6. Testing Overcurrent Protection (50!51!67)

The Relay Testing Handbook Testing Overcurrent Protection (50/51/67)

Chris Werstiuk Professional Engineer Journeyman Power System Electrician Electrical Engineering Technologist

THE RELAY TESTING HANDBOOK: Testing Overcurrent Protection (50/51/67)

THE RELAY TESTING HANDBOOK: Testing Overcurrent Protection (50/51/67)

Chris Werstiuk Professional Engineer Journeyman Power System Electrician Electrical Technologist

Valence Electrical Training Services 7450 w. 52nd Ave, M330 Arvada, CO 80002

www.relaytesting.net

Although the author and publisher have exhaustively researched all sources to ensure the accuracy and completeness of the information contained in this book, neither the authors nor the publisher nor anyone else associated with this publication, shall be liable for any loss, damage, or liability directly or indirectly caused or alleged to be caused by this book. The material contained herein is not intended to provide specific advice or recommendations for any specific situation. Trademark notice product or corporate names may be trademarks or registered trademarks and are used only for identification, an explanation without intent to infringe. The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67) First Edition ISBN: 978-1-934348-12-3 Published By: Valence Electrical Training Services 7450 w. 52nd Ave, M330, Arvada, CO, 80002, U.S.A. Telephone: 303-250-8257 Distributed By: www.relaytesting.net Edited by: One-on-One Book Production, West Hills, CA Cover Art: © James Steidl. Image from BigStockPhoto.com Copyright © 2010 by Valence Electrical Training Services. All rights reserved. Neither this book nor any part may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, microfilming, and recording, or by any information storage and retrieval system, without permission in writing from the publisher. Published in the United States of America

Author’s Note The Relay Testing Handbook was created for relay technicians from all backgrounds and provides the knowledge necessary to test most of the modern protective relays installed over a wide variety of industries. Basic electrical fundamentals, detailed descriptions of protective elements, and generic test plans are combined with examples from real life applications to increase your confidence in any relay testing situation. A wide variety of relay manufacturers and models are used in the examples to help you realize that once you conquer the sometimes confusing and frustrating man-machine interfaces created by the different manufacturers, all digital relays use the same basic fundamentals; and most relays can be tested by applying these fundamentals. This package provides a step-by-step procedure for testing the most common overcurrent protection applications: Instantaneous Overcurrent (50), Time Overcurrent (51), and Directional Overcurrent (67). Each chapter follows a logical progression to help understand why overcurrent protection is used and how it is applied. Testing procedures are described in detail to ensure that the overcurrent protection has been correctly applied. Each chapter uses the following outline to best describe the element and the test procedures. 1. 2. 3. 4. 5.

Application Settings Pickup Testing Timing Tests Tips and Tricks to Overcome Common Obstacles

Real world examples are used to describe each test with detailed instructions to determine what test parameters to use and how to determine if the results are acceptable. Thank you for your support with this project, and I hope you find this and future additions of The Relay Testing Handbook to be useful.

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Acknowledgments This book would not be possible without support from these fine people David Magnan, Project Manager PCA Valence Engineering Technologies Ltd. www.pcavalence.com Ken Gibbs, C.E.T. PCA Valence Engineering Technologies Ltd. www.pcavalence.com Les Warner C.E.T. PCA Valence Engineering Technologies Ltd. www.pcavalence.com John Hodson : Field Service Manager ARX Engineering a division Magna IV Engineering Calgary Ltd. Do it right the first time www.esps.ca www.avatt.ca www.vamp.fi

Robert Davis, CET PSE Northern Alberta Institute of Technology GET IN GO FAR www.nait.ca Lina Dennison My mean and picky wife who Made this a better book Roger Grylls, CET Magna IV Engineering Superior Client Service. Practical Solutions www.magnaiv.com

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Table of Contents Chapter 1 – Instantaneous Overcurrent (50) Protection 1. 2.

Application....................................................................................................................... 1 Settings ............................................................................................................................. 4 A) Enable Setting.......................................................................................................................................4 B) Pickup...................................................................................................................................................4 C) Time Delay ...........................................................................................................................................4

3.

