1Substation Equiptment

8/3/2019 1Substation Equiptment

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2/18

THE FOLLOWING ARE THE MAIN EQUIPMENT AT 33/11 KV

SUBSTATIONS

Circuit breakers 33 kv, 11 kv

Power Transformer 33/11 kv

AB Switches 33 kv,11 kv

Station Battery or small size multiple tripping units foreach CB

Lightening Arrestors 33 kv, 11 kv

Instrument transformers CTs & PTs 33 kv,11 kv

Control & Relay panels Control cables and circuitry

Station Earth


3/18

Regular inspections and preventive maintenance to bedone on each of the above equipment are codified as

Preventive Maintenance schedules fixing periodicity for each

item.

The main objective of the maintenance is to maintainthe insulation in good condition and to avoid entry of

moisture and to remove dirt.

The sustained operating temperature of about 8 to 10

Degrees Centigrade more than the operating temperature of

75 Degrees Centigrade will shorten the life of transformer oil,

circuit breaker etc. Hence, over loading should be avoided.


4/18

As far as possible the temperature of oil and

windings shall be maintained at 4

0

C and 45

0

C aboveambient temperature. If the acidity of oil exceeds 1.0

mg. KOH/Gm of Oil, the oil should be replaced with

fresh oil.


5/18

STATION BATTERY

Battery Operation and Maintenance

(A) The Ampere hour capacity of 220V batteries at

smaller Sub- station shall be 80.

(B) The same at EHT Sub-stations shall be 200

(C) Batteries with 300 Amps hour capacity shall be

used only at Power house or Sub- stations where

solenoid closing of circuit breakers is in use.

The trickle charging rate shall be

Amp hour capacity x 2/24x100 plus regular discharge

in amps.


6/18

The boost charge rate shall not exceed Amp. Hour

capacity divided by ten. The individual cell voltage shall not go down below 2.1

volt.

The specific gravity should not differ by more than 30

points between cells in the same battery maximum and

minimum. Where the difference is more: electrolyte

should be diluted by adding distilled water in cells with

higher specific gravity thus narrowing down the

difference and all cells in the battery given a boost

charge. Under no circumstance electrolyte orconcentrated acid should be added to cells with low

specific gravity.


7/18

Usage of alkali cells and acid cells in the same substation

should be avoided to avert inadvertent mix up of

electrolyte or usage of accessories of one with the other.

Leakage indication lamps should be compulsorily connectedon the charges panel for continuous indication of healthiness.

Every D.C. Circuit takes off should be through protective fuses

(H.R.C) or m.c.bs.

(i) Once in a day A.C. Supply to charges should beswitched off and D.C voltage measured and noted.

(ii) In that condition with no A.C. supply to charger, the

duty performance of the battery by closing or

tripping of a relatively un-important breaker is to be

ensured. Mere availability of D.C Voltage is no indexof healthiness of battery.

(iii) A.C Supply to charger is to be restored immediately

after this test.


8/18

Certain charger panels have Switch Off

arrangement whenever A.C supply fails. There

should be switched on after each restoration ofsupply.

Leakages in D.C circuitry should be attended on

top priority first by sectionalisation, then byisolation and finally be rectification.


9/18

Lead Acid Batteries (Common)

Check up the Electricity to level in the cell of all the cells

in morning shift every day. If the electrolyte is low, top upthe cell with distilled water.

Check up the voltage and specific gravity of six cells in

each shift and record as per cell numbers given ( PILOT

CELLS)

Check up the D.C voltage of the combined cell (battery)

after switching off the battery charger every day in the

morning shift. Record the battery voltage and current

with the charger off.

Ensure that the battery is in floating condition normallyby adjusting the rheostat of the charger.


10/18

Never charge a battery at a voltage higher than 2.4 V per

cell i.e., it works out to 264 V for 220 V Battery and limit

the charger ampere capacity also.

If any of the cells is found to be having low voltage and

specific gravity, by pass the cell. The removed cell should

be charged separately and replaced after the voltage and

specific gravity attains normal value. Improvementshould not be attempted by adding acid to electrolyte.

Check the condition of all the cells every month for

voltage and specific gravity. Charge the battery if

required. The voltage and specific gravity readings shall

be taken before and after charging . The charging rate

shall be limited to 10 hours rating to avoid excessive

gassing and evaporation of Electrolyte.


11/18

All the cells shall be physically checked for fracture and

buckling of the container and excessive rise. Check

battery terminals for tightness. Apply Vaseline

( Petroleum jelly) whenever necessary. This check shouldbe attempted after the battery is brought to full charge.

Keep the charger off, observe the voltage with D.C lighting

on continuously for two hours. Observe the voltage

and current. The voltage should not fall by 10% when

the discharge on the battery is at 10Hr i.e., 25 Ampsfor 250Hrs. battery 30 Amps for 300hrs. battery etc.

Every discharge shall be compensated by charging.

As the ampere hour efficiency is always less than unity,

the charging ampere hours shall be more than discharge

ampere hours.

The battery charger panels, in some case have a no volt

trips. Whenever A/C supply fails, the charger should be

switched on after restoration ofAC supply.


12/18

Instrument Transformers

An instrument transformers role is to provide accurate

inputs to protection, control and metering systems includingrevenue metering.

The main tasks of Instrument Transformers are:

To transform currents or voltages from usually a highvalue to a value easy to handle for relays and

instruments.

To insulate the metering circuit from the primary high

voltage system

To provide possibilities of standardizing the instruments

and relays to a few rated currents and voltage.


13/18

Current Transformer:

The Primary winding in a current transformer is

incorporated in the line and carries the current flowing in the

network. The magnitude of the secondary current is dependent

of the Ratio of the transformer.


14/18

Accuracy:

The quality of measurement which characterize the

ability of measuring instrument to give indication equivalent tothe true value of the quantity measured. Accuracy limits

specified in a particular standard for different loads and power

factor differs.

Failure of Its can cause malfunction of system

protections , controls and metering devices and, in some

catastrophic failures, damages to nearby power equipment, or

injury to personnel in the vicinity.


15/18

Dissipation Factor:

The ratio of the power loss in a dielectric material to thetotal power transmitted through the dielectric, the imperfection

of the dielectric. Equal to the tangent of the loss angle.

Most plastics have a low Dissipation Factor , a desirable

property because it minimizes the waste of elec. Energy as heat.

= tan De=1/2


16/18

Where

F= Frequency of applied voltageCp= Equivalent parallel capacity

Rp= Equivalent parallel Resistance

= Loss angle


17/18

Loss Angle

A measure of the power loss in an inductor or acapacitor, equal to the amount by which the angle

between the phasors denoting voltage and current

across the inductor/ capacitor differs from 900.

For an ideal capacitor , it is ZERO.


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1Substation Equiptment