1 - composition, operation and maintenace - revgb

DL GTU103.2 S

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ContentPREFACE Pag. VII

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Pag. 9Pag. 9

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Composition, operation and maintenance

Protection relays. DL GTU103.2 S description and layout

Hardware layout and description

Communication between hardware and software

Wiring diagram

Operation

Maintenance and repair

Installation of the trainerDescription and layout

Component level software description MSCom2

Process level software description SCADA

Theoretical section

3.1 Power systems protection. General considerations

Introduction

Faults and Abnormal Operating Conditions

Faults and protection methods in electric power systems

Important elements for power system protection

Basic principles and components of protection Pag. 33

Preface

Page IV Version 1.0

6. Methods of discrimination to type of fault Pag. 37

7. Components of protection Pag. 39

8. Types of protections Pag. 43

3.2 Power systems protection. Overcurrent Protection Relays Pag. 43

1. Introduction Pag. 47

2. Discrimination in overcurrent protection Pag. 48

3. Particularities in overcurrent protection Pag. 57

4. ANSI overcurrent protection functions Pag. 62

3.3 Power systems protection. Directional Protection Relays Pag. 65


2. Classical concepts for directional analysis Pag. 66

3. Unit Protection of Feeders Pag. 71

4. Practical schemes of directional protection Pag. 73

5. ANSI directional current protection functions Pag. 75

3.4 Power systems protection. Over and under voltage Relays Pag. 77


2. Overvoltage Protection Pag. 79

3. Under voltage considerations Pag. 85

4. ANSI voltage protection functions Pag. 86

3.5 ANSI numbers, IEEE Standard Electric Power System DeviceFunction Numbers according to IEEE C.37.2 1991 Pag. 87

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4. Experimental Section Pag. 97

4.1 Instantaneous and definite time overcurrent protection Pag. 97

1. Introduction. Description of the experiment Pag. 97

2. Objectives Pag. 100

3. Components list Pag. 100

4. Procedure outline Pag. 101

5. Conclusions Pag. 126

4.2 Inverse time overcurrent protection Pag. 127






4.3 Earth fault protection Pag. 153






4.4 Under voltage protection Pag. 173






Preface

Page VI Version 1.0

4.5 Overvoltage protection Pag. 193






4.6 Unbalanced load protection Pag. 211






4.7 Directional overcurrent protection Pag. 233





5. Questions Pag. 282


5. References Pag. 285

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3. Theoretical section

3.1 Power systems protection.General considerations

1. Introduction

A protection scheme in a power system is designed to continuously monitor thepower system to ensure maximum continuity of electrical supply with minimumdamage to life, equipment, and property.

While designing the protection schemes, one has to understand the faultcharacteristics of the individual power system elements. One should also beknowledgeable about the tripping characteristics of various protective relays.

The job of the protection engineer is to devise such schemes where closest possiblematch between the fault characteristics and the tripping characteristics is obtained.

The design has to ensure that relays will detect undesirable conditions and then tripto disconnect the area affected, but remain restrained at all other times. However,there is statistical evidence that a large number of relay tripping is due to improperor inadequate settings rather than due to genuine faults.

It is, therefore, necessary that students should be equipped with sound concepts ofpower system protection to enable them to handle unforeseen circumstances inreal life.

Whenever a tripping takes place, it has all the elements of intrigue, drama, andsuspense. A lot of detective work is usually undertaken to understand the reasonbehind the tripping. It needs to be established why the relay has tripped whetherit should have tripped at all. What and where was the fault? These are some of thequestions required to be answered.

This is because a power system is a highly complex and dynamic entity. It is alwaysin a state of flux. Generators may be in or out of service. New loads are added allthe time. A single malfunction at a seemingly unimportant location has thepotential to trigger a system wide disturbance.

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In view of such possible consequences, a protection system with surgical accuracy isthe only insurance against potentially large losses due to electrical faults.