Pickup Testing................................................................................................................. 4 A) B) C) D)

Test Set Connections ............................................................................................................................5 Pickup Test Procedure if Pickup is Less Than 10 Amps ......................................................................8 Pickup Test Procedure if Pickup is Greater Than 10 Amps .................................................................8 Avoid Setting Changes and Interference Test Procedure .....................................................................9

4.

Timing Tests .................................................................................................................. 10

5. 6.

Residual Neutral Instantaneous Overcurrent Protection ......................................... 12 Tips and Tricks to Overcome Common Obstacles .................................................... 12

A) Timing Test Procedure .......................................................................................................................11

Chapter 2 – Time Overcurrent (51) Element Testing 1. 2.

Application..................................................................................................................... 15 Settings ........................................................................................................................... 18 A) B) C) D) E)

3.

Enable Setting.....................................................................................................................................18 Pickup.................................................................................................................................................18 Curve ..................................................................................................................................................18 Time Dial/Multiplier...........................................................................................................................18 Reset ...................................................................................................................................................18

Pickup Testing............................................................................................................... 19 A) Test Set Connections ..........................................................................................................................19 B) Pickup Test Procedure ........................................................................................................................22

4.

Timing Tests .................................................................................................................. 24 A) B) C) D)

Using Formulas to Determine Time Delay.........................................................................................25 Using Graphs to Determine Time Delay ............................................................................................26 Using Tables to Determine Time Delay .............................................................................................28 Timing Test Procedure .......................................................................................................................29

5.

Reset Tests ..................................................................................................................... 29

6. 7.

Residual Neutral Time Overcurrent Protection ........................................................ 29 Tips and Tricks to Overcome Common Obstacles .................................................... 30

A) Reset Test Procedure ..........................................................................................................................29

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Table of Contents (Cont.) Chapter 3 – Directional Overcurrent (67) Element Testing 1.

Application..................................................................................................................... 31 A) Parallel Feeders.................................................................................................................................. 32 B) Transmission Line Ground Protection ............................................................................................... 34 C) Power Flow........................................................................................................................................ 34

2. 3.

Operation ....................................................................................................................... 35 Settings ........................................................................................................................... 36 A) B) C) D) E) F) G) H) I) J) K) L) M) N)

4.

Enable Setting.................................................................................................................................... 36 Pickup ................................................................................................................................................ 36 Curve ................................................................................................................................................. 36 Time Dial/Multiplier.......................................................................................................................... 36 Reset .................................................................................................................................................. 36 Phase Directional MTA (Maximum Torque Angle).......................................................................... 37 Phase Directional Relays ................................................................................................................... 37 Minimum Polarizing Voltage ............................................................................................................ 37 Block OC When Voltage Memory Expires ....................................................................................... 37 Directional Signal Source .................................................................................................................. 37 Directional Block............................................................................................................................... 37 Directional Target.............................................................................................................................. 37 Directional Events ............................................................................................................................. 37 Directional Order ............................................................................................................................... 38

Pickup Testing............................................................................................................... 38 A) Test Set Connections ......................................................................................................................... 41 B) Determine Maximum Torque Angle in GE Relays............................................................................ 42 C) Quick and Easy Directional Overcurrent Test Procedures................................................................. 43

5. 6.

Timing Test Procedures ............................................................................................... 45 Tips and Tricks to Overcome Common Obstacles .................................................... 45

