EEE 420 HIGH VOLTAGE
TECHNIQUES
Course Content
1)Introduction
Definition of High Voltage and Standard Voltage Ranges Transmission of Electric Energy (AC and DC)
Standards and Regulations
2)High Voltage Power System Components and Technology
Isolators, Disconnectors, Circuit Breakers
Instrument Transformers, Surge Arresters, Transformers
3)HV Substations and Design Principles
Circuit Configurations For High Voltage Substations Substation systems and arrangements
Feeder components and configurations Design Approach and Calculations
Course Content
4) Electrostatic Fields
Field Analysis Methods
Experimental and Numerical Methods
5) Electrical Breakdown in Gases
Ionization Process Electronegative Gases
Streamer-Kanal mechanism, Breakdown in non-uniform fields
Partial Breakdown and Corona Discharges
6) Electrical Breakdown of Liquids
Breakdown theories for liquids Liquid insulating materials
7) Electrical Breakdown of Solids
Breakdown theories for solids Solid insulating materials
Course Content
8) Generation and Measurement of High Voltages
AC, DC Voltages
Electrostatic Generators Testing Systems
9)Protective Measures for Persons and Installations
Protection against contact in installations above 1000V Earthing
Lightning Protection EMC
10) A Review of Local Regulations
Elektrik İletim Sistemi Arz Güvenilirliği ve Kalitesi Yönetmeliği Elektrik Kuvvetli Akım Tesisleri Yönetmeliği
References
High Voltage Engineering: Fundamentals by E. Kuffel , Newnes
2000
High Voltage Engineering Fundamentals by E. Kuffel , W. S.
Zaengl, Pergamon Press 1984
Yüksek Gerilim Tekniğinin Temelleri by Prof. Dr. Sefa Akpınar,
1997
Yüksek Gerilim Tekniği by Prof. Dr. Muzaffer Özkaya, 1996
Various Industrial Booklets
Introduction
The potential benefits of electrical energy supplied to a number of consumers from a common generating system were recognized shortly after the development of the “dynamo” commonly known as the generator.
Power transfer for large systems, whether in the context of interconnection of large systems or bulk transfers, led engineers invariably to think in terms of high voltages.
The rapidly increasing transmission voltage level in recent decades is a result of the growing demand for electrical energy, coupled with the development of large hydroelectric power stations at sites far remote from centres of industrial activity and the need to transmit the energy over long distances to the centres.
Introduction
In order to meet the growing demand, more and more power stations, substations and transmission lines are being built and the transmission voltages are being raised for efficient transmission.
Increase in transmission voltage by 20 times results in 400 times reduction in
transmission losses. This illustrates the main reason for the need of “High Voltage”. It is desirable to increase the transmission voltage to obtain higher efficiency, but “the insulation of high voltage system “ limits this desire. The insulation of all parts of high voltage power system (generators, transformers, cables, insulators, circuit breakers, etc.) should be preserved in order to provide an “uninterruptable energy supply”or continuous energy flow.
Gas, liquid and solid insulating materials are utilized for the insulation of high voltage systems. The loss of insulation is technically called “breakdown”. Mechanisms of
Introduction
In High Voltage Installations Regulation (Elektrik Kuvvetli Akım Tesisleri Yönetmeliği) published by Turkey Ministry of Energy and Natural Sources ;
Low Voltage is the phase-phase voltage with rms value of 1000 Volts and less than 1000 Volts
High Voltage is the phase-phase voltage with rms value of greater than 1000 Volts These voltage ranges are also valid for IEC (International Electrotechnical Commission) Definition of some important standardized rated insulation levels for high voltage
Introduction
Rated voltage: Upper limit of the highest voltage of the network for which a switching
device is rated.
Rated short duration power frequency withstand voltage : rms value of the sinusoidal
a.c voltage at operating frequency that the insulation of a device must withstand under the specified test conditions for 1 minute.
