CALIFORNIA STATE UNIVERSITY NORTHRIDGE
Power Systems Line and Machine Protection System Study and Hardware
Implementation
A Graduate Project submitted in Partial fulfillment of the requirements
For the degree of Master of Science in
Electrical Engineering
By
Ehsan Mahmoody
May 2015
The graduate project of Ehsan Mahmoody is approved by:
_________________________
Dr. Kourosh Sedghisigarchi
_________________
Date
_________________________
Dr. Xiaojun (Ashley) Geng
_________________
Date
_________________________
Dr. Bruno Osorno Chair
_________________
Date
California State University, Northridge
ii
Table of Contents
Signature page………………………………………………………………………………………….………..ii
List of Tables…………………………………………………………………………………………………..iv
List of Figures…………………………...…………………………………………………………………………..v&vi
Abstract ......................................................................................................................... vii
1.
Introduction .............................................................................................................. 1
1.1 Overview ............................................................................................................... 1
1.2 Objective ............................................................................................................... 2
2.
Technical Requirements........................................................................................... 3
2.1 Hardware ............................................................................................................... 3
2.2 software ................................................................................................................. 6
3.
Approach .................................................................................................................. 9
3.1 LG (line to ground) fault [1]................................................................................... 9
3.2 LL (line to line) fault [1] ...................................................................................... 11
3.3 LLG (Line to Line to Ground) Fault [1]............................................................... 13
3.4 Induction Motor Protection [2]............................................................................. 16
3.5 SEL Device Setting ............................................................................................. 17
4.
Case Study ............................................................................................................. 36
4.1 SEL 351S faults .................................................................................................. 36
4.2 SEL 710 Faults.................................................................................................... 47
5.
Results and Conclusions ........................................................................................ 53
References ..................................................................................................................... 54
iii
List of Tables
Table 1 SEL 351S parameters setting for overcurrent relay setting ................................ 24
Table 2 SEL 710 characteristic settings for quick set....................................................... 27
iv
List of Figures
Figure 1 SEL 351 line protective micro-processor relay machine ..................................... 4
Figure 2 SEL machine protective relay .............................................................................. 5
Figure 3 SEL 3530 Real Time Automation Controller (RTAC) .......................................... 6
Figure 4 AcSELerator Quickset options for task assignment ............................................. 7
Figure 5 Graphical modeling environment on diagram builder software ......................... 8
Figure 6 Single phase to ground fault circuit ................................................................... 10
Figure 7 Pos-Neg-Zero sequence of single line to ground fault...................................... 11
Figure 8 Line to Line short circuit fault diagram ............................................................. 12
Figure 9 Sequence circuit diagram of LL fault................................................................. 13
Figure 10 LLG fault circuit with fault impedance ............................................................ 14
Figure 11 LLG fault sequence circuit diagram ................................................................ 15
Figure 12 Induction motor internal circuit of theory ....................................................... 16
Figure 13 AcSELerator Quick set communications settings ............................................ 19
Figure 14 Communication parameters for SEL 351......................................................... 19
Figure 15 Quick set software window while setting of SEL 351S .................................... 21
Figure 16 General setting of SEL 351S ............................................................................ 22
Figure 17 Logic setting of SEL 351S ................................................................................ 23
Figure 18 Setting window of SEL 710 on Quickset software............................................ 25
Figure 19 SEL 710 parameters assignment and protection method choosing ................. 26
Figure 20 RTAC setting software login ............................................................................ 28
v
Figure 21 SEL devices to RTAC software......................................................................... 29
Figure 22 Project startup on SEL diagram builder window ............................................ 30
Figure 23 Connection test and establishment to RTAC from PC using SEL diagram
builder ............................................................................................................................... 31
Figure 24 Available tags on SEL diagram builder ........................................................... 32
Figure 25 HMI design on SEL diagram builder software ................................................ 33
Figure 26 HMI designed network for proposed protection system .................................. 35
Figure 27 Proposed system HMI in normal condition ..................................................... 37
Figure 28 SEL 351 back side wiring connections ............................................................ 38
Figure 29 Circuit of relay test machine and wiring to SEL 351 relay ............................. 38
