THE SIGNIFICANCE OF POWER SYSTEM SUBSTATION

ABSTRACT

A substation is a part of electrical generation, transmission and distribution system. Substation transformed voltage from high to low, or the reverse, or perform any of several other important functions. Between the generating station and consumer, electric power may flow through several substations at different voltage levels. A substation may include transformers to change voltage levels between high transmission voltage and lower distribution voltage, or at the inter connection of two different transmission voltages.

INTRODUCTION

The substation comes from the days before the distribution system became grid. As central generation station became larger, small generating were converted to distribution stations, receiving their energy supply from a large plant instead of using their own generators. The first substations were connected to only one power station, where the generators were housed and were subsidiaries of that power station.

 

Element of a substation

1.   Primary power lines

2.   Ground wire

3.   Over head lines

4.   Transformer for measurement of electric voltage

5.   Disconnect switch

6.   Circuit breaker

7.   Current transformer

8.   Lightening arrestor

9.   Main transformer

10.                 Control building

11.                 Security fence

12.                 Secondary power line

AIM AND OBJECTIVES

Aim: the aim of this study is to examine the significance of power substation in electrical energy transmission; to achieve the above aim stated the following objectives were pursued.

–         To examine the concept of power substation.

–         To identify various types of substation equipment and overhead lines.

–          To examine the significance of power substation in electrical energy transmission.

POWER SUBSTATION

Substations generally have switching, protection, control equipment, and transformers. In a large substation, circuit breaker is used to interrupt any short circuit or over load current that may occur in the network. Smaller distribution station may use reclosen circuit breaker or fuses for protection of distribution circuit. Substation themselves do not usually have generators, although a power plant may have a substation nearby. Other device such as capacitor and voltage regulation may also be located at a substation.

TYPES OF SUBSTATION

Substation may be described by their voltage class, their application within the power system, the method used to insulate most connector and by the style and materials of the structure used.

1.   Transmission Substation

It connects two or more transmission lines. A transmission stationary has transformers to convert between two transmission voltages, voltage control power factor correction device such as capacitor reactor or static VAR compensation and equipment such as phase shiftily transformers to correct power flow between two adjacent power systems. 

 

2.   Distribution substation: transfer power from the transmission system to the distribution system of an area. It is uneconomical to directly connect electricity consumers to the main transmission network unless they use large amount of power, so the distribution station reduces voltages to a level suitable for local distribution.

 

3.   Collector substation: in distributed generation project such as a wind farm, a collector substation may be required. It resembles a distribution substation although power flow in the opposite direction.

 

4.   Converter Substations

These power system substations are complex which are required for high voltage direct current (HVSOC) transmission or inter connection of two alternating current systems which for a variety of reason cannot be connected by on AC connection. The main function of converter station is the conversion of power from AC to DC and vice versa.

The highest priority in a power system substation is to detect and isolate failures in the transmission system as quickly as possible. Short circuit or over load current in large substation can leave thousands of people without electricity. Current transformers often detect such large fault currents. With higher voltage power circuit breakers tripping within tens of milli second. Maintaining power quality is also one of a power operators most important objectives and it affect operating condition of the whole transmission and distribution networks. Power quality information is of strategic importance for electricity companies and essential for ensuring competitive operation.

Another important function performed by a power system substation is switching which is the connecting and disconnecting of transmission lines or other components to and from the system. Switching event may be “planned” or “unplanned”. A transmission line or other component may need to be de-energized for maintenance or for adding or removing a transmission line or a transformer. To maintain reliability of supply, no company ever brings down its whole system for maintenance. All work to be performed, from routine testing to adding entirely new substations must be done while keeping the whole system running perhaps more important, a fault may develop in a transmission line, some example of this: a line is by lightening and develops an arc, or a tower is blown down by high wind. The function of the substation is to isolate the faulted portion of the system in the shortest possible time. De-energizing faulted equipment protect it from further damage, and isolating a fault helps keep he rest of the electric grid operating with stability.

Figure 1: A 115 kv to 41.6/12 47k MVA 60 Hz sub station with circuit switcher, regulators, recloser and control building.

Figure 2: SF 6 11 o kv instrument current transformer TG fm series

Figure 3: A 50Hz electrical substation

The main significance associated with major power system sub-station in the transmission and distribution systems include:

1.       Protection of transmission system

2.       Controlling the exchange of energy

3.       Ensure steady state & transcend stability

4.       Load shielding and prevention of loss of synchronism

5.       Voltage regulator/control

6.       Securing the supply by providing adequate capacity.

7.       Fault analysis and pin pointing

8.       A transmission substation is useful in increasing voltage on during transmission and distribution substation is used in regulating the voltage before distributing it to consumers.

9.       An important function performed by a substation is switching, which is the connecting and disconnecting of transmission lines or other components to and from the system.

10.    It also isolates the faulted portion of the system in the shortest possible time. De-energizing faulted equipment protects it from further damage.

11.    Voltage transformation (reduction)

12.    Connection point for local networks

13.    Switchyard for network configuration

14.    Monitoring point for control center

15.    Fuses and other protection

CONCLUSION

In conclusion, selection of the sub station must consider many factors sufficient land area is required for insulation of equipment with necessary clearance for electrical safety and for access to maintenance large apparatus such as transformers. The site must be secure from intrusion by passers-by both to protect people from injury by electric shock or arcs and to protect the electrical system from mis-operation due to vandalism

REFERENCES

Theraja B.L (2010) Electrical Technology. Twenty fourth Revised Edition Revindra printers Put Ltd.

Allan R. H. (2008) Electrical Engineering Principles and Application. Pearson Education Singapore Pte Ltd. 

Donald G. (1978) Substation design, Eleventh editon, Mc. Craw Hill.

Theraja A. K. (2005) Electrical Technology. Twenty fourth Revised Edition Revindra printers Put Ltd.