Rated lightning impulse withstand voltage: peak value of the standard voltage surge
1.2/50us that the insulation of a device must withstand
Rated switching impulse withstand voltage: peak value of the unipolar standard
voltage surge 250/2500us which the insulation of a device with a rated voltage of 300 kV and above must withstand.
Introduction
Table of 154 kV and 380 kV insulation levels and table of electrical parameters used for design of power distribution substations as stated in “Elektrik İletim Sistemi Arz
1.Anma Değerleri
a) Normal işletme gerilimi kV rms 380 154 33 10.5
b) Max. sistem gerilimi kV rms 420 170 36 12
c) Anma frekansı Hz 50 50 50 50
d)Sistem topraklaması Direkt Direkt Direkt veya direnç üzerinden
Direkt veya direnç üzerinden
e) Max. radio interference level µV (RIV)
(1.1 Sistem geriliminde ve 1 MHz'de) 2500 2500 -
-f) 3 Faz simetrik kısa devre termik akımı kA (Ith)
-Tüm primer teçhizat baralar ve bağlantılar 50 31.5 25 25
-Kısa devre süresi (sn) 1 1 1 1
-Dinamik kısa devre akımı 2.5x(Ith) 2.5x(Ith) 2.5x(Ith) 2.5x(Ith)
2.İzolasyon Değerleri
(Güç Trafosu Hariç) 380 154 33 10.5
a) Yıldırım darbe dayanım gerilimi kV-tepe - Toprağa Karşı - Açık Uçlar Arası
1550 1550(+300)
750
860 170 75
b) Açma-kapama darbe dayanım gerilimi kV-tepe
- Toprağa Karşı - Açık Uçlar Arası
1175 (900+430)
- -
-c) 1 dakika Güç frekansında dayanım gerilimi (yaşta) kV-rms
-Toprağa Karşı - Açık Uçlar Arası
620 760 325 375 70 28 3.İzolasyon Değerleri (Güç Trafosu için)
-Yıldırım darbe dayanım gerilimi
kV-tepe(faz-toprak) 1425 650 170 95 (YG nötrü)
-Açma-kapama darbe dayanım
gerilimi kV-tepe 1050 - -
--1dk. Güç frekansında dayanım
gerilimi (yaşta) kV-rms 630 275 70 38 (YG nötrü)
4.Yardımcı Servis Besleme Gerilimi :
-3faz-N AC sistem 380 V + % 10 - % 15, 50 Hz
-1faz-N AC sistem 220 V + % 10 - % 15, 50 Hz
Transmission of Electric Energy
Although the bulk of world’s electric transmission is carried on ac systems, recent progress in high-voltage direct current (HVDC) technology has enabled the development of large scale dc transmission by overhead lines and submarine cables which have become economically attractive in long distance transmission of large bulk power. HVDC permits a higher power density on a given right-of-way than a.c. Transmission and thus helps the electric utilities in meeting the environmental requirements imposed on the transmission of electric power.
HVDC transmission can transmit more power per line and is much more efficient and cost effective over large distances. In addition the losses are quite low.
Transmission of Electric Energy
Today’s HVDC transmission schemes can carry up to 3000 MW of power over distances between 1000 – 1500 km. Atypical scheme consists of two stations that convert AC to DC and vice versa. It uses overhead lines or cables with only two conductors.
Transmission of Electric Energy
Increasing demands and strict environmental regulations mean that more and more remote hydro power plants are being considered. There is an almost unlimited source of solar power. If it could be harnessed properly and combined with hydro, wind and pump storage a totally renewable electrical system is possible.
Standards and Regulations
Standardization work for the field of electrical engineering is conducted almost entirely on an international level.
In Europe IEC (International Electrotechnical Commission), in USA ANSI (American National Standards Institute) are valid. There are other Canada, Russian and Japan standards.
In Turkey TSE standards are valid. They are mostly Turkish versions of IEC standards. Some of IEC standards related with hih voltage systems is listed below.