Figure 30 Time overcurrent short circuit fault detected by SEL 351S and alarm
announcement is shown with red on its box...................................................................... 39
Figure 31 Single phase to ground fault current and voltage during cycles of fault .......... 40
Figure 32 Phasor diagram of three Phases voltage and current during fault .................... 41
Figure 33 Single phase fault harmonic during first cycles of fault ................................... 42
Figure 34 Steady state condition harmonics ..................................................................... 42
Figure 35 Fault report from sel 351 .................................................................................. 43
Figure 36 Relay actions during fault condition................................................................. 44
Figure 37 Instantaneous overcurrent fault detected by SEL 351 and announcement is
shown on screen ................................................................................................................ 45
Figure 38 LL Fault on power line and detection of SEL 351 ........................................... 46
Figure 39 Phasor diagram of LL fault during fault ........................................................... 47
Figure 40 SEL 710 hardware setup and prepared for operation ..................................... 48
Figure 41 SEL 710 operation due to overcurrent fault on three phase induction motor . 49
Figure 42 Fault announcement of SEL 710 for overcurrent fault and motor jam ........... 50
Figure 43 Motor overcurrent fault wave shape from SEL 710 ......................................... 51
Figure 44 Phasor diagram of current during fault condition of motor measured by SEL
710..................................................................................................................................... 52
vi
Abstract
Power Systems Line and Machine Protection
System Study and Hardware Implementation
By
Ehsan Mahmoody
Master of Science Electrical Engineering
Objective of this project is to study and implement a power protection system for line and
motor protection. As it has been concerned during several years, transmission, subtransmission and distribution lines are of high level of importance to power delivery and
reliability. Protection against electrical hazards and incidents is subject to long studies. In
this study, protection of power lines from theory to hardware implementation is elaborated.
Induction motors in various applications constitute half of power system loads. Thereby,
protection of induction motors is studied theoretically and implemented on hardware.
“SEL (Schweitzer Engineering Laboratories)” incorporation is a famous and reputed brand
in protection systems. The company provides comprehensive support and products to
protect most of power system elements. They also provide other products for Supervisory,
Control and Data Acquisition System (SCADA) for power system monitoring. In this
study, SCADA system hardware setup is accomplished. Data acquisition and equipment
status monitoring are also explained in details.
vii
During this research, various case studies are designed. Protection system capacities is
experimented and network response monitoring, data logging, trip triggering and other
factors can be analyzed. Implementation of this system is demanding and need to work on
different areas of electrical systems. For fault condition creation, simulation of fault
condition on protection devices input has to be designed and provided for the equipment.
Results from case studies are observable on PC through HMI software and also logged on
device memory and PC memory as well. All results are satisfactory and usable for other
applications.
viii
1. Introduction
In this chapter, basic definitions of power system protection and types of protection in
power systems are discussed. Also, description of project approach and reasons for
conducting this research are provided.
1.1 Overview
Short circuit fault protection in power systems is of superior importance to every element
from power production to transmission and distribution. Also at customer levels, need for
protective systems is crucial as well. Power systems fault analysis shows that every element
should be protected specifically in coordination with other elements as required.
Transmission and distribution lines are always in high risk of arch flashes due to exposure
of bare conductors reaching to other phases or grounded equipment. Other equipment such
as synchronous or asynchronous machines also constitute major power consumers in power
systems. Therefore, fault protection on this major area of power systems has additional
importance and hence became subject of this research.
Fundamental rules of power systems protection are used in elaborated systems as well as
less complicated systems. In this study, such principals are used and detailed in some cases
such that desired outcomes reached and finalized. Study and simulation of protection
systems always give better understanding of systems behavior and reactions to various
inputs. Moreover, hardware implementation provides the opportunity to get in touch real
experimental data. Thereby, hardware implementation of SEL protective relays executed
and responses are evaluated accordingly.
1
1.2 Objective
For this study, power lines of transmission and distribution are under different
circumstances of faults and protective relays have the duty of fault detection and clearance
based on different scenarios. All protective relays will report the situation to the control
center through the communication ports of real time automation and control (RTAC).
Case studies are consisting of various LG, LL and LLG faults on power lines and over load
machine protection. SCADA control center construction is the goal of the hardware
implementation. Monitoring and protecting all assigned equipment are fundamental tasks
of SCADA system. Each element has a graphical representative on HMI (Human Machine
Interface) and measuring pre-defined values of voltage and current of each element is
constantly streaming into graphical medium. Therefore, system is represented as schematic
icons on software and shows the equipment conditions. Additionally, control orders and
tasks for operations on equipment can be directly assigned from human machine interface.
Also, Equipment feedback for assigned orders is visible on screen.
