POWER SYSTEMSLAB YEAR SEM EEE. Dr. J. Sridevi

Transcription

1 POWER SYSTEMSLAB YEAR SEM EEE By Dr. J. Sridevi Gokaraju Rangaraju Institute of Engineering & Technology Bachupally 1

2 GOKARAJU RANGARAJU INSTITUTE OF ENGINEERING AND TECHNOLOGY (Autonomous) Bachupally, Hyderabad CERTIFICATE This is to certify that it is a record of practical work done in the Power Systems Laboratory in sem of year during the year Name: Roll No: Branch:EEE Signature of staff member 2

3 INDEX S.No Date Topic Page no. Signature of the Faculty 1. Tripping Characteristics of Fuse & MCB 9 2. Characteristics of Over current relay for Phase fault 3. Characteristics of Over current relay for Earth fault Characteristics of Induction disc type relay Characteristics of over load relay Testing of Differential relay Model of a Transmission Line with Lumped parameters Characteristics of Over voltage Relay Characteristics of Under voltage Relay Zones Protection Short circuit analysis Tripping sequence of protective devices Testing of Negative sequence Relay 80 3

4 ETAP SOFTWARE INTRODUCTION ETAP stands for Electrical Transient Analysis Program, This amazing software suite covers a wide range of electrical engineering domains; from software for network analysis to power distribution. The wide range of software modules from ETAP are one of the most beneficial and effective for electrical engineers. The Arc flash analysis software from ETAP allows engineers to use simulation models to identify and mitigate arc flash hazards in the electrical power system and other arc flash related issues. Here we are using this software to analyse basic operation of power system during transients, normal operation and fault conditions without actually interfacing with practical power system. The main parts a power system we come across are as follows 1. Power Grid 2. Bus bar 3. Power Cable 4. Transformer 5. Circuit breaker 6. Relays 7. Fuse 8. Load(motor) The detailed meaning of them is given below 1. Power Grid: An electrical grid is an interconnected network for delivering electricity to consumers. It consists of generating stations that produce electrical power, high voltage transmission lines that carry electrical power from distance sources to demand centres 4

5 and distribution lines that connect individual consumers. It looks as shown below in ETAP. 2. Bus bar: A bus as regard to the power system is an electrical junction (node).it is a strip or bar of copper, brass or aluminium that conducts electricity within a switchboard, distribution board, substation, battery bank, or other electrical apparatus. Its main purpose is to conduct a substantial current of electricity. 3. Power Cable: A power cable is an assembly of one or more electrical conductors, usually held together with an overall sheath. The assembly is used for transmission of electrical power. Power cables may be installed as permanent wiring within buildings, buried in the ground, run overhead, or exposed. In ETAP it looks as: 4. Transformer: Electrical power transformer is a static device which transforms electrical energy from one circuit to another without any direct electrical connection and with the help of mutual induction between two windings. It transforms power from one circuit to another without changing its frequency but may be in different voltage level. It steps up or steps down the voltage by changing the number of windings in primary and secondary. 5. Circuit breaker: A circuit breaker is an automatically operated electrical switch designed to protect an electrical circuit from damage caused by 5

6 overload or short circuit. Its basic function is to detect a fault condition and interrupt current flow. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset (either manually or automatically) to resume normal operation. Mainly here we come across two types of CB s. They are High Voltage Circuit Breaker (HVCB): High-voltage breakers are nearly always solenoid-operated, with current sensing protective relays operated through current transformers of about 72.5KV or higher. Low Voltage Circuit Breaker (LVCB): Low-voltage (less than 1,000 VAC) types are common in domestic, commercial and industrial application. 6. Relays: A relay is an electrically operated switch. Many relays use an electromagnet to mechanically operate a switch. Relays are used where it is necessary to control a circuit by a low-power signal (with complete electrical isolation between control and controlled circuits), or where several circuits must be controlled by one signal. There are mainly relays we use in ETAP. They are Over Current Relay, In-line Overload Protection Relay, Voltage Relay, Differential Relay, Frequency Relay. i. In-line Overload Relay: A relay that opens a circuit when the load in the circuit exceeds a preset value, in order to provide overload protection; usually respondsto excessive current, but ma y respond to excessive values of power, temperature, or other quantitiesalso kno 6

7 wn as overload release. In ETAP it is denoted by 49 which is ANSI code for Inline overload relay. ii. Over Current Relay: A digital over current relay is a type of protective relay which operates when the load current exceeds a pickup value. The ANSI device number is 50 for an instantaneous over current (IOC) and 51 for a time over current (TOC). In a typical application the over current relay is connected to a current transformer and calibrated to operate at or above a specific current level. When the relay operates, one or more contacts will operate and energize to trip (open) a circuit breaker. iii. Voltage Relay: A relay which operates when the system voltage when the system falls below or above a certain preset value. For an under voltage relay the ANSI code is 27, which is used as a standard in ETAP. iv. Differential Relay: A relay which responds to a difference in two voltages or currents. For example, such a relay may have two coils and only respond when the respective currents of said coils vary beyond a specified amount. It s denoted by the ANSI code no.87 in ETAP. v. Frequency Relay: Relay which functions at a predetermined value of frequency; may be an overfrequency relay, an under-frequency relay, or a combinationof both. It is denoted by the ANSI code no. 81 in ETAP to determine it s specific function. 7. Fuse: A fuse is a type of low resistance resistor that acts as a sacrificial device to provide overcurrent protection, of either the load or source circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, interrupting the circuit that it connects. Short circuits, overloading, mismatched loads, or 7

