Implementation of Transformer Protection by Intelligent Electronic

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Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50

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RESEARCH ARTICLE

OPEN ACCESS

Implementation of Transformer Protection Electronic Device for Different Faults

by

Intelligent

Y V Aruna, Beena S (Assistant Professors, Department of EEE, Cambridge Institute of Technology, Bangalore-36)

ABSTRACT Protection of power system equipments was traditionally done by using electromagnetic relay, static relays, and numerical relays. At present the microprocessor based relays are replacing the old Electromagnetic relays because of their high level accuracy and fast operation. RET670(Transformer protection relay ), an IED (INTELLIGENT ELECTRONIC DEVICE) provides fast and selective protection, monitoring, and control of all types of transformer. The configured IED is tested under different fault conditions simulated by using mobile test kit to ensure IED’s reliable operation on site. With preconfigured algorithms, the IED will automatically reconfigure the network in case of a fault, and a service restoration is carried out within milliseconds by giving trip signal to the corresponding Circuit breakers. On receiving the trip signal the circuit breaker operates providing quicker isolation of transformers under the fault condition. This enables to have a complete and an adequate protection to the specified power transformer. Keywords – Transformer protection, IED, RET670

I. INTRODUCTION An Intelligent Electronic Device (IED) is a term used in the electric power industry to describe microprocessor-based controllers of power system equipment, such as circuit breakers and transformers. 1. RET670 Introduction RET670 provides fast and selective protection, monitoring and control for two- and three-winding transformers, autotransformers, generatortransformer units, phase shifting transformers, special railway transformers and shunt reactors. The transformer IED is designed to operate correctly over a wide frequency range in order to accommodate power system frequency variations during disturbances and generator start-up and shut-down as in Fig.1 A very fast differential protection function with settable CT ratio matching and vector group compensation makes this IED the ideal solution even for the most demanding applications. Since RET670 has very low requirements on the main CTs, no interposing CTs are required. It is suitable for differential applications with multi-breaker arrangements with up to six restraint CT inputs. The differential protection function is provided with 2nd harmonic and wave-block restraint features to avoid tripping for magnetizing inrush current, and 5 th harmonic restraint to avoid tripping for over excitation. The differential function offers a high sensitivity for low-level internal faults. The unique and innovative sensitive differential protection feature of the RET670 provides the best possible

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coverage for winding internal turn-to-turn faults, based on the theory of symmetrical components.

Fig.1: Internal Conventions of the directionality in the IED. Tripping from pressure relief/Buchholz and temperature devices can be done through the transformer IED where pulsing, lock-out contact output and so on, is performed. The binary inputs are heavily stabilized against disturbance to prevent incorrect operations at for example dc system capacitive discharges or DC earth faults. The transformer IED can also be provided with a full control and interlocking functionality including Synchrocheck function to allow integration of the main and/or a local back-up control. Out of Step function is available to separate power system sections close to electrical centre at occurring out of step. RET670 can be used in applications with the IEC 61850-9-2LE process bus with up to two Merging Units (MU) as in fig1.1. Each MU has eight analogue channels, normally four current and four voltages. Conventional and Merging Unit channels can be mixed freely in your application. 45 | P a g e

Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50 1.1RET 670 hardware

Fig.1.1 Rear side view of RET670 1.1.1 Available functions of RET670 Differential protection, Distance protection, Current protection, Voltage protection, Frequency protection, Multipurpose protection, Control, Logic, Metering, Monitoring, Station communication etc are the functions carried out by RET670.

II. Block diagram The block diagram in fig.2 shows the implementation of RET670 in transformer protection

Fig.2. Block Diagram of Implementation of RET670 in transformer protection. PCM600 is a connectivity package which provides the means for system products and tools to connect and interact with the IED in an efficient way as well as data to allow efficient engineering of system products. RET670 supports IEC 61850 standard. Configuration of RET670 is done by using signal matrix tool of PCM600, generating a .pcmi file. After establishing communication with RET670 the .pcmi file is uploaded to RET670 and then the parameter setting is done as per the required transformer protection scheme. The CT’s and VT’s will provide the necessary actuating signals to RET670 under the fault condition. Operation of RET670 gives the trip signal to the physical trip coils. When once the IED is configured for different protection schemes the fault voltage is applied by simulating the fault condition through Mobile test kit.) 2.1. Protection and Control Manager (PCM 600) with Connectivity Package for Relay. PCM600 is used to do complete engineering and configuration activities needed for the IEDs. Product www.ijera.com

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type and version specific engineering data needed by PCM600 for protection, control and communication engineering of a particular IED is given in an IED connectivity package. A PC with PCM600 can be connected to any 670 series IED within a station using the Ethernet connection. The connection allows to reading and writing all configuration data needed for proper operation from or to the IED. The IEDs have communication interfaces for protocols and media used for station communication. IED IEC-61850 station communication files can export from PCM600 to station engineering tools for engineering of station communication between bay IEDs and station IEDs. 2.1.1 Tasks of PCM600 in IED engineering process IED engineering management ,Communication engineering, Disturbance record management Service management are the tasks of PCM600 in IED engineering process. 2.1.2 Available Protection The following are the few among the various protections which is provided to the above mentioned transformer by an IED, RET670. i. Two winding differential protection. ii. High impedance differential protection (REF). iii. Over current and Earth fault protection. iv. Over excitation protection. v. Transformer troubles.

