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CHAPTER 4

A POWER SYSTEM MODEL – TO STUDY

SCADA AUTOMATION AND DIGITAL NUMERICAL DISTANCE RELAY

CHAPTER CONTENTS

4.1 Design of the Power System Model, 87

4.2 Model’s Utility as a Benchmark, 88

4.3 Components mounted on the Model, 94

4.4 SCADA, 95

4.5 Power Flow Studies, 99

4.6 Fault Studies Using DND Relay, 103

4.7 Discussions and Conclusions, 105

4.1 DESIGN OF THE POWER SYSTEM MODEL

A Power System Model with SCADA (Supervisory Control and Data Acquisition)

Automation was designed and constructed to simulate overhead transmission line

faults. Experiments were conducted to study the working of the Digital Numerical

Distance Relay (DNDR) for its performance and utility by simulating different faults

on the transmission line.

This model comprised three phase generator, transmission lines (representing 400

kV, 500 km in two sections of 300 km and 200 km) and Resistive and inductive

loads. The model was provided with circuit breakers, reverse power relay, over

current relay for protection and DND Relay.

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Distance Numerical Relay (DNDR) has become vital device for the protection and

fault localization of modern transmission systems. Many of the existing transmission

lines which do not have DND Relays are now being modernized by adding on these

relays. The Power System Model provides complete information and know-how

about usage of the DND Relay and SCADA Automation and their utility in the real

systems to contribute to efficient and reliable maintenance management.

A basic prototype DND Relay was designed by utilizing a multifunction meter that

displayed voltage (V), current (A), V/A (which gives the impedance Z) value and

distance to fault in kilometer. The meter was designed for an input signal of voltage

between 70 to 250 volts and current rating from 0.3 to 10 Amperes. The reading Z is

divided by 0.33 (value of resistance and inductive reactance per kilometer) to obtain

distance to fault.

Image 4.1 Shows 400 kV Overhead High Voltage Transmission Lines

4.2. MODEL’S UTILITY AS A BENCH MARK

This Dynamic Model constructed comprising two, three phase Generators, four

Transmission lines, two Loads was found to be suitable benchmark design for

simulating the real system. The model could be operated both manually and through

remote data access and Supervisory Control using a computer (with SCADA

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software). It was suitable for the following:

1. FAULT MANAGEMENT: Different types of faults were simulated on the

transmission lines and distance to faults was obtained through DND Relay device

which was found to be satisfactory.

2. STUDY OF POWER FLOW: This was studied by interconnecting the network of

transmission lines to form the grid and operation was controlled manually and

through SCADA.

The functionality of the MPCB, MCB, Short circuit relay, Contactor, etc., mounted

on the model was also verified

SIMULATED STUDY CONDUCTED:

DATA OF SULTANPUR—LUCKNOW TRANSMISSION LINE

The RLC parameters of 400 KV EHV lines per km

Resistance 0.03 ohms / phase / Km

Inductance 1.00 m H / phase / Km

Inductive Reactance 0.33 ohms / phase / Km

Capacitance 12 n F / phase / Km

Y 3.7 x / phase / Km

Table 4.2 Data taken from: Sultanpur – Lucknow line (UP India)

The Sultanpur – Lucknow transmission line has capacity to carry 900 Amps of per

phase that is equal to a power of: V x I = 400 x1000 x 900 =360 MVA per phase

Parameters 300 km 200 km

Resistance 9 ohms 6 ohms

Inductance 300 Mh 200 mH

XL 99 Ohms 66 Ohms

Capacitance 3.6 micro Farads

(for pi 1.8 + 1.8)

2.4 micro Farads

(for pi 1.2 + 1.2)

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Table 4.3 RLC Parameters of 400 kV line for 300 km and 200 km Trans Lines

