SUB STATION KNOWLEDGE AND ELECTRICAL TUTORIAL: Substation

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PERMIT IN ELECTRIC SYSTEM

WHAT IS THE MEANING OF PERMIT ON ELECTRIC EQUIPMENT AND LINES?

PERMIT: Permit in electric system means permission taken for a fix time by authorize person from controlling authority to work on electric equipment and feeders.

Permit on electric system means electric equipment and feeder are in off ( no current flow) position for a fix time and now the feeder and equipment is in safe position to work on it.

WHY AN ELECTRICAL PERMIT IS REQUIRED?

The requirements of permit on electric lines and equipment is given below:

At the time of attending breakdown of lines (feeders) at the time of fault.
Schedule maintenance of electric equipment and lines.
At the time of tree trimming of lines.
At the time of attending breakdown of feeder, if another feeder cross the faulty feeder or if both the lines (feeder) on same pole.Then permit is also issue on normal feeder, this permit issue on normal feeder for safety purpose.
At the time of preventive maintenance of equipment and lines.
For clearing fault of electrical equipment (substation power transformer, circuit breaker etc).
Some time for new connection of consumers.
Erection of new feeder (safety purpose).

PROCESS OF ISSUING PERMIT: Mainly permit issues by substation staff (substation operator, substation attendant) to field staff.Substation staff issue permit to authorize person of field staff.

Firstly field staff writes the reason of permit on feeder in massage book and also writes the approximate time of completion of work.After this substation staff and field staff fill a permit that follow permit issue process.After filling the permit book, substation staff issue a permit page to the field staff or issue a Permit To Work (PTW) code (permit page number).The given below image shows the permit format.

Permit Page

Following work should be done after issuing written permit:

Check the feeder/line circuit breaker panel on which permit issue.
Wear the safety dress (helmet, gloves, safety shoes etc).
Trip the circuit with the help of TNC (TRIP - NEUTRAL - CLOSE) switch or mechanically by trip push button in circuit breaker trolley.
Check the electrical and mechanical indication that shows the breaker in OFF condition.
Check the load current in all three phases (R - Y - B) of ammeter.
After this Rack out the trolley of circuit breaker and check the circuit breaker position indicator.The circuit breaker position indicator shows the three position of circuit breaker that is given below.

Breaker is in ON position - SERVICE
Breaker is in OFF position - SERVICE/INTERMEDIATE
Trolley is in RACK OUT position - TEST

Open the main isolator/G.O. (Gang operated ) switch of the feeder.It is mainly situated at the first H pole of the feeder near the substation.
Put the PTW tag on the circuit breaker panel on which permit is issue.

After doing above work, substation operator give fully permit to field staff for the work on line or electrical equipment.

After completing the work by field staff.The following processes should be follow by substation staff and field staff before operating the circuit breaker of the permit issuing feeder.

Fill the permit book that follow cancellation process.
Remove the PTW tag from the circuit breaker panel.
Close the main isolator/G.O. switch.
RACK IN trolley of circuit breaker and check the circuit breaker position indicator.It shows SERVICE/INTERMEDIATE position.
Check the D.C. supply (trip circuit healthy) of the circuit breaker.

Before close the circuit breaker once again confirm by field staff, line is clear for operation.

All the staff is away from feeder/line.

After confirmation by field staff close the circuit breaker by the TNC switch or mechanically by close push button in circuit breaker trolley.
Check the electrical and mechanical indication that shows the breaker in ON condition.
Once again check the D.C. supply (trip circuit healthy) of the circuit breaker.
Check the load current in all three phases (R - Y - B) of ammeter.

The above process should be follow by the substation staff at the time of issuing permit.

PRECAUTIONS AT THE TIME OF PERMIT:

The given below things should not be done at the time of permit:

Permit should not be issue on mobile phone.
After issuing permit check the right feeder on which permit is issue.
Permit should not be cancelled on phone.
At the time of operation of circuit breaker should not be do any other work (attending phone calls etc).
Do not take quick action at the time of ON/OFF operation of circuit breaker.

Conclusion: The final conclusion is that permit on line/equipment is very necessary at the time of work.Because after the permit on line/equipment, it is safe to work.So, it is necessary to follow all the above given process at the time of issue permit .Because a small mistake can be cause of a big accident or even a cause of death.

