Power Systems Protection Lab Manual in PTUK, Lab Reports of Electrical Engineering

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Faculty of Engineering and Technology

Department of Electrical Engineering

Electrical Power Systems Protection Lab Manual

( 12120204 )

First Edition

Student Manual

Prepared by:

Eng. TareQ FoQha

2021

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

II | Page Electrical Power Systems Lab

Abstract

The power systems protection laboratory is designed to directly apply theory learned in lectures to devices that will be studied in the laboratory. Power system protection is concerned with protecting electrical power systems from faults within the network by isolating the faulted components so as to leave as much of the remaining the electrical network operational as possible. Moreover, by properly protecting the system components from overloading, the probability of fires and other catastrophic and expensive system failures can be minimized.

In understanding power protection, it is necessary to understand what is actually being protected. Providing superior protection is essential in mitigating the effects of disruptions on system stability. As such, it is essential for power engineers to understand the concepts and practices underlying power protection.

The creation of a Power System Protection Lab at Palestine Technical University gives students the opportunity to gain some real world experience in protection. Moreover, a laboratory of this type facilitates educational opportunities. It also provides numerous additional benefits such as research.

Objectives

The laboratory course is intended to provide practical understanding of power system protection. The main goal is to enable students to apply and test theoretical knowledge they mastered in previous years of studies. The laboratory course enables them to develop practical skills in various fields of power engineering in a controlled environment.

The Laboratory covers all phases for the Protection devices specific of this field. All protection and control devices of the electrical machines are exactly equal to those installed in the industrial units. So, the sequences of control maneuvers in the control stations are exactly equal to those necessary in the industrial units.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

III | Page Electrical Power Systems Lab

Faculty of Engineering and Technology | Electrical Engineering Department

Electrical Power Systems Protection Lab || Eng. TareQ FoQha

• Chapter (1) Introduction^01 - IV | Page Electrical Power Systems Lab
• Experiment (1): General Considerations on Protection Devices 02 -
  • Chapter ( 2 ) Protection Relays For High And Low Voltage Networks^06 -
• Experiment (1): Overcurrent Relay (SR1).^07 -
• Experiment (2): Max/Min three-phase voltage Relay (SR3). 12 -
• Experiment (3): Directional Relay (SR10).^17 -
• Experiment (4): Differential Relay (SR14).^25 -
  • Chapter ( 3 ) Synchronous Generators Protection 39 -
• Experiment (1): Protection of Synchronous Generator using Protective Relays. 40 -
  • Chapter ( 4 ) Transmission Lines Protection^52 -
• Experiment (1): Protection of Transmission lines using Electromechanical Relays.^53 -
• Experiment (2): Protection of Transmission lines using Digital Relays.^57 -
  • Chapter ( 5 ) Distribution Systems Protection 70 -
• Experiment (1): Checking Differential Current the Operation. the Protection Devices with 71 -
• Experiment (2): Selectivity among Protection Devices. 81 - - Appendices 94 -

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Chapter 1

Introduction

Contents

Experiment (1) General Considerations on Protection Devices 02 - 05

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Introduction:

This part of the manual describes the main protection devices employed on electrical lines or central stations. The purpose is to obtain a set of easily consultable news referring to the bibliography for the known notions.

For the relays we will generally provide the following information:

1) Function identification number ( ANSI / IEEE C37.2 ), 2) News on the purpose and possible applications, 3) Characteristic equations and functional diagrams, 4) Base insertion diagrams and relays block diagram, 5) Service controls and installation modes.

The standard CEI 94-4 (Italian), CEI EN 61810-1 (European) "Non-specified time ON/OFF electromechanical relays" (Standard processed on the base of international publications IEC 61810-1); we suggest a set of definitions for the protection relays, protection systems, etc.

There are three kinds of electrical protections:

1) Electromechanical, 2) Static and 3) Microprocessor.

The electromechanical protections exploit the electrodynamic forces (electromagnetic and induction relays) and the thermal power (thermal, bimetallic relays) to cause the intervention of the cut-off devices.

In the static protections (electronic) the electromagnetic and thermal functions are performed by the electronic circuits without parts in motion (static) except for the output relays contacts. These protections enable finer and more accurate calibrations than those that can be obtained from the electromagnetic relays, besides more functions can be grouped into a single envelope.

The microprocessor protections are more evolved and complete and can also be programmed and transmitted at a distance from the detected data. The microprocessor protections enable not only finer and more continuous calibrations than the last protections but also the modification of the intervention curve to be matched to the different needs. These protections, interfaced to personal computer can provide a large quantity of data for the statistic analysis. They are obviously provided with output relay contacts to act on external opening and/or signaling circuits.

