Protection of Electrical Systems(Relays,Fuses,switches,CB,CTs)

Relay:
The device which detects the fault and isolates the operation of CB is called relay

Protection Of Alternators

1.Sudden Loss of Prime Mover
--it causes failure of prime mover it tends to alternator runs get inverted by using
reverse power relay this effect is protect
2.Sudden loss of Field
-- this cause the machine continuous to run as induction generator
3.Over Current
--- Because of overloading or Insulation breaking this will appear in alternators
over current relays are used for this problem
4.over speed
---partial reduction of load causes over speeds
-- Mechanical Con figural Governor will take care of this situation

5. over voltages
---partial withdraw of load causes overvoltages
automatic voltage regulators and automatic excitation controls will take care of the protection

Unbalancing Conditions
For this protection we use MergePrice schema

Pole slipping
when the 3 phase fault occurs this will appear in synchronous machines
electrical power suddenly becomes zero which causes max acceleration of the machine and rotor swings by a large angel with this it may loss its pole pitch
which causes dead short circuit or dead open circuit
--- it should be protected by tripping the field switch

Over Heating
-- Overloading
--failure of pulling mechanism
--Core Faults
this is protected by syristors(silicon controlled resistor)is used this schema is developped by using bridge balance method

Protection of Transformers

1.Internal faults---Buccholz Relay
2. Excess Leakage Current--By Using CT we Can Protect
3. unsymmetrical faults--Merze Price Schema
4. over Heating---- By using CT and heating element and Hating Sensor it will protect

Protection of Lines

--over currect protection-time,current,time/Current Gradding
--distance protection--Impedence,Reactane,Admittance
--pilot Relaying--For High Frequency Signals(wire pilots-upto 1kHz, CarrierPilot-1kHZ to 100KHz,Microwave-3 MHz to 900MHz)

Distance
Basic Equation
Torque-T
Gain Constants-K1,K2,K3,K4
T=K1 Isqure+K2 Vsqure+K3 VI cos(@-t)+K4
where K4 correction Factor

--Impedence-NonDirectional
K3=0,K4=0
used for protection of Distribution Lines and Short Transmission lines

Reactance Relay
--Change reactance due to
1. Frequency
2.Reactive power
3. Change of Sequence Operation
---NonDirectional Relay
for protection of Medium T/M lines
Negative Sequence Relay
Admittance Relay
--Directional Relay
For Long T/M Lines

PlugSettingMultiplier
PSM=Fault current/CurrentSetting*CT ratio