SIMULATE AND ANALYSE LIGHTNING TRANSIENT PROPAGATION IN THE HIGH VOLTAGE TRANSFORMER STATION BY EMTP

i Content CHAPTER 1: LIGHTNING TRANSIENT PROPAGATION IN THE HIGH CHAPTER 5: SURVEY THE EMULATION CASES COMPARE 5.1.2 Line layout triangle and horizontal 70 5.1.3 Back – flash and ligh

VIET NAM NATIONAL UNIVERSITY OF TECHNOLY HO CHI MINH

P.F.I.E.V PROGRAM ENERGY SYSTEM

i

Content

CHAPTER 1: LIGHTNING TRANSIENT PROPAGATION IN THE HIGH

CHAPTER 5: SURVEY THE EMULATION CASES COMPARE

5.1.2 Line layout triangle and horizontal 70 5.1.3 Back – flash and lightning discharge directly on the phase line 71 5.1.4 Surveying the changes in the lightning maximum stepness 71 5.1.5 Surveying the changes of the distance between the valve arrester

5.2.2 Back – flash and lightning discharge directly on the phase line 76 5.2.3 Surveying the changes in the lightning maximum stepness 77 5.2.4 Surveying the changes of the distance between the valve arrester

and the transformer 78

This thesis, with topic: ”Simulate and analyse lightning transient propagation in the high voltage transformer station by EMTP-RV”, is done on commercial software EMTP-

RV at the Station Office – Power Engineering Consulting Joint Stock Company 3 (PECC3)

- Electricity Vietnam (EVN) with actual data provided by this company to help us look at more specific on this issue

The contents of this thesis include:

Chapter 1: summary of the theory

Chapter 2: introduction EMTP software

Chapter 3, Chapter 4: Simulation of the transformer stations 400kV and 500kV Nha

Be with EMTP-RV

Chapter 5: compare and evaluate the results of the simulation

B CONTENTS

CHAPTER 1 LIGHTNING TRANSIENT PROPAGATION IN THE HIGH

VOLTAGE TRANSFORMER STATION 1.1 LIGHTNING

1.1.1 Lightning concept:

Lightning is an atmospheric discharge of electricity usually accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms

In the atmospheric electrical discharge, a leader of a bolt of lightning can travel at speeds of 60,000 m/s (220,000 km/h), and can reach temperatures approaching 30,000 °C (54,000 °F), hot enough

to fuse silica sand into glass channels known as fulgurites which are normally hollow and can extend some distance into the ground

There are some 16 million lightning storms in the world every year

Lightning can also occur within the ash clouds from volcanic

eruptions, or can be caused by violent forest fires which generate sufficient dust to create a static charge

The terrestrial atmosphere is very good dielectric located between two conductors - a surface of the ground from below and the top layers of an atmosphere, including an ionosphere, from above These layers are passive components of a global electric circuit Between negatively charged surface of the ground and positively charged top atmosphere the constant potential difference of about 300.000 V is supported Lightning occurs because the bottom of a thundercloud becomes negatively charged, and repels the negative charge of the ground deeper in

so the positive charge is more towards the surface

1.1.2 Characteristics of lightning and its influence on the power system:

Most of the causes of the overvoltage is transitional, it only lasts a few micro-second

to several period and originate from inside or outside the system The external origination is mainly lightning, a unpredictable phenomenon, create pressure for the power system

Lightning is the mainly origination of the harmful overvoltage on the power system,

it can be born by lightning discharge directly or back-flash The overvoltage impulse can change from a relatively small value to several times larger than the normal phase-ground voltage These impulse will propagate in the line with the speed of light

Therefore, the more understanding the characteristics of the lightning, the more effective in the installation of devices to protect A typical lightning has the very large maximum steepness, meaning that its voltage increases with the rate of millions of volt on a second In the fact, 15% of the top of the lightning occur under 1μs The wave font is connected by the wave tail of a short wave, that means after the voltage reaches the peak value, time that voltage is reduced to half the value of the voltage peaks during 200μs and completely disappear during 1000μs

The lightning current is measured by its impact on the equipment The sensitive equipment such as arrester will allow the lightning run through Many modern science devices is used to measure and record the lightning current, has found that the scope of change is very large: 1000A → 200KA The research showed that the current through the arrester is about 1/10 the total value of the lightning current but only about 5% of the lightning on the distribution system exceeds 10kA