Experiment (1)

General Considerations on Protection

Devices

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

For the static equipments, the term relay can be used when it carries out a specific elementary logic function while the term relay device is applied to equipment including a total logic function corresponding to the combination of more elementary logic functions.

Protection Device or Automatic Relay Device:

Relay device performing a specific protection or automatism function as it results from the qualification of the same device.

Relay Protection System:

These are among plant engineering systems designed for a specific purpose, in which a determinant part is played by the electrical relays which are sets with the purpose of protection. A protection system includes the measurement transformers , the transmission channels , the cables or conductors , the release circuits , etc. necessary to achieve the purpose. The designer qualifies the protection system specifying the job it must perform and describing in details the characteristics of the elements composing the same system.

Electrical Relay:

Equipment to be used to cause predetermined changes of state in its output electrical circuits when particular power supply conditions occur across its input electrical circuits.

Relay Device:

Set of relays connected between them so that they fulfill the purpose the device is supposed to perform and with which the manufacturer qualifies the same device. The terms relay and relay device are usually applied equipments of electromechanical kind, while for those of static kind it is sometimes difficult to find the border between the relay and relay device.

Characteristic Variable of a Measurement Relay:

Electrical variable which passage across a specified value, which is associated to a given accuracy, determines the relay operation; the characteristic variable characterizes the name of the relay. In the relays with one input power supply variable the names of the characteristic variable and the input power supply ones usually coincide; however there are exceptions: e.g. those relays in which the characteristic variable is the frequency, that are generally powered with a voltage.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Measurement Relays with Characteristic Variable:

Relay in which the output circuits state change depends on the passage of the characteristic variable across a specific service value which is associated to a given accuracy. Besides the characteristic variable, other elements characterize the relay and are included in its denomination; in particular the indication determining if the accuracy refers to the operation increasing or dropping the characteristic variable (maximum or minimum relay) and, in case, the indication if it is a relay with specified intervention time.

Measurement Relay with Characteristic Threshold Line:

Relay in which the output circuits stage change depends on the shift of the input circuits conditions from those corresponding to the relay characteristic threshold line, shift at which a given accuracy is associated to.

Characteristic Angle (or inner angle) in a Measurement Relay:

In an alternated current measurement relay with two input power supply circuits, central value in the field of the angles composed by the representative vectors of the two input power supply variables, for which the relay is invited to intervene; the value of the characteristic angle can characterize the relay denomination. In the electromechanical relays, there is the maximum relay operative torque in correspondence to the characteristic angle of the relay and the range of the angles has a particular value.

Ranges of Intervention:

In a measurement relay with characteristic threshold line, the two ranges defined by the threshold line set on the same relay; for the conditions corresponding to one of the two ranges, the relay is forced to intervene in a direction, for the conditions corresponding to the other range the relay is forced to intervene in the reverse direction (or not to intervene).

Characteristic Theoretical Line (or indicated or adjusted):

In a measurement relay with characteristic threshold line, it is the line for which the relay - in conditions specified according to the indications reported at the regulation elements or however defined by the manufacturer - is in still.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Characteristic Threshold Limit Lines:

In a measurement relay with characteristic threshold line, the lines located on the two sides of the theoretical line, delimiting the maximum and minimum values, within which the relay, in specified conditions, could not intervene.

Maximum or Minimum Relay:

Measurement relay with characteristic variable in which the prescriptions related to the accuracy refer to the achievement of the operation value of the same characteristic variable when its values rise or drop.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Chapter 2

Protection Relays For High And Low Voltage Networks

Contents

Experiment (1) Overcurrent Relay (SR1) 07 - 11

Experiment (2) Max/Min three-phase voltage Relay (SR3) 12 - 16

Experiment (3) Directional Relay (SR10)^^17 -^24

Experiment (4) Differential Relay (SR14)^ 25 - 38

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Objectives:

1. Connection and study of a fixed time maximum current relay and of a 3- phase line short-circuit one with different currents. 2. To measure the tripping time of maximum-current (over load and short-circuit) in a three-phase network with different current values;

Theory and concepts:

Code CEI: 50 Instantaneous intervention relays 51 Delayed intervention relays 50N-51N max homopolar current relays.

These are the most famous protection relays. Main purpose is the detection of the phase to phase or phase to ground faults. In particular the relay 50N or 51N can be used also with networks with insulated neutral under particular conditions.