Standards and Regulations
• IEC 60038 Standard Voltages
• IEC 60265-1 High Voltage Switches - Switches for Rated
Voltages above 1 KV and less than 52 KV
• IEC 60265-2 High Voltage Switches for Rated Voltages of 52
KV and above
• IEC 60282-1 High Voltage Fuses – Current Limiting Fuse
• IEC 62271-1 Common specifications for high voltage
switchgear and controlgear standards
• IEC 62271100 High voltage switchgear and controlgear
-high voltage alternating current circuit breakers
• IEC 62271102 High voltage switchgear and controlgear
-alternating current disconnectors and earthing switches
Standards and Regulations
Besides standards there are also local regulations for
transmission, distribution of electric energy and energy market.
In Turkey EPDK
is the regulating agency.
Below are some
important local regulations for energy market.
• Elektrik İletim Sistemi Arz Güvenilirliği ve Kalitesi Yönetmeliği
• Elektrik Kuvvetli Akım Tesisleri Yönetmeliği
High Voltage Power System
Components and Technology
Main components used in high voltage power systems are as follows: • Synchronous generators
• Power transformers • Disconnectors
• Circuit breakers
• Overhead lines and conductors • Towers
• Insulators • Cables • Bus bars
High Voltage Power System
Components and Technology
Measuring and protection components used in high voltage power systems are as follows:
• Voltage and current transformers • Relays
• Surge arresters • Control circuits • Voltage dividers • Earthing switches
Voltage regulating components used in high voltage power systems are as follows:
• Series and shunt reactors • Series and shunt capacitors
Insulators
to insulate means "to separate or cover with a nonconducting material in order to
prevent the passage or leakage of electricity, heat, or sound." Communication and electric line wires in service must be kept as dry as possible in order to function
efficiently, and to cut down on loss of current. The wires are kept off of the ground by being strung between poles. But something was needed to keep the wires and
(sometimes wet) poles apart. This "something" had to meet three basic needs: • it must be made of a fast-drying nonconducting material
• it must be able to hold the line wire in place • it must stay on the pole
This "something" is the insulator. It was developed and improved upon over the years to meet those basic requirements is most commonly made of glass or porcelain
Insulators
There are a lot of insulator types used for various purposes: • Post insulators
• Pin type insulators • String insulators
• Transformer bushing insulators • Lightning arrester insulators • Wall bushing insulators
• Capacitive voltage transformer bushings • Special type insulators.
Disconnectors
Disconnectors are used for galvanic isolation of networks or sections of switchgear installations. As an independent air insulated-device, they form a visible isolating distance in their open position.
More than 10 different designs are in use around the world. The most important are:
• knife -contact disconnectors • rotary disconnectors
• two column vertical break disconnectors • single-column disconnectors.
Knife-contact disconnectors
The classic design of the disconnector is the knife-contact disconnector. Their moving contacts have the knife shape. There are indoor and outdoor types. They can be actuated manually and in remotely operated installations by motor or compressed air drives.
Indoor knife-contact disconnectors
Indoor types are used in switchgears in buildings. Control arm is brought out to a safe distance .
They are used in 10,15,30,45 KV systems with current ratings of 400, 630 and 1250 Amps. They have a simple and standard structure. The parts are: chassis, post insulator, fixed and moving contacts and armed moving mechanism.
Outdoor knife-contact
disconnectors
Outdoor types are used out of the buildings and are subject to environmental conditions like rain, dust, wind etc.
Disconnectors with fuse
These connector include a pair of fuse for protection against short circuits. There are indoor and outdoor knife-types.
They are used at the feeders of consumers with low power demand, at measuring voltage transformer feeders, and at auxiliary transformer feeders for substations.
Two column rotary disconnectors
This disconnector type is used for rated voltages of 72.5 to 420 kV preferably in smaller installations and also in larger switchgear installtions as incoming feeder or sectionalizing disconnector. An earthing switch can be installed on both sides.
Two rotating bases are mounted on a sectional steel frame and connected by a braced tie-rod. Post insulators are fixed to the rotating bases and carry the swivel heads with the arms and the high-voltage contacts. Both arms swivel 90 degrees with their insulators during the switching movement.