2
2. Technical Requirements
Hardware used in this study is widely known as SEL protective relays and are generally
central processor based computers in which operation calculations are based on its
firmware design uploaded to each device. For different applications, SEL designed a
specific module to execute designated operations such as protection on power lines,
machine protection, differential protection or communication and automation modules and
they are widely used in power systems. In this study, some of SEL products are used and
experienced for different case studies.
2.1 Hardware
SEL has designed devices to setup automation system on power protection and monitoring.
In this study, SEL 351, SEL 710, SEL 3530 are used to set up a SCADA system and
screening data on PC.
2.1.1 SEL 351
SEL 351 protective relay consist of opto-isolated inputs which are voltage and currents of
each phase A, B and C. and one ground input for voltage and one for current. These inputs
are isolated from the micro-processor board. From input ports, opto-couplers carry the
signals to ADCs. Therefore all the work is done within processors and commands of circuit
breaker is sent to relay contacts. There are also communication ports provided for the relay
to spread out all data to designated devices within control network. Thereby data reading
and order enforcement from other devices is available and remote control of breaker and
coordination of relays can be easily done.
3
Figure 1 SEL 351 line protective micro-processor relay machine
2.1.2 SEL 710
Machine protection relay is designed to analyze machine real time conditions and compare
them to pre-defined setting and make the decisions accordingly. Same as other relays of
SEL, it has opto-isolated inputs and outputs. Three phase voltage and currents of machine
sampled by CTs (Current Transformers) and VTs (Voltage Transformers) are analyzed on
processor and required actions is ordered. Same as SEL 351, communication ports are
provided for monitoring and coordination.
4
Figure 2 SEL machine protective relay
2.1.3 SEL 3530 (RTAC)
Communication ports of SEL have developed during time and from previous versions with
limited operation and monitoring capabilities evolved to present real time automation and
control modules. RTAC has the capability of transferring data through different
communication mediums and different protocols. Hereby other devices of the network with
various protocols and connection mediums can connect to RTAC and transfer data to the
control center.
In this research RTAC acts as RTU and collects all devices data and transmits to destination
PC. For monitoring and decision making purposes, HMI is designed on PC so that operator
can read and maneuver on different devices.
5
Figure 3 SEL 3530 Real Time Automation Controller (RTAC)
2.2 Software
AcSELerrator Quickset
Processor based protective relays are working based on its firmware which is designed and
embedded on board. For setting purposes, a software medium gives the required
information to the firmware and from then, relay works on its own. SEL has designed its
own software in order to set relays for different protection scenarios. This software is called
AcSELerrator Quickset and is consisting of multiple options for device settings. Some of
available choices are graphical, command and logic settings. SEL quick set also gives the
opportunity to monitor real time information from device which is connected to the PC.
Voltage magnitude and angles can be checked. Also, correct relay machine parameter
setting is more facilitated.
6
Figure 4 AcSELerator Quickset options for task assignment
AcSELerrator RTAC
In other side, for communication sake, setting of ports connections, protocol definitions
and routing is performed using other software named AcSELerrator RTAC. Using this
software devices defined on RTAC network can be set and roll of each is set accordingly.
AcSELerrator Diagram Builder
Automation systems need to have a central control command such that system status and
events are supervised and tasks are assigned to designated sections of system. Modeling
system, data reading and sequences etc. need a software medium that enables human
operator to read and write commands as required. Such software is named Human Machine
Interface (HMI), design of each system HMI and assigning appropriate path for connection
between devices require specific software that is capable of such design. SEL Diagram
7
Builder performs this task and is compatible with various data communication systems.
Power system element including power line, switchgears loads etc. can be modeled in this
software. Each element has its own graphical block and can be differentiated by some
tweak on its setting.
Basic equipment of proposed system are SEL 351, SEL 710 and SEL RTAC. Each
equipment graphical representative is shown on software environment. Therefore
measurements and operation handles are reachable within the designed HMI.
Figure 5 Graphical modeling environment on diagram builder software
8
3. Approach
During this chapter, theory behind protective relays setting and calculations is explained.
In other side, hardware setting procedure and relay connections is explained as well. Wiring
and input/output connections to relay test machine and also PC connections to relays is
explained. Also software setting and programming is included such that this paper can be
used for protections system settings.
Power system line protection is concerned with three major types of short-circuit fault in
different levels of transmission, sub-transmission and distribution. Revising different types
of such faults and theoretical calculation for relay settings is our mission in this study.
3.1 LG (line to ground) fault
[1]
In order to represent power system network, synchronous generator along with reactance
can show a good electrical model. In the circuit of “Figure 6” a single line to ground fault
from line A to ground is modeled. Fault impedance and other factors are also considered.
