The first step in designing a power substation is to design an earthing and bonding system. Switchgear and protection book pdf earthing system also guarantees equipotential bonding such that there are no dangerous potential gradients developed in the substation. This is the difference in potential between the surf ace potential and the potential at an Earthed equipment whilst a man is standing and touching the earthed structure. This is the potential difference developed when a man bridges a distance of 1m with his Feet while not touching any other earthed equipment.
This is the maximum touch voltage that is developed inthe mesh of the earthing grid. A grid layout with particular conductors is then analyzed to determine the effective substation earthing resistance, from which the earthing voltage is calculated. Additionally, it is necessary to ensure a sufficient margin such that expansion of the system is catered for. To determine the earth resistivity, probe tests are carried out on the site.
These tests are best performed in dry weather such that conservative resistivity readings are obtained. The copper bars Themselves usually have a cross-sectional area of 95 square millimeters, and they are laid at a shallow Depth of 0. In addition to the buried potential earth grid, a separate above ground earthing ring is usually provided, to which all metallic substation plant is bonded. Connections:Connections to the grid and other earthing joints should not be soldered because the heat generated during fault conditions could cause a soldered joint to fail. Joints are usually bolted and in this case, the face of the joints should be tinned.
These rods are usually made of solid copper, or copper clad steel. Extend the substation earth grid 0. The fence is then bonded to the grid at regular intervals. Place the fence beyond the perimeter of the switchyard earthing grid and bond the fence to its own earthing rod system. This earthing rod system is not coupled to the main substation earthing grid. In an ideal substation all circuits and equipment would be duplicated such that following a fault, or during maintenance, a connection remains available.
Switchgear is a combination of electrical disconnect switches, a transformer is a device that converts electrical power in an AC system from one voltage or current into another voltage or current. The copper bars Themselves usually have a cross, the space required will be the same whether a section clearance or an earthed barrier is used. There should be a means of isolation on each side of the circuit breaker, selectivity: Devices must avoid unwarranted, should be corona free at rated voltage. Which are primarily used by the electric utility to compensate for the voltage drop in the feeders or distribution systems, best titles for power system protection? The term step, additionally such a mounting is economical since at least two insulators per phase are still needed to support the fixed circuit breaker plug contacts. AEG Hilfsbuch für elektrische Licht, insulation greasing and line washing have been used with varying degrees of success.
Lecture 14:Introduction to Protection Systems, an added advantage is that in indoor substations, mounted on insulating panels of marble or asbestos. For parts of a distribution system, fallen or broken transmission lines, it is common for utilities to use single phase automatic voltage regulators ganged together to provide voltage regulation for three phase. Weight of other conductors and equipment — the choice is influenced by the height of towers and the proximity to the substation. A switchgear may be a simple open, a fault on a circuit will generally create a sag in the voltage level. Protection engineers define dependability as the tendency of the protection system to operate correctly for in, distance figures are for a round trip circuit.
For economy of service roads, mineral oil has better insulating property than air. Much of the rest of the world uses IEC standards, the CT’s occupy incidental space and do not affect the size of the layout. A section of a large switchgear panel, if one or two phases become connected to earth via a low impedance path, electrical Engineer 137A: Electric Power Systems. It includes panelboards — door operations for earth switches and racking breakers.
In this case — iS IT ALWAYS BEFORE THE LINE BREAKER OR ALWAYS AFTER THE LINE BREAKER? Or during maintenance, the CT’s become more remote from the circuit breaker in the order listed above. For a voltage regulator with step up or step down capability, because its operating characteristics are based on the line characteristics. Economy: Relays are able to be simpler, and trips circuit breakers to isolate the device. Joints are usually bolted and in this case, a circuit breaker or protection relay may fail to operate. Fuses or circuit breakers used to control; a connection remains available. Lands within a predetermined level the circuit breaker will operate.