Two column rotary disconnectors in their open position form a horizontal isolating distance. The rotary bases should be weather protected and should have maintenance-free ball bearings.
Three column rotary disconnectors
These disconnector types are used with a side-by-side configuration of the three poles of a group. In comparison to two column rotary disconnectors, they allow smaller pole spacings and higher mechanical terminal loads.The two outer insulators are fixed to the base frame and carry the contact system. The middle insulator is fastened to a rotating base and carries the one-piece arm, which rotates approximately 60 degrees during a switching operation and engages the contact systems on the outer insulators.
Single column (pantograph)
disconnectors
In installations for higher voltages (> 170 kV) and multiple busbars , the single column disconnector (also referred to as pantograph or vertical-reach disconnector) requires less space than other disconnector designs. For this reason and because of the clear station layout , it is used in many switchgear installations. The switch status is clearly visible with the vertical isolating distance.
The base of the disconnector is the frame, which holds the post insulator carrying the head piece with the pantograph and the gearbox. The actuating force is transferred through the rotating insulator to the gearbox. The suspended contact is mounted on the busbar situated above the disconnector. On closing, it is gripped between the pantograph arms.
During the closing movement, the pantograph arms swivel through a wide range and are therefore capable of carrying the fixed contact even under extreme position changes caused by weather conditions. The feeder line is connected to the high-voltage terminal of the gearbox. In general, the single column disconnector allows higher mechanical terminal loads than the two column rotary disconnector.
Single column (pantograph)
disconnectors
Single column (pantograph)
disconnectors
Single column (pantograph)
disconnectors
Two column vertical-break
disconnectors
This type of disconnector is preferred for higher voltages (>170 KV) as a feeder or branch disconnector. It differs from two-column rotary disconnectors by smaller space savings (with side-by-side configuration) and higher mechanical terminal loads. In its open state there is a horizontal isolating distance with the contact arm open upwards.
The two post insulators are mounted on a frame. The gearbox with contact arm and high-voltage terminal and the fixed contact with high-voltage terminal are mounted on them. The rotating insulator fastened to the rotary bearing transfers the actuating force to the gearbox, which transmits the force into a torque for opening the contact arm.
For rated voltages up to 245 KV one mechanism per three-phase disconnector is sufficient, at higher nominal voltages one mechanism per pole is generally used.
Two column vertical-break
disconnectors
Circuit Breakers
High voltage circuit breakers are mechanical switching devices capable of making, carrying continuously and breaking electrical currents both under normal circuit conditions and for a limited period, abnormal circuit conditions such as in the event of a short circuit. Circuit breakers are used for switching overhead lines, cable feeders, transformers, reactor coils and capacitors. They are also used in bus ties in installations with multiple busbars to allow power to be transmitted from one busbar to another.
The following points are important when selecting circuit breakers.
• Maximum operating voltage on location
• Maximum load current occurring on location
• Maximum short circuit current occurring on location • Network frequency
• Duration of short circuit current • Switching cycle
Circuit Breakers
Important standards are IEC
62271-1 General and definitions
62271-100 Classification, Design and construction, Type and routine testing, Selection of circuit breakers for service, Informationin enquiries, tenders and orders
ANSI (American National Standards Institute) C37 04 – 1979 Rating structure
C37 06 – 1979 Preferred ratings C37 09 – 1979 Test procedure C37 10 – 1979 Application guide
C37 11 – 1979 Application guide for transient recovery voltage C37 12 – 1979 Capacitance current switching
Electrical Characteristics
Rated value: Value of a characateristic quantity used to define the operating
conditions for which a switching device is designed and built and which must be verified by the manufacturer.
Rated normal current: The current that the main circuit of a switching device
can continuously carry under specified conditions.
Rated short-time withstand current: Current that a switching device in closed
position can carry during a specified short-time under prescribed conditions.
Standardized rated normal currents: 200, 250, 400, 500, 630, 800, 1000,
1250, 1600, 2000, 2500, 3150, 4000, 5000, 6300A.