SUBSTATION

WHAT IS SUBSTATION? TYPE OF SUBSTATIONS?

EQUIPMENT USED IN SUBSTATION?

Substation: It is a place where lot of electric equipment (like transformer, circuit breaker, Current transformer, voltage transformer etc) install and operate for control of transmission and distribution of electric power.

It is a place where mainly voltage transformation take place with the help of electric equipment (transformer).

Main functions of substation is given below:

To close and open the power lines.
To raise or lower the voltage,this operation is known as voltage transformation operation.
To convert a.c. into d.c. or vice versa.
To change the frequency of supply,this operation is known as frequency operating operation.
To improve the power factor at the end of the line by the use of capacitor bank or synchronous condenser,this operation is known as power factor correction operation.

TYPES OF SUBSTATIONS:

According to design substation has two types.

Outdoor substation
Indoor substation

1.OUTDOOR SUBSTATION: In this type of substation the electric equipment are installed in open,so this type of substation is called outdoor substation.This type of substation is mainly used for voltage up to 66 kV and above.It is used for receive and transmit large electric energy,so high rating of equipment used.So, such type of electrical substations require a large site and generally installed outside the city.

Main parts of outdoor substation:

1.Control room: In this type of substation a small building is required (as compared to indoor substation) for control room.It is a place from all the electric equipment can be control and operate.

The given below image show the building of control room and equipment installed in control room:

Building of control room

Control Room

The given below equipment install in control room:

a) Power transformer control panel: By the operation of this panel we can switch on and off the power transformer.

b) Circuit Breaker: By the operation of CB we can switch on and off the power lines (outgoing feeders).

c) Tap changer panel: By the help of tap changer panel we can change the secondary voltage of transformer.

d) Miscellaneous equipment: Battery,DC distribution panel,AC distribution panel,Battery charging panel etc is also installed in substation building.

2.YARD: It is the place where all the equipment is installed and operate in open.

The given below image show the yard of substation and the equipment installed in yard:

Substation yard

The given below equipment is installed in substation yard:

a) Isolator cum earth switch: It is a switch that can connect and break the main circuit (power line) from substation.It is always operate at no load.A earth switch also connect to it.With the help of this earth switch be can earth the main circuit.

b) Potential transformer: It is used for metering purpose.

c) Supporting isolator: This isolator is used for the support of main circuit.

d) Breaker panel (Primary side): This is used for switch on and off main circuit.This is mainly operate by control panel that is situated in control room.

e) Current transformer: This is used for metering and protection purpose.

f) Lighting Arrestor: This is used to protect the other equipment from lighting.

g) Power transformer: It is a device that transfer power by the transformation of voltage (primary side to secondary side).

(For more information see the transformer topic in this site).

h) Neutral current transformer (NCT): It is a device used for earthing of neutral of power transformer ( transformer which have star winding).

The advantages and disadvantages of outdoor substation is given below:

1.Advantages:

a) Small building is required.

b) The fault location is easier.

c) In future the extension of installation is easier.

d) The construction work required is less.

e) Maintenance is easy.The work of maintenance can be carried out without making more of substation dead.

2.Disadvantages:

a) More space is required for the substation.

b) The dirt and dust deposits upon the outdoor substation equipment.

c) More maintenance is required.

d) The effect of temperature on equipment due to change in weather reduces the life of equipment.

2.INDOOR SUBSTATION: In these type of substation all the electrical equipment is installed in the building of substation.It is generally used up to 66 KV.It is mainly used where the surrounding atmosphere is contaminated with impurities and metal corroding gases,conductive dust etc.

In this type of substation all the electric equipment used same as outdoor substation but it is install in a panel.The panel is divided in different chamber and all the electrical equipment install in different chamber and it is insulated by sulfur hexa-fluoride (SF6) gas.

The advantages and disadvantages of outdoor substation is given below:

1.Advantages:

a) If a fault occurs on any section of the bus bar,that section can be isolated without affecting the supply from other section.

b) Easy operation.

c) Less space required.

2.Disadvantages:

a) Fault location is difficult.

b) Risk of fire is more.

c) Future extension is not easy.

d) Capital cost is high.

e) Time required for completion is more.

→Thus final conclusion is that outdoor substation is suitable for transmit and receive large electric power above 66 KV and indoor substation is used for transmit and receive small power up to 66 KV in urban area.