1.2 PROTECT THE LIGHTNING TRANSIENT PROPAGATION IN THE HIGH VOLTAGE TRANSFORMER STATION

1.2.2 The characteristic of the voltage impulse at the protected equipment:

Value: The largest value of the voltage impulse at the protected equipment is ratio

of the distance between the valve arrester and the transformer and the maximum stepness a

Wave shape: a damped oscillation

1.2.3 Principle of lightning protection:

• The largest value of the voltage impulse at the protected equipment must be smaller than the value of the basic lightning impulse insulation level of the protected equipment

• The largest value of the current run through the valve arrester must be smaller than the classifying current of the valve arrester (according to voltage levels and their types)

• Distance between the valve arrester and the protected equipment must be in

U tnx pđ

2

)

+ Utnx: basic lightning impulse insulation level of the protected equipment

+ Upđ: discharge voltage of the valve arrester

+ Maximum stepness: a = 11kV/µs/kV×MCOV ÷2000kV/µs/kV×MCOV + v: velocity of the wave propagation; v = 300m/µs

1.2.4 The equivalent capacity value of the high voltage equipment:

Equipment Characteristic Capacity (  F)

Limit value Average value

Transformer

Large power and there is compensator 0.001  0.003 0.0015 Small power and

there is compensator 0.0003  0.001 0.0005

Switch When close circuit 0.00004  0.00008 0.00006

When open circuit 0.00003  0.00006 0.00004

Breaker When close circuit 0.0003  0.0008 0.0005

When open circuit 0.0002  0.0005 0.0003

Bushing Capacitor 0.00015  0.0003 0.0002

Other 0.0001  0.0002 0.00015 Compensator

CHAPTER 2 INTRODUCE EMTP SOFTWAVE

2.1 BRIEF HISTORY OF THE EMTP

The EMTP stands for electromagnetic transiets program It is a computer program for the simulation electromagnetic, electromechanical, and control system transients on multiphase electric power systems

It was first developed as a digital computer counterpart to the analog Transient Network Analyzer (TNA) Many other capabilities have been added to the EMTP over the years and it has become the standard in the utility industry

The EMTP was developed in the late 1960's by Dr Hermann Dommel, who brought the program to Bonneville Power Administration (BPA) When Professor Dommel left BPA for the University of British Columbia in 1973, two versions of the program started to take shape: the relatively small UBC version, used primarily for model development, and the BPA version, which expanded to address the needs of utility engineers The BPA version of the EMTP grew as a result of the co-operative development effort of Dr Scott Meyer and

Dr Tsu-huei Liu from BPA, as well as a number of other contributors from North American power companies and universities In order to rationalize the development of the program and to attract funding from other utilities, the EMTP Development Coordination Group (DCG) was founded in 1982 Original members of the DCG included BPA, the US Bureau

of reclamation, Western Area Power Administration (WAPA), the Canadian Electrical Association (CEA), Ontario Hydro, and Hydro Quebec

Since the inception of DCG, a number of changes have taken place in the EMTP community In 1986, Dr Scott Meyer left DCG (due to what at the time was described as philosophical and political differences) to develop, and to aggressively advocate an independent version of the EMTP which he called the ATP (Alternative Transients Program) In 1989, UBC further developed and marketed the original version of the EMTP and concentrated on PC platforms under the trade name MicroTran In the mid 80's Manitoba HVDC Research Centre developed a version of the EMTP (EMTDC) targeted primarily for the simulation of HVDC systems

As these developments took place, DCG continued to fund EMTP research and

CRIEPI (Central Research Institute of Electric Power Industry) from Japan, Eletricité de France, and NEG (Nordic EMTP Group) representing Imatran Voima Oy of Finland, Sydkdraft AB and Vattenfal AB of Sweden

These efforts resulted in the release of version 3 of the DCG version of the EMTP in

1996 (EMTP96) EMTP96 represents the last version of the EMTP based on the original BPA code This program will be superseded by the results of a complete re-structuring of the EMTP code presently under development by DCG, and scheduled to be released in

2001 This third-generation version of the EMTP will include all the functionality of EMTP96, but will also include advanced features such as variable time step, plug-in solution modules, dynamic memory allocation, and more

EMTP-RV is the end result of the "EMTP Restructuring project" undertaken by the DCG in 1998 for modernizing the EMTP96 software EMTP-RV is the enhanced computational engine and EMTPWorks its new graphical user interface (GUI) The package

is a sophisticated computer program for the simulation of electromagnetic, electromechanical and control systems transients in multiphase electric power systems It features a wide variety of modeling capabilities encompassing electromagnetic and electromechanical oscillations ranging in duration from microseconds to seconds Examples

of its use include switching and lightning surge analysis, insulation coordination, shaft torsional oscillations, ferroresonance and power electronics applications in power systems