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Table of Figures Figure 1: Ground Fault Protection Single-Line-Drawing.......................................................................................2 Figure 2: Ground Protection TCC ..........................................................................................................................2 Figure 3: 50/51 TCC #1..........................................................................................................................................3 Figure 4: 50/51 TCC #2..........................................................................................................................................3 Figure 5: 50/51 TCC #3..........................................................................................................................................3 Figure 6: 50/51 TCC #4..........................................................................................................................................3 Figure 7: Simple Instantaneous Overcurrent Connections .....................................................................................6 Figure 8: High Current Connections #1..................................................................................................................6 Figure 9: High Current Connections #2..................................................................................................................7 Figure 10: Neutral or Residual Ground Bypass Connection ..................................................................................7 Figure 11: Neutral or Residual Ground Bypass Connection Via Ø-Ø Connection ................................................7 Figure 12: Pickup Test Graph.................................................................................................................................8 Figure 13: Pickup Test Graph - Jogging.................................................................................................................9 Figure 14: 50-Element Timing Test .....................................................................................................................10 Figure 15: GE D-60 Relay Overcurrent Technical Specifications .......................................................................10 Figure 16: GE D-60 Relay Output Contact Technical Specifications ..................................................................11 Figure 17: Manta Test Systems M-1710 Technical Specifications ......................................................................11 Figure 18: 50-Element Minimum Pickup .............................................................................................................11 Figure 19: 50-Element Alternate Relay Connection.............................................................................................12 Figure 20: 51-Element North American Curves...................................................................................................16 Figure 21: 51-Element IEC European Curves ......................................................................................................16 Figure 22: ANSI Extremely Inverse with Different Pickup Settings....................................................................17 Figure 23: ANSI Extremely Inverse with Different Timing Settings...................................................................17 Figure 24: Simple Time Overcurrent Connections...............................................................................................20 Figure 25: High Current Connections #1..............................................................................................................20 Figure 26: High Current Connections #2..............................................................................................................21 Figure 27: Neutral or Residual Ground Bypass Connection ................................................................................21 Figure 28: Neutral or Residual Ground Bypass Connection Via Ø-Ø Connection ..............................................21 Figure 29: Pickup Test Graph...............................................................................................................................22 Figure 30: SEL-311C 51 Time Overcurrent Specifications .................................................................................23 Figure 31: 51-Element North American Curves...................................................................................................24 Figure 32: 51-Element Timing Test .....................................................................................................................24 Figure 33: 51-Element SEL-311C Timing Curve Characteristic Formulas..........................................................25 Figure 34: 51-Element Example Time Coordination Curve.................................................................................27 Figure 35: 51-Element Time Delay Calculation with Table.................................................................................28 Figure 36: 51-Element Timing for GE D-60 ........................................................................................................28 Figure 37: 51-Element Alternate Relay Connection.............................................................................................30 Figure 38: Parallel Transmission Lines with Standard Overcurrent Protection ...................................................32 Figure 39: Parallel Transmission Lines with Directional Overcurrent Protection................................................33 Figure 40: Directional Ground Overcurrent Protection for Transmission Lines ..................................................34 Figure 41: Directional Overcurrent Protection in an Industrial Application ........................................................34 Figure 42: Standard Phasor Diagram....................................................................................................................35 Figure 43: Directional Polarizing .........................................................................................................................35 Figure 44: Directional Polarizing .........................................................................................................................39 Figure 45: Typical Directional Polarizing using SEL Relays...............................................................................40 Figure 46: Directional Polarizing Using GE Relays and a 60º MTA Setting .......................................................40 Figure 47: 3-Line Drawing for Example Test Set Connection .............................................................................41 Figure 48: Directional Overcurrent Test Set Connections....................................................................................41 Figure 49: Normal Phasors...................................................................................................................................42 Figure 50: Phase A Characteristic Phasor ............................................................................................................42

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Chapter 1: Instantaneous Overcurrent (50) Protection