4.2.1. THE MODEL LAYOUT

The Power System Model constructed here has three panels, on the left (panel no 1)

comprises metering and Control of Generator no.1 and Load no.1 and on its front

desk the transmission lines 1 and 2. The panel on the extreme right (panel no 3)

comprises Metering and Control of Generator no.2, Load no. 2 and on the desk

Transmission lines 3 and 4 and each provided with respective MFM, MCB and

Relays. The central panel (Panel no 2) has a bus bar arrangement where the ends of

Generator 1 & 2, Load 1 & 2 and transmission line 1, 2, 3 & 4 are terminated and can

be interconnected through patch cords to form the desired circuit. The inductors,

resistors and other components are mounted behind the panel. The front layout of

the panel has only the controls. The dimensions of each panel are 2.5feet length with

a height of 5.5feet. This makes the total length of the equipment as 7.5 feet.

PANEL NO 1 PANEL NO 2 PANEL NO 3

GENERATOR 1 /LOAD 1 BUS BAR GENERATOR 2 /LOAD 2 METERING ETC FOR METERING ETC FOR TRANS LINE 1 &2 ON THE DESK TRANS LINE 3 & 4 ON DESK

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Image 4.4 shows the 3 panels joined together

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Figure 4.5 shows the block diagram of circuit

connection of the Power System Model

The power system model simulating 400 kV, 500 km transmission line system was

designed with scaled down parameters of Base Values to co-relate the parameters of

the study obtained on the model to the real system. The Power System Model

comprised 2 nos. of 400 volts, three phase motor-generator sets provided with motor

drives, reverse power relay, short circuit relay with circuit breakers for their

protection. Three phase digital Multi Function Meters (MFM) displayed voltage,

current, power factor, frequency, active and reactive power. The multifunction

meters also had RS485 port for data communication with computer software.

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4.2.1.1 THE MOTOR-ALTERNATOR CONTROL PANEL

The two 3 Phase / 3 kVA motor alternator sets (Generator supply 1and 2) have a

separate Control Panel with digital meters and variac arrangement to control speed

and excitation of motor-generator and another variac for varying the voltage.

4.2.1.2 CENTRAL PANEL

This panel has interconnecting arrangement linking generator, load and transmission

lines. It can be referred to as the main Bus Bars.

1. There are two Red color (on / off) switches marked as Area 1 & Area II to control

the respective supply.

2. This panel has Banana Sockets in (R-Red, Y- Yellow and B- Blue) colors where

the two ends of generator, transmission line and loads terminate. These can be

interconnected to form the grid network

3. The Green Sockets are the earth points.

4. The RYB Switches on the panel of Generator, Transmission Line and Load of

Area I and Area II control the circuit connectivity of the Central Panel. For example

even if patch cords are connected to RYB of Generator to RYB of Transmission Line

to RYB of Load, the voltage and current will not flow unless the RYB Switches of

Generator, Transmission Line, and Load of Area (I) are in ON position. The status of

the continuity between the Generator, Transmission Line, and Load is through the

LED Lights that will glow on the central panel. The same system is for Area (II).

4.2.1.3 THE DESK OF THE CENTRAL PANEL

3-Phase Digital Numerical Distance Relay [DNDR] is provided with connection in

series between the generator and sending ends of Transmission Line RYB

respectively. The DNDR is calibrated to read distance to fault when a fault is created

at any point on the Transmission Line. The calibrated values are: Z = V/ I in ohms.

Distance to fault: D = Z / 0.33 in kilometers

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4.2.1.4 TRANSMISSION LINE PANEL

The transmission line (TL) was provided with the digital MFM with RS485 Port

with similar display and arrangements for communication like the one used in Panel

1. The TL configuration is in the form of a pi-section with RLC values as shown in

table no 4.3. One MFM is provided at the Sending end of the TL and another at the

Receiving end of the last section. The transmission line is provided with Digital

Numerical Distance Relay (DNDR). It performs two functions: 1) Gives Protection

to the transmission line 2) Provides distance to fault.