Standardized rated short-time currents: 6.3, 8, 10, 12.5,16, 20, 25, 31.5, 40,
Electrical Characteristics
Rated voltage: upper limit of the highest voltage of the network for which a
switching device is rated.
Standardized rated voltages: 3.6, 7.2, 12, 17.5, 24, 36, 52, 72.5, 100, 123,
145, 170, 245, 300, 362, 420, 550, 800 kV.
Peak making current: peak value of the first major loop of the current in one
pole of a switching device during the transient period following the initiation of current during a making operation.
Breaking current: current in one pole of a switching device at the instant of
Electrical Characteristics
Applied voltage: voltage between the terminals of a circuit breaker pole
immediately before making the current.
Recovery voltage: voltage occurring between the terminals of a circuit
breaker pole after interrruption of the current
Opening time: interval of time between application of auxiliary power to the
copening release of a switching device and the seperation of contacts in all three poles.
Closing time: interval of time between application of auxiliary power to the
Electrical Characteristics
Break time: interval of time between the beginning of opening time of a
switching device and the end of the arcing time
Make time: interval of time between application of the auxiliary power to
the closing circuit of a switching device and the instant in which the current begins to flow.
Rated insulation level: standardized combination of the rated values for the
lightning impulse voltage, the switching impulse withstand voltage and the short time power frequency withstand voltage assigned to a rated voltage.
Electrical Characteristics
Rated short duration power frequency withstand voltage : rms value of the
sinusoidal a.c voltage at operating frequency that the insulation of a device must withstand under the specified test conditions for 1 minute.
Rated lightning impulse withstand voltage: peak value of the standard
voltage surge 1.2/50us that the insulation of a device must withstand
Rated switching impulse withstand voltage: peak value of the unipolar
standard voltage surge 250/2500us which the insulation of a device with a rated voltage of 300 kV and above must withstand.
Electrical Characteristics
1. Transient recovery voltage e(t) system voltage 2. Recovery voltage ea(t) arcing voltage 3. Breaking time ik short circuit current
Circuit breaker types
There are still a number of “small-oil-volume” circuit breakers in use for rated voltages up to 52 kV in systems, but for new installations only vacuum or SF6 circuit breakers are used.
Circuit breakers can be stationary mounted or integrated into the panel in withdrawable unit design ith appropriate interlocking mechanism.
Circuit breakers must be capable of making and breaking all-short circuit and service currents occurring at the operational site.
Vacuum circuit breakers
Vacuum circuit breakers are available for short circuit breaking currents up to 63 KA with rated currents from 400 to 4000 A with rated voltages 12, 17.5, 24 and 36/40.5 KV.
Vacuum circuit breakers
The components of the main current path (upper breaker terminal, vacuum interrupter, lower terminal etc.) are embedded in cast resin and thus
completely enclosed by insulating material. The contacts are
copper/chromium composite material, a copper base containing evenly distributed fine-grained chromium particles, which has a good extinguishing and arc-resistant response when switching short-circuit currents.
Vacuum circuit breakers
Actuating systems
The travel of the moving contact between the open and closed positions in the vacuum circuit breaker is between 8 and 14 mm depending on the rated voltage. At the end of closing stroke , the energy for tensioning the contact pressure spring is required. The relatively low total energy requirement for vacuum circuit breaker is generally provided by mechanical spring stored energy operating mechanisms. Tripping is initiated by magnetic releases or manually.
SF6 circuit breakers
Sulphur hexafluoride (SF6) is an inert, heavy gas having good dielectric and arc extinguishing properties. The dielectric strength of the gas increases with pressure and is more than of dielectric strength of oil at 3 kg/cm2.
The puffer type arc quenching principle provides an effective arc-quenching gas flow by a mechanically driven piston.
SF6 circuit breakers
During the arcing period SF6 gas is blown axially along the arc. The gas removes the heat from the arc by axial convection and radial dissipation. As a result, the arc diameter reduces during the decreasing mode of the current wave. The diameter becomes small during the current zero and the arc is extinguished. Due to its electronegativity, and low arc time constant, the SF6 gas regains its dielectric strength rapidly after the current zero, the rate of rise of dielectric strength is very high and the time constant is very small.