9
Figure 6 Single phase to ground fault circuit
The initial state of systems can be described as equation 1 and equation 2:
0, 0, 0
∗ Equation 1
Equation 2
Using symmetrical components for currents at fault, transform matrix is as equation 3:
1 1
1 1 1 0 0
Equation 3
This general equations is used for transforming “ABC” sequence into “012” sequence.
After calculations, currents are as per equation 4:
Equation 4
The same procedure can be applied for voltage of phase A in equation 5:
Equation 5
10
By substituting equation 1 and equation 2 into equation 5, equation 6 and equation 7 are
concluded:
3 3 ೌ
Equation 6
Equation 7
బ భ మ ೑
Figure 7 Pos-Neg-Zero sequence of single line to ground fault
CTs (Current Transformers) and PTs (Potential Transformers) are the first medium
between high voltage and high current values to the standard values of relay reading.
Transformation ratio should be considered while calculating relay setting values. Error
percentages of such ratios is the factor which is important on relay setting.
3.2 LL (line to line) fault [1]
Line to line fault of power systems occur when two phases of feeder contact each other.
Solidly shorted or have an impedance in between, are both definable for relay. In general
11
case, we consider LL fault with fault impedance and required circuitry and calculations.
Thereby, relay setting and installation is based on such theories. “Figure 8” shows the
presumed LL fault circuit:
Figure 8 Line to Line short circuit fault diagram
Based on the theory, voltage and current in faulted lines is derived from equation 8:
0, , 0
Equation 8
In order to obtain symmetrical components, equation 9 is applicable:
1 1
1 1 0
1
Equation 9
Symmetrical values can be calculated as equation 10 through equation 13:
12
0, , Equation 11
ೌభ
మ
Equation 10
Equation 12
ೌ
Equation 13
భ మ ೑
Thereby sequence diagram is provided as in figure 9:
Figure 9 Sequence circuit diagram of LL fault
Relays are designed such that it’s capable of detecting various types of short circuit fault.
Required action can be set based on studied logics accordingly. LL type of fault is also
defined to the relay and in case of occurrence, appropriate actions are addressed.
3.3 LLG (Line to Line to Ground) Fault
[1]
Even though LLG is a rare case, while setting protective relay all considerations are done
such that in case of happening, it can be detected instantly. Each of fault types is known
13
using standard ANSI codes, then report generating is abbreviated using ANSI codes.
Theoretical formulation of LLG is known to be as provided in equation 14 through equation
16:
Equation 14
3 Equation 15
Equation 16
Figure 10 LLG fault circuit with fault impedance
Sequence diagram of LLG fault illustrates better understanding of short circuit fault
development and currents contributing to the fault from each source. In “Figure 11”
14
complete sequence diagram of LLG fault is provided and current flow to fault locations is
indicated.
Figure 11 LLG fault sequence circuit diagram
In terms of Pos-Neg-Zero sequence, it can be recalculated and provided as equation 17
through equation 20:
ೌ భ ೌభ Equation 17
ೌ భ ೌభ Equation 18
బ ೑ మ
ೌ
భ 3
Equation 19
ೋమ ቀೋబ శయೋ೑ ቁ
ቀೋబ శೋమ శయೋ೑ ቁ
Equation 20
Thevenin equivalent circuit of LLG along with its equations is modeled in figure 11. This
can be used in relay setting and coordination purposes. Figure 11 circuit shows positive
and negative sequences of LLG fault to be paralleled to each other and the result is
continued to be connected to zero sequence by fault impedance.
15
3.4 Induction Motor Protection
[2]
Induction motors in general consume half of energy injected to power system. They are
heart of industry, commercials, and many times in agriculture and residential
consumptions. Any failure in motor causes hesitation on production line or normal
operation of commercial firms. Also in residential or agricultural daily works same
problems may occur. Protecting an induction motor is revolving around basic concepts
such as motor size, importance and load.
Various factors cause failure in motor operation and are from different sources. Induction
motor failure can be due to mal-operation, environmental related disturbances, load
disturbances or internal circuit failure of motor.
Electrical circuit of induction motor is start of protection study as it represent every
element of motor circuit theoretically. Main components consist this machine, are
modeled in figure 12.