Chapter 1 Instantaneous Overcurrent (50) Element Testing 1. Application Although the official designation of the 50 element is “instantaneous overcurrent,” a time delay is often added to transform it into a definite-time overcurrent element. A 50-element will operate if the current is greater than the pick-up setpoint for longer than the time delay setting. When the instantaneous overcurrent element is used for phase overcurrent protection, it is labeled with the standard IEEE designation “50.” Ground or neutral instantaneous overcurrent elements can have the designations 50N or 50G depending on the relay manufacturer and/or relay model. The 50-element can be used independently or in conjunction with time overcurrent (51) functions. When used in a grounding scheme, typically all feeders have identical pick-up and time delay settings. The main breaker would have a slightly higher setting and/or longer time delay to ensure that a ground fault on a feeder will be isolated by the feeder breaker before the main breaker operates. An example 50-element ground protection scheme is shown in the following figures. The 50-element protective curve looks like an “L” on a Time Coordination Curve (TCC, see previous packages of The Relay Testing Handbook for details). The element will operate if the current is on the right side of the vertical line for longer than the time indicated by the horizontal line of the protective curve in Figure 2. In this example, a feeder ground fault greater than 10 Amps must last longer than one second before the 50-element will operate. The main breaker protection will operate if any ground fault is greater than 15 Amps for longer than two seconds

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The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67)

Time Co-ordination Curve 10.00

MAIN

Main Ground Protection

PCB2

Time in seconds

50G

PCB3

1.00

Feeder Ground Protection

50G

50G

Current in amperes

100

FEEDER 1 FEEDER 2 Figure 1: Ground Fault Protection Single-Line-Drawing

10

1

0.10

Figure 2: Ground Protection TCC

The 50-element can also be applied in conjunction with inverse-time overcurrent elements to better protect equipment during high-current faults. The amount of damage created during a fault can be directly related to the amount and duration of fault current. To limit equipment damage, the relay should operate faster during high fault currents. The following figures display how the 50-element can enhance equipment protection as well as coordination with other devices. In Figure 3, the time overcurrent (51) relay curve intersects the cable damage curve and, therefore, does not provide 100% protection for the cable. The cable is only 100% protected if its damage curve is completely above the protection curve. Adding a 50element to the time overcurrent element will provide 100% cable protection as shown in Figure 4. However, the addition of the 50-element creates a mis-coordination between the R2 relay and downstream Fuse 1 because the two curves now cross. The relay will operate before the fuse when the relay curve is below and to the left of the fuse curve. This problem can be solved by adding a slight time delay of 0.03 seconds, which will coordinate with the downstream fuse as shown in Figure 5. If we wanted to provide the best protection for the cable and fully utilize the available options of most relays, we could add a second 50-element with no intentional time delay set with a pickup setting higher than the maximum fuse current. This is shown in Figure 6. Adding another 50element will cause the relay to trip sooner at higher currents and will hopefully reduce the amount of damage caused by fault.

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Chapter 1: Instantaneous Overcurrent (50) Protection

Time Co-ordination Curve

Time Co-ordination Curve

10.00

10.00

Cable Damage Curve

Cable Damage Curve

R2 Time Overcurrent Relay Curve

1.00

Mis-Coordination PCB2

R2

Time in seconds

0.10

1.00

PCB2

R2 Instantaneous Relay Curve

R2

CABLE 2 0.10

FUSE 1

CABLE 2

Fuse 1 Operating Curve

FUSE 1

Mis-Coordination Fuse 1 Operating Curve

100,000

1,000

10,000

100,000

0.01 1,000

0.01

10,000

Time in seconds

R2 Time Overcurrent Relay Curve

Current in amperes

Current in amperes

Figure 3: 50/51 TCC #1

Figure 4: 50/51 TCC #2

Time Co-ordination Curve

Time Co-ordination Curve

10.00

10.00

Cable Damage Curve

Cable Damage Curve

R2 Time Overcurrent Relay Curve

R2 Time Overcurrent Relay Curve

PCB2

R2 Instantaneous Relay Curve R2

CABLE 2 0.10

Time in seconds

Time in seconds

PCB2 1.00

1.00

R2 Instantaneous Relay Curve #1

R2

CABLE 2

0.10

FUSE 1

FUSE 1

Fuse 1 Operating Curve Fuse 1 Operating Curve

R2 Instantaneous Relay Curve #2

Figure 5: 50/51 TCC #3

100,000

10,000

1,000

1,000

Current in amperes

100,000

0.01 10,000

0.01

Current in amperes

Figure 6: 50/51 TCC #4

50-elements can also be used to determine if the downstream equipment is operating and/or the circuit breaker or motor starter is closed. When used in this fashion, the 50-element is set very low, at some level below the minimum expected operating current. If the current flow exceeds the 50-element setpoint, the circuit breaker is considered closed because there would be no current flow if the circuit breaker was open. This method of breaker status indication will also detect flashovers or insulation breakdown inside the circuit breaker that would not be detected by a 52a or b contact and is often used in breaker failure (50BF) or inadvertent energization (50/27) protection. www.RelayTesting.net