Switchgear
There are two types of switchgear commonly applied today for switching and protection of high voltage power distribution systems. One is metal-clad
switchgear using draw-out circuit breakers and relays for protection. The other is metal enclosed switchgear using interrupter switches for load switching and power fuses for fault protection. Metal-clad switchgear
contains drawout circuit breakers which are removed for required scheduled maintenance and removal of a breaker interrupts its load. Metal-clad
switchgear also contains insulated bus which, when tested periodically, requires a shutdown of the gear.
Metalenclosed switchgear is available with interrupter switches and fuses that require no scheduled maintenance, and the air-insulated bus does not require periodic dielectric testing. Annual maintenance normally
consists of little more than a visual inspection through the windows of the gear. This switchgear should be seriously considered if only infrequent Interruptions can be tolerated by plant operations.
Switchgear
Switchgears are designed to comply with fixed minimum clearances of live components from one another, from earth potential and from protecting barriers.
When setting up these installations in electrical equipment rooms with restricted accessibility, protection against accidental contact with live components is sufficient.
Metal enclosed switchgear are generally assembled from type-tested panels. The metallic and earthed enclosure protects personnel against approach to live components and against contact with moving parts. It also protects the installation against the penetration of foreign bodies.
Switchgear
A third type of switchgear is the gas insulated switchgear (GIS). The term “gas-insulated” refers to the fact that atmospheric air is not used as the gaseous insulating material inside the panels, i.e. The enclosure of the installation must be gas-tight against the environment.
The advantage of gas-insulated switchgear compared to an air insulated installation is its independence from environmental influences such as moisture, salt fog and pollution. This results in less maintenance, increase operational safety and high availability. The samller dimensions due to compact design and increased dielectric resistance of the gaseous insulating material are also advantages.
Control systems for Switchgear
A wide range of devices for protection, control and monitoring tasks is available for conventional secondary technology in medium voltage switchgear installations. The planning engineer selects the required units and combines them into one installation. The outputs are predominantly standardized to 1 A for current and 100 V for voltage.
Circuit breakers > 52 KV
Basic design of HV outdoor circuit breakers with the following components is shown in the next figure: operating mechanism, insulators, interrupting chamber .
Higher voltages and higher capacities are dealt with by increasing the number of interrupting chambers. Single chamber breakars are used for voltages up to 300 KV and breaking currents of 50 KA. Multiple chamber breakers are used for higher currents up to 80 KA in this voltage range. Multiple chamber breakers are used for voltages >300 KV.
In the lower voltage range and for three-phase autoreclosure, it is best to mount the three poles on a common base frame.
Single pole mounting and a seperate mechanism for each pole are standard for voltages above 245KV.
The same interrupting chambers and mechanisms as indoor circuit breakers are also used with the integrated circuit breakers of gas insulated switchgear installations.
Some requirements for electrical
control of circuit breakers
SF6 Gas monitoring : The breaking capacity of a circuit breaker is dependent
on the gas density in the breaker chamber. This is measured by a temeperature-compensated pressure gauge. If the gas pressure falls to aspecified value, an alarm is triggered.
Local/remore control: To allow work on the breaker, it can generally be
controlled from the local control cubicle; control can be switched from remote local by a selector switch.
Autoreclosing: A single or three-pole autoreclosing is selected on the type of
system earthing, the degree of the interconnection, the length of the lines and the amount of infeed from large power plants.
Instrument transformers for
switchgear installations
Instrument transformers are transformers used to feed measuring instruments, electricity meters, protection relays and similar equipment.
Their function is to transform high voltages and currents to values that can be unified or measured safely with low internal losses. With current transformers , the primary winding carries the load current, while with voltage transformers, the primary winding is connected to the service voltage. The choice of a current transformer is based on the values of the primary and secondary rated current, the rated output of the transformer cores at a given accuracy class rating and the overcurrent limit factor or accuracy limit factor. Selection of the values for the primary and secondary rated currents should be based on standard levels. Secondary rated currents of 1A, 2A or 5A are available. Modern protection devices and measuring instruments have a relatively low burden, and so 1A is becoming the most frequently used secondary current.