Protection relays role is to mitigate the effects of faults. There is a large spectrum ofrelays, from electromechanical to the state of the art numerical relays, forprotection of transmission lines, turbo alternators, transformers, busbars, andmotors.

In many cases, it is proved that additional protection relay also increases thepossibility of disturbance by way of its (relay's) own malfunction.

2. Faults and Abnormal Operating Conditions

Shunt Faults (Short Circuits)

When the path of the load current is cut short because of breakdown of insulation,we say that a 'short circuit' has occurred. The insulation can break down for avariety of reasons, in different behaviors, from a single line to ground fault on atransmission line due to flashover of spark gap across the string insulator, up tothree phase short circuit the most violent phenomenon.

Such faults due to insulation flashover are many times temporary, i.e. if the arc pathIs allowed to deionize, by interrupting the electrical supply for a sufficient period,then the arc does not re strike after the supply is restored.

This process of interruption followed by intentional re energization is knownreclosure. In low voltage systems, up to three reclosures are attempted, after whichthe breaker is locked out.

At times, the short circuit may be total (sometimes called a dead short circuit), or itmay be a partial short circuit. A fault which bypasses the entire load currentthrough itself is called a metallic fault. A metallic fault presents a very low,practically zero, fault resistance.

A partial short circuit can be modeled as a non zero resistance (or impedance) inparallel with the intended path of the current.

Most of the times, the fault resistance is nothing but the resistance of the arc that isformed as a result of the flashover. The arc resistance is highly nonlinear in nature.Early researchers have developed models of the arc resistance.

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Causes of shunt faults

Shunt faults are basically due to failure of the insulation. The insulation may failbecause of its own weakening, or it may fail due to overvoltage. The weakening ofinsulation may be due to one or more of the following factors:

Ageing Temperature Rain, hail, snow Chemical pollution Foreign objects Other causes

The overvoltage may be either internal (due to switching) or external (due tolightening).

Effects of Shunt Faults

If the power system just consisted of isolated alternators feeding their own loads,then the steady state fault currents would not be much of a concern. In aninterconnected power system, all the generators (and even motors) will contributetowards the fault current, thus building up the value of the fault current to coupleof tens of times the normal full load current.

Faults, thus, cause heavy currents to flow. If these fault currents persist even for ashort time, they will cause extensive damage to the equipment that carries thesecurrents. Over currents, in general, cause overheating and attendant danger of fire.

Overheating also causes deterioration of the insulation, thus weakening it further.Not so apparent is the mechanical damage due to excessive mechanical forcesdeveloped during an over current.

Transformers are known to have suffered mechanical damage to their windings,due to faults. This is due to the fact that any two current carrying conductorsexperience a force. This force goes out of bounds during faults, causing mechanicaldistortion and damage.

Further, in an interconnected system, there is another dimension to the effect offaults. The generators in an interconnected power system must operate insynchronism at all instants. The electrical power output from an alternator near thefault drops sharply.

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However, the mechanical power input remains substantially constant at its pre faultvalue. This causes the alternator to accelerate. The rotor angle starts increasing.Thus, the alternators start swinging with respect to each other.

If the swing goes out of control, the alternators will have to be tripped out. Thus, inan interconnected power system, the system stability is at stake. Therefore, thefaults need to be isolated as selectively and as speedily as possible.

Those faults, which involve only one of the phase conductors and ground, are calledground faults. Faults involving two or more phase conductors, with or withoutground, are called phase faults.

Power systems have been in operation for over a hundred years now. Accumulatedexperience shows that all faults are not equally likely. Single line to ground faults isthe most likely whereas the fault due to simultaneous short circuit between all thethree lines, known as the three phase fault, is the least likely. This is depicted in thenext table.

Type of fault Probability of occurrence (%) Severity

Phase to ground 85% Least severe

Two phases 8%

Two phases to ground 5%

Three phases 2% Most severe

Further, the probability values of faults on different elements of the power systemare different. The transmission lines which are exposed to the vagaries of theatmosphere are the most likely to be subjected to faults.

