WHITE PAPER

Date Code 20140324 SEL White Paper LWP0005

SEL Recommendations on Periodic Maintenance Testing of Protective Relays

Karl Zimmerman

INTRODUCTION There continues to be high interest in testing practices for protective relaying systems. For example, in 2007, the U.S. Federal Energy Regulatory Commission (FERC) issued Order No. 693, which mandates that all users, owners, and operators of the bulk power system comply with electric reliability standards.

To address the FERC comments from this order, the North American Electric Reliability Corporation (NERC) developed Standard PRC-005-2, Protection System Maintenance, which merges the following previous standards:

PRC-005-1 Transmission and Generation Protection System Maintenance and Testing PRC-008-0 Underfrequency Load Shedding Equipment Maintenance Programs PRC-011-0 Underfrequency Load Shedding System Maintenance and Testing PRC-017-0 Special Protection System Maintenance and Testing

NERC Standard PRC-005-2 defines what elements of a protection system should be tested and how often. The standard also includes requirements for developing and documenting the implementation of a test plan [1].

FERC issued the order approving PRC-005-2 on December 19, 2013. The enforcement date for PRC-005-2 will be April 1, 2015, which is the first date that entities must be compliant with the standard. The regulatory approval date in the United States is February 24, 2014.

The purpose of this paper is to provide recommendations for testing SEL relays and guidance for developing a test program. Utilities and other entities should use their own experience and expertise to develop and implement their test plans.

BACKGROUND The goal of testing relays is to maximize the availability of the protection and to minimize the risk of a misoperation. The paper Philosophies for Testing Protective Relays describes an approach to testing digital relays and the factors that affect a maintenance interval [2].

An important factor in analyzing test intervals is monitoring the self-test alarm of a relay. SEL relays continually monitor and control power protection systems in addition to continuously monitoring their internal self-test diagnostics. Relay self-test diagnostics are capable of detecting approximately 85% of component failures. The paper Assessing the Effectiveness of Self-Tests and Other Monitoring Means in Protective Relays shows a strategy for relay testing [3].

Using the best testing method is integral to a good testing philosophy. The paper A Comparison of Line Relay System Testing Methods provides guidance for selecting the best test method [4].

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SEL White Paper LWP0005 Date Code 20140324

Finally, developing a plan for periodic testing assumes that a system is properly and comprehensively commissioned. The paper Lessons Learned From Commissioning Protective Relaying Systems describes best practices for commissioning protective relay systems [5].

Observed field return data show that SEL relays have a mean time between failures (MTBF) of about 500 years. This is a measurement of hardware failures and equates to about 0.2% (1/500) failures per year. Also, historical data show that self-tests detect about 85% of relay failures. Thus, about 15% of the 0.2% failures (about 0.03% per year) go undetected. The SEL maintenance indicator (MI), which tracks all maintenance performed on a particular relay, is approximately 130 years. Using the MI, the number of undetected failures per year is 0.12% (1 undetected failure in 870 relays).

RECOMMENDED APPROACH The following describes the SEL recommended approach to relay testing and best practices:

1. Perform comprehensive commissioning testing at the time of installation. Use thorough checklists, simulations, laboratory testing, and/or field checks to verify the performance of the protection system, including inputs, outputs, and settings.

2. Monitor the relay self-test alarm contact in real time via supervisory control and data acquisition (SCADA) or other monitoring system. If an alarm contact asserts, take immediate steps to repair, replace, or take corrective action for the alarmed relay.

3. Monitor potential relay failures not detected by self-tests. Specifically, these are logic inputs, contact outputs, and analog (voltage and current) inputs. Use continuous check of inputs (e.g., loss-of-potential logic) when available. If a secondary relay system is in place, compare the metering values between the primary and secondary systems.

4. Analyze event reports to root cause, and verify logic inputs and output contact operation. Use event reports as documentation to validate correct operation of the protection system.

5. Observe and act on all product service bulletins. Not every service bulletin requires action, but each bulletin should be evaluated. Upon request, SEL can provide specific information or a secure website to track affected relays.

If Steps 1 through 5 are followed, periodic testing, if performed, will not identify any additional failures.

Many users follow Steps 1 and 2 but do not perform Steps 3 through 5 consistently. In this case, perform periodic testing (e.g., once every ten years) on portions of the relay not tested by self-tests. This includes injecting known current and voltage signals to verify relay measuring accuracy, asserting inputs, and pulsing output contacts. This need not include reverifying settings, plotting time-current curves or mho circles, and so on. These characteristics are verified at commissioning and do not change. This testing may identify the small number of failures not detected by self-tests (e.g., using the previous failure rates, testing every ten years would detect 0.12% 10 = 1.2% failures, or 1 failed relay found in 83 relays tested).

This philosophy also applies to systems that do not operate frequently (e.g., bus or transformer differential protection).