In addition to the versions of the EMTP mentioned above, there are other transients analysis programs for electrical circuits worth mentioning in this context:

NETOMAC (Siemens, commercial product) Morgat and Arene ( Eletricite de France, commercial products) PSIM (commercial product, aimed at power electronics studies) SABER (commercial product, aimed a power electronics studies) SPICE, PSPICE (commercial product, for electronic circuits, occasionally used in power electronics studies)

2.2 APPLICATIONS OF EMTP

The EMTP is a very versatile simulation tool, and it can be used for most state calculations, as well as most transient simulatons generally not exceeding one or two seconds

steady-The EMTP is generally used for one of two purposes:

1 To aid in the design and specification of the power system and its components

In other words, the EMTP is used in insulation coordination studies, specification of equipment ratings, protective device specification, control system design, power quality assessment, harmonic studies, etc

2 To find solutions to existing system problems such as unexplained outages or equipment failures

A partial list of typical EMTP studies follows:

Switching Surges

Deterministic line energization Probabilistic line energization Single-pole switching High-speed reclosing Capacitor switching

Transient recovery voltages Cable switching transients and sheath protection Lightning Surges

Backflashover Direct strokes Incoming surges at stations Arrester specification Insulation coordination

Overhead lines Underground cables Outdoor Stations Gas-insulated substations Arrester duty

Shaft torsional stress - subsynchronous resonance High Voltage DC (HVDC)

Controls Electrical transients Harmonics

Static VAR Compensation

Controls Overvoltages Harmonics

Temporary overvoltages Power electronics and FACTS (HVDC, SVC, VSC, TCSC) General purpose electrical and electronic circuit simulations Power quality issues

Carrier frequency propagation Harmonics

Ferroresonnance Distribution networks and distributed generation Power systems dynamics and load modeling Subsynchronous resonance and shaft torsonial stresses Power systems protection issues

Series and shunt resonance Motor starting

Out-of-phase synchronization Islanding or other disturbing events General control systems

Grounding Asymmetrical fault current evaluation

This is only a partial list One of the EMTP's major advantages is its flexibility inmodelling; an experienced user can apply the program to a wide variety of studies, many

of which were not even considered when the EMTP was first designed Unfortunately, with flexibility often comes complexity: the EMTP is not easy to use The difficulty lies not so much in the absence or presence of graphical user interfaces, but rather in the fact that the phenomena the EMTP is normally used to simulate are usually conceptually complex and difficult to model The user is expected to have a fair understanding of the phenomena being simulated

2.3 STATES OF SIMULATION

Typical EMTP studies deal with steady-state and switching or lightning transients

We will now establish working definitions for these

2.3.1 Steady-state Simulations

As the name indicates it, steady-state is the normal operating state of an electrical power system

In power system analysis, steady-state calculations are typically made in the

“frequency domain” using phasor analysis In other words, instead of using the time domain

representation of a voltage as V  Vocos(t  ), in the frequency domain it become Vrms, the angular frequency  is implicitly 50 or 60 Hz

Phasor analysis simplifies calculations significantly in traditional power system analysis, it is the basis of most load flow and short-circuit analysis programs

The EMTP uses steady-state calculations in the frequency domain to initialize the network in preparation for a transient simulation (rather than starting the transient simulation from zero initial conditions)

2.3.1 Transient Simulations

The simulation of transient events is the main purpose of the EMTP As indicated earlier, a transient can be defined as what happens between two steady-state events: For example, before and after a line-to-ground fault

There are many types of transients Some are caused by more or less unpredicatable

“external” events such as lightning, faults, and equipment failure, while others are caused

by intentional switching maneuvers

The simulation of a transient event is intimately tied to the frequency content of the voltages and currents involved in the event A working definition of the significant frequency content of a surge would be the dominant or significant frequency that would be obtained if harmonic analysis were to be carried out over the time the transient event takes place

Table below, groups the frequency range of common transient events

Transformer energization ferroresonance

(DC) 0.1 Hz – 1 kHz

Fault initiation 50/60 Hz – 20 kHz Line energization 50/60 Hz – 20 kHz Line reclosing (DC) 50/60 Hz – 20 kHz Transient recovery voltage (terminal

restrike) and faults in GIS

100 kHz – 50 MHz

In an EMTP simulation, the frequency range of a transient simulation is important for several reasons:

