Item 5 - SEL 751-1102 Feeder Protection Relay.pdf

SEL-751 Feeder Protection Relay Comprehensive Feeder Protection and Control With Arc-Flash Detection

Five-Inch, Color Touchscreen Display Model With Four Pushbuttons

Five-Inch, Color Touchscreen Display Model With Eight Pushbuttons

Two-Line Display Model With Four Pushbuttons Two-Line Display Model With Eight Pushbuttons Schweitzer Engineering Laboratories, Inc. SEL-751 Data Sheet

New Features ➤ Updated IEC 61850 protocol implementation to IEC 61850 Edition 2.1.

➤ Added the ability to use the VBAT channel as an ac voltage input with the over- and undervoltage elements.

➤ Added manual closing voltage check conditions and voltage difference supervision to the synchronism-check elements.

➤ Introduced the 51SAT setting to enable or disable time-overcurrent curve saturation.

➤ Introduced the AUTO2 directional control setting for systems with a weak negative-sequence source.

➤ Extended the maximum event report length to 300 power system cycles.

➤ Added the 97FM element to monitor the magnitude of user-selected frequency components in different analog signals.

Major Features and Benefits The SEL-751 Feeder Protection Relay provides a comprehensive combination of protection, fault-locating features, monitoring, control, and communication in an industrial package.

➤ Standard Protection Features. Protect lines and equipment with an extensive range of protection elements, including:

➢ Overcurrent elements

➢ Over- and underfrequency elements

➢ Second- and fifth-harmonic current blocking

(inrush blocking)

➢ Demand metering elements

➢ Breaker failure protection

➢ Phase discontinuity detection

➢ Cold-load pickup

➢ Incipient cable fault detection

➢ Frequency component detection

➢ Breaker failure protection

➢ SELOGIC® control equations

➢ Cable or line thermal elements that conform to the IEC 60255-149 standard ➤ Additional Protection Features. Use the SEL-751 with one of the voltage input options to protect lines and equipment with rate-of-change of frequency elements, fast rate-of-change of frequency elements, definite-time and inverse-time over- and undervoltage elements