We insist on this type of fault because, according to technical literature, in most ofthe cases it is the initiator of many other types of faults, and in some other cases itis the way other faults manifest themselves.

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The variety of the faults with their behaviors covers all components of the powernetworks (from the generators’ side i, through the transmission and distribution’sside ii, up to the consumer’s side iii) see the next figure.

Protection against faults in electric systems is nowadays well known and only leftimprovement of designs and co ordination of different protection devices.

The reliability and speed of standard protection devices is very high because theyreceive very few signals, processing is simple, and they have to send orders to veryfew and established equipment.

The continuous increasing in production and consumption of electricity makespossible that problems encompassing several buses or areas in an electrical systemappear.

These problems can be summarized in:

• transient angle instability

• small signal angle instability

• frequency instability

• short term voltage instability

• long term voltage instability

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4. Experimental Section

4.1 Instantaneous and definite time overcurrentprotection

1. Introduction. Description of the experiment

This experiment studies the instantaneous and definite time overcurrent protection(I>) that is a form of protection designed to clean fault situations, when the currentexceeds the rated value (In) of the protected element (generator, powertransformers, transmission lines, motors).

An over current (OC) relay has a single input in the form of AC current, as shown infigure 1a. The output of the relay is a normally open contact, which changes over toclosed state when the relay trips.

The protection relay DL 2108T23 has six output relays (Rk, k= 1÷6) used to give theswitch off command to the circuit breaker (CB).

The relay has two settings: system setting and function setting.

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Using the system setting, the rated current (In) of the overcurrent relay isprogrammed, while using the function setting the operation current level (Is) andthe trip time delay (ts) are programmed.

Figure 1 Instantaneous and definite time overcurrent relay characteristic (CT –current transformer; In – rated current; Ix – largest phase current; ILk – phase current(k=1,2,3); Is – operation current level; f(t) = D independent definite time operationcharacteristic): a) Block diagram of an over current relay; b) Instantaneous overcurrent relay characteristic; c) Definite time over current relay characteristic.

The instantaneous overcurrent protection, shown in figure 1b, operates irrespectiveof the time when the fault current reaches the preset trip value. Instantaneousactually means no intentional time delay. Howsoever fast we want the relay tooperate, it needs a certain minimum amount of time.

The operating time of an instantaneous relay is in the order of a few milliseconds.Such a relay has only the trip (operation current Is) setting and does not have anytime setting. The relay takes an operating time (t1) around 5÷10 [msec] as relayprocessing time. In the relay characteristics, the curve becomes a vertical straightline since the relay does not have any time delay.

At definite time overcurrent protection, shown in figure 1c, the operating time isfixed irrespective of the fault current. The operating time (t2) can be programmedusing a dedicated software MSCom2 (i.e. setting a relay to operate at 10 seconds,for 5 Amps, means the relay allows 5 Amps for 10 seconds; beyond 10 seconds, therelay trips the circuit).

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Since the operating time of the relay is constant, these relays are used as feederover load protection, motor overload, busbar overload, etc. The relay should becoordinated with other definite time relays.

Figure 2 Single line diagram for overcurrent protection (50 instantaneous (definite)time overcurrent relay; 52 circuit breaker; L load). The definite time relay has loweroperating times at the lower current values.

In this experiment, the instantaneous and definite time overcurrent functions (50)will be used. An overcurrent relay has a minimum operating current, known as thecurrent setting of the relay. In figure 2, every protected area has an overcurrentrelay (Rk, k=1÷4) that has an operation current level (Iks, k=1÷4). The current settingmust be chosen so that the relay does not operate for the maximum load current(Ik, k=1÷4) in the circuit being protected, but does operate for a current equal orgreater to the minimum expected fault current.

In the relay, three definite time over current protection elements are available: 1I>,2I>, 3I>. The current threshold and delay time can also be set. There are three typesof overcurrent protections (instantaneous, definite time and inverse time):

instantaneous (the operation criterion is only the current magnitude without

time delay),

definite time (two conditions must be satisfied for tripping: the current must

exceed the set value and the fault must be continuous for at least a time equal to

the time setting of the relay).