Figure 12 Induction motor internal circuit of theory
16
Based on circuitry of induction motor, current consumed by motor is calculated using
equation 21 and equation 22:
‫=ݏ‬
‫=ܫ‬
௡ೞ ି௡
Equation 21
௡ೞ
௏
ೃ
(ோభ ା మ )ା௝(௑భ ା௑మ )
Equation 22
ೞ
While V is the RMS voltage per phase, R1 is primary resistance, R2 is the secondary
resistance, X1 is primary reactance, X2 is secondary reactance and s is slope.
Additionally, mechanical parameters are reachable through torque and frequency
equations. Access to motor mechanical behavior and any variations are observable
through equation 23.
ூమ ோమ
߬ = ௦.ఠ
Equation 23
ೞ೤೙೎೓
Alternatively, equation 21 through equation 23 can be merged to form final formula for
torque to voltage relations:
ೇమ ೃమ
ೞ.ഘೞ೤೙೎೓
ೃ
(ோభ ା మ )మ ା(௑భ ା௑మ )మ
ೄ
ଷ
߬ሺ‫ݏ‬ሻ =
Equation 24
Most of protection systems are based on current and voltage analysis of element. Based
on such calculations, decision making logic is formed. In this case both current and
torque characteristics of induction motor is provided. If required, each case can be
applied to the logic.
3.5 SEL Device Setting
SEL products are design in a very common method to be programmable through a common
software for most of protective relay products. AcSELerator Quickset is used in relays
17
setting. This software communicates with relay firmware and defined settings will be
loaded into machine.
Communication ports on different devices of SEL products are designed to be compatible
with different communication protocols. Serial ports of these devices can communicate to
PC and other SEL products if assigned and compatible. One of the common
communication cables used in such devices is DB-9 serial cable. Other connection is USB
communication cable. It has been added to new features of SEL products and is widely
accepted. By the way, “Ethernet” connection is the most important communication method
for advanced machine applications.
3.5.1 SEL 351 Setting
[3]
In this study, SEL 351 is the first machine to be set. Each screen of programming software
is consisting of multiple fields that are defined to carry a value, string or logical rule.
Thereby it can load instructions to each machine.
On the first window of AcSELerator Quickset, communication method to device should be
set. Then, appropriate parameters shown on figure 13 are chosen.
18
Figure 13 AcSELerator Quick set communications settings
Parameters in communication, set type and pattern of communication. For this case serial
port using 9600 data speed and 8 data bits is chosen.
Figure 14 Communication parameters for SEL 351
19
After reading data from device port, software prompts to relay settings. This window
provides different parameters of line protection for setting purposes and let you define
each element threshold. Additionally, various fields are provided for logical operation of
system. Using logic section, logical actions and orders on processor are set in accordance
to pre-defined triggering values of each measurement.
20
Figure 15 Quick set software window while setting of SEL 351S
Each of choices under set 1 is modifiable. Name of each parameter explains a task and
can be assigned accordingly. For instance, the first option “General Settings” provide
setting values of CTR and PTR. Nominal voltage of PT, labels for relay identification etc.
are defined as well.
21
Figure 16 General setting of SEL 351S
After setting all threshold parameters and activation of required protections on “set 1”
section, logic setting is required. In order to make relay understand what tasks are ordered
to do, upon recognition of each case scenario, relay follows your logics. Relay is in
charge of detection of various types of faults and making decisions based on its logics. As
logic section of setting provides “trip/communication” option. It can be arranged such
that in case of happening of several incidents together, what kind of actions should be
done. Eliminate the fault and report the events to other relays and control center can be
defined as well.
22
Figure 17 Logic setting of SEL 351S
In this study, overcurrent relay setting is configured such that in case of short circuit for
any of phases, time overcurrent and instantaneous overcurrent relays will trip the breaker.
Breaker contact is located at contact 101 of relay output.
Table 1 provides setting parameters for this case.
23
Table 1 SEL 351S parameters setting for overcurrent relay setting
Parameter name
Value assigned
Relay identifier
First SEL 351S
CTR
120
PTR
180
Nominal voltage
67
Positive sequence line impedance
2.14e(68.86)
Zero sequence line impedance
6.38e(72.47)
50P1P pickup current
0.6 amp sec
51P1P
0.5 amp sec
51P1C
U3 curve
Trip condition (logic)
50P1+ 51P1
3.5.2 SEL 710 Setting
[4]
Motor protection relay is designed to analyze electrical machine behavior simultaneously,
and protect it against any abnormal condition. SEL 710 has the capability to do multiple
protection actions and make appropriate communication orders to protect feeders and upper
hand equipment. Same as other relay devices of “SEL”, 710 relay machine is
programmable through quickset software. Numerous parameters of motor voltage and
current measurements are provided inside firmware so that various types of motor
protection approaches are executable.