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Date Code 20140324 SEL White Paper LWP0005

TESTING WHEN SELF-TEST ALARM IS NOT MONITORED In some rare applications (installations without SCADA or communications), the self-test alarm is not monitored. This is not recommended. For these applications, the relays should be tested every one to six years, including the following:

Check that the self-test alarm is not asserted. Inject known current and voltage signals to verify proper metering. Assert inputs, and pulse outputs.

This need not include reverifying settings, plotting time-current curves or mho circles, and so on. These characteristics are verified at commissioning and do not change.

NERC PRC-005-2 GUIDANCE Table 1-1 and Table 3 of PRC-005-2 establish a specific maximum maintenance interval and required maintenance activities for components that possess the attributes stated in Table 1-1 as follows:

Monitored microprocessor protective relay with the following: Internal self-diagnosis and alarming Voltage and/or current waveform sampling three or more times per

power cycle, and conversion of samples to numeric values for measurement calculations by microprocessor electronics.

Alarming for power supply failure [1]

SEL protective relay products include self-diagnostics, alarm functions, and sampling functions that are capable of fulfilling these requirements.

REFERENCES [1] NERC Standard PRC-005-2, Protection System Maintenance, February 2014. Available:

http://www.nerc.com.

[2] J. J. Kumm, M. S. Weber, E. O. Schweitzer, III, and D. Hou, Philosophies for Testing Protective Relays, proceedings of the 48th Annual Georgia Tech Protective Relaying Conference, Atlanta, GA, May 1994.

[3] J. J. Kumm, E. O. Schweitzer, III, and D. Hou, Assessing the Effectiveness of Self-Tests and Other Monitoring Means in Protective Relays, proceedings of the PEA Relay Committee Spring Meeting, Matamoras, PA, May 1995.

[4] C. Araujo, F. Horvath, and J. Mack, A Comparison of Line Relay System Testing Methods, proceedings of the 33rd Annual Western Protective Relay Conference, Spokane, WA, October 2006.

[5] K. Zimmerman and D. Costello, Lessons Learned From Commissioning Protective Relaying Systems, proceedings of PowerTest 2009, San Antonio, TX, March 2009.

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SEL White Paper LWP0005 Date Code 20140324

BIOGRAPHY Karl Zimmerman is a regional technical manager with Schweitzer Engineering Laboratories, Inc. in Fairview Heights, Illinois. His work includes providing application and product support and technical training for protective relay users. He is an active member of the IEEE Power System Relaying Committee and vice chairman of the Line Protection Subcommittee.

Karl received his BSEE degree at the University of Illinois at Urbana-Champaign and has over 20 years of experience in the area of system protection. He is a registered Professional Engineer in the state of Wisconsin.

Karl was a recipient of the 2008 Walter A. Elmore Best Paper Award from the Georgia Institute of Technology Protective Relaying Conference, is a past speaker at many technical conferences, and has authored over 40 technical papers and application guides on protective relaying.

2009, 2010, 2013, 2014 by Schweitzer Engineering Laboratories, Inc. All rights reserved.

All brand or product names appearing in this document are the trademark or registered trademark of their respective holders. No SEL trademarks may be used without written permission.

SEL products appearing in this document may be covered by U.S. and Foreign patents.

*LWP0005*

Date Code 20150213 SEL Application Note 2015-02

Application Note AN2015-02

Monitoring and Control of a Lift Station With the SEL-2411 Programmable

Automation Controller Emery Perry and Clay Mallett

INTRODUCTION Municipal sanitary and storm water systems often have their lift stations strategically located in the lower elevations of collection systems to convey water to treatment facilities. Most of these lift stations are remotely located and are controlled manually or via remote supervisory control and data acquisition (SCADA).

This application note describes the control functions in the SEL-2411 Programmable Automation Controller that can be used in a duplex lift station with primary SCADA control and a failover to local automatic or manual control.

PROBLEM Remotely located lift stations require local, automatic control and continuous monitoring.

SOLUTION The SEL-2411 offers automatic and manual control functions for these types of pumping systems. In addition to local control functions, the SEL-2411 is capable of remote control via several communications protocols. The SEL-2411 can monitor, control, and provide indication of a wells water level. This level is sensed by four sensors (float switches), as shown in Figure 1, indicating low-low, low, high, and high-high level conditions.

SCADA Fail

Low-Low Level

Low Level

High Level

High-High Level IN304

IN303

IN302

IN301

IN305

SEL-2411To AC Control

Voltage

Float

Figure 1 Sensor Connections

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SEL Application Note 2015-02 Date Code 20150213

During increases in flow due to inflow or infiltration, the controller automatically starts wet well pumps for a high-water condition. The SEL-2411 alarms for a high-high water level and manages the operating duty of the pumps by running in alternation mode. For a low-low level, the controller shuts off automatic mode and allows manual operation from a human-machine interface (HMI). When SCADA is unavailable, IN305 deasserts, allowing the controller to function in local mode.

Front-Panel Operation The operator interface on the SEL-2411 configurable front panel is customized to user preferences. Figure 2 shows the operator interface functions and indicating LEDs for the example application.