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The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67)

2. Settings The most common settings used in 50-elements are explained below:

A) Enable Setting Many relays allow the user to enable or disable settings. Make sure that the element is ON or the relay may prevent you from entering settings. If the element is not used, the setting should be disabled or OFF to prevent confusion.

B) Pickup This setting determines when the relay will start timing. Different relay models use different methods to set the actual pickup and the most common methods are: ¾ Secondary Amps – the simplest unit. Pickup Amps = Setting ¾ Per Unit (P.U.) – This method can only exist if the relay settings include nominal current, watts, or VA. This setting could be a multiple of the nominal current as defined or calculated. If no such setting exists, it could be a multiple of the nominal CT (5A) secondary or a multiple of the 51-element pickup setting. Pickup Pickup Pickup Pickup Pickup

= = = = =

Setting Setting Setting Setting Setting

x x x x x

Nominal Amps, OR Watts / (nominal voltage x √3 x power factor) OR VA / (nominal voltage x √3), OR CT secondary (typically 5 Amps) 51-Element Pickup

¾ Primary Amps – There must be a setting for CT ratio if this setting style exists. Check the CT ratio from the drawings to make sure that the drawing match the settings. Pickup = Setting / CT Ratio, OR Pickup = Setting * CT secondary / CT primary

C) Time Delay The time delay setting for the 50-element is a fixed-time delay that determines how long the relay will wait to trip after the pickup has been detected. This setting is set in cycles, milliseconds, or seconds.

3. Pickup Testing Instantaneous overcurrent testing is theoretically simple. Apply a current into the appropriate input and increase it until you observe pickup indication. However, the actual application can be frustrating and require some imagination. High currents are usually involved and the relay could be damaged during testing. Most protective relay current inputs are rated for a maximum of 10 continuous Amps. Any input current greater than 10 Amps must be applied for the minimum amount of time possible to prevent damage. It’s not a good feeling when you apply too much current for too long and get that slight smell of burning insulation, quickly followed by smoke billowing from the relay. Instantaneous elements often interfere with time-overcurrent (51) testing and many relay testers turn the 50-element off during 51-element testing. This practice may be required by the testing specification but is NOT recommended when testing micro-processor relays. If the 50-element is disabled, it MUST be tested AFTER the 51-element tests are complete and the 50-element has been enabled. The opposite problem could occur because the 51-element function can interfere with the instantaneous pickup tests. Do NOT turn off the time-overcurrent (51) element to determine instantaneous pickup.

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Chapter 1: Instantaneous Overcurrent (50) Protection

Before you begin testing, write down the pickup and time settings, and then calculate the pickup current. Make sure that you know which unit is used. Some relays use secondary Amps for timeovercurrent (51) and multiples of that pickup for 50-elements. Use the formulas described in the “Settings” section of this chapter to determine what the pickup actually is. Now that you have determined the pickup and time delay settings, convert the current to primary values using the following formulas: ¾ Primary Current = Secondary pickup current * CT ratio, OR ¾ Primary Current = Secondary Pickup current * CT Primary / CT Secondary.