Instrument transformers for
switchgear installations
Measuring instruments or meters, for instance KW,KVAR or KWH measure under normal load conditions. These devices require high accuracy, a low burden and low saturation. They normally function in the range of 5-120% of the rated current in accordance with accuracy classes 0.2 to 0.5.
Burden is the load which may be imposed on a transformer secondary by cables and connected devices without causing an error greater than the stated accuracy classification.
For protection relays and disturbance recorders, the information about the fault on the primary side has to be transmitted to the secondary side. Measurement under fault conditions in the overcurrent range requires lower accuracy, but the ability to transmit high fault currents which enable the protection relay to measure and selectively shut down the fault. Typical classes are 5P, 10P or TP.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Depending on the design of primary winding , current transformers are divided into various types. This basically depends on the application (high or low voltage).High voltage transformers are as a rule designed with oil-paper or SF6 insulation.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Voltage transformers can fundamentally be divided into two groups: inductive and capacitive voltage transformers. Inductive voltage transformers are the most economical solution for voltages up to 145 KV and above that level capacitive transformers have advantages.
High voltage transformers are generally designed as oil-paper insulated transformers.
Apart from inductive voltage transformers, capacitive voltage transformers ara available for higher system voltages up to 765 KV. They fundamentally consist of a capacitive divider and an inductive voltage transformer.
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Instrument transformers for
switchgear installations
Optical current transformers use the Faraday effect in crystalline structures for passive measurement of currents. Monochromatic light is sent polarized into a solid body of glass, which surrounds the current carrying conductor. Reflection from the bewelled corners of the glass container directs the light beam around the conducting line before it exits again on one side.
The magnetic field around the conductor rotates the polarization plane of the light, whose phase difference is proportional to the magnetic field intensity H. The phase difference at the end of the path in the glass body is directly
Instrument transformers for
switchgear installations
Surge arresters
Surge arresters are used for protection of important equipment, particularly transformers, from atmospheric overvoltages and switching overvoltages. Arresters are primarily selected on the basis of two basic requirements: -the arrester must be designed for stable continuous operation
-it must provide sufficient protection for the protected equipment.
Today surge arresters are based on metal oxide (MO) resistors, which have an extremely nonlinear U/I characteristic and a high energy absorption capability. They are known as metal oxide surge arresters.
The metal oxide arrester is characterized electrically by a current/voltage curve. The current range is specified from the continuous operating range (range A of the curve, order of magnitude 10-3 A) to a minimum of the double
value of the rated discharge current (order of magnitude 103 A). The MO
arrester corresponding to the characteristic is transferred from the high resistance to the low resistance range at rising voltage without delay. When the voltage returns to the continuous operating voltage or below, the arrester becomes high ohmic.
Surge arresters
Surge arresters are preferably installed parallel to the object to be protected between phase and earth.Because of the limited protection distance with steep lightning voltages, the arresters must be installed adjacent to the equipment that is to be protected as much as possible.
Monitoring systems (surge counters) may be used to monitor surge arresters. They are installed in the ground conductor of the arrester.