24
Figure 18 Setting window of SEL 710 on Quickset software
Threshold values of time overcurrent, thermal protection, rotor jam, motor start overcurrent
and current imbalance can be set if needed.
For this study overcurrent and motor start overcurrent is considered and set on SEL 710
hardware.
25
Figure 19 SEL 710 parameters assignment and protection method choosing
26
After choosing proper method of protection and substituting calculated values on place,
logic of protection determines operation method. Overcurrent timing and motor starting
are defined on relay firmware.
Some of parameters defined on this relay are provided on Table 2:
Table 2 SEL 710 characteristic settings for quick set
Parameter name
Value assigned
CTR
120
Nominal frequency
60
Full load amp
50 amp
Locked rotor amp
6 times nominal
Locked rotor time
3 sec
Acceleration factor
1
Phase overcurrent amp
12 time FLA
3.5.3 SEL RTAC (Real Time Automation and Control) [5]
Process automation and remote supervisory of systems made outstanding changes on
control based systems. Power systems automation is desirable and during previous years
the need for real time monitoring and control on power systems has increased.
SEL incorporation came with a new product. Capable of data communication and transfer
which is known to be flexible for communication with different devices of other makes.
Secured with new and previous communication protocols, namely RTAC.
27
For this specific device, SEL designed new software known as “AcSELerator RTAC”.
Using this software, we may set up communication routes, method, protocol, type of
connection etc. PC connection to RTAC is usually done through USB cable but still other
methods of serial cable and Ethernet is available.
RTAC software environment and setting windows give the required access to the installed
firmware fields to be set and routed to designated ports as shown on figure 20:
Figure 20 RTAC setting software login
28
RTAC setting revolves around device recognition and assignment to each port of RTAC.
In this case two types of relay are connecting to RTAC through serial ports. Data collected
by RTAC transfer to PC via USB cable.
On software, different types of SEL products are listed and can be added to the project.
Communication port number, data bit, baud rate, parity etc. is definable on this window as
shown on figure 21.
Figure 21 SEL devices to RTAC software
3.5.4 SEL Diagram Builder [6]
For connection setup and monitoring of all devices on SCADA system, there is a
fundamental need to a medium software that operates as graphical connection of system
29
and human. Giving an on demand statistics and equipment status report. SEL diagram
builder gives the flexibility to design system graphically. Also it can show the
measurements values on graphical interface. System is modeled on block sets and wired
according to its real hardware connections. Additionally, measured values are assigned to
each block as well.
Now every variation on system is observable on software interface and control access to
circuit breakers and relay internal data logging is available.
Figure 21 shows system project startup. Complete setup system is configured afterward.
Figure 22 Project startup on SEL diagram builder window
Figure 22 shows project building start point on SEL diagram builder window. This
software gives the option to create project from start or complete your project as saved.
30
By defining project properties, a new project can be assigned in a location on PC storage.
To establish a reliable connection to SEL RTAC hardware serial connection or USB
connection should be utilized. Then PC is connected to relay hardware and ready to
explore.
By software means which was elaborated formerly, we can test our connection using SEL
diagram builder on this window. It can be found as figure 23.
Figure 23 Connection test and establishment to RTAC from PC using SEL diagram builder
By submitting credentials to designated IPs and assigned username and password,
connection to PC is testable. Thereby, all information loaded to RTAC through
SELeratorRTAC is accessible. After completing connection test, it is required to extract all
assigned tags inside RTAC to use in graphical design interface.
31
By loading tags into PC through diagram builder software, all the necessary tools for
network design is ready. Figure 24 provides a complete presentation of accessible tags
inside this software for assigned tasks on RTAC device.
Figure 24 Available tags on SEL diagram builder
It is known from manual review that “OUT 101” is designated output port for circuit
breaker of SEL 351S and other OUT ports can be allocated to different applications as well.
32
Additionally, relay data log is also available from diagram builder. Report generations and
event recording done by SEL 351S is stored inside hardware and also transmitted to central
control base. Using this software, we can have access to both database and make complete
reports based on either one as required.
After designing our protection and operation network on software using blocks and
diagrams, final design on hardware is operational and well stablished. Figure 25 presents
designed network after inserting tags and connections to each block of system from
hardware connections:
Figure 25 HMI design on SEL diagram builder software
33
In this design, feeder from a generator source which is representative of bulk grid is feeding
our system. One power line and one induction motor are constituting our loads in this
system.