8 device failure are the prime reasons for excessive current. Fuses are an alternative to circuit breakers. It can be seen in ETAP as: 8. Load (Motor): The electric power delivered by a power source to a power user. If variations in voltage a re small, load can becharacterized by magnitude of current. The term load is also often applied to the device consuming the electric power that is, to a piece of equipment, such as a motor or a lighting device. In ETAP we come across mainly Induction Motor, Synchronous Motor and Lumped load 8

9 Date: Experiment-1 TRIPPING CHARACTERISTICS OF FUSE & MCB AIM:To study the Time current characteristics of FUSE and MCB for given network. SOFTWARE USED: ETAP Software THEORY: Time Current Characteristics of protective devices: Time is plotted on the vertical axis and current is plotted on the horizontal axis of all timecurrent characteristic curves. Log-log type graph paper is used to cover a wide range of times and currents. Characteristic curves are arranged so that the area below and to the left of the curves indicate points of "no operation, and the area above and to the right of the curves indicate points of "operation." The procedure involved in applying characteristic curves to a coordination study is to select or set the various protective devices so that the characteristic curves of series devices from the load to the source are located on a composite time-current graph from left to right with no overlapping of curves. The result is a set of coordinated curves on one composite time current graph. The MCB has some advantages compared to fuse 1. It automatically switches off the electrical circuit during abnormal condition of the network means in over load condition as well as faulty condition. The fuse does not sense but miniature circuit breaker does it in more reliable way. MCB is much more sensitive to over current than fuse. 2. Another advantage is, as the switch operating knob comes at its off position during tripping, the faulty zone of the electrical circuit can easily be identified. But in case of fuse, fuse wire should be checked by opening fuse grip or cutout from fuse base, for confirming the blow of fuse wire. 3. Quick restoration of supply can not be possible in case of fuse as because fuses have to be rewirable or replaced for restoring the supply. But in the case of MCB, quick restoration is possible by just switching on operation. 9

10 4. Handling MCB is more electrically safe than fuse. Because of to many advantages of MCB over fuse units, in modern low voltage electrical network, miniature circuit breaker is mostly used instead of backdated fuse unit. Only one disadvantage of MCB over fuse is that this system is more costlier than fuse unit system. Working Principle Miniature Circuit Breaker There are two arrangement of operation of miniature circuit breaker. One due to thermal effect of over current and other due to electromagnetic effect of over current. The thermal operation of miniature circuit breaker is achieved with a bimetallic strip whenever continuous over current flows through MCB, the bimetallic strip is heated and deflects by bending. This deflection of bimetallic strip releases mechanical latch. As this mechanical latch is attached with operating mechanism, it causes to open the miniature circuit breaker contacts. But during short circuit condition, sudden rising of current, causes electromechanical displacement of plunger associated with tripping coil or solenoid of MCB. The plunger strikes the trip lever causing immediate release of latch mechanism consequently open the circuit breaker contacts. 10

11 PARAMETERS: SI.NO COMPONENT MANUFACTURER RATING OTHER PARAMETERS TO BE SPECIFIED 1. Power Grid MVASc X/R=5 2. Buses Bus1 Bus2 Bus kV 12.47KV 12.47KV 3. CT1 CT2 ABB 300:5 300: OCR Cable Fuse Transformer GE Multilin 735/737 (Lib-220) ICEA Seimens A KV 1000KVA Pri-12.47KV Sec-0.48KV POWER- 1000KVA 1.Add circuit breaker. 2.choose any type of relay TCC KA Phase length-100 Tolerance-0 Impedance typical Z&X/R ratio 8. CB1 CB2 Siemen Allis LA-1600A Siemens Static-Trip III 9. Synchronous motor Lib 1HP 0.46KV(MTR) 2HP 0.46KV 11

12 ETAP NETWORK DIAGRAM: PROCEDURE: Open the ETAP software in the pc. On the right hand side of the software equipments are present. Construct the circuit as shown in circuit diagram in Edit mode tab. Click on the star protective devices icon present at the top of the edit mode. Then select a part of the circuit and click on the star view at right. The graphs are obtained and studied 12