The inverse time characteristic, when the relay operating time is

inversely proportional to the fault current, is the subject of the

next experiment.


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2. Objectives

Students are expected to learn about the fundamental principles of instantaneousand definite time overcurrent protection. By running this experiment, students willface some main objectives:

To understand the schematic diagram and the circuit diagram corresponding tothe instantaneous and definite time overcurrent protection experiment.

To learn which are the conditions when the instantaneous and definite timeovercurrent fault occurs.

Based on the schematic diagram, to learn how to connect the laboratorymodules accordingly.

To create different operation functions of overcurrent protection (instantaneousand definite time).

To know how to configure the relay software according to the overcurrentprotection basics.

3. Components list

According to the formulated objectives, for running this experiment the followingmodules are needed:

A. Software:

PC with Windows OS

MSCom2 software (+ Laptop from local resources for relay programming)

SCADA software (GTU 103.2)

B. Hardware:

DL 2102AL Three phase power supply

DL 1080TT Three phase transformer

DL 2108T23 Feeder manager relay (FMR)

DL 2108T02 Power circuit breaker

DL 2108T02A Power circuit breaker

DL 1017R Resistive load

DL 2109T29 Three phase power meter

DL HUBRS485F Communication Modbus

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4. Procedure outline

Schematic diagram

Instantaneous overcurrent protection (50): This protection function comprises the

short circuit protection for transformers, transmission lines, electrical machines.

The overcurrent protection is a practical application of the relays since it picks up

when the current exceeds some value (set value). The overcurrent relays can be

used to protect practically any power system elements, i.e., transmission lines,

transformers, generators, or motors. Figure 3 shows the three phase diagram of the

overcurrent protection. Overcurrent relays utilize the current amplitude for

estimating the fault. This requires measuring the current using specific sensors

(current transformers). The information regarding the current is represented by IL1,

IL2, IL3.

In this figure, for overcurrent protection the FMR feeder manager relay is used. To

give the switching off command to the circuit breaker DL 2108T02, the FMR has the

availability of six output relays. The relays are normally deenergized and are user

programmable. We use for this experiment the output R1 of the relay DL 2108T23.

For this experiment we simulate an overcurrent fault by increasing the load current

(Ix) over the preset operation current level (Is). The function of this protection is to

detect single phase, two phase or three phase overcurrents. This protection can be

time delayed and, in this case, it will only be activated if the monitored current rises

above the setting threshold for a period of time at least equal to the selected time

delay.

Figure 3 Three phase schematic diagram of instantaneous and definite timeovercurrent protection.



The schematic diagram from figure 3 is close to the student’s theoretical knowledge (it uses the classical electrical symbols). Use this diagram to perform the experiment, having as reference the wiring diagram of figure 4.

Follow the diagram from the next figure and connect the power cables accordingly:

Figure 4 Three phase wiring diagram of instantaneous and definite timeovercurrent protection.

DL GTU103.2 S


Experimental procedure and learning plan

Once we have understood all these preparatory aspects, we can proceed with the

experiment.

Before starting any wiring activity, check all power connections: all switches must be OFF. Do not miss the ground-connecting terminal! All equipment must be connected to the protective network by specific connector and cable.

1) Switch ON all the electronic devices connected to the experiment. Connect

every module to the mains power switch.

Check that the DL 2102AL and the resistive load DL 1017R are OFF (these experiments have as main objective the electrical fault protection and it is important to simulate different faults after you set up the relay).

2) Connect the relay module DL 2108T23 and the PC via a USB – RS485 cable

(check for the correct installation in Windows/Control Panel/Device Manager).

The relay configuration can be performed through SCADA. Both actions (configuration-MSCom2 and use-SCADA) are performed through the same serial communication port. This means that we cannot perform both actions at the same time.