In addition, our system has circuit breakers that receive protection system orders to operate
effectively and disconnect the feeding path. Every variation on our system is visible
graphically through this human machine interface (HMI) and orders to connect or
disconnect a circuit breaker is actionable as well.
Figure 26 shows better presentation of graphical interface of our designed system on
software. This system is working in normal operating conditions with no errors or faults:
34
Figure 26 HMI designed network for proposed protection system
35
4. Case Study
This research is aimed to study fault condition detection and reporting on hardware. Also
Supervision of network status and fault clearance reporting is expected from system setup.
After complete installation of protection network and configuration of associated software
for each case, signals from each device on RTAC and consequently on PC are observable.
System goes under practical test of equipment. Reaction of protection system to faulty
conditions can be analyzed afterward.
For this study there are two cases considered, which are comprising of different case
scenarios for different devices.
4.1 SEL 351S faults
On this type of protective relay, we are able to set the device for various types of protection
on power system lines. Some of them are listed as following
•
Instantaneous overcurrent relay 50
•
Time overcurrent relay 51
•
Directional overcurrent relay 67
•
Overvoltage relay 59
•
Running circuit breaker 42
In this specific case study, 50 and 51 fault protections are imposed to our system and SEL
351S has the duty to recognize each of the faults and react accordingly. As is shown on
figure 27, system is operating in normal conditions and no faults has been detected so far.
36
Figure 27 Proposed system HMI in normal condition
4.1.1 Time Overcurrent Protection
An external short circuit fault imposed to three phase power line. Simulated circuit was
designed such that a time overcurrent relay can detect it and trigger the circuit breaker.
Circuitry and photos of figure 28 and figure 29 show general connection of the relays.
37
Figure 28 SEL 351 back side wiring connections
Figure 29 Circuit of relay test machine and wiring to SEL 351 relay
38
While imposing the described conditions to the relay, detection of fault and
announcement happened through HMI software. Fault existence and type of it is shown
as blocks on figure 30.
Figure 30 Time overcurrent short circuit fault detected by SEL 351S and alarm announcement is shown with red on its
box
SEL products have the capability to report all the events to its data base.
Based on information recorded, time of fault, type of fault, equipment status while fault
occurrence etc. can be extracted for analysis. In this case study, we have single phase to
ground fault event report to provide analysis on fault occurrence during fault interval.
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Figure 31 Single phase to ground fault current and voltage during cycles of fault
Figure 31 shows that during this type of overcurrent fault, phase voltage significantly
drops and in other way phase current increases. At cycle 5 of this measurement, single
phase fault occurs and voltage and current changes during this interval are clearly visible.
Phasor diagrams of this fault interval provide good understanding of what has happened
to voltage and current profiles during fault condition. Figure 32 gives better perspective
of Phasor and comparison of voltage and currents during fault.
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Figure 32 Phasor diagram of three Phases voltage and current during fault
Phasor diagram of figure 32 shows that during fault occurrence, current magnitude of
phase A significantly increases and its angle deviate from its original location to the point
that fault impedance along with line impedance constitute total impedance seen from
relay sight.
Second diagram of figure 32 shows sequence diagram of voltages and currents during
fault time. Positive and negative voltage of phase exist in sequence diagram as it is a
single phase fault. Data gathered from relay can be analyzed to determine harmonics
percentages on figure 33.
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Figure 33 Single phase fault harmonic during first cycles of fault
Harmonic analysis proves that during first cycles of fault, DC component of wave is
dominant and consists almost 96% of wave shape. After this transient condition, steady
state condition of line appears as in figure 34.
Figure 34 Steady state condition harmonics
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Upon fault, relay generates a report to the control center and also record it on its database.
This report is consisting of fault type, clearance, time of fault etc. Figure 35 shows this
report from SEL 351.
Figure 35 Fault report from sel 351
On this report different parameters are shown and each indicates some measurements of
fault freeze frames. Some of these actions are named as: trip to breaker on OUT101,
ALRMOUT, FUALT=51P1, 51G1.
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Figure 36 Relay actions during fault condition
4.1.2 Instantaneous Overcurrent Protection
SEL 351 can be set to protect the line against overcurrent faults using different curves
and also by instantaneous protection.
While using instantaneous protection, relay is set to operate in shortest time defined for
the relay. This should be considered that the pickup current for this setting is higher than
normal time overcurrent curves and can be set based on line characteristics and
coordination properties.