 The three-phase amperometric relay set to maximum current (overload) protection function enables to fix the limit of the current provided by an alternator (its nominal power) or the current that a power line can usually stand.  The values of the currents are adjustable and so is the intervention time delay.  The three-phase amperometric relay set to protection function against short-circuit intervenes instantly when the controlled current overcomes the set value. The current values are adjustable, but the time delay is not so as it is instantaneous. Usually the relay acts on the main switch to set the controlled object out of service (alternator or line).  The current value (overload, short-circuit) as well as the delay time, must be adjusted and checked during the test phase and next in the periodical testing to be sure the protection device operates.

For the fixed time relay: (figure 1)

Iint = K I 1 /In for the overload Iint = K I^2 /In^ for the^ short-circuit

Experiment (1) Overcurrent Relay (SR1)

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Figure (1)

SR1 Max current three-phase relay description:

Three-phase maximum-current (overload and short-circuit) relay at definite time and three-phase short-circuit.

Overcurrent Relay settings/Current and time settings (overload and short circuit):

The technical characteristics of the device are shown in appendix A.

SI 1 first level regulation range (overload). SI 2 second level regulation range (short-circuit)

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Necessary Material:

1. AMT-3/EV: Variable three-phase power supply mod. 2. SR-1/EV: Overcurrent relay. 3. RC3-PT/EV: Three-phase rheostat 3 x 50. 4. Contactor with on-off control. 5. AZ-VIP : Digital instrument.

Experimental Procedures:

1. Connect the circuit as shown in figure 2.

Figure (2)

2. Connect the auxiliary power line of 230 Vac with the relay, without powering it. 3. Connect the relay between the variable power line and the load rheostat (Y-connection). 4. Suppose to adjust the device with the following design data:  Overload threshold = 0.5-A ;  Tripping delay time = 5-s ;  Short-circuit threshold = 1-A;  Tripping delay time = **0.1-s.

5. Normal Condition** : Power the relay with the auxiliary supply voltage and check whether which led will goes on in the frontal panel. Check the contacts of the contactor.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

6. Adjust the voltage of the variable power line and the load rheostat to obtain a current lower than 0.5-A.

Condition Relay operation

Normal

Load Current Tripping Time Notes

7. Overload Condition : Increase the test current over 0.5-A , record the load current and the tripping time and check the operation of the relay. 8. This condition is kept stored in memory even after the current drops below the preset value; therefore the device will be reset with the corresponding button, resetting manually the device by pressing the RESET button.

Condition Relay operation

Overload

Overload Current Tripping Time Notes

9. Short Circuit Condition : Increase the test current over 1-A, record the load current and the tripping time and check the operation of the relay. 10. This condition is kept stored in memory even after the current drops below the preset value; therefore the device will be reset with the corresponding button, resetting manually the device by pressing the RESET button.

Condition Relay operation

Short Circuit

Short Circuit Current Tripping Time Notes

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Questions:

1. Suppose you have to protect a three–phase induction motor from an overload condition, the nameplate of the motor is shown in figure 1. (A) Sketch the connection needed to connect three-phase induction motor with: (1) 3-phase supply (2) Contactor (3) SR1: Overcurrent relay (B) Explain how to put the settings of the relay? (C) Explain how to reset the relay after removing the cause of overload? (D) Explain the operation of the relay in this case?

Hints:

1. Motors with a service factor (SF) of 1.15 or more, the settings of the overload relay should be 125% of the full load current.
2. Motors with a service factor (SF) less than 1.15, the settings of the overload relay should be 115% of the full load current.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Objectives:

1. Connection and study of a maximum and minimum voltage relay in a 3-phase network.
2. To measure the tripping time of maximum/minimum in a three-phase network with different voltage values;

Theory and concepts:

Code CEI: 59 Maximum voltage relay 27 Minimum voltage relay

The purpose of the maximum and/or minimum voltage relays is to detect anomalous voltage rising or dropping near the production or usage centers so to prevent damages of machines or OFF parallel situations.

The three-phase voltage relay detects the limits of the triad of voltage generated in ordinary service of the alternator or distributed by the transmission line. Usually, the relay acts on the main switch to set the controlled object out of service (alternator or user connected to the line) when a rise or drop of voltage can cause malfunctions or damages.

The characteristic equation is: V = KV 1 / VN

Experiment ( 2 ) Max/Min 3 - phase voltage Relay (SR 3 )

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Operation diagram of the relay

Figure (1)

The technical characteristics of the device are presented in appendix A.