Oil Immersed Type Distribution Transformers
Hermetic With conservator
Dry Type Distribution Transformers
With tap changer In metal encase
1.Core limbs 2.LV winding 3.HV winding 4.Tapping winding 5.Conductors 6.LV bushings 7.HV bushings 8.Pressing equipment 9. On-Load tap changer 10.Motor-drive mechanism 11.Oil conservator
12.Radiators 13. Tank
Stacking of core laminations Lifting up of the core with special apparatus.Three limbed transformer
A transformer core with five limbs
The difference between Transformers and Reactors ; Reactors have only primary winding and their core has air-gaps as shown below.(But their periodical test and maintenance are the same as transformers except turn ratio and magnetizing current measurings)
Single phase reactor core
Winding apparatus for disc winding
Winding apparatus for layer winding Winding apparatus for layer winding
INTRODUCTION
Active part of a transformer
Upper clamping ring
INTRODUCTION
Active part with on-load tap changer
Active part with off-load tap changer Due to the voltage variations in
the networks or in the substations, transformers are normally equiped with tapping windings having necessary taps to accomplish the requested voltage level. The connections of these taps are either made with no-load tap changer(off-load tap changer) when the transformer is
deenergized or with on-load tap changer when the transformer is under operating conditions. The motor drive mechanism is used for the, control of on-load tap changer.This control can either be made locally on the transformer or remotely from the control
room.The operation of off-load tap changers can either be made on the cover or on the sidewall of the transformer by manual drive mechanism.Upon request, motor drive mechanism can be provided to operate the off-load tap
INTRODUCTION
Protection and control equipment
Bucholz relay
Pressure relief device
Oil level indicator
It is mounted on the pipe
connection from transformer tank to conservator.The gasses which occur in transformer for any reason are collected here and depending on the volume of gas it gives an alarm or tripping signal.
It is mounted on the transformer cover.It replies to the sudden pressure increase that may occur by an arc in the oil in the
transformer and gives tripping signal by the contacts on itself.
It is mounted onto the sidewall of the conservator. Depending on the oil temperature
variations, it indicates the oil level in conservator and gives too low or too high indications by the contacts on itself.
INTRODUCTION
Dehydrating breather
Oil thermometer
Winding thermometer
Oil flow indicator
It is mounted onto the
conservator.It takes the moisture and dust in the air that enters the conservator and increases service security of the transformer, the amount of silicagel particles in it varies with the amount of the oil in the transformer.
It controls the temperature of the oil in the transformer tank and gives alarm and trip signal at the adjusted temperature limits.It gives start and stop signal for the fans used at forced cooling.If remote control is required,Pt 100 resistance or 4-20 mA output is added to it.
It controls the temperature of the windings with its monitoring circuit and gives alarm and trip signal at the adjusted temperature limits.Like the oil temperature,it is used for the controls of fans and pumps and if reqired Pt 100 resistance or 4-20 mA output is added to it.
It controls the oil flow at forced oil cooled transformers.It is mounted on the pipe connection in which the oil flows through.It gives alarm signal if the oil does not flow for any reason.
HV B us hi ng turr et Air Cell C T03 1 o il te m p . ind ic a to r C T03 3 w ind ing te m p . ind ic a to r A T 00 1 ai rc el l b re a th in g CL06 0 oi l l ev el CL 0 64 oi l l ev el O LT C A T 00 5 O LT C breath ing CF 05 0 B UCHH O Z CF101 air cell alarm relay CP 0 96 pres s ure rel ief v al v e for O LT C B Q 0 1 1 T h e rm o m e te r p o c k e t fo r w in d . T e m p . BQ 01 0 T he rm om ete r po c k et CP 0 81 pres s ure rel ief v al v e for m ai n t an k RADIATOR Main Tank O LT C bu c ho lz r el ay C F 06 1
SECTION .2 - CONSTRUCTION
•O-ring
•Radiators (cooling elements)
•Oil Drain plug • Air ejecting plug (vent screw)
•Lifting eye
Radiators are important part of the cooling of the transformers.Radiators have two ducts for connection to transformers. On upper and bottom connection pipes ,there are butterfly valves.
On upper side there is a ventilation plug. On bottom side there is a draining plug. On top of it, there is a lifting eye. Butterfly
valve
Transformer Tank
Ø The Fans and their Connections SECTION .2 - CONSTRUCTION FAN CONTROL CUBICLE TANK RADIATOR FAN
Transformer Power Efficiency can be increased by adding fans. They are built under radiators to blow air upwards for cooling the oil inside the radiators. They are operated automatically / manually when the oil temperature rise. The basically cooling operations;
ONAN (Oil Natural Air Natural) (without fan or pumps) ONAF (Oil Natural Air Forced) (air forced with fan)
SECTION .2 - CONSTRUCTION