A higher current fault imposed to the relay in order to force the instantaneous setting to
operate. It is visible from figure 37 that SEL 351 has detected the fault and reported the
event to control center.
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Figure 37 Instantaneous overcurrent fault detected by SEL 351 and announcement is shown on screen
Next type of fault study is LL fault which happens while short circuit between two phases
of line occurs. Figure 38 shows wave shape of LL fault during fault condition. In this
type, fault has been detected during less than half cycle of frequency and report
generation is logged.
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Figure 38 LL Fault on power line and detection of SEL 351
Figure 38 provides better understanding of wave shapes during fault condition. Phasor
diagram of this fault provides better understand of all the incidences which happened to
grid during fault. Figure 39 shows Phasor diagram of LL fault.
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Figure 39 Phasor diagram of LL fault during fault
4.2 SEL 710 Faults
Motor protection same as line protection can be protected against overcurrent faults in
different case scenarios. First protection proposed for setting on SEL 710 is instantaneous
overcurrent protection. Setting for this type of protection is variable depending on the
motor characteristics.
Stator rating current, isolation rating and motor starting can be read from the motor
nameplate and all settings are done on SELeratorQuickset. Wiring and installations are
done using standard connection for three phase induction motor through manufacturer
manuals. Figure 40 shows the common setup of SEL 710.
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Figure 40 SEL 710 hardware setup and prepared for operation
4.2.1 Instantaneous Overcurrent Protection
On this case we imposed a short circuit fault between the two phases of induction motor
while motor is running in normal condition. Figure 41 provides protection network
monitoring system on this type of fault.
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Figure 41 SEL 710 operation due to overcurrent fault on three phase induction motor
4.2.2 Overcurrent Protection Because Of Rotor Jam
Rotor jam occur when a heavy load is overloaded to the induction motor or it might
happen because of failure in bearing and axis of motor. In case of motor jam, SEL 710
has the duty to detect it and react accordingly. In this case, if motor jam happens, relay
also detect instantaneous overcurrent protection.
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Figure 42 Fault announcement of SEL 710 for overcurrent fault and motor jam
Data gathered from SEL 710 shows wave shape during fault condition and gives
understanding from events happening inside motor windings. Figure 43 provides data
extracted from SEL 710 during fault condition.
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Figure 43 Motor overcurrent fault wave shape from SEL 710
Phasor diagram of fault condition present magnitude and phase change of fault while
other inherited parameters of device stay the same as all the time. Figure 44 gives
graphical understanding of current and phase changes during faulty condition of the
motor.
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Figure 44 Phasor diagram of current during fault condition of motor measured by SEL 710
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5. Results and Conclusions
On this study the theoretical concepts and protection patterns applicable on SEL protection
relay, implemented on hardware and relay operation for different case studies reporting
and announcement on SCADA system achieved. Using this system for protection and
monitoring of power system, complete automation and surveillance of power network in
any level of transmission, sub-transmission, distribution and generation are feasible and
beneficiary on several perspectives.
Operation and communication of SEL 351 which is designed for line protection, was highly
satisfactory and all theoretical expectation of relay operation was completely met. Two
different types of protection implemented on this device act as expected. While detection,
clearance and fault announcement addressed appropriately.
Motor protection and power consumption monitoring were reported to data loggers. During
case studies of short circuit, SEL 351 reacted in the shortest time and removed the fault by
triggering the circuit breaker. Announcement of fault to control center (which in this case
is PC) is done successfully.
Based on the calculations and theoretical considerations of system clearance time of fault
in both protective relays were satisfactory. Results were good enough that during the
clearance time no damage created to any of simulated circuits and also communication,
announcement and report generation on fault matched the standards.
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References
[1] Power system analysis, John J. Grainger, William D. Stevenson, McGraw-Hill, Jan 1,
1994
[2] Protective Relaying: Principles and Applications, Third Edition (Power Engineering)
Hardcover – December 21, 2006by J. Lewis Blackburn (Author), Thomas J. Domin
(Author)
[3] SEL-351-5, -6, -7 Protection System Instruction Manual, schweitzer engineering
laboratories inc
[4] SEL-710 Relay Motor Protection Relay Instruction Manual, schweitzer engineering
laboratories inc
[5] Ac SEL erator RTAC manual, schweitzer engineering laboratories inc
[6] ACSELERATOR Diagram Builder User’s Guide, schweitzer engineering laboratories
inc
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