13 ETAP Simulation diagram: 13

14 TIME CURRENT CHARACTERISTIC CURVES: 14

15 Result: Signature of the faculty 15

16 Date: Experiment-2 CHARACTERISTICS OF OVER CURRENT RELAY FOR PHASE FAULT AIM: To study the characteristics of over current realy for phase fault APPARATUS: Over current relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 2A) Ammeter (0-2A) Rheostat (110Ω, 1.8A) THEORY: The function of a relay is to detect abnormal conditions in the system and to initiate through appropriate circuit breakers the disconnection of faulty circuits so that interference with the general supply is minimized. Relays are of many types. Some depend on the operation of an armature by some form of electromagnet. A very large number of relays operate on the induction principle. When a relay operates it closes contacts in the trip circuit.the passage of current in the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker, disconnecting the faulty system. OVER CURRENT PROTECTION: The protective relaying which responds to a rise in current flowing through the protected element over a pre-determined value is called 'overcurrent protection' and the relays used for this purpose are known as overcurrent relays. Earth fault protection can be provided with normal overcurrent relays, if the minimum earth fault current is sufficient in magnitude. The design of a comprehensive protection scheme in a power system requires the detailed study of time-current characteristics of the various relays used in the scheme. Thus it is necessary to obtain the time current characteristics of these relays. The overcurrent relay works on the induction principle. The moving system consists of an aluminum disc fixed on a vertical shaft and rotating on two jeweled bearings between the poles of an electromagnet and a damping magnet. The winding of the electromagnet is provided with seven taps (generally0, which are brought on the front panel, and the required tap is selected by a push-in -type plug. The pick-up current setting can thus be 16

17 varied by the use of such plug multiplier setting. The operating time of all overcurrent relays tends to become asymptotic to a definite minimum value with increase in the value of current. This is an inherent property of the electromagnetic relays due to saturation of the magnetic circuit. By varying the point of saturation, different characteristics can be obtained and these are 1. Definite time 2. Inverse Definite Minimum Time (IDMT) 3. Very Inverse 4. Extremely Inverse Principle: Overcurrent protection is practical application of magnitude relays since it picks up when the magnitude of current exceeds some value (setting value). Overcurrent relays can be used to protect practically any power system elements, i.e. transmission lines, transformers, generators, or motors. As an example, a radial transmission line can be used. For a fault within the zone of protection, the fault current is smallest at the end of the line and greatest at the relay end. If the minimum fault current possible within the zone of protection is greater than the maximum possible load current, it would be possible to define the operating principle as follows: Where I is the current in the relay and is Ip the pickup setting of the relay. Instantaneous overcurrent relays : Its operation criterion is only current magnitude (without time delay). This type is applied to the outgoing feeders. Characteristics of instantaneous over current Relay 17

18 Definite Time Overcurrent Relays : In this type, two conditions must be satisfied for operation (tripping), current must exceed the setting value and the fault must be continuous at least a time equal to time setting of the relay. Modern relays may contain more than one stage of protection each stage includes each own current and time setting. Characteristics of definite time over current Relay Definite time overcurrent relay is the most applied type of over current. It is used as: 1. Back up protection of distance relay of transmission line with time delay. 2. Back up protection to differential relay of power transformer with time delay. 3. Main protection to outgoing feeders and bus couplers with adjustable time delay setting. Inverse Time Overcurrent Relays In this type of relays, operating time is inversely changed with current. So, high current will operate overcurrent relay faster than lower ones. There are standard inverse, very inverse and extremely inverse types Characteristics of inverse time over current Relay 18

19 CIRCUIT DIAGRAM: Experimental procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the pick-up value of the current marked 1 A(100 % f. l current) 3. Set the Time Multiplier Setting (TMS) initially at Adjust the load current to about 1.8 times the f.l current. Record the time taken for the overload condition. 5. Vary the value of the load current in steps and record the time taken for the operation of the relay in each case with the help of the timer. 6. Repeat steps 5 and 6 for TMS values of 0.2, 0.4,0.6 and Repeat the above experiment with different pick up current values using the plug setting bridge. 19

20 Tabular form-range of Experimental values: Pick-up current = 1 Amps IP - Current setting: 10% = 0.1A S.No Current(A) Current(A) times the Tp- Operating time in sec. for TMS of plug setting multiplier Tabular form-practical values: Pick-up current = 1 Amps IP - Current setting :10% S.No Current(A) Current(A) times the Tp- Operating time in sec. for TMS of plug setting multiplier

21 TIME(Sec) Power Systems Lab Model graph-characteristics of over current relay PSM TMS-1 TMS-0.8 TMS

22 22

23 RESULT: Signature of the faculty 23

24 Date: Experiment-3 CHARACTERISTICS OF OVER CURRENT RELAY FOR EARTH FAULT Aim: To study the characteristics of over current relay for earth fault Apparatus: Earth Fault relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 2A) Ammeter (0-2A) Rheostat (110Ω, 1.8A) Theory: The function of a relay is to detect abnormal conditions in the system and to initiate through appropriate circuit breakers the disconnection of faulty circuits so that interference with the general supply is minimized. Relays are of many types. Some depend on the operation of an armature by some form of electromagnet. A very large number of relays operate on the induction principle. When a relay operates it closes contacts in the trip circuit.the passage of current in the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker, disconnecting the faulty system. Overcurrent Protection The protective relaying which responds to a rise in current flowing through the protected element over a pre-determined value is called 'overcurrent protection' and the relays used for this purpose are known as overcurrent relays. Earth fault protection can be provided with normal overcurrent relays, if the minimum earth fault current is sufficient in magnitude. The design of a comprehensive protection scheme in a power system requires the detailed study of time-current characteristics of the various relays used in the scheme. Thus it is necessary to obtain the time current characteristics of these relays. The overcurrent relay works on the induction principle. The moving system consists of an aluminum disc fixed on a vertical shaft and rotating on two jeweled bearings between the poles of an electromagnet and a damping magnet. The winding of the electromagnet is provided with seven taps (generally0, which are brought on the front panel, and the required tap is selected by a push-in -type plug. The pick-up current setting can thus be 24