Figure 2 SEL-2411 HMI

Example Settings SELOGIC control equations combine Relay Word bits and I/O information to create control and monitoring functions. Table 1, Table 2, and Table 3 show the setting categories, SELOGIC control equation values, and functions used in the example application. Refer to the SEL-2411 Instruction Manual for a more detailed description of the Relay Word bits.

Table 1 Global Settings

Input Debounce Value Function

IN301DIN308D AC Sense ac

Table 2 SELOGIC Control Equation Settings

SELOGIC Enables Value Function

ELAT 10 Quantity of latch bits enabled

ESV N NA

ESC 1 Quantity of SEL counters enabled

EMV 1 Quantity of math variables enabled

Latch Bits Value Function

SET01 MV01 = 1.00 AND LT04 AND IN303 AND

LT05 AND NOT LT02 OR MV01 = 2.00 AND IN304

Automatic run and alternation mode for Pump 1

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Date Code 20150213 SEL Application Note 2015-02

RST01 PB01_PUL AND LT01 OR (NOT IN302) OR (NOT IN301) OR (NOT LT05) Stop Pump 1 when wet well level

falls below low level

SET02 PB02_PUL AND NOT LT02 AND NOT LT01 Manually run Pump 1

RST02 PB02_PUL AND LT02 Manually stop Pump 1

SET03 MV01 = 2.00 AND LT06 AND IN303 AND

LT05 AND NOT LT08 OR MV01 = 1.00 AND IN304

Automatic run and alternation mode for Pump 2

RST03 PB03_PUL AND LT03 OR (NOT IN302) OR (NOT IN301) OR (NOT LT05) Stop Pump 2 when wet well level

falls below low level

SET04 PB01_PUL AND NOT LT01 Pump 1 automatic mode

RST04 PB01_PUL AND LT04 OR LT02 Pump 1 stop and manual mode

SET05 IN305 Asserts for SCADA fail input

RST05 NOT IN305 NA

SET06 PB03_PUL AND LT04 OR NOT LT03 Pump 2 automatic mode

RST06 PB03_PUL AND LT06 OR LT08 Pump 2 stop and manual mode

SET07 0 NA

RST07 0 NA

SET08 PB04_PUL AND NOT LT08 AND NOT LT03 Manually run Pump 2

RST08 PB04_PUL AND LT08 Manually stop Pump 2

SELOGIC Counters Value Function

SC01PV 1 Preset value for pump alternation

SC01R NA NA

SC01LD R_TRIG OUT101 AND MV01 = 0.00 Load counter for pump alternation

SC01CU F_TRIG OUT101 Count up when Pump 1 stops

SC01CD MV01 = 2.00 AND F_TRIG OUT102 Count down when Pump 2 stops

Math Variables Value Function

MV01 SC01 Store value of Counter 1

Output Value Function

OUT101 LT01 OR LT02 Automatic or manual output to Pump 1

OUT102 LT03 OR LT08 Automatic or manual output to Pump 2

OUT103 NOT (HALARM OR SALARM) Hardware software alarm

Slot 4 Output Value Function

OUT401 IN301 Low-low level indication

OUT402 IN305 SCADA fail indication

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SEL Application Note 2015-02 Date Code 20150213

Table 3 Front-Panel Settings

General Value Function

EPD 12 Enable display points

ELB N NA

FP_TO 15 Front-panel time out

FP_CONT 5 Front-panel contrast

Target LED Value Function

T01_LED LT01 OR LT02 Pump 1 running

T02_LED LT03 OR LT08 Pump 2 running

T03_LED NOT IN301 Low alarm shut off

T04_LED (LT01 OR LT02) AND (LT03 OR LT08) High water level

T05_LED LT05 SCADA failure

T06_LED 0 Spare

PB01_LED LT01 Pump 1 automatic mode

PB02_LED LT02 Pump 1 manual mode

PB03_LED LT03 Pump 2 automatic mode

PB04_LED LT08 Pump 2 manual mode

Display Points Value Function

DP01 OUT101, Lead Pump Run Lead pump indication

DP02 LT04, PUMP1, AUTO Pump 1 operate mode

DP03 LT02, PUMP1, MANUAL Pump 1 operate mode

DP04 LT06, PUMP2, AUTO Pump 2 operate mode

DP05 LT08, PUMP2, MANUAL Pump 2 operate mode

CONCLUSION In the example application described in this application note, the SEL-2411 configuration had a minimum I/O requirement (Part Number 0241101A3A2X0X0X0130). The SEL-2411 modular design and flexible SELOGIC control equations provide an ideal retrofit solution for wet well controls requiring multiple operating modes. The SEL-2411 communications options can be interfaced to an existing SCADA system to provide continuous monitoring and remote control.

2015 by Schweitzer Engineering Laboratories, Inc. All rights reserved.

*LAN2015-02*

0005_SEL_Recommendations_KZ_20140324AN2015-02_20150213IntroductionProblemSolutionFront-Panel OperationExample Settings

Conclusion