Open the MSCom2 software (to program the relay in terms of instantaneous

and definite time overcurrent protection to be fulfilled).



The main screen of the software should look like in the next figure. After

starting MSCom2, you can connect to the relay by clicking “On serial port”.

3) The “Scan” option must be used when we want to connect to the relay through

a serial port, real or virtual. MSCom2 can open more than one relay at the same

time.

Based on your hardware configuration, to obtain a successful connection between the DL 2108T23 relay and the PC you may have to check different Baud rates (click on one Baud rate and if the scanning is taking more than 30 seconds it will not be successful and you need to select another one).

DL GTU103.2 S


When the scanning process is finished, in this window we will also see the

available communication ports, and we can configure the proper

communication baud. When the relay has been found, click on “Connect”.

Check the connection with the communication cable between the

relay and the PC. During the relay connection, you must wait for

a few seconds for all data to be created.

Setting of the relay can be done either through the Front Panel

Keyboard or via the serial communication bus from the MSCom2

interface program.



4) After relay connection, MSCom2 will display the first available data window

associated to the relay. The relay has integrated the function of overcurrent

protection – 50 ANSII IEEE code.

We can open more instances of the same relay. The last relay we

have selected is the Active Relay. To change the active relay, we

have selected another relay or variable.

The password to modify the parameters is: 1111.

After relay connection, the first available data window associated to the relay

will be displayed.

DL GTU103.2 S


5) To display the list of available data groups (ex: measures, events, settings,

status, inputs, outputs, commands) click on the “Relay icon” button. Every time

you need to configure a parameter or to visualize the events record, use the

“Relay icon” button like in the next figure.



6) Configure the FMR relay by entering into the “System settings” option from the

MSCom2 software. From this window, you can set up the main parameters of

the equipment used for the experiment.

For this experiment, use the presented configuration and set up the Nominal

current at 5000mA (5A).

7) Configure the functions of the FMR relay by entering into the “Functions

Setting” from the MSCom2 software. You need to set to ON the 1I> (First

overcurrent element F50 51). The relay will function when the AC input current

exceeds a predetermined value.

DL GTU103.2 S


8) Click on 1I> (First overcurrent element), then choose the ON option and press

OK. This will enable the overcurrent protection of the relay.

The relay can be set up by programming the variable “f(t)” regarding the

operation characteristic (Time/Current curve) to (Type D) Independent

definite time.



The relay can be set up by programming the variable “1I>” regarding the

operation characteristic Is (Maximum operation level):

Function: 1I> (First Overcurrent Element side 1)

Description of variables: 1I> (First Overcurrent Element side 1)

For protection understanding, adjust the current trip value at 0.5 A (easy to establish, without creating electrodynamic stress to the network) and the delay time at 0.5 sec (in the relay software events recorder this time can be identified).

Over current Fault trip setting in MSCom2 software:

Is = 0.1 x In = 0.1 x 5A = 500 mA (operation current level – see figure 1b)

ts = 0.5 second (operating time delay – see t1 from figure 1c)

DL GTU103.2 S


Set up the maximum operation level of the current (instantaneous magnitude):

Use the function ts to configure the trip time delay (definite time). For this

example, use 0.5s delay until the relay will trip. As shown in the figure below,

the time range for the trip delay is between 0.02 ÷ 100 sec.



When the FMR relay is programmed to work as an instantaneous and definite

time overcurrent protection (50), press the send button to upload the program

into the relay.

9) Configure the output relays of the FMR by entering the “DO Configuration”

from the MSCom2 software. As you can see in the next two figures, the output

relay that must be configured is relay R1.

Based on the wiring diagram from figure 4, the output relay R1 of DL 2108T23 is

used to trip the circuit breaker (DL 2108T02). Select the function “pulse” to

reset the relay, because the enable/reset command will be done from SCADA.

The output relay R1 used in the experiment is normally closed (see in figure 4

the output relay R1 of DL 2108T23).