25 varied by the use of such plug multiplier setting. The operating time of all overcurrent relays tends to become asymptotic to a definite minimum value with increase in the value of current. This is an inherent property of the electromagnetic relays due to saturation of the magnetic circuit. By varying the point of saturation, different characteristics can be obtained and these are 1. Definite time 2. Inverse Definite Minimum Time (IDMT) 3. Very Inverse 4. Extremely Inverse Principle: Overcurrent protection is practical application of magnitude relays since it picks up when the magnitude of current exceeds some value (setting value). Overcurrent relays can be used to protect practically any power system elements, i.e. transmission lines, transformers, generators, or motors. As an example, a radial transmission line can be used. For a fault within the zone of protection, the fault current is smallest at the end of the line and greatest at the relay end. If the minimum fault current possible within the zone of protection is greater than the maximum possible load current, it would be possible to define the operating principle as follows: Where I is the current in the relay and is Ip the pickup setting of the relay. Protection against earth faults can be obtained by using a relay that responds only to the residual current of the system, since a residual component exists only when fault current flows to earth. The earth-fault relay is therefore completely unaffected by load currents, whether balanced or not, and can be given a setting which is limited only by the design of the equipment and the presence of unbalanced leakage or capacitance currents to earth. This is an important consideration if settings of only a few percent of system rating are considered, since leakage currents may produce a residual quantity of this order. 25

26 Circuit Diagram: Experimental procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the pick-up value of the current marked 1 A(100 % f. l current) 3. Set the Time Multiplier Setting (TMS) initially at Adjust the load current to about 1.8 times the f.l current. Record the time taken for the overload condition. 5. Vary the value of the load current in steps and record the time taken for the operation of the relay in each case with the help of the timer. 6. Repeat steps 5 and 6 for TMS values of 0.2, 0.4,0.6 and Repeat the above experiment with different pick up current values using the plug setting bridge. 26

27 Tabular form-range of Experimental values: Pick-up current = 1 Amps IE - Current setting: 10% = 0.1A S.No Current(A) Current(A) times the plug setting multiplier Tp- Operating time in sec. for TMS of Tabular form-practical values: Pick-up current = 1 Amps IE - Current setting : S.No Current(A) Current(A) times the plug setting multiplier 1 Tp- Operating time in sec. for TMS of

28 TIME(Sec) Power Systems Lab Model graph-characteristics of Earth fault relay PSM TMS-1 TMS-0.8 TMS

29 29

30 RESULT: Signature of the faculty 30

31 Date: Experiment-4 CHARACTERISTICS OF INDUCTION DISC TYPE RELAY Aim: To study the characteristics of induction disc type relay Apparatus: Induction disc type relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 20A) Ammeter (0-20A) Rheostat (110Ω, 1.8A) Theory: The function of a relay is to detect abnormal conditions in the system and to initiate through appropriate circuit breakers the disconnection of faulty circuits so that interference with the general supply is minimized. Relays are of many types. Some depend on the operation of an armature by some form of electromagnet. A very large number of relays operate on the induction principle. When a relay operates it closes contacts in the trip circuit.the passage of current in the coil of the trip circuit actuates the plunger, which causes operation of the circuit breaker, disconnecting the faulty system. Induction disc type relay: The electromagnetic induction disc relay is frequently used where the time of relay operation should depend upon the amount of an overcurrent. The relay is essentially a small induction motor. This is probably the most widely used protective relay in the industry. It starts to turn when the current exceeds a (previously selected) threshold current, and rotates faster as the current increases. This relay has one set of stationary contacts and one set which moves as the disc turns. The distance which the disc must travel to close the contacts is adjusted by setting the position of the time dial control. The magnitude of current which initiates disc movement is set by the choice of the tap on the current coil. The results is that relay contact operation is 31

32 dependent upon the tap and the time dial settings. The relay timing can be varied from a few cycles to as long as 30 seconds. An induction relay works only with alternating current. It consists of an electromagnetic system which operates on a moving conductor, generally in the form of a disc or cup, and functions through the interaction of electromagnetic fluxes with the parasitic Fault currents which are induced in the rotor by these fluxes. These two fluxes, which are mutually displaced both in angle and in position, produce a torque. Induction disc type Relay Basic torque/current equation T= Κ1.Φ1.Φ2.sin θ Where Φ1 and Φ2 are the interacting fluxes and θ is the phase angle between Φ1 and Φ2. It should be noted that the torque is a maximum when the fluxes are out of phase by 90º, and zero when they are in phase. The relay's primary winding is supplied from the power systems current transformer via a plug bridge, which is called the plug setting multiplier (psm). Usually seven equally spaced tappings or operating bands determine the relays sensitivity. The primary winding is located on the upper electromagnet. The secondary winding has connections on the upper electromagnet that are energised from the primary winding and connected to the lower electromagnet. Once the upper and lower electromagnets are energised they produce eddy currents that are induced onto the metal disc and flow through the flux paths. This relationship of eddy currents and fluxes creates torque proportional to the input current of the primary winding, due to the two flux paths been 32

