Batteries

a. Cell testing voltmeterb. Hydro meterc. Thermometerd. Acid jugs for toping the cellse. Rubber gloves f. rubber aprong. Tool boxh. battery log hooki. distilled waterJ. distilled water plant

6. Accessories

1. Battery room a. Battery room should be well lit with acid proof fitting b. The room should be closed no direct sun lights on the

cellsc. Exhaust fans should be provided in the room to exhaust

the gases produced during initial and trickle chargingd. Entry for fresh air should be given from bottom of the

room by providing a small window with wire mesh e. The floor and side walls up to 5 feet height should be

provide with acid proof tilesf. One basin should be provided with water tap for washing

hands and preparation of distilled water g. The distilled water plant is fitted near the basin on a wall

so that distilled water can be prepared as and when required. This is required for levelling the electrolyte the battery cells

Erection and charging procedure of DC batteries

a. The battery cells should be unpacked carefully without any damage to container. The cells should be lifted from the bottom and not by holding the battery terminals. after unpacking the batteries should be cleaned. Any dust or other material.

b. The electrolyte containers are packed in wooden packages these wooden packages are not to be removed even while pouring the electrolyte in to battery cells

c. The sulfuric acid is the electrolyte used in battery cells. The supplied sulfuric acid is concentrated to specific gravity around 1.8 to 1.9 hence has to be diluated to specific gravity of 1.2 by adding acid to distilled water and not vice versa. In a clean plastic container and should be rinsed by glass rod. The solutions should be allowed to be cooled for overnight and specific gravity and temperature should be checked. If the required specific gravity is not obtained add acid or distilled water as the case may be till correct specific gravity is obtained.

d. The proper care should be taken to wear apprans, gloves, protective goggles while preparing the solution.

Initial preparations and precautions before battery erection and charging

j) Arrange the wooden stands as per the battery layout drawing supplied and place underneath the legs of the stands stand insulators supplied, which are normally PVC sheets. Level the stands properly.

ii) Place the cell insulators on the stands at the appropriate locations and mount the cells on the cell insulators duly ensuring correctness of levels.

iii) Arrange the cells on the wooden stands, such that the positive terminal(s) of anyone cell, adjoin the negative terminal(s) of the cell throughout the battery.

iv) Where cells are to be placed in two rows and/or two-tiers, ensure that the positive terminal(s) of the end cell of one-row (or one tier as the case may be), is connected to the negative terminals(s) of the end cell of other row, (or other tier as the case may be).

Specific Instructions:

The connection between two-rows or tiers are made with the help of inter-row or inter-tier connectors supplied, wherever specified in the scope of supply.

v) Wipe out any dust collected on the top of the cover of the cells by means of a clean duster. Smear a little Petroleum Jelly on the threads, bolting faces and the bolt holes before bolting up the various connector. Connect the inter -cell / inter-row / inter-tier connectors sufficiently tight, to avoid any loose connections and again smear petroleum jelly over nuts, bolt-heads and washers. Even the exposed surfaces of inter-cell /inter-row /inter-tier connectors have also to be smeared with petroleum jelly.

vi) Connect the external cable from the battery charger, to the respective end terminals of the battery bank, once again ensuring the polarities. The positive terminals of the charger has to be connected to positive of the battery bank and similar is the case of negative to negative connections.

vii) While making connections care should be taken not to remove the throwaway plugs, so that no fastening material falls into the cell. Also, no metal should be left on top of the cells at any time.

Filling of Electrolyte A. Remove the throw-away plugs provided on the holes of

the cover and fix the vent plug cum level indicator in one hole wherever the cells have two holes, one for vent plug and other for vent plug cum level indicator. This applies to our cells of capacities 100 AH & above. Lift the electrolyte carboys containing dilute sulphuric acid "(supplied ready mixed or prepared previously, as the case may be alongwith the packing cases in-tact and pour the electrolyte carefully into the jugs supplied, from where pour the electrolyte into the cells through the vent hole with the help of a funnel. The level of electrolyte in each cell should be adjusted to correspond to the top red-mark on the float-guide. The bottom red-mark indicates the minimum level below which electrolyte should not go.

B. After filling-in with electrolyte, leave the cells idle for a period of not less than 12 hours and not more than 24 hours, until the electrolyte temperature falls down nearest to the ambient temperature. The plates will absorb the electrolyte causing a drop in the electrolyte level. Restore the electrolyte level by adding some more electrolyte of the same specific gravity used earlier for initial filling. Again replace the vent plugs without tightening. The battery is now ready for first charge.

First Charging

1. Check again the polarity of inter-celi/row/tier connections. Ensure that all fastenings and connections are tight. It is of utmost importance that the positive lead of the battery is connected to the positive terminal of the charger) The polarity is usually marked near the terminal provided on the charger. If the deflection is in the positive (clockwise) direction, the connections are in order. In case of reverse deflection, the leads should be interchanged and the test repeated as described above. The AC mains switch of the charger should remain switched off while taking the polarity test. After the correct polarity is ascertained, switch of the DC output switch of the charger.