DL GTU103.2 S


The output configuration in MSCom2 needs to be selected as “Normally

Energized”. This means that the instantaneous and definite time overcurrent

relay will keep the R1 closed until the trip conditions will be fulfilled.

As shown in the figures below, choose from the available functions (1) the

overcurrent value 1I>. This will trip the relay instantaneously.

The relay is programmed to work as an instantaneous and definite time

overcurrent protection.

10) Switch ON the three phase power supply (DL

2102AL). First, raise the current circuit breaker for

the sinusoidal AC fault currents (1). Turn the key (2)

of the three phase supply. At this point, the three

phase lamps must be switched ON.



11) Switch ON the DL 2108T02 circuit breakers by

following the figure. By pressing the “green”

button, the circuit breakers are enabled.

Remember that the switch ON and switch OFF

command will be given using the SCADA software.

As shown in the wiring diagram from figure 4, the first circuit

breaker is enabled (1) by the relay R1 of DL 2108T23. The

switch ON and OFF (2) will be given from SCADA via the HUB

communication relay R1 (normally open).

The second circuit breaker is enabled by manually pressing the

button (3). The switch ON and OFF (4) will be given from SCADA

via the HUB communication relay R2 (normally open).

DL GTU103.2 S


4.1 First operation function INSTANTANEOUS protection

12) Enter the SCADA software and select EXERCISE 1 – Instantaneous and definite

time overcurrent protection.

13) A general independent (definite) time protection schematic diagram is shown in

the main window of the SCADA. The relay carries out the processing of the

information provided by the current transformers (CT). The overcurrent

protection is defined as the relay that operates only when the value of the

current is higher than the relay trip. It compares it with the settings to take a

trip decision (0,1).



14) Open the three phase power meter by clicking on it from SCADA. You will see a

pop up window with the real panel of the laboratory module.

DL GTU103.2 S


15) Check that the three phase power supply (DL 2102AL) is switched ON. You can

do this in two ways: one is to check that the lamps on the front panel are ON,

and the other one is to check, in SCADA, the measured phase to neutral voltage

of the power supply. Click on the voltage (U) menu of the DL 2109T29 power

meter.

16) Click again on the voltage (U) menu of the DL 2109T29 power meter, to

measure the phase to phase voltage.



17) Close the first circuit breaker by clicking on the HR1 switch from SCADA. This

will close the circuit breaker located between the power transformer (DL

1080TT) and the Instantaneous and definite time overcurrent relay (DL

2108T23).

18) Close the second circuit breaker by clicking on the HR2 switch from SCADA. This

will close the circuit breaker located between the instantaneous and definite

time overcurrent relay (DL 2108T23) and the resistive load (DL 1017R).

DL GTU103.2 S


19) First, you need to enable the instantaneous and definite time overcurrent relay

by clicking on the “Enable Protection” from SCADA. By clicking on the DL

2108T23 relay, you will see a pop up window with the real panel of the DL

2108T23 and by clicking on the DL 2109T29 you will see a pop up window with

the real panel of this instrument.

A small amount of current is drawn from the primary side, to

set up the required magnetic flux in the magnetic core. This

current is known as the "no-load current". At no load, the

secondary current becomes zero due to the open circuit at the

secondary.

20) Change the value of the load by adjusting the switches corresponding to the

resistances R1, R2 and R3. Turn all the switches from off to 1. Keep turning until

you measure a phase current of approximatively 200mA.

Modifying the load resistance will have the effect

of increasing the current on all three phases. The

currents can be seen in the “Actual

measurement” window of MSCom2. See the

currents Ia, Ib, Ic.



The measured values of the phase current can be seen in the SCADA software.

The load current values are indicated on every line from the schematic diagram.

Also, the same values of currents can be read on the power meter (DL 2109T29)

and on the relay (DL 2108T23) interface.

21) Keep turning until you measure a phase current of approximatively 300 350mA.

Check the MSCom2 measurements. As shown in the figure below, the

measured phase current is below the trip overcurrent value of 500mA.

