TABLE OF CONTENT
2.0 General Analysis and Background Theory
2.1 Power System Earthing
2.2 Lightning Protection
2.3 Control of Static Electricity
2.4 Signal Ground
3.0 Materials and Methods
SEASONAL AND TEMPERATURE VARIATION IN PORT HARCOURT
The strategic position of Port Harcourt in the Niger Delta region has made the city one of the fastest growing cities in Nigeria. The Niger Delta which is rich in oil and gas provide Nigeria with Ninety-five percent foreign earnings. The oil companies operating in the state has attracted several small, medium and large scale industries. The telecommunication industry which is the fastest growing company in Nigeria has provided job opportunities through several mini companies. Whether small, medium or large companies require the use of electricity and electrical equipments and therefore require proper and safe earthing (grounding). The electrical, electronics and the telecommunication industries require various grounding methods, therefore it is necessary to study the seasonal variation and temperature effect on the grounding systems.
All calculations related to the design of grounding system and the determination of transfer, step and touch potential require information about the soil resistivity at site. Resistivity of soil depends on the physical composition of the soil, moisture content, dissolved salts, season variation, current magnitude and soil temperature. Different soil compositions have different average resistivity but moisture has great influence on the resistivity value of soil. For example, the resistivity of clay varies from 4ohm-m to 150 ohm-m depending on the water content. The study therefore will enable earth system designers, installation engineers to have available records of the earth parameters in this growing city that will enable designers and installer to install safe and reliable system.
2.0 GENERAL ANALYSIS AND BACKGROUND THEORY:
Earthing forms an intrinsic part of the electricity system but it still remains in general a misunderstood subject, even sometimes by well qualified engineers. In recent years there have been rapid developments in the modeling of earthing systems at power frequencies and higher, mainly facilitated by computer hardware and software (Ala and Di-Silvestre, 2009, Lui et al, 2004). This has increased our understanding of the subject at the same time that the design task has become significantly more difficult and emerging standards are requiring a more detailed, safer design. There is thus an opportunity to explain earthing concepts more clearly and a need for this to be conveyed to earthing system designers and installers so that a greater understanding may be gained.
Earth may be defined generally as the reference point in an electrical circuit from which other voltages are measured or a common return path for electric current or a direct physical connection to the earth. Sometimes earth (ground system) can be described as a conducting connection, whether intentional or accidental, by which an electric circuit or equipment is connected to the earth or some conducting body of relatively large extent that serves in place of the earth mass (Cooray et al, 2004,Razevig, 2003).
The most often quoted reasons for having an earthed system are as follows:
- To provide a sufficiently low impedance to facilitate satisfactory protection operation under fault conditions.
- To ensure that living beings in the vicinity of substations are not exposed to unsafe potentials under steady state or fault conditions.
- To retain system voltages within reasonable limit under fault conditions (such as lightning, switching surges or inadvertent contact with higher voltage systems) and ensure that insulation breakdown voltages are not exceeded.
- To limit the voltage to earth on conductive materials which enclose electrical conductors or equipment.
- To eliminate persistence arcing ground faults.
- To ensure that a fault which develops between the high and low windings of transformer can be dealt with by primary protection
- To provide an alternative path for induced current and thereby minimize the electrical “noise” in cables.
- To provide an exponential platform on which electronics equipment can operate.
- To stabilize the phase to earth voltages on electricity lines under steady state conditions eg by dissipating electrostatic charges which have built up due to clouds, dust sleet etc.
For these reasons an effective earthing system is a fundamental requirement of any modern structure or system for operational and or safety reasons. Without such a system of a structure, the equipment contained in it and its occupants is compromised.
Earthing systems typically fall into (but not limited to) one of the following categories (Razevig, 2003 Mousa 1994).
- Power Generation, transmission and distribution
- Lightning protection
- Control of undesirable static electricity