33 out of phase by 90.A restraining spring forces the disk to rotate in the direction that opens the trip contacts while current creates operating torque to close the contacts. The net positive torque closes the contacts. The IPU relay setting fixes the value of the pickup current. When the current applied to the relay equals the pickup current, the contact closing torque just equals the restraining torque and the disk will not move regardless of its position. If the applied current increases above the pickup current, the disk will begin to rotate so that the trip contacts come closer together Wiring Diagram: 33

34 Experimental procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the pick-up value of the current as 2.5A 3. Adjust the load current to about 1.3 times the full load current. Record the time taken for the overload condition. 4. Vary the value of the load current in steps and record the time taken for the operation of the relay in each case with the help of the timer. 5. Repeat the above experiment with different pick up current values. Tabular form-range of Experimental values: Pick-up current = 2.5 Amps S.No Current(A) 1 2 Current(A) times the plug setting multiplier Operating Time in seconds

35 TIME(Sec) Power Systems Lab Model graph :Characteristics of induction disc type relay PSM TMS-1 TMS-0.8 TMS

36 RESULT: Signature of the faculty 36

37 Date: CHARACTERISTICS OF OVER LOAD RELAY Experiment-5 AIM:To study the characteristics of over load relay. SOFTWARE USED: ETAP Software Theory: Overload relays protect a motor by sensing the current going to the motor. Many of these use small heaters, often bi-metallic elements that bend when warmed by current to the motor.when current is too high for too long, heaters open the relay contacts carrying current to the coil of the contactor. When the contacts open, the contactor coil de-energizes, which results in an interruption of the main power to the motor. These contacts do not affect control power. Overload relays and their heaters belong to one of three classes, depending on the time it takes for them to respond to an overload in the motor. The overload relay itself will have markings to indicate which class it belongs to. These include Class 10, 20, and 30. The class number indicates the response time (in seconds). An unmarked overload relay is always Class 20. Typical NEMA-rated overload relays are Class 20, but you can adjust many of them about 15% above or below their normal trip current. IEC relays are usually Class 10, and you can usually adjust them to 50% above their normal trip current. 37

38 PARAMETERS: SI.NO COMPONENT MANUFACTURER RATING OTHER PARAMETERS TO BE SPECIFIED 1. Power Grid MVASc X/R=5 2. Buses Bus1 Bus2 Bus kV 12.47KV 12.47KV 3. CT1 CT2 ABB 300:5 300: OCR Cable Fuse Transformer GE Multilin 735/737 (Lib-220) ICEA Seimens A KV 1000KVA Pri-12.47KV Sec-0.48KV POWER- 1000KVA 1.Add circuit breaker. 2.choose any type of relay TCC KA Phase length-100 Tolerance-0 Impedance typical Z&X/R ratio 8. CB1 CB2 Siemen Allis LA-1600A Siemens Static-Trip III Induction motor Thermal Over load Heater MTR Lib 1HP 0.46KV General Electric 2HP 0.46KV 0.48 kv 38

39 ETAP Network Diagram: PROCEDURE: Open the ETAP software in the pc. On the right hand side of the software equipments are present. Construct the circuit as shown in circuit diagram in Edit mode tab. Click on the star protective devices icon present at the top of the edit mode. Then select a part of the circuit and click on the star view at right. The graphs are obtained and studied. 39

40 TIME CURRENT CHARACTERISTIC CURVES: 40

41 RESULT: Signature of the faculty 41

42 Date: Experiment-6 TESTING OF DIFFERENTIAL RELAY Aim: To study the operation of Differential Relay Apparatus: Differential Relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 2A)-2 No.s Ammeter (0-2A)-2 No.s Rheostat (110Ω, 1.8A) -2 No.s Theory: The relay which is used to checks the difference between the output and input currents for power system current in known as differential relay. The difference amongst the currents may also be in phase angle or in magnitude or in eachthe angle and magnitude variations must be zero. In case there's a difference which difference go beyond some value, the relay can work and interconnected electrical fuse can disconnect. Principle Operation of differential relay: Consider a power transformer with transformation magnitude (ratio) relation 1:1 and (Y/Y) connection and therefore the CT1 and CT2 ensure a similar transformation magnitude relation as 42

43 shown. The current flows within the primary side and secondary side of power transformer are equal, presumptuous ideal power transformer. The secondary current I1 and I2 are same in magnitude and reverse in direction. Therefore, the net current within the differential coil is nil at load situation (without any fault), and therefore the relay won't operate. External Fault Condition in Differential Relay: Assigning the previous one the power transformer with an external fault F is shown in figure. During this case the 2 currents I1, and I2 can increase to terribly high magnitudes values however there's no modification in phase angle. Hence, net current within the differential coil continues to be zero and therefore the relay won't operate. Internal Fault Condition in Differential Relay: 43