It is extremely unlikely that you will find a microprocessor relay out of calibration. We perform these tests to check relay operation, verify the settings have been correctly interpreted by the design engineer, and that the settings were entered into the relay correctly. Check the primary values and time delays against the coordination study and make sure they match. Make sure the supplied TCC curves are at the correct voltage levels as discussed in previous packages of The Relay Testing Handbook. Use the voltage conversions discussed in those packages if necessary. If you do not have the coordination study, quickly check that the upstream 50-element setting is higher and the downstream 50-element setting is lower than the relay under test. The interrupting device (circuit breaker, etc…) must be rated to operate at the 50-element pickup level or it may not be able to clear the fault once a trip signal is initiated. Check the interrupting rating of the switchgear and circuit breaker or other disconnecting means. Make sure the equipment interrupting rating is greater than the setting. Look in the short circuit study and determine the maximum fault level at the switchgear. The maximum fault level should be higher than the 50-element setpoint. If it’s not, question the setting because the 50-element will likely never operate because there is not enough fault current available. If no coordination study is provided, look at the next upstream transformer and use the following formula to determine the maximum fault current that could flow through the transformer. The setting should be less than this value. Maximum Fault Current = Transformer VA / (System Voltage * %Z)

A) Test Set Connections Because of the high currents involved with 50-element testing, you may need to try some of the alternative test set connections shown below. Some technicians carry an older test-set when their modern test sets are unable to reach the 50-element test levels. You can prove the element is applied correctly by temporarily lowering the setting, but only use this method as a last resort. In the past, there have been some relay models that did not operate when secondary currents exceeded 100 A although the relay allowed settings larger than 100A. If the testers who discovered this had not tested at the higher fault current levels, it would never have been discovered.

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The Relay Testing Handbook: Testing Overcurrent Protection (50/51/67)

Residual ground (externally connected or internally calculated) and negative sequence elements often interfere with 50-element tests. This problem can be overcome as shown in the following figures if your test set is powerful or flexible enough. There will be some instances where the residual and negative sequence setting will have to be disabled but, disabling settings is a last resort and should only be undertaken if all other possibilities have been exhausted. All disabled elements must be tested AFTER the instantaneous element tests have been performed. Connections are shown for AØ related tests. Simply rotate connections or test set settings to perform BØ and CØ related tests. Simple phasor diagrams are shown above each connection to help you visualize the actual input currents. If your test set experiences problems during the test, even though the output is within its theoretical capabilities, you may need to connect two or more test leads in parallel for the phase AND neutral connections to lower the lead resistance. If this doesn’t work, try connecting directly to the relay terminals as the circuit impedance may be more than your test set can handle. RELAY

RELAY TEST SET

A Phase Amps

Phase Angle

A Phase Amps

AØ Test Amps

0°

B Phase Amps

0A

C Phase Amps

0A

+

+

B Phase Amps

-120° (240°)

+

+

+

120° Alternate Timer Connection DC Supply +

+

C Phase Amps

Element Output

Magnitude +

+

Timer Input

-

Element Output

+

Timer Input

Figure 7: Simple Instantaneous Overcurrent Connections RELAY INPUT TS#1 PU/2 RELAY

TS#2 PU/2 RELAY TEST SET

A Phase Input = Pickup

Magnitude

A Phase Amps +

+

AØ Test Amps / 2

0°

B Phase Amps

AØ Test Amps / 2

0°

C Phase Amps

0A

+

C Phase Amps

Element Output

A Phase Amps +

B Phase Amps +

Phase Angle

+

+

120° Alternate Timer Connection DC Supply +

+

Timer Input

Element Output

+

Timer Input

Figure 8: High Current Connections #1

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Copyright©2010: Valence Electrical Training Services

Chapter 1: Instantaneous Overcurrent (50) Protection

RELAY INPUT AØ PU/3

BØ PU/3

CØ PU/3

RELAY

RELAY TEST SET A Phase Input = Pickup

Magnitude

A Phase Amps

A Phase Amps

AØ Test Amps / 3

0°

B Phase Amps

AØ Test Amps / 3

0°

C Phase Amps

AØ Test Amps / 3

0°

+

+

B Phase Amps +

+

+

Alternate Timer Connection DC Supply +

+

C Phase Amps

Element Output

Phase Angle

+

+

Timer Input

-

Element Output

+

Timer Input

Figure 9: High Current Connections #2 RELAY INPUT TS#1 PU

TS#3 5%