2. Magnetic Core 7. Radiator 8. Windings 10. Load Tap Changer (LTC) On-load Tap Changer (OLTC)
Transformer Cooling Methods 6
Air Cooling For Dry Type Transformers: Air
natural Type (A.N.)
Air
Forced type (A.F.)
Cooling For Oil Immersed Transformers: Oil
Natural Air Natural Type (O.N.A.N.)
Oil
Natural Air Forced Type (O.N.A.F.)
Oil
Forced Air Natural Type (O.F.A.N.)
Oil
Forced Air Forced Type (O.F.A.F.)
Oil immersed Water Cooling: Oil Natural Water Forced (O.N.W.F.) Oil
Forced Water Forced (O.F.W.F.)
Transformer Cooling Methods 7
Air Cooling For Dry Type Transformers: Air
natural Type (A.N.): transformer is cooled by nature surrounding
air. Air
Forced type (A.F.): air is forced on to the tank surface to increase the rate of heat dissipation.
Apply
for dry type transformer
A dry type transformer is one which does not employ a liquid as a cooling or insulating medium.
Transformer Cooling Methods 8
Tap Changing System 9
Insulation requirements: tap points is placed at the low voltage end of the winding: Near
the star point in a star connected winding.
In delta connected windings: the tapings are usually at the center of the winding.
Tap Changing System 10
On-load Tap Changer Mechanism
Tap Changing System 11
Switching sequence
Tap Changer - Fitted 12
Tap changer
External control box
Other type of transformer: Autotransformer 13
In an autotransformer: A
portions of the same winding act as both the primary and secondary: common winding.
An autotransformer: Smaller
size
Lighter & cheaper
However: does not provide electrical isolation.
Transformer - Bushings 14
Bushings are used on transformers, circuit breakers... as connection points Bushings connect outside conductors to conductors inside equipments
Transformer – Bushings CTs Location 15
Bushing CT
Circuit Breaker 16
Switchgear: combination of electrical disconnects, fuses and/or circuit breakers used to isolate electrical equipment. Switchgear: used both to: De-energize To
equipment to allow work to be done
clear faults downstream.
Type of Circuit Breaker – Based on Interrupting Media 17
Bulk Oil Circuit Breakers (BOCBs)
Minimum Oil Circuit Breakers (MOCBs)
Air Circuit Breakers (ACBs)
Air Blast Circuit Breakers (ABCBs)
SF6 Gas Circuit Breakers
Vacuum Circuit Breakers (VCBs)
Type of Circuit Breaker – Based on Interrupting Media 18
Bulk Oil Circuit Breakers (BOCBs) Contacts Oil
is immersed in oil
as insulation: live part & earthed metal tank
Type of Circuit Breaker – Based on Interrupting Media 19
unit in insulating chamber at live potential reduce requirement of oil
Interrupting
Type of Circuit Breaker – Based on Interrupting Media 20
Air Circuit Breakers (ACBs) Contacts
open & close in air at atmospheric pressure
Normally,
apply for low voltage system only
Type of Circuit Breaker – Based on Interrupting Media 21
Air Blast Circuit Breakers (ABCBs)
Type of Circuit Breaker – Based on Interrupting Media 22
Air Blast Circuit Breakers (ABCBs)
Type of Circuit Breaker – Based on Interrupting Media 23
SF6 Gas Circuit Breakers
Contacts open & close in Sulphur Hexafluoride (SF6)
Type of Circuit Breaker – Based on Interrupting Media 24
Advantages over oil and air circuit breakers:
Due to property of SF6 : very short arcing time Dielectric strength of SF6 gas is 2 to 3 times that of air can interrupt much larger currents. Noiseless operation due to its closed gas circuit No risk of fire as SF6 is non inflammable Low maintenance cost, light foundation requirements and minimum auxiliary equipment
Disadvantages:
SF6 breakers are costly due to high cost of SF6
Type of Circuit Breaker – Based on Interrupting Media 25
SF6 Gas Circuit Breakers
Type of Circuit Breaker – Based on Interrupting Media 26
SF6 Gas Circuit Breakers
Type of Circuit Breaker – Based on Interrupting Media 27
Vacuum Circuit Breakers (VCBs) Arc
interruption takes place in vacuum
Type of Circuit Breaker – Based on Interrupting Media 28
Vacuum Circuit Breakers (VCBs) Arc
interruption takes place in vacuum
Type of Circuit Breaker – Based on Interrupting Media 29
Vacuum Circuit Breakers (VCBs) Arc
interruption takes place in vacuum
Air Disconnect Switches - Isolator 30
Isolate or de-energize equipment for maintenance purposes (isolator) Transfer load from one source to another in planned or emergency conditions
Provide visual openings for maintenance personnel
Being normally gang operated (or group operated)
Have low current interrupting ratings compared to circuit breaker
Air Disconnect Switches - Types 31
Vertical break type
Air Disconnect Switches - Types 32
Horizontal break type
Air Disconnect Switches - Types 33
Operating Mechanism
Lightning Arrester 34
Designed to limit the L-G voltage in the event of lightning or other excessive transient voltages
For substation
Lightning Arrester 35
Designed to limit the L-G voltage in the event of lightning or other excessive transient voltages
