Installation commissioning and maintenance part - 7

Topic includes

- Patrolling and inspection of line

- Types of faults

- Relay with it's types

- Fire extinguishers 

- Types and use of fire extinguishers

- Characteristics of insulating oil

- Testing of oil

- Murray and Varley loop test

- Sag

Patrolling and inspection of line

Patrolling means a regular or routine or schedule for inspection of line or power supply.

Power lines are required to be inspected visually by the responsible crew of the understanding for detection of defects which mein letter on develop up into fault and disturb the entire power system.

This patrolling or inspection takes place by following ways

- Patrolling by Supervisory staff

The engineer in charge of the line may patrol the line as frequency as possible but specially before  the concept of rainy season and snow season and takes necessary steps to rectify the faults which are detected.

so that the line may remain reliable during inclement weather when the supply is needed most point after rainy e and snow seasons detailed petroleum should again be carried out and defects removed so that lines may be more dependable or adjustable according to requirement.

- Regular Patrolling

Regular petrol in schedule be checked out and meticulously followed. Detailed patrolling should be done by lines main in case of improvement lines regularly at the interval of 30 days. 

- Emergency Patrolling

In case of forced outage patrolling should be ordered forthwith. the basic purpose of such patrolling is to locate the fault as early as possible and to restore the supply of power. 

While ordering the emergency patrolling a permit to work should be obtained.

Line should be always considered "Alive" unless it has been positively made dead. 

when the fault has been located, the engineer in charge should be informed and necessary action be taken to repair the lines point.

During repairing of the lines or faults, the engineer and lineman should remain in contact on telephone. 

Types of faults 

Defaults in the power system occur because of the insulation failure in the plant which may be caused bhaiya system over voltage, such as switching surges or lightning strokes maybe due to broken insulators and conductors and various other reasons for causes on the transmission line.

The different types of faults can be characterized such as

- 1 phase to ground fault

- phase to phase fault

- two phase to ground

- phase to phase and third phase to ground

- 3 phase to ground

- three faces get short circuited

In order to overcome or location of the fault or power failure, Patrolling and inspection is must.

Relays

It is a sensing element, comparing element and control element.

Protective relay

The protective relay is defined as an electrical device connected between the main circuit and the circuit breaker that detects the fault and initiate the operation of the circuit breaker to isolate the defective section from the rest of the system.

They are electrical devices that detect abnormal conditions in electrical circuits by constantly measuring the electrical quantities which are different under normal and fault conditions.

voltage, current, phase angle and frequency are the basic electrical quantities which may change during fault conditions.

after detecting the fault, the relay operates to complete the trip circuit which results in the opening of the circuit breaker and in the disconnection of the fault circuit.

the relay ensure the safety of the circuit equipment from any damage which might be otherwise caused by the fault.the protective relay is interposed between the main circuit and the circuit breaker.

Types of Relays

- Over current relay

These corporate when current rises above specified value.

- Over voltage relay

These operate when voltage rises above specified value.

- Thermal relay

this type of release operate on the principle of thermal effect of passage of current through the relay element. Such relay are actuated both by AC and DC.

- Time lag relay

the time of operation is quite independent of the magnitude of current or other quantity causing operation.

- Induction type relay

these relays are based on the principle of operation of induction motor and operated by AC quantity.

Distance relay

Their operation depends upon the ratio of voltage to current.

Static relay

it is a type of relay which incorporates solid state components like transistor, diode for the measurement for comparison of electrical quantities.

Firefighting Equipments

Right type fire fighting equipment must be provided near dangerous locations so that a fire can be tacked quickly before its pet store nearby locations.

Types and use of fire extinguishers

Class A

Fire in ordinary combustion material such as wood paper, textiles exactra where the cooling effect of water is essential for the extinction of fire.

Class B

Fire is flammable liquid like well, solvents, petroleum products, paints etc where blanket effect is essential.

Class C

Fire involving electrical equipment where the electrical conductivity of the extinguishing media is of first importance.

As we see, there should be supported by brackets family fixed to the wall at a convenient height at of all fire points.

Alongside is extinguisher as instruction plate should be displayed which give details of operation and the type of fire for which the extinguisher is suitable.

There are six basic types of extinguisher in common use

1. Horse Reels

This provide best method of fire red fire fighting for A class fires. they consist of 25.4 metre of length having 63 mm diameter of reinforced rubber tubing connected to a pressurized water supply with the shut off nozzle attached to the end of hose.

This type of extinguisher is unsuitable for petrol, oil, spirit and electrical fires.

2. Carbon Dioxide Extinguisher

This type of extinguisher is used for fighting the fire In cotton, cloth or wood. It consists of container filled with aqua solution of sodium bicarbonate. A sealed glass bottle filled with dilute sulphuric acid is placed in the sodium bicarbonate solution in such a way that it can be broken up by a gentle push on the screw fitted over it. when sulphuric acid comes in contact with sodium bicarbonate it produces carbon dioxide gas and water mixture. 

carbon dioxide filled extinguishers are the most suitable type for class A fires and must not be used on other class B class C fire.

3. Water filled extinguisher

it is the most suitable type for use against fire in world solid materials, usually of an organic nature, in which combustion normally takes place with the formation of glowing embers. 

There are two methods of operation stored pressure and gas cartridge type.

4. Halogen extinguishers

these extinguishers may be filled with chloro bromo ethane, bromo chloro difluoro methane. they may be either gas cartridge or stored pressure type. Halogen extinguishers are used mainly because of their effectiveness in rapidly extinguishing small fires involving burning liquids.

5. Dry powder extinguisher

extinguishers filled with dry powder maybe of gas cartridge for stored pressure type. They are similar in appearance to their waterfield counterparts and have the same method . Tof operation. The main distinguishing feature is the fan shapped nozzle.

6. Foam Extinguisher

Form extinguishers may be stored pressure or gas cartridge. they are most suitable for use on flammable liquid fires such as petrol, oil grease and fats where the risk of ignition is height and where the liquid is contained. They are not suitable for running liquid fires and must in to be used on fire where electrical equipment is involved.

Characteristics of insulating oil

- it should have high dielectric strength.

- it should be free from moisture content and water vapour.

- the oil should be frequently clear and plain in colour, transparent and free from suspended matter of sediments.

- acidity content should be very low in the oil.

- it should have high flash point.

- the oil should be chemically stable.

- it should have low viscosity.

Testing of oil

Flash point or breakdown test 

-  The point at which the spark occurs and Transformer trips is known as the flash point.

-  This test is performed in the oil testing set.

-The sample of soil is drawn from near the top and bottom of Transformer and tested in the oil testing.

-A lower than 30 KV dielectric strength for 4 mm gap of electrodes would indicate presence of moisture in the oil.

-The actual testing is done as follows:

- The gap of electrodes is first check with a gauge. 

- The cup is then filled with simple oil to be tested up to about 1 cm above the electrodes.

- the cup top is covered with a clean glass plate.

- supply is switched ON and voltage is raised gradually by the variac, the stage comes when the final breakdown of the oil takes place and the circuit is got tripped, which disconnect the Transformer from the main supply. 

- this value is noted down which must be 30 KV rms for 4 mm positive or negative 0.02 gap and 20 KV rms for 2.5 mm gap.

This test is performed with two or three consecutive samples of oil turn-by-turn.

Murray and Varley loop test

Murray earth fault

Murray short circuit and Varley test

Varley short circuit and earth fault

Sag