Power System

3

a three-phase system uses a minimum of ___ conductors

three, 1.5

a three-phase system can transmit ____ times as much power using just ___ times as many wires

1/3 period

in a three-phase system, each phase has a phase difference of ____

rotating magnetic field

transformers

a three-phase system produce a _____ in an electric motor and generate other phase arrangements using _____

voltage

frequency

phases

connection

parameters of a polyphase system

real power and the apparent power

the power factor is the ratio of the ____ and _____

use of bank of static condensers

use of synchronous condenser (motor)

use of power conditioners

methods of correcting power factor

electric distribution system

the final stage in the delivery of electric power

carries electricity from the transmission system to individual consumers

circuit breakers

fuse

cut-outs/reclosers/load-break switch

current/potential transformer

lightning arrester

capacitor banks/reactor

meters

Major components of EDS

circuit breakers

an automatically operated electrical switch designed to protect an electrical circuit from damage caused by excess current, typically resulting from an overload or short circuit

heating or magnetic effect of electric current

the circuit breaker detects fault and trips off through _____

external voltage source

for higher voltage, circuit breakers need an _____

normal current (expected to carry)

maximum short-circuit current (it can safely interrupt)

circuit breaker are rated by ___ and ____

MCB

MCCB

examples of Low Voltage CB

Vacuum CB

Air CB

SF6 CB

examples of medium voltage CB

oil cb

air blast cb

vacuum cb

sf6 cb

co2 cb

examples of high voltage cb

fuse cutout or cut-out fuse

a combination of a fuse and switch, used in primary overhead feeder lines an taps to protect distribution transformers from current surges and overloads

recloser (or autorecloser)

a circuit breaker equipped with a mechanism that can automatically close the breaker after it has been opened due to a fault

recloser

used on overhead distribution systems to detect and interrupt momentary faults

instrument transformers

high accuracy class electrical devices used to isolate or transform voltage or current levels

instrument transformers

most common use is to operate instruments or metering from high voltage or high current circuits

current transformer

a series connected type of instrument transofrmer

voltage of potential transformer

parallel connected type of instrument transformer

lightning arresters

a device used to protect the insulation and conductors of the system from the damaging effects of lightning

thyrite

____ was once a trade name for the silicon carbide used in arresters

Transient Voltage Surge Suppressor

a general classification of an array of devices that are designed to react to sudden or momentary overvoltage conditions

capacitor banks

a group of several capacitors of the same rating that are connected in series or parallel with each other to store electrical energy

capacitor banks

used to counteract or correct a power factor lag or phase shift in an ac power supply

line-to-ground

line-to-line

line-to-line to ground

balanced three-phase

three-phase to ground

series/shunt fault

different types of fault

symmetrical fault

a sudden short circuit at the terminals of a synchronous generator or distribution line

assymetrical fault

analysis using sequence impedances namely positive, negative and zero

arc flash

also called flashover

a type of electrical explosion or discharge that result from a low-impedance connection through air to ground or another voltage phase in an electrical system

light and heat produced as part of an arc fault

arc blast

produces supersonic shockwave when uncontrolled arc vaporizes the metal conductor

continuous luminous bridge is formed on the gap

highly ionization of air

temp reaches up to 35k F

pressure wave causes workers to be thrown away

can cause permanent ear damage

what happens/produced during arc flash

no system is perfect

during accident

protection of maintenance personnel

used to rate the necessary PPEs

indicator if review of protection coordination studies are needed

why do we need arc flash studies

0 - <1.2

1 - 1.2 to 4

2 - 4 to 8

3 - 8 to 25

4 - 25 to 40

hazard risk category - minimum rating of PPE

earthing or grounding

connection of the supply system to the general mass of earth such as a way to immediately discharge of electricity can take place without danger

lightning and voltage surges

grounding systeem provides additional protection to equipment against ___ and ___

grounding resistance

resistance between the system of electrodes and other infinitely large electrodes in the ground of infinite spacing

resistance earthing

reactance earthing

arc suppression coil or resonant earthing

voltage transformer earthing

earthing transformer

methods of grounding distribution system

arc suppression coil

a coil is tapped in order to select the reactance depending upon the length of transmission line and the capacitance to be neutralized

neutral and ground

arc suppression coil is connected between the ____

maximum earth fault current

coil rating is continuous and equal to the _____

arc suppression coil

used in medium overhead transmission line which are connected to system generators through intermediate power transformers

voltage transformer earthing

neutral point is earthed through a single phase voltage transformer

system acts as a insulate neutral system

system grounding

the grounding of neutral bus using solid or impedance grounding system

provides for a flow of current to allow detection of an unwanted connection between system conductors and ground

equipment grounding

the grounding solidly of non-current carrying parts of an equipment or apparatus in a power system

two-point (dead earth) test method

three-point (fall of potential) method

four-point method

clamp-on method

grounding tests

two-point test method

also called dead-earth method

simplest way to obtain a ground resistance readiing

most effective for quickly testing, but should only be used as a last resort

resistance of two electrodes in a series is measures

Two-point test method

Test method where resistance of two electrodes in a series is measured

connecting the P1 and C1 terminals to the ground electrode under test

All-metallic grounding point

In two-test method, p2 and c2 connect to separate ____

Three-point test method

also called fall of potential method

most thorough and reliable test method

measuring resistance to earth of an installed grounding electrode

P1 and C1 terminals on the instrument are jumpered, connected to the earth electrode under test

Four-point test method

Also known as Wenner four-pin method

most commonly used for measuring soil resistivity

Clamp-on method

ability to measure resistance without disconnecting the ground system quick and easy

measurement includes the bond to ground and overall grounding connection resistances

measures the current via a receive coil, carried out at a high frequency

effective only in situations with multiple grounds in parallel