2. Before placing battery on charge check and record the open circuit voltage of every cell. After this connect the battery for boost charge at the rate specified for about 80 hours by using direct constant current. After 80 hours of charging disconnect the battery and give it a rest of 4 hours. The battery is to be charged for a further period of 40 hours at the specified rate. Specific rate is 15 amp for 300 Ah & 10 Amp for 200 AH

As soon as the battery is on charge take another set of voltage readings and enter these readings opposite the open circuit voltage readings. If the battery is connected upright and there are no reversed cells, proceed with the charge. During the first charge take individual cell voltage, specific gravity and temperature readings every eight hour and record. First charge input 1800 AH for 300 AH & 1200 AH for 200 AH batteries

3. The cells are considered to be fully charged when values of cell voltage and specific gravity of electrolyte corrected to 27°C remain constant for three consecutive hours at the end of approximately 120 hours of charge.

4. At no stage during charging, the temperature be allowed to exceed 50° C. If the temperature tends to rise beyond 45° C, reduce the current to one third the value so that the temperature ceases to rise. However, if at any time, the current is reduced, the time of charging shall be correspondingly increased so that at the end of charging, the specified ampere hours input has been put into the cells.The charging may be suspended for some time to allow the cells to cool, provided 50% of the total ampere hour input is fed. Under no circumstances, initial charging be stopped prior to 50% of the total input is given.

At places, where high ambient temperature normally prevails and where electrolyte temperature limit of 50°C would make charging impossible, it is recommended that the cells be filled during night- time and charging undertaken during the night and suspended during the day.

5. If the electrolyte level goes down the specific limit during charge, the same may be topped up by adding 1.200 specific gravity acid as originally filled in.

6. At the end of charging the specific gravity of the electrolyte is to be adjusted to 1.200 +/- 0.005 at 27°C. If the specific gravity at the end of charging is above 1.200 add distilled water and if it is below 1.200 add 1.400 specific gravity acid and charge for a couple of hours and check the gravity again.

7. After the cells have cooled to ambient temperature adjust the level by withdrawing electrolyte from the cell.

8. The top and. sides of the cells should be wiped clean and dry. Any acid dripped or spilled on stand and. floor should be neutralised and cleaned up.

9. Towards the end of charge, all cells start gassing freely. The voltage will reach a final value of 2.50 to 2.55 V per cell and the specific gravity to 1.210 +/- 0.005. Do not terminate the charge even if the specific gravity and voltage readings exceed the above values until the specific ampere hour input is fed into the battery that the cell are freshly gassing during charging

FOLLOWING POINTS TO BE NOTED AND INVARIABLY OBSERVED

1. Smoking or use of a naked flame in the battery room should be strictly prohibited.

2. Ensure correct polarity between adjacent cells between the battery and the charging source. Charging the cell or battery in the wrong direction will ruin it.

3. Never make the specific gravity adjustment on a cell which does not gas freely on charge. Report the matter immediately to the Manufacturer.

4. Use calibrated meters for measuring current, cell voltage, specific gravity and temperature.

5. The Performance of a battery during its service depends to a great extent on how completely the initial or first charge is carried out. Never therefore, terminate the charge until the specific ampere hour input is put in the battery even though the cells may show constant or higher specific gravity readings, before completion of full Amper-Hour input. .

a. After initial charging 4 to 6 hrs rest is given b. Then the battery is discharged through water load at

the rate of 10% of its capacity till either the voltage of each cell is reached upto 1.8 volts or specific gravity to 1.1 which ever is earlier for 3 consecutive readings. The time taken for this discharging is measured. If it is 10 Hrs or more then full capacity of batteries is obtained.

c. If the capacity is not obtained the same procedure of charging and discharging is carried out once again till it is obtained.

d) After the capacity of batteries are obtained they are again charged at the rate of 10% of 10 hrs capacity of battery till gassing point, and at the rate 5% of 10 hrs capacity till are fully charged.

The batteries are fully charged when they gas freely and cell voltage and specific gravity remain constant till 3 consecutive hourly reading.

The batteries are now ready for putting them into service.

The batteries are then kept on trickle charge in float mode at 2.2 to 2.3 V per cell this is required to compensate for internal discharging of battries due to internal resistance.

The batteries then supply the load in event of failure of AC supply and DC source from the charger.

Batteries for PLCC

The PLCC pannels required 48 V DC supply for their operations the battery set of 24 cells of 100 AH is used for this purpose The erection and commissioning procedure are same as that of sub station batteries

Battery chargers

a. Two modes are available, Boost and float

b. Chargers are required for i. charging the battery sets - through boost chargerii. The continous trickle charging the batteries during

service

c. Supply voltage is 415 Volts 50 Hz.

d. Boost charger is used for initial charging and discharging of batteries

e) Rating :- Higher current rating upto 20 amps to 50 amps depending on the requirement.

f) Float charger - i. For providing load currentii) The trickle charging for battries

Rating :- upto 10 to 15 amps depending upon the requirements

g) The charger is installed in charger room near the cable trench so that the cable can convinently be taken in

h) The load test on boost charger is taken for rated current by putting external load on it. The charger is kept on load for 4 to 6 hrs to check its performance.

i) The battery terminals are then connected. The charger can be put in to service for battery charging

j) The float charger is also taken into service and can feed the load.