Consider the values from the software interface as a reference.

Based on your mains and laboratory conditions, the actual

measurements values might differ.

DL GTU103.2 S


The relay is NOT in the operating zone and will not trip (see the symbol from

the figure above). This is because the operating principle of the relay (see figure

1b) is: Input current above the set level: Ix > [Is] (this condition is not fulfilled

yet).

22) Change the value of the load by adjusting the switches corresponding to the

resistances R1. Turn the switch from phase 1 until the phase current exceeds

the value of 500mA.

Check the MSCom2 measurements. As shown in the figure below, the

measured current on phase 1 is above 500mA (similar to the value measured in

the above figure in SCADA). This value is above the trip overcurrent value of

500mA.

The relay is in the operating zone and will trip (see the symbol from the

figure above). Input current above the set level: Ix > [Is] (this condition is

fulfilled now).



23) The relay DL 2108T23 will open immediately the relay R1 and the circuit

breaker DL 2108T02 will switch OFF. The measured current is zero and the only

parameter that can be measured is the power supply voltage.

24) Open Events Recorder: In this window, all information regarding the fault and

which output relay has tripped are shown.

25) Turn the resistive load to zero (R1=R2=R3=0).

26) Remember to reset the Circuit Breaker, by clicking the “Reset protection” from

the main menu of the SCADA software. You will need to press the DISABLE

PROTECTION and then the RESET PROTECTION.

Press the green button of the circuit breaker DL 2108T02 to

enable the protection again. Pay attention, if you do not remove

the fault, the multifunction relay will trip again.

27) You need to press the green button (from the front panel of the circuit breaker)

to enable the DL 2108T02.

28) Switch OFF the circuit breakers by pressing HR1 and HR2.

DL GTU103.2 S


4.2 Second operation function DEFINITE TIME protection

29) Configure the functions of the FMR relay by entering the “Functions Setting”

from the MSCom2 software. Remember that you set in the previous example

1I> to ON and f(t) to Type D. Following the information presented in figures1c,

an operating time (delay) was configured (ts=0.5s).

30) Configure the output relays of the FMR by entering the “DO Configuration”

from the MSCom2 software. As you can see in the next two figures, the output

relay that must be configured is relay R1.



Set up the overcurrent protection (definite time overcurrent): t1I>

Select the instantaneous overcurrent 1I> (1). Remove (2) this parameter from

the digital output set up.

When the setup of the relay is complete, you need to press the “Send” button

from MSCom2 in order to upload the software configuration to the

instantaneous and definite time overcurrent relay.

By performing this set up, the relay is programmed to work as instantaneous

and definite time overcurrent protection.

DL GTU103.2 S


31) Perform again steps 18 21 of the previous procedure.

32) Check the SCADA and MSCom2 measurements. Keep turning until the phase

current is above the trip overcurrent value of 500mA.

After the operating time ts delay that you have programmed (0.5sec), the relay

will trip via one of the output relays.

33) As mentioned, in the relay software events recorder this time can be identified.

34) When the experiment is complete, switch OFF the circuit breaker that

interconnects the power supply with the load. Turn the switches of the resistive

load from R7 to R0 in steps of one. Record the values through the software

facility for later processing (using the oscilloscope function of MSCom2).



5. Conclusions

The overcurrent protection protects electrical power systems against excessive

currents which are caused by short circuits, ground faults, etc.

Overcurrent relays can be used to protect practically any power system elements,

i.e. transmission lines, transformers, generators, or motors.

This experiment studied the instantaneous and definite time overcurrent

protection. By creating the proper functions, we can program the relay that reacts

to:

Short circuit situations in the protected area (instant protection).

Over currents with associated delay that allows also leaving the power system

working in the transitory regime (delayed protection).

If the system is working as a backup protection system, when we adjust the

steps of the delay, when both conditions are fulfilled (overcurrent and delay),

the relay will clean the fault.

1 - composition, operation and maintenace - revgb

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