The EMTP simulates the network in discrete time steps The size of the time step puts a theoretical limit on the resolution of the transient that can reproduced This theoretical limit is the Nyquist frequency fN=1/2 t One way to visualize the meaning of the Nyquist frequency is that, in theory, only two (equally spaced) samples of a sinusoidal wave are necessary to determine its frequency In practice, the time step must be smaller because the EMTP uses the trapezoidal rule of integration to solve the differential equations that describe the system The trapezoidal rule of integration only approximates an analytical solution, and the smallest the time step of integration the better the approximation A time step 5 times smaller than the Nyquist frequency produces reasonable answers Therefore, as

a rule of thumb, the time step of a simulation is chosen to be so that t is smaller than 1/10fmax

The detail in which the network needs to be modelled depends on the maximum significant frequency of the phenomena being simulated For instance, in lighning simulations, it is necessary to model each span and each tower of a transmission line in detail, whereas in a line energization simulation such detail is not necessary As a rule of thumb, the higher the frequency of interest the higher the amount of detail

The size of the network being modelled also depends on the maximum significant frequency of the transient being studied The lower the frequency the larger the system that needs to be modelled (albeit in less detail) For instance, even though in a lightning simulation it is necessary to model towers and spans in detail, only a few of these spans need to be modelled at all

Group Frequency range for

representation

Shape designation Representation maily for

I 0.1 Hz – 3 kHz Low frequency oscillations Temporary overvoltages

II 50/60 Hz – 20 kHz Slow front surges Switching overvoltages

III 10 kHz – 3 MHz Fast front surges Lightning overvoltages

IV 100 kHz – 50 MHz Very fast front surges Re-strike overvoltages

Table: Classification of frequency ranges

EMTP-RV accepts several simulation options which are performed for arbitrary network configurations All options are applicable to all devices within documented rules of device behavior These are:

 Frequency scans

 Steady-state solutions: linear harmonic steady-state solution, non-linear harmonic steady-state solution and three-phase power flow

 Time domain solutions: fixed time-step trapezoidal with/without backward Euler method, automatic initialization from steady-state, startup from manual initial conditions and special option for power electronics instantaneous switching conditions within a time-step

 Statistical/systematic analysis

2.4 ARCHITECTURE OF EMTP FILE

 EMTPWorks has a 3-Layer design The lowest is a framework for the actual interface code A second layer is added for supporting scripting methods The third layer is the user or developer access layer It provides a large collection of scripts for modifying and/or updating almost anything appearing on the design canvas The scripting language is JavaScript with added methods for communicating with the framework layer

 All built-in devices are scripted for data and device symbol handling Device symbols can be contextually updated through scripts A device symbol editor is also available

 In addition to device scripting, EMTPWorks provides full design scripting Scripts are used to search for devices or to retrieve and modify data for a large number of devices using a few lines of script Scripts can be also applied to signals

 Scripts are also used to generate the static Netlist submitted to EMTP-RV

 EMTPWorks provides unsurpassed customization options and can be easily converted and used for other applications in power system analysis

2.5 DEVICE LIBRARY

The devices are created and maintained in EMTPWorks and transmitted to

EMTP-RV in the Netlist file There are built-in devices, built-in encapsulated devices and defined devices Built-in devices are the fundamental ones supported by the EMTP-RV code Encapsulated devices are devices created in EMTPWorks by interconnecting built-in devices User-defined devices may be created by using various techniques for data hiding and encapsulation or by providing complete device codes through DLL's

user-Devices are found in EMTPWorks libraries which will be continuously updated The first commercial version of EMTP-RV will contain the following libraries:

Pseudo device: Signal interconnections devices all built-in

RLC branches:

- Built-in devices: single or three-phase RLC's, single/three or multi-phase PI sections, single/three or multi-phase coupled RL and multi-phase FDB branches

- Encapsulated devices: three-phase RLC load (PQ)

Control: Built-in complete control system devices

Control devices of TACS: Encapsulated supplemental devices of the old TACS (type 50,

51, etc.)