44 An internal fault F is shown in this figure. Now, there are 2 anticipated conditions: There s other supply to feed the fault thus I2P includes a nonzero value Idiff = I1S + I2S which can be terribly high and sufficient to function the differential relay. Radial system, I2P = 0. So, Idiff = I1S and additionally the relay can work and disconnect the breaker. Circuit Diagram Procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the Bias current and current setting. 3. With zero bias current (ammeter A2=0), inject operate current in to phase A. When the relay operates, shown bythe LED "Trip" illuminating, record the value of the current indicated on ammeter A1. 4. Repeat the test with increasing bias currents up to 2times the relay rating. 5. Record the results in Table. 44

45 Model Tabular Form: Initial settings Bias settings Bias current Ammeter A2 multiples of rated current in Operate current, ammeter A1 Amps 10% 10% % 20% % 30% % 40% % 50% % % Tabular form :practical readings Intial settings Ammeter A2 multiples of rated current in 10% 20% 30% 40% 50% Operate current, ammeter A1 Amps - 45

46 RESULT: Signature of the faculty 46

47 Date: Experiment-7 MODEL OF A TRANSMISSION LINE WITH LUMPED PARAMETERS AIM:To run the load flow for a given transmission line network SOFTWARE USED: ETAP Software Theory: The power-flow study, or load-flow study, is a numerical analysis of the flow of electric power in an interconnected system. A power-flow study usually uses simplified notation such as a oneline diagram and per-unit system, and focuses on various aspects of AC power parameters, such as voltages, voltage angles, real power and reactive power. It analyzes the power systems in normal steady-state operation. Power-flow or load-flow studies are important for planning future expansion of power systems as well as in determining the best operation of existing systems. The principal information obtained from the power-flow study is the magnitude and phase angle of the voltage at each bus, and the real and reactive power flowing in each line. The goal of a power-flow study is to obtain complete voltage angle and magnitude information for each bus in a power system for specified load and generator real power and voltage conditions. [2] Once this information is known, real and reactive power flow on each branch as well as generator reactive power output can be analytically determined. Due to the nonlinear nature of this problem, numerical methods are employed to obtain a solution that is within an acceptable tolerance. The solution to the power-flow problem begins with identifying the known and unknown variables in the system. The known and unknown variables are dependent on the type of bus. A bus without any generators connected to it is called a Load Bus. With one exception, a bus with at least one generator connected to it is called a Generator Bus. The exception is one arbitrarilyselected bus that has a generator. This bus is referred to as the slack bus. 47

48 PARAMETERS: SI.NO COMPONENT MANUFACTURER RATING OTHER PARAMETERS TO BE SPECIFIED 1. Buses Bus1 Bus2 Bus KV 100KV 100KV 2. Impedances Z Percentage base KV-100kv R=2,X=4,Y=0 3. Z Percentage base KV-100kv R=1,X=3,Y= Z12 Sych.Generator Percentage base KV-100kv 100KV, 250 MW R=1.25,X=2.5,Y=0 Reference or Slack bus 6. Sych.Generator KV, 250 MW Generator bus Var limits:200& Lumped Load MW,471MVA Conventional model, Rated 100kv 48

49 ETAP Network Diagram: Transmission line model PROCEDURE: Open the ETAP software in the pc. On the right hand side of the software equipments are present. Construct the circuit as shown in circuit diagram in Edit mode tab. Run the load flow analysis for a given network. Get the power flow values at each bus. And get the results through load flow result analyser 49

50 SIMULATION RESULTS: 50

51 RESULT: Signature of the faculty 51

52 Date: Experiment-8 CHARACTERISTICS OF OVER VOLTAGE RELAY AIM: To study the characteristics of over voltage relay APPARATUS: Over voltage relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 2A) Voltmeter (0-200v) Rheostat (110Ω, 1.8A) THEORY: OVERVOLTAGE PROTECTION The function of a relay is to detect abnormal conditions in the system and to initiate through appropriate circuit breakers the disconnection of faulty circuits so that interference with the general supply is minimized. There are always a chance of suffering an electrical power system from abnormal over voltages. These abnormal over voltages may be caused due to various reason such as, sudden interruption of heavy load, lightening impulses, switching impulses etc. These over voltage stresses may damage insulation of various equipments and insulators of the power system. Although, all the over voltage stresses are not strong enough to damage insulation of system, but still these over voltages also to be avoided to ensure the smooth operation of electrical power system. These all types of destructive and non destructive abnormal over voltages are eliminated from the system by means of overvoltage protection. For generator protection an overvoltage relay is used to detect failure in voltage regulation. For transformers and transmission lines, overvoltage protection is sometimes used to detect excessive voltages Principle: An overvoltage relay is one that operates when input voltage exceeds a predetermined(pick up) value.over voltage relays must be instantaneous or time-delayed devices.in order to set a time overvoltage relay,pickup voltage and time dial need to be specified and VT ration needs to be documented.time overvoltage relays start to time out every time input voltage exceeds the 52

53 setpoint.overvoltage relays complete their function and close the output contact when the duration of the overvoltage exceeds the time delay described by the time voltage curve. Inverse time characteristics of overvoltage relay The inverse characteristic for overvoltage V>, is defined by the following equation: where: t = operating time in seconds TMS = time multiplier setting V = applied input voltage Vs = relay setting voltage NOTE: this equation is valid for V> Vs 53

