SUBSTATION

            Substation is a media by which we receive HT supply & provide to the plant with necessary safety precautions.

What is called a substation?  A substation is an intermediate switching, transforming or converting station between the generating station and the low tension distribution network situated generally at the consumer’s load centre.

 What is the function of a substation?

The substation receives power from the generating station by a single or more feeders at a high voltage, transforms the same to different distribution voltages and sends the power to different consumers through distribution network.

Operational safety features of substation:

1. Person with valid wireman’s license should be employed for carrying out electrical work

2. Qualified supervisor or engineer for supervision.

3. Work permit system

4. Switch off, isolate, Discharge and Earth before starting maintenance job on electrical equipment.

5. Non conducting handles for tools and equipment.

6. Dry rubber mat in high voltage area

8. For fire fighting – isolation and using carbon di-oxide extinguisher.

What are the classifications of the substations according to the design?

 1. Indoor substation, 2. Outdoor substation, 3. Pole mounted substation, 4. Underground substation.

What is called indoor substation?

            The substation, of which the equipments are installed indoor for voltages up to 11 kV because of economic consideration, is called as indoor substation. In case of contaminated atmospheric condition these substations can be erected for voltages up to 66 kV.

What is called outdoor substation?

            The substation for voltage 33 kV and above, where the equipments are installed outdoor because for such voltages, the clearance between conductors and the space required for various equipments becomes so great that it it not economical to install indoor, is called outdoor substation.

What are the factors to be considered for selection of site of an outdoor type substation?

            The following factors are to be considered in selecting the site of an outdoor type substation:

i)          The site should be located close to the centre of its supply area.

ii)         Sufficient land is to be available at a reasonable cost and without much difficulty for the                      construction of substation and the accommodation of the operating staff.

iii)        The site should be away from the densely populated locality.

iv)        The site should have easy access for having transport.

Advantages of outdoor substation over indoor substation:

a.         All equipments are within sight and accessible; faults and defects can therefore, be easily

              located and rectified.

b.         The substation equipments can be spaced sufficiently apart.

c.         The effect of fault in one section do not affect the healthy section.

d.         The cost of erection is comparatively less as no large buildings area required to be erected to

              house the substation equipments.

e.         The time required for erection is lesser.

f.          Future extensions and alterations can be made without much difficulty.

Disadvantages of outdoor type substation:

a.         As the equipments are open to atmosphere the influence of rapid fluctuation in ambient

              temperature, dust and dirt deposited on the equipments makes it necessary to install

              specially designed equipments which are costlier.

b.         More space is required for the outdoor substation as bushes and other live parts are bare and

              more clearance is necessary.

c.         The various switching operations, fault repair and maintenance become difficult in rough and

              inclement weather.

Classification of substations  according to its functions.

1. Transformer substation: A substation, in which the voltage is either stepped up or stepped down by means of a transformer, is called a transformer substation.

2. Converting substation: A substation where AC energy is converted into DC energy.

3. Frequency substation: A substation in which the frequency is changed from one value to the another value with the help of frequency converter is known as frequency substation.

4. Switching substation: A substation, in which simply switching operation of power lines is performed wdithout changing the voltage level, is called as switching substation.

5. Power factor correction substation: A substation located at the receiving end of the transmission lines in which power factor correction is performed by using generally synchronous condensers, is called as power factor-correction substation.

6. Industrial substation: Substation, from which the power is supplied to individual industrial concern, is known as industrial substation.

Classification of a substation according to their location in the power system network?

1. Step up substation: The set up substation is associated with the power station where the generation voltage is stepped up to the primary transmission voltage.

2. Primary Grid substation: The substation created at suitable load centre along the primary transmission line, in which the primary transmission voltage is stepped down to a number of suitable secondary transmission voltages, is called primary grid substation.

3. Secondary substation: The substation created at actual load point along the secondary transmission lines, where the voltage, is further stepped down to sub-transmission or primary distribution voltage, is called secondary substation.

4. Distribution substation: The substation, where the sub transmission voltage or the primary distribution voltage is stepped down to supply voltage for feeding the consumers through a network of distribution lines, is called distribution substation.

5. Bulk supply and industrial substation: The distribution substation created for an individual bulk supply consumer or an industrial consumer of large or medium supply group is known as bulk supply and industrial substation.

6. Mining substation: The mining substation is a specially designed substation created for the purpose of mining installation which provides extra precaution for safety in the operation of electric supply.

7. Mobile substation: The substation which is created for temporary requirements of mainly construction purposes, is called mobile substation.

Minimum size of earth bus for substation earthing: A minimum size of 65 sq.mm with a ;minimum thickness of 1.6 mm for copper and 200 sq. mm with a minimum thickness of 4 mm for galvanized iron and steel is recommended.

Earthing switch and uses: An earthing switch is basically an isolating switch connected between the line conductor and earth which is mounted on the frame of the isolator with a high speed operating mechanism controlled by protective relays and is used for rapid automatic earthing o faulty sections of the electric circuit by the system of protection.

Electrical bus bar, its types, uses and max. length of bus bar: Electrical bus bar is the collector of electrical energy at one location operating at constant voltage. The bus bars used in a substation are either rigid type or flexible type. Rigid bus bars are made up of aluminum alloy tubes of 50 to 250mm diameter and supported on post insulators with clamps and connectors. Flexible bus bars are made up of A.C.S.R. conductors and supported at both ends by strain insulators, clamps and connectors.

            Long lengths of bus bars are obtained either by welding or by clamping adjacent sub-lengths.

Different types of bus bar arrangements generally used in the electrical system:

a. Single bus-bar system in which the generators or incoming feeders, outgoing lines and transformers are connected to the bus-bar, and it is used in small outdoor substation.

b. Single bus-bar system with sectionalisation in which the bus-bar is sectionalized by means of a circuit breaker with both end isolators and it is used in large generating station where several unit are installed.

c. Duplicate bus bar system in which two bus bars, a main bus bar and a spare bus bar are used for the benefit of maintenance work without interrupting the supply and it is used in large important substation.

d. Ring bus bar arrangement in which all the sectionalized buses are connected in a ring to receive supply from any adjacent section.

e. Mesh bus bar arrangement in which the circuit breakers are arranged in the mesh formation by the buses so that the number of circuit breakers needed will be exactly half the feeders to be controlled.

f. On and a half breaker arrangement in which three circuit breakers are needed for controlling two circuits.