Control functions: Encapsulated various control system functions, such as PWM, PID, etc

Control of machines: Encapsulated various synchronous machine exciter, turbine and

speed regulator models

Flip-flops: Encapsulated various types of flip-flops

HVDC: Encapsulated basic HVDC control functions

Lines:

- Built-in devices: Line data, cable data, Corona, single/three or multiphase CP line model, multiphase FD line model, multiphase FDQ cable model and multiphase Wideband line model

Machines:

- Built-in devices: Generic three-phase multi-mass synchronous and asynchronous machine model

Meters: Various built-in scopes/probes and meters for power and control systems signals

Meters periodic: Metering functions specific to periodic signals, vrms, P, Q, Vsequences,

etc

Non-linear:

- Built-in devices: Point by point voltage-dependant non-linear resistor model, controlled non-linear resistor model, time-varying point by point/staircase resistor model, non-linear inductance model and corresponding data calculation function, Hysteretic reactor and corresponding hysteresis fitter, SiC arrester model, Zno arrester model and corresponding data calculation function, various circuit-breaker arc models

Options: Simulation option, data converter and translator for old EMTP-V3 files, statistic

Switches:

- Built-in devices: Ideal switch, controlled switch, Air-gap model, controlled gap model, statistical/systematic switches, ideal diode and power electronic switches

Symbols: Built-in library of symbols for simple drawings or for sub-circuit creations

Transformations: Encapsulated control elements for classical transformation functions,

such as three-phase to dq0, sequences to three-phase, etc

Transformers:

- Built-in devices: Single/multiple secondary windings single phase ideal transformer model, BCTRAN - TOPMAG - TRELEG - transformer data calculation modules, EDDY currents data calculation module and FDBFIT fitter for high frequency transformer model data calculation

- Encapsulated devices: Non-ideal single phase transformer, various two and three windings three phase transformers and three phase ZigZag grounding banks

CHAPTER 3 SIMULATE TRANSFORMER STATION 400kV

Survey transformer station 400kV with the one-line circuit diagram of stations are shown in the below picture:

The circuit diagram of the transformer station 400kV

Survey the case of lightning discharge on the line 1, the lines 2 and 3 is connected to the bus, while the lines 4 and 5 are not connected to the bus The transformer is protected by normal SiC arrester

The one-line circuit diagram of stations are shown in the below picture:

The simulated fault is a single - phase back - flashover caused by the lightning discharge to a tower far from station 900m

The numbers written on top of the bus and the line specified the length of the line in

The back - flashover is simulated by using the simple models Ideal flashover switch

The influence of the frequency voltage source to the back - flashover rate can not be ignored at this voltage level In the case of this study, it is simulated by using the Thevenin equivalent 3 phase source is connected with line 2 and line 3

The lines and bus in the transformer station are simulated by using the single - phase Constant Parameter (CP) line models

The compensator (TU) is replaced by 1 capacitor 0.5 nF

The transformer is replaced by 1 capacitor 3 nF

The valve arrester is replaced by 1 nonlinear resistor

The EMTP circuit of the power station and the lines to the station are presented in the following picture:

3.1 PARAMETERS Line FD:

Parameter of the FD line

The circuit of the transmission line outside the station:

Parameter of the 3 phase CP line

Parameter of the arrester CP line

The circuit of the tower:

Parameter of the CP line

Parameter of RL

Parameter of resistor

Ideal flashover switch:

Parameter of the Ideal flashover switch

The circuit of the lightning source:

Parameter of the lightning source

Parameter of the resistor connected with the lightning source

The circuit inside the station:

Parameter of the CP line at the front of the line 1

Parameter of the switch

Parameter of RL connected with the voltage source

Parameter of the voltage source

Parameter of the valve arrester

Phase A:

The overvoltage impulse at the TU1 on phase A

The overvoltage impulse at the TU1 on phase A

Phase B:

The overvoltage impulse at the TU1 on phase B

Phase C:

The overvoltage impulse at the TU1 on phase C

The overvoltage impulse at the TU1 on phase C

- The overvoltage impulse at the transformer:

Phase A:

The overvoltage impulse at the transformer on phase A

The overvoltage impulse at the transformer on phase A

Phase B:

The overvoltage impulse at the transformer on phase B

Phase C:

The overvoltage impulse at the transformer on phase C

The overvoltage impulse at the transformer on phase C

- The current of the valve arrester:

Phase A:

The current of the valve arrester on phase A

The current of the valve arrester on phase A

Phase B:

The current of the valve arrester on phase B

Phase C:

The current of the valve arrester on phase C

The current of the valve arrester on phase C

CHAPTER 4 SIMULATE TRANSFORMER STATION 500kV NHA BE 4.1 TRANSFORMER STATION 500kV NHA BE

From the look of the line to the transformer stations 500kV Nha Be

From the outside line to look at the transformer stations 500kV Nha Be