4.2.2 BASE VALUES OF THE REAL SYSTEM

Base power: 20 MVA

Base Voltage: 200 kV

I = 20MVA/ 200 kV = Base Current: 100 Amps -------------------- (1)

Z = 200kV/100 A = Base Impedance: 2000 ohms

The Base Impedance of 2000 Ohms of Real System and the same value on the model

co-relates conversion made to real system as indicated in equation (2)

4.2.3 BASE VALUES OF THE SCALED DOWN SYSTEM

(ON THE MODEL)

400 Volts of the 3 phase generator output is stepped down

to 100 volts / phase for the 3 phase through a three phase transformer

Base Voltage: 100 Volts per phase ----------------------- (2)

V/Z = 100/2000 = Base Current: 50 mA

50 mA represents 20MVA Power in real system

and 100 Volts represents 200kV of real system see equation (1)

Base Impedance: 2000 ohms

Frequency: 50 Hz

Lower voltage for the base is preferable as it permits the model to represent higher

data of Generator, Transmission Line & Loads for power flow values of a grid

network. This gives the relationship between the Base values of Real System and the

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Base Values of the Model. It means the current of 50 mA on the model at 100 volts

represents 100 Amps of the real system and 50 mA represents 20 MVA power of the

real system.

Experiments were conducted by simulating 400 kV for a 500 km TL length. The

simulated RLC parameters of the transmission line were taken from Sultanpur -

Lucknow line. Fault was created at the End of the transmission line to verify the

maximum current flowing through the line under a short circuit fault between line to

ground. The results were obtained on a three phase transmission line by sending 100

volts per phase for all the 3 phases.

4.3 COMPONENTS MOUNTED ON THE MODEL

List of components Generator

Panel I &

Panel II

Load

Panel

I & II

Transmission

Line Panel I

& Panel II

DC Motor

Alternator

Control Panel

Desk of

Central

Panel

Dimmer stat 2

MPCB 2

Multi Function Meter 2 2 4 3

Over Current Relay 2 2 4 3

Miniature Circuit Breaker 2 6 8

R, Y, B Switches 6 6 12 3

Rotary Switch 2 6

Resistors 4 12

Inductors 4 12

Capacitors 4

Numerical Distance Relay 1

DC Motor, 5HP 220V/ 1500 rpm 2

AC Alternator 3phase / 3kVA,

415V

2

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4.4 SCADA (SUPERVISORY CONTROL AND DATA ACQUISITION)

4.4.1 HARDWARE

SCADA implementation on this Power System Model comprised of:

1. Programmable Logic Controller (PLC) controls the relays as and when the

command from the computer is received and PLC also acquires data from the

communication ports of the Power System Model and transmits to the computer.

2. Five sets of Relays (each relay set comprising eight relay points) are connected to

the PLC and controlled by the computer via PLC. These relays are for control as

well as to check the status of signal reaching at different nodes.

3. 24 Volts DC supply (SMPS -Switched Mode Power Supply) supplies power to

PLC for its function.

4. Computer with the programmed Software is the main controlling and data

acquiring station where the user operates the required functions, that is, controlling

the Power System Model.

The figure 4.6A shows that the computer is connected to the PLC to acquire the data

on the computer and all the control settings and options for the operation of the

model are sent to the PLC from the computer. The PLC operates on 24 Volts DC

supply and controls all five relay sets connected to the power system model.

The relays can perform:

a. The ON / OFF functions

b. Selection function

c. Monitor the status of signal

All the Multi-Function Meters are provided with RS485 ports. Positive and negative

points are connected in series and then finally connected to the PLC. The PLC is then

set to recognize and identify and save each meters’ IP address and then acquire the

data in sequence. This information is transferred to the computer software.

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Communication wire

Figure 4.6A shows the block diagram of

SCADA Hardware used for the Power System Model

PLC

Computer

With

SCADA

Relay 1

Relay 2

Relay 3 Relay 5

Relay 4

24 V DC

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4.4.2 SOFTWARE

The front end design of the software displayed on the desktop computer screen is

shown in the image 4.6B. It can be seen that it is a replica of the Power System

Model therefore it is more user friendly because the controlling and data displayed

can be identified and controlled easily. On this model the SCADA is controlling the

ON / OFF function of generator, load and transmission lines for coupling and

decoupling. The status of every node is monitored for the power reaching at circuit

breakers, over current relays, rotary switches and central panel.