Necessary Material:

1. AMT-3/EV: Variable three-phase power supply mod. 2. SR-3/EV: Max/min three phase voltage relay.

3. IL-2/EV: Variable inductive load mod.

4. Contactor with on-off control. 5. AZ-VIP : Digital instrument.

Experimental Procedures:

1. Connect the circuit as shown in figure 1.

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Figure (1)

2. Connect the relay to a variable three-phase power supply line. 3. Connect a voltmeter to measure the line voltage. 4. Adjust the device with the following design data:  Line nominal voltage Ue = 380 V;  Maximum voltage threshold (MAX VOLTAGE) = 105 %;  Intervention delay for maximum voltage (DELAY MAX) = 5 s;  Minimum voltage threshold (MIN VOLTAGE) = 90 %;  Intervention delay for minimum voltage (DELAY MIN) = 5 s. 5. Normal Condition: Adjust the voltage of the variable power supply line up to 380 V (with no load condition).

Condition Relay operation

Normal

Voltage Tripping Time Notes

6. Overvoltage Condition: Increase the test voltage over 400 V , record the line voltage and the tripping time and check the operation of the relay (with no load condition).

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7. The relay has a hysteresis of 3% in respect to the set point, take back the voltage to the nominal value (380 V) and record the reset value.

Condition Relay operation

Overvoltage

Voltage Tripping Time Reset Value Notes

8. Undervoltage Condition: Drop the test voltage under 342 V , record the line voltage and the tripping time and check the operation of the relay (with no load condition). 9. The relay has a hysteresis of 3% in respect to the set point, take back the voltage to the nominal value (380 V) and record the reset value.

Condition Relay operation

Undervoltage

Voltage Tripping Time Reset Value Notes

10. Undervoltage Condition: Set the system under load with the insertion of the inductive load and measure the following:

Inductive Load

Minimum voltage threshold %

Line voltage (V)

intervention delay

Measured delay (Sec)

Reset Value (V) B 95% 5 sec A||B 90% 5 sec

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Questions:

1. Suppose you have to protect a three–phase induction motor from an undervoltage condition, the nameplate of the motor is shown in figure 1. (A) Sketch the connection needed to connect three-phase induction motor with: (1) 3-phase power supply; (2) Contactor; (3) SR3: Max/Min voltage relay. (B) Explain how to put the settings of the relay to protect the motor from undervoltage condition; the voltage applied to the motor should be at least 95% of the nominal voltage? (C) Explain how to reset the relay after removing the cause of undervoltage? (D) Explain the operation of the relay in this case?

Faculty of Engineering and Technology | Electrical Engineering Department Electrical Power Systems Protection Lab || Eng. TareQ FoQha

Objectives:

1. Connection and study of a maximum current directional relay for maximum current.
2. To measure the tripping time with inverse current flow.

Theory and concepts:

Code CEI: 67 Directional relay 32 Directional or power inversion relay

It is a much extended family of equipment sharing the capacity to operate a control on the power direction. The concept of direction in the alternated currents is not proper; we should rather talk of angular relation between the voltages and the phase currents. However, by convention, we have fixed to consider as positive a vector direction resulting from the composition of a reference vector with another set within ± 90° from the first; as negative the one resulting from the composition with a superior angle.

The diagram of figure 1 shows straight line “L” called inversion or limit or threshold. One of the pros of directional relays is just the one to operate, near the inversion straight line, without operation uncertainties. To fulfill their purpose, the directional relays carry out the measurement comparing two variables in module and in phase: the voltage and the current.

Generally they are defined on the plane V–I and can be reproduced by the equation:

Figure (1)

Experiment ( 3 ) Directional Relay (SR 1 0)

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Generally, with the help of watt-meters, ammeters and voltmeters, the positive or negative power directions are checked associating the open or closed state of the output relay.

The control of the power provided by the production central station or absorbed by the user is a need appeared since the first electrical power distribution. This is due by the fact that the power market is made of more producers and also by the control of the contractual conditions (active, reactive power, absorbed power excess, etc.). It is more obvious that the simple current control, actuated with the maximum or minimum current protections, in case of more or less shifted loads does not show the actual degree of work or the involved power. As function of the needs of the different users and producers, it is advisable to carry out protections sensible to the power expressed in one of the three relations:

Apparent power: S = V I Active power: P = V I cos φ Reactive power: Q = V I sin φ

In fact, while the generators keep equally employed for the production of the components in quadrature, the dissipation by Joule effect considers only the resistive component, so, in different power factor conditions, there are different dissipations to equal active power, too. The power relays must measure the two variables, V and I , so that it is possible to compare the phase (analogously to the watt-meters).