III. TWO WINDING DIFFERENTIAL PROTECTION The task of the power transformer differential protection is to determine whether a fault is within the protected zone, or outside the protected zone. The protected zone is delimited by the position of current transformers , and in principle can include more objects than just transformer. If the fault is found to be internal, the faulty power transformer must be quickly disconnected. Thus the IED will always internally measure the currents on all sides of the power transformer with the same reference direction towards the power transformer windings. 3.1 Configuration The functions Transformer differential protection, two-winding (T2WPDIF) is provided with internal CT ratio matching and vector group compensation and when required zero sequence current elimination is also made internally in the software. T2WPDIF is the functional block of two winding differential protection.

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Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50

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Fig 3.1 : Two winding differential protection functional block The configuration of the particular functional block is as shown in fig.3.1. 1 - T2WPDIF Analog inputs from SMAI. 2 - T2WPDIF output signals to SMBO. 3- Outputs which gives the magnitude of fundamental frequency differential currents. 4 - OR logic functional blocks which gives the indication for the presence of 2nd and/or 5 th harmonics. 5 - Output indicating the presence of harmonics. Analog inputs from SMAI AI_HV_1MS = Current reading from the HV side CT obtained from SMAI. AI_LV_1MS = Current reading from the LV side CT obtained from SMAI. Output signals to SMBO DIFF_TRIP _ General differential trip signal. DIFF_RESTRAIN_TRIP = Trip signal under restrained condition. DIFF_UNRESTRAIN_TRIP = Trip signal under unrestrained condition. These trip signals are given to the trip logic and inturn goes to SMBO block. 3.2 Parameter setting This is done in PCM600 by using Parameter Setting Tool (PST) as in table 3.2The specified settings for the parameters of the physical IED for communication channels, CT and VT conversion values of the transformer modules, presentation parameters for local HMI, settings for protection and control functions, number of setting groups etc., are provided by using PST. www.ijera.com

Table 3.2:Parameter Settings of Two winding differential protection 3.3 Transformer Differential Protection Details Description Setting Trans.Rating Trans.Vector Group HV side full load current (pri)

75MVA YY0 197A

HV side full load current (sec)

0.985A

LV side full load current (pri)

1972A

LV side full load current (sec)

0.986A

Diff. Pickup Id>(restraint)

30% of full load current 30% of full load current

Diff. Pickup Id>(restraint)

Diff. Pickup Id>(Unrestraint)

10 Times of full load current

Slope Section 2

40%

Slope Section 3 2nd Harmonic Blocking

80% 15%

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Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50 3.4 Testing procedure When once the complete configuration of an IED is done it is tested for its operation and reliability by using mobile test kit (Doable, Omicron). Differential protection test is classified based on the parameters which are to be checked. They are, i. Pick up test ii. Stability test iii. Slope test 3.4.1. PICK UP TEST Pick up test is done to verify the pick-up value of the relay on both HV and LV side of the transformeras in fig 3.4.1 & 3.4.1.1. For a 75MVA, 220kV/22kV power transformer, HV tripping value = 0.985A We have Idmin = 0.3 Therefore, HV pick up = 0.985 * 0.3 = 0.295A Similarly, LV tripping value = 0.984A We have Idmin = 0.3 Therefore, LV pick up = 0.984 * 0.3 = 0.295A This value of current is injected to the relay for each one of the phases and also for all the three phase by using Doble or omicron test kit and is checked for its reliability. Pick up value of current is been injected to the R phase of HV as in table3.4.1.2 & for LV side as in table 3.4.1.3. As soon as the injected current exceeds 295mA the relay gets tripped.

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3.4.1.2 PICK UP TEST MEASURED IN 1Φ INJECTION Phase INJECTE OPERATIN DIFFERENTIA BIAS D G L CURRENT CURR CURREN TIME(MS) ENT T(HV SIDE) 0.295 26.3 59 59.09 R-PH 0.296 29.3 59 59.18 Y-PH 0.295 27.2 59 59.99 B-PH TABLE 3.4.1.2 PICKUP TEST TABULATION ON HV SIDE

Phase

R-PH Y-PH B-PH TABLE

INJECTED OPERATIN DIFFERENTIA BIAS CURRENT G L CURRENT CURR (LV SIDE) TIME(MS) ENT 0.294 26.1 59 59.29 0.293 29.8 59 59.37 0.295 27.1 59 59.93 3.4.1.3 PICKUP TEST TABULATION ON LV

SIDE

3.4.2. STABILITY TEST This test is done to check the stability of the relay. The transformer under consideration is a Y-Y connected transformer with 0 degree phase shift. An equal current of magnitude 1A is been injected to both HV and LV (when both HV and LV has CTs of same ratio) or current of magnitude equal to the pickup value of HV and LV respectively is been injected. The phase angle of any one of the phases of either HV or LV is changed. When once the current goes out of phase the relay is tripped. This is indicated by indication LED as in the Figure 3.4.2. 75MVA, 220kV/22kV power transformer has different CT ratios of HV and LV is different. Hence, the actuating value of 0.295A is been injected for R phase of HV and LV. Since the phase angles are balanced the relay is under stable state.When once the phase angle of either HV or LV is changed the currents become out of phase issuing a trip.