54 Circuit Diagram: Experimental procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the pick-up value of the voltage. 3. Set the Time Multiplier Setting (TMS) initially at Adjust the voltage from 1.2 to 1.8 times the pick up voltage step wise. Record the time taken for the overvoltage condition. 5. Vary the value of the over voltage in steps and record the time taken for the operation of the relay in each case with the help of the timer. 6. Repeat steps 4 and 5 for TMS values of 0.8,0.6,0.5, Repeat the above experiment with different pick up voltage values using the plug setting bridge. 54

55 Tabular form Pick-up voltage = volts S.No Voltage(v) Voltage(v) times the plug setting multiplier Tp- Operating time in sec. for TMS of Model graph-characteristics of over voltage relay : 55

56 56

57 RESULT: Signature of the faculty 57

58 Date: Experiment-9 CHARACTERISTICS OF UNDER VOLTAGE RELAY AIM: To study the characteristics of under voltage relay APPARATUS: Under voltage relay Auxiliary supply kit (Step-down Transformer-230/24V, Bridge rectifier, filter) Auto transformer (0-230v, 2A) Voltmeter (0-200v) Rheostat (110Ω, 1.8A) THEORY: UNDER VOLTAGE PROTECTION The function of a relay is to detect abnormal conditions in the system and to initiate through appropriate circuit breakers the disconnection of faulty circuits so that interference with the general supply is minimized. There are always a chance of suffering an electrical power system from abnormal under voltages. An undervoltage protection is used to disconnect motors at low system voltage to prevent problems with inrush at system voltage recovery. Single-phase versions connected phase-phase are used for asynchronous motors, whereas measuring of positive sequence voltage is used for synchronous motors. Principle: An undervoltage relay is one that operates when input voltage drops below a predetermined value(dropout value).undervoltage relays are usually instantaneous devices.if time delays are needed,timers,initiated on undervoltage relay,are utilized.undervoltage relays should complete their function every time input voltage drops below the setpoint.the dropout voltage needs to be specified and VT ratio needs to be documented.a typical time voltage curve for undervoltage relay is shown below. 58

59 Characteristics of under voltage relay The inverse characteristic for undervoltage V<, is defined by the following equation: where: t = operating time in seconds TMS = time multiplier setting V = applied input voltage Vs = relay setting voltage NOTE: this equation is valid for Vs>V 59

60 Circuit Diagram: Experimental procedure: 1. Study the construction of the relay and identify the various parts. 2. Set the drop out value of the voltage. 3. Set the Time Multiplier Setting (TMS) initially at Adjust the voltage from 0.5 to 0.9 times the dropout voltage step wise. Record the time taken for the under voltage condition. 5. Vary the value of the under voltage in steps and record the time taken for the operation of the relay in each case with the help of the timer. 6. Repeat steps 4 and 5 for TMS values of 0.8,0.6,0.5, Repeat the above experiment with different dropout voltage values using the plug setting bridge. 60

61 Tabular form Drop-out voltage = volts S.No Voltage(v) Voltage(v) times the plug setting multiplier Tp- Operating time in sec. for TMS of Model graph- Characteristics of under voltage relay : 61

62 62

63 RESULT: Signature of the faculty 63

64 Date: ZONES PROTECTION Experiment-10 AIM:To study the zones protection characteristics of Transformer and Motor zone of a given network. SOFTWARE USED: ETAP Software THEORY: The protected zone is that part of a power system guarded by a certain protection and usually contains one or at the most two elements of the power system. For a non-unit scheme, the zone lies between the current transformers and the point or points on the protected circuit beyond which the system is unable to detect the presence of a fault which is shown in figure. For a unit scheme, the zone lies between the two or several sets of current transformers and the point or points which together with the relays constitute the protective system A power system is composed of number of sections (equipments) such as transformer, motor, generator, bus bar and transmission line. These sections are protected by protective relaying systems comprising of Instrument Transformers, protective relays, circuit breakers (CB s) and communication equipment.these are called zones of protection.the protective system are planned in such a way that the entire power system is collectively provided by them and thus no part of the system is left unprotected In case of fault occurring on a section, its associated protective relays should detect the fault and issue trip signals to open their associated CB s to isolate the faulted section from the rest of the power system in order to avoid further damage to the power system.when a fault occurs, the protection scheme is required to trip only those circuit breakers whose operation is required to isolate the fault. This property of selective tripping is also called 'discrimination' and is achieved by two general methods: 1. Time Grading Protection systems in successive zones are arranged to operate in times that are graded through the sequence of equipments so that upon the occurrence of a fault, although a number of protection equipments respond, only those relevant to the faulty zone complete the tripping function. The others make incomplete operations and then reset. The speed of 64