The adjustment of the intervention threshold of the power directional relays is expressed by the following equation: F = K Iiv cos φ

where the constant K is a factor of proportionality depending on the relay constructional characteristics.

In the protection relays against inverse power it is necessary for the polar operating quadrants, block and threshold, to be clearly defined to prevent operation uncertainties near the inversion zone when the generator is used to produce reactive instead of active power. A characteristic situation is represented in figure 2 where a small alternator is set in parallel on a considerable network.

Figure (2)

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In the example mentioned in the last figure 1 – during normal operation– the users coming from the lines E and F absorb the current I 1 + I 2 as they are powered by the line as well as the local generator. In case the national line would be missing, all charge of the sector would rest on the local generator with logical intervention of the maximum current protections. All this is regular but in case the point A is to be sectioned for electrical maintenance and with no-load users D E F or those with weak absorptions, there is a danger situation and the distribution societies force the generator separation although no actual power inversion occur. The solution consists in adding a protection device against inverse power in point C provided with high sensitivity. The completion of the circuit under test sees a further protection against the inverse power in point D.

The intervention characteristics of a power inversion relay should be the as shown in figure 2.

The directional relays are a very large family of equipment sharing the capacity to control the power direction. The concept of direction comes from the angular relations between phase voltages and currents where, by convention, positive is considered the direction of a vector resulting from the composition of a reference vector with another set within ± 90° from the first; negative the one resulting from the composition with a superior angle. To fulfill their purpose, the directional relays carry out the measurement comparing two variables in module and phase: voltage and current. The adjustment of the intervention current threshold, the delay time and the characteristic angle α (+/- 30°) enables to use the relay in different applications.

 This protection relay senses the current direction, and consequently, operates the output contacts.  According to the relay model, and the selected connection, the relay is able to:  Block the active power direction of a generator (Reverse Power Relay). Generators prime movers (Diesel engines or turbines) are designed to develop mechanical power, not to accept power. Mechanical power is directly related with the generated active power. When in parallel, it is possible that a generator becomes a motor (“accepting” power). Then this “motor” drags the prime mover, with eventual danger for the Diesel or the turbine.

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 Control the current increase in an out of step of a synchronous machine.  Control the current increase in the ph-to ph fault.

Use of the relay to block the reverse current and active power. The following figure shows the voltages vectors in a 3-ph balanced system.

Vector V 12 is the Reference vector in the second figure, with the following parameters:

 E 1 is the phase 1 voltage vector  Ψ = insertion angle; it is the (-30°) angle between the V 12 and E 1 vectors.  α = relay characteristic angle. The relay is manufactured with (+/-30°) angle.  φ = phase shift among R current and voltage vectors.  φMS= (α – Ψ) phase shift for relay max. sensitivity.

The current I 1 R is the current active component of I 1 RL, and its direction coincides with the E 1 vector. I 1 R = I 1 RL * cos (φ + Ψ- α) I 1 R is max when cos (φ + Ψ- α) = 1 → (φ + Ψ- α); φ = α - Ψ = -30°- (-30°)= 0.

 If I 1 RL is absolutely inductive cos (φ + Ψ- α) = 0 and I 1 R = 0.  Current Isc is the acceptable reverse current, a limit to be set in the relay. When the active reverse current I 1 R is greater than Isc, the relay will trip. It is clear that if I 1 RL is absolutely inductive and I 1 R = 0, Isc is never reached, whatever the value of I 1 RL.

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Necessary Material:

1. AMT-3/EV: Variable three-phase power supply mod. 2. SR-10/EV: Maximum current directional relay. 3. RL-2/EV: Variable resistive load mod. 4. IL-2/EV: Variable inductive load mod. 5. AZ-VIP : Digital instrument.

SR10 Maximum current directional relay description:

Maximum current directional relay

The installed device is a directional relay (In = 5 A) which, with the current or power direction following the input one (input in the higher terminals) does not enter alarm state; with current a little over the threshold set in Is and with the current or power in the reverse direction, it alarms after the time Ts.

Intervention Current Is = Inominal (5 A) x [Weight of the dip-switches (0-8.5) + 1] x K (0.02)

Intervention time Ts = [Weight of the dip-switches (0-16.5) + 0.1]

The technical characteristics of the device are shown in appendix A.