Table 3.4.1Testing procedure for 1- Phase

Table 3.4.1.1 Testing procedure for 3- Phase

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TABLE 3.4.2 TESTING PROCEDURE FOR STABILITY TEST

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Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50 3.4.2.1 STABILITY TEST RESULTS Phase INJECTED INJECTED CURRENT(HV CURRENT(HV SIDE) SIDE) CURR ENT

PHASE (DEG)

CURR ENT

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3.4.3.2 CALCULATION: STABI LITY

PHASE (DEG)

1A 1800 R-PH 1A 00 0 1A 600 Y-PH 1A 240 0 1A 3000 B-PH 1A 120 Table 3.2.2.1 Stability Test Tabulation

OK OK OK

3.4.3. SLOPE TEST The operate restrain characteristic has three regions. One is non operating region in which the relay won’t operate. Operating region in which the relay operates but conditionally. The unrestrained region in which the relay is operated unconditionally. This operation of the relay is verified by conducting slope test as in fig3.4.3.

3.4.3.3 SLOPE TEST(HV&LV) RESULTS FOR SLOPE-2 Current injected as below:

Current injected at HV side and LV side 2 times of full load current and LV side current is reduced.

3.4.3 Fault currents with DC offset during an external fault Slope = (ΔIoperate/ ΔIrestrain) *100 3.4.3.1 SLOPE TEST(HV&LV) RESULTS FOR SLOPE-1 Current injected as below: Table 3.4.3.3 Slope-2 Test Results 3.4.3.4 CALCULATION:

Current injected at HV side and LV side 2 times of full load current and LV side current is reduced.

IV. APPLICATIONS

Table 3.4.3.1 Slope-1 Test Results www.ijera.com

The protection and control IEDs have many functions included. They included self supervision with internal event list function block provides good supervision of the IED. The fault signals make it easier to analyze and locate a fault. Both hardware and software supervision is included and it is also possible to indicate possible faults through a hardware contact on the power supply module and/ or through the software 49 | P a g e

Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50 communication. Internal events are generated by the built-in supervisory functions. The supervisory functions supervise the status of the various modules in the IED and, in case of failure, a corresponding event is generated. Similarly, when the failure is corrected, a corresponding event is generated.

V. CONCLUSION The Protection Scheme with a particular rating of the transformer has been designed. For that rating of the transformer the CT ratio on primary and secondary sides are calculated and by using that ratio HV and LV tripping values are calculated. Now by using PCM600 Connectivity Package the configuration is done. In PCM600 there are different functional blocks by using those functional blocks the configuration for different faults is done according to the scheme .The harmonic effect and stable operation regions are also taken into consideration. once the configuration is done it is tested using doble or omicron and parameter setting are done. The test involves pickup test, slope test, stability test etc..the protection for different faults have been done. Hence by doing this, the protection system has become more reliable and efficient. The transformer is protected against different faults by Intelligent electronic device.

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Proceedings of EMPD’98 Conference, Vol. 2, pp. 422-425, March 1998. Books: [1] ABB Book, “Transformer Handbook”1LAC 000 010 ABB Power Technologies Management Ltd. Transformers Switzerland. [2] Transformer Book, Tampere University of Technology, (http://www.e-leeh.org/transfor mer/)

References [1]

[2]

[3]

[4]

Å. Carlson, “Power Transformer Design Fundamentals”, ABB Transformers, Ludvika 2000-08-25. A. R. van C. Warrington, Protective Relays: Their Theory and Practice, Volume One and Two, London: Chapman and Hall, 1962 & 1969. ABB Document 1MRK 504 086-UEN, "Technical reference manual, Transformer Protection IED RET 670", Product version: 1.1, ABB Power Technologies AB, Västerås, Sweden, Issued: March 2007 J.A.B. Elston, Methods and Apparatus for Differential Current Measurement in a three-phase power system, U.S. Patent 6,507,184; 2003-01-14.

Journal Papers: [1] A.G. Phadke, J.S. Thorp “A New ComputerBased Flux-Restrained Current-Differential Relay for Power Transformer Protection”, IEEE Transactions on Power Apparatus and Systems Volume PAS-102, Issue 11, pp. 3624-3629, Nov. 1983. [2] K. Tian, P. Liu “Improved Operation of Differential Protection of Power Transformers for Internal Faults Based on Negative Sequence Power”, IEEE www.ijera.com

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Implementation of Transformer Protection by Intelligent Electronic

Y V Aruna Int. Journal of Engineering Research and Applications ISSN : 2248-9622, Vol. 5, Issue 1( Part 4), January 2015, pp.45-50 www.ijera.com RES...

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