The boost charger can function as the float charger in event of failure of float charger.

48 Volts battery charger us used of PLCC

Rating :- Boost - 65 Volts, 12 to 24 amps depending upon the requirement

Float Charges :- Voltage 48 Volts +/- 1%

Current 10 to 30 amps depending upon requirement

The commissioning process is the same as that for main battery charger

ACDB :- 1. ACDB is used for supply of AC power to various load

circuits in the sub station

2. The ACDB has two in comers and bus coupler switches and number of outgoing circuits with proper ratings

3. ACDB when received on site should be unpacked and checked for any visual damage of any component.

4. ACDB should be properly cleaned before installation

5. The bus provided in ACDB should be meggared with all in comer and out going switches in open position

ACDB is mounted in ACDB room near cable trench so that cables can be taken inside conveniently

The cable from sub station transformer (2) are connected in two numbers of in comer switches of ACDB as two independent sources.

The two sources can be paralleled through bus coupler switch or separately operated.

Suitable inter locking is provided on ACDB so that bus coupler can not be made ON unless one in comer switch is OFF.

Parallel operations of both sources is checked before in comer switches are made ON.

After checking as above the ACDB can be put into service.

The ammeters showing the in comer and outgoing currents, the voltmeter showing the in comer and out going voltages are provided

Lighting System

1. Internal electrification of control room is carried out as per requirement

2. The switch yard lighting is provided on masts with HPSV lamps of varies wattage ranging from 150 to 800 watts depending upon the requirement.

3. The lighting is controlled centrally from a separate ACDB in control room .

Earthing

1. Earthing is useda To provide protection against damages to plant

equipments and personnel associated with the use of electrical energy.

b. To maintain the uniform earth potential nearly zero all over the ground under and around the sub station. This is to ensure that

1. All parts of equipments connected to earthing systems should be at ground potential

2. Operators and attendants should always be at ground potential

3. The sub station earthing is in the form of grid, comprising of number of squares and rectangles meshes of earthing conductor burred approximately 600 mm below ground and connected to earthing electrodes driven in ground at certain intervals.

4. The soil resistivity of soil in switch yard should be measured and soil strata should be considered to design the earth mat.

5. The flow of ground fault currents in the earthing system results into voltage gradients on earth surface in the vicinity of grounding system.

6. All the equipments and their structures should be earthed at two points and connected to earthing mesh.

Fencing

Grounding strip should be run generally at 1 m distance from out side the fence and the fence is connected to earthing strip at corners and distance of 15 m. This is to avoid the accidents to persons tuching the fence during system fault conditions.

The cable tray brackets in cable trenches should be earthed at some interval however the cable trays should be earthed continuously.

Control cable trenches and Control cables

1. The control cable trench lay out is prepare as per requirement / size of switch yard and number of bays included in it. They run through switch yard to control room

2. Generally a separate main cable trench runs through the switch yard to control room for carring control cables from various equipments in switch yard of 1 voltage level. i.e. in 132/33 KV two main control cable trenches will run each from 132 and 33 kv switch yard. Small cable trenches run from each equipment to main cable trench.

3. The depth and width of cable trenches are decided on number of cables required to be laid through the trench.

4. The slope is given to cable trenches towards lowest portion of switch yard for draining rain water out of switch yard.

5. The MS brackets (2 & 3 tier) are grouted along the wall of the cable trench to run the cable trays on them.

6. The cable trenches are either of brick work or RCC.

7. The slabs are cast on these control cable trenches where they cross the roads, so that cranes, trucks carrying the heavy equipments can cross them.

8. The entry of cable trench in control room may be at one place or number of places depending upon the lay out of control and relay pannels in the control room.

9. The cable trays run on the MS brackets. The size and number of cable trays depends upon number of cables to be run on them.

10. The cable trench layout in control room is decided on the basis of control and relay pannels layout in control room.

11. In 400 KV sub station control and relay pannel rooms are different and cable gallery is provided.

12. The control cable should be laid first on the cable trays from the bottom tier. The care should be taken while laying so that they are not damage during pulling from cable drums.

13. The Al. tags showing the cable number purpose of cable, from - to number of cores etc. should be tied on each cable at both the ends as well at some interval for cable identification.

14. The control cable are laid as per schedule prepared earlier.

15. The control cables are taken in MBs, C & R pannels and control cabinets of equipments by glanding.

16. The control cables are connected to the terminals after crimping the lugs on the cores. Proper dressing of cables and continuity of cables should be checked before connections.

17. The control cables have very important role in controlling the operations of vital equipments in switch yards also in indication and annunciation systems and hence should be properly handeled and connected as said above.

Control cable trenches and Control cables

1. The control cable trench lay out is prepare as per requirement / size of switch yard and number of bays included in it. They run through switch yard to control room

2. Generally a separate main cable trench runs through the switch yard to control room for carring control cables from various equipments in switch yard of 1 voltage level. i.e. in 132/33 KV two main control cable trenches will run each from 132 and 33 kv switch yard. Small cable trenches run from each equipment to main cable trench.