65 response will often depend on the severity of the fault, and will generally be slower than for a unit system. 2. Unit Systems It is possible to design protection systems that respond only to fault conditions occurring within a clearly defined zone. This type of protection system is known as 'unit protection'. Certain types of unit protection are known by specific names, e.g. restricted earth fault and differential protection. Unit protection can be applied throughout a power system and, since it does not involve time grading, is relatively fast in operation. The speed of response is substantially independent of fault severity. Unit protection usually involves comparison of quantities at the boundaries of the protected zone as defined by the locations of the current transformers Transformer Protection: The primary objective of the Transformer Protection is to detect internal faults in the transformer with a high degree of sensitivity and cause subsequent deenergisation and, at the same time be immune to faults external to the transformer i.e. through faults. Sensitive detection and deenergisation enables the fault damage and hence necessary repairs to be limited. Motor Protection: The abnormalities in motor or motor faults may appear due to mainly two reasons 1.Conditions imposed by the external power supply network, 2.Internal faults, either in the motor or in the driven plant. Unbalanced supply voltages, under-voltage, reversed phase sequence and loss of synchronism (in the case of synchronous motor) come under former category. The later category includes bearing failures, stator winding faults, motor earth faults and overload etc. The motor characteristics must be very carefully considered in selecting the right motor protection scheme. 65

66 PARAMETERS: SI.NO COMPONENT MANUFACTURER RATING OTHER PARAMETERS TO BE SPECIFIED 1. Power Grid MVASc X/R =5 2. Buses Bus 1 Bus 2 Bus 4 Bus kV 0.48kV 0.48kV 0.48kV HVCB ABB 15.5kV In TCC kv= Current Transformer / Fuses Fuse 1 Fuse 2 General Electric General Electric 12kV 6.25Kv LVCB CB1 CB2 CB3 CB4 ABB ABB ABB ABB 5kV 3.3kV 2kV 1.01kV In TCC kv=13.5 In TCC kv=0.48 In TCC kv=0.48 In TCC kv=0.48 Synchronous HP Motor 7. Lumped Load kVA Over Current Relay ABB )Choose any type of relay in OCR 2) Add CB in Output 9. Transformer kVA Impedance: Typical Z and X/R 10. In-Line Relay Allen Bradley Cable ICEA (220 in library) 100ft Impedance: R=5.75 X=

67 ETAP Network Diagram: Procedure: Construct the above network diagram in ETAP software Specify the ratings of each device as given in the parameter table In star protective devices select the zone of protection and get the time current characteristics for individual Transformer, Motor, Bus Bar zones 67

68 Characteristics of Transformer, Motor and Bus Bar zones: 68

69 RESULT: Signature of the faculty 69

70 Date: Experiment-11 SHORT CIRCUIT ANALYSIS AIM: To perform short circuit analysis to a given network or transmission line. SOFTWARE REQUIRED: ETAP Theory: A short circuit analysis helps us to ensure that equipment are protected by establishing proper interrupting rating of protective devices on power systems and is required to determine the switch gear ratings and relay ratings.the short circuit calculations must be maintained and periodically updated to protect the equipment.the short circuit in the system cannot always be prevented; its effect can only be reduced by considering its consequences on the system at the time of planning and design stage. The system components, transformers, cables, switchgears, protection equipments etc must be designed and selected to havefault withstand capability to match system fault current rating. The objectives of performing sort circuit study are: To prepare basis for the selection of the interrupting equipment and also to verify adequacy of existing interrupting equipment; To determine the system protective device settings; To coordinate protective devices To determine the effects of the fault currents on various system components during the time the fault persists; Conceptualization, design and refinement of system layout, neutral grounding, and substation grounding; To ascertain the minimum short-circuit current. Short Circuit analysis is required to ensure that existing and new equipment ratings are adequate to withstand the available short circuit energy available at each point in the electrical system. A Short Circuit Analysis will help to ensure that personnel and equipment are protected by establishing proper interrupting ratings of protective devices (circuit breaker and fuses). If an electrical fault exceeds the interrupting rating of the protective device, the consequences can be devastating. It can be a serious threat to human life and is capable of causing injury, extensive equipment damage, and costly downtime. On large systems, short circuit analysis is required to determine both the switchgear ratings and the relay settings. No substation equipment can be 70

71 installed without knowledge of the complete short circuit values for the entire power distribution system. The short circuit calculations must be maintained and periodically updated to protect the equipment and the lives. It is not safe to assume that new equipment is properly rated. Benefits of a Short Circuit Analysis Performing a Short Circuit Study provides the following benefits: Reduces the risk a facility could face and help avoid catastrophic losses. Increases the safety and reliability of the power system and related equipment. Evaluates the application of protective devices and equipment. Identifies problem areas in the system. Identifies recommended solutions to existing problems. PARAMETERS: SI.NO COMPONENT MANUFRACTURER RATING OTHER PARAMETERS TO BE SPECIFIED 1. Power Grid MVASc X/R=5 2. Buses Bus 1 Bus 2 Bus kV 12.47kV 0.48kV HVCB ABB 12kV In TCC kv = Transformer MVA Choose typical Z & X/R 5. Fuse General Electric 6.25kV LVCB ABB 1.01kV In TCC kv= Synchronous HP Motor 8. Cable ICEA(220 in library) 100ft Impedance: R=5.75 X=

72 Circuit Diagram: Procedure: Construct the above circuit diagram in ETAP software. Specify the ratings of the parameters as given in the table. Perform the short circuit analysis for a given network by inserting fault at desired location. Get the fault current values after simulation 72