In the screen image 4.6B on the extreme left are generator 1, load 1, transmission line

1 & 2 and on extreme right generator 2, load 2, transmission line 3 & 4. There are

contactors and RYB illuminated push buttons which are selectable and control the

coupling and decoupling of the circuit. The ELR, OCR, MCB nodes status points are

monitored for whether the voltage supply has reached the bus bars or not. The central

portion of the image gets lighted up with red, yellow and blue color indicating that

the voltage has reached the bus bars.

The entire control, monitoring the status of all nodes and data acquisition is for all

the three phases. There is also option provided to select auto / manual operation. In

the auto mode the entire system is controlled by SCADA and manual mode the

SCADA functions gets defunct. The F.SCRN option enlarges the particular area to

full screen.

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SOFTWARE LAYOUT OF THE MODEL ON THE COMPUTER SCREEN

Figure 4.6B shows layout on the computer screen for

Data Acquisition and Control

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4.5 SECTION A - POWER FLOW STUDIES

EXPERIMENT 1:

This experiment comprises one generator, one 300 km transmission line, one 200 km

transmission line and one load (see figure 4.1A). Here the power flow study was

made to examine the functionality of power transmission from generator to load via

the transmission lines.

Experiment Figure no 4.1A

In the above figure there is a Generator, Transmision Line divided

into two section one in 300 km and the other 200 km, and one Load.

This is a three phase (RYB) system which represents the power flow.

The experiment was conducted by operating the model manually and through

SCADA. The generator voltage was kept at 100V. The generator current, power and

other data was seen on MFM. The functionality of the related componants mounted

on the model was verified through this experiment.

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EXPERIMENT 2:

This experiment comprises two generators, three transmission lines and two loads.

Power flow was studied in Area (I) G1, TL1 and L1 and G2, TL2 and L2 in Area (II)

and there is a TL 3 which is a Tie Line that interconnects the two areas. In this power

flow study the importance of direction of power flow and synchronization of the two

generators were studied. See figure 4.2A.

Experiment Figure no 4.2A

The figure shows the circuit of power system where two generators, two loads

and three transmssion line are interconnected.

In this experiment the synchronization between two generators is achieved and

process is studied, here a synchroscope was used for monitoring synchronization.

The main factors which have to be controlled to achieve synchronizing state are:

Frequency, Voltage and Phase Angle. These factors can be controlled by speed and

excitation of motor generator and voltage regulation through voltage regulating

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variac. This is necessary because exactly at that time the circuit breaker is switched

on to join the tie line connected between the two generators. Without synchronization

the two generators should not be connected to the bus bar as it may swing the

alternator. There is Reverse Power Relay placed for protection to prevent power flow

in reverse direction.

Figure no 4.2B

The generator is provided with reverse power relay for its protection.

Figure 4.2A shows the circuit that was tested using the maximum configuration

provided on the equipment i.e. two generator, three transmission line and two loads.

At load bus 1 and load bus 2 are interconnected by a Tie Line to demonstrate the

flow of power from bus 1 to bus 2. This was achieved by keeping the Voltage at load

bus 1 higher than the load bus 2. The following information was obtained from the

test. The power generated by the alternator 1 was 4 Ampere at 250 volts where as

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the load 1 was 3 Amperes, therefore the 1 Ampere power could be diverted through

the Tie Line to the load bus 2 to supply the load 2 of 3 Ampere capacity, whereas the

generator 2 contributed 2 Ampere. The process here was controlled manually as well

as through computer command.

PARALLELING AC GENERATORS

Most electrical power grids and distribution systems have more than one AC

generator operating at one time. Normally, two or more generators are operated in

parallel in order to supply the demand of power. Three conditions must be met

prior to paralleling of (or synchronizing) AC generators:

1. Their terminal voltages must be equal. If the voltages of the two AC

generators are not equal, one of the AC generators would act as a reactive load to the

other AC generator. This causes high currents to be exchanged between

the two machines, possibly causing generator or distribution system damage.

2. Their frequencies must be equal. A mismatch in frequencies of the two AC

generators will cause the generator with the lower frequency to act as a load on the

other generator a condition referred to as motoring.

3. Their output voltages must be in phase. A mismatch in the phases will

develop opposing voltages. The worst case would be 180° out of phase, resulting

in an opposing voltage between the two generators of twice the output voltage. This

high voltage can cause damage to the generators and distribution system due to high

currents.

During paralleling operations, voltages of the two generators that are to be

paralleled are indicated through the use of voltmeters. Frequency matching is

accomplished through the use of output frequency meters.

Phase matching is accomplished through the use of a synchroscope, a device that

senses the two frequencies and gives an indication of phase differences and a

relative comparison of frequency differences.

4.6 SECTION B - FAULT STUDIES USING DND RELAY

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EXPERIMENT 3

Different types of faults were studied which frequently occur in the transmission

lines which are:

1. Double Line Fault (Figure 4.6.1)

2. Triple line Fault (Figure 4.6.2)

3. Line to Ground Fault (Figure 4.6.3)

4. Double Line to Ground Fault (Figure 4.6.4)

5. Triple Line to Ground Fault (Figure 4.6.5)

Here the purpose of simulating the faults was to study the functions of DNDR which

would trip the circuit and indicate the distance to fault.

Figure 4.6.1 Figure 4.6.2

Double Line Fault Triple Line Fault

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Figure 4.6.3 Figure 4.6.4 Figure 4.6.5

Line to Ground Fault Double Line to Triple Line to

Ground Fault Ground Fault

Figure

no.

Fault Type Distance to Fault in km indicated

by the DNDR

300 km

Transmission Line

500 km (300+200 km)

Transmission Line

4.6.1 Double Line Fault 302 499

4.6.2 Triple Line Fault 304 502

4.6.3 Line to Ground Fault 299 501

4.6.4 Double Line to Ground

Fault

301 498

4.6.5 Triple Line to Ground

Fault

302 503

Table 4.6.6 shows the distance to fault indicated by the DNDR

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4.7 DISCUSSIONS AND CONCLUSIONS

The Power System Model designed here simulates 400 kV, 500 km High Voltage

Transmission Line. The following experiments were performed using this model:

1. Simulating Faults clearing in the two sections (300 km and 200 km) of the

simulated

transmission line.

2. Obtaining distance to fault.

3. Power flow in Interconnected Grid network.

4. Data Acquisition and Supervisory Control using the SCADA architecture

provided on the model.

The experiments conducted on the Power System Model was to study DNDR which

provides protection to the transmission line by tripping the circuit and indicating

distances of different types of faults (L-G, L-L, LL-G, LLL, LLL-G) common in

overhead transmission lines.

These experiments indicate satisfactory performance of the DNDR. The results

obtained were within the accuracy of + 1% i.e. the transmission line of 500 km

showed result of 503 km in one experiment and 505 km in other experiment. Further

accuracy can be increased if the per kilometer inductance and resistance value of the

transmission line is correctly measured and fed in the DNDR.

This has resulted in to a portable overhead transmission line ‘test set’ to find the

distance to fault in 11 kV and 33 kV distribution lines. As in the most cases these

lines are not provided with the arrangement of DNDR due to the cost factor.

The SCADA automation was implemented on the model to understand the

architecture and its performance on a grid network of power system. The software

screen indicate the layout of facilities for data acquisition from the MFM and remote

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supervisory control command that is used to control operational function of the

model image shown in 4.6A and 4.6B.

List of operations performed by using SCADA application:

The SCADA architecture implemented on the power system model comprised

Siemens PLC, relays, software and software program. The SCADA tested on the

model works smoothly and accurately. The precautions were taken for providing

good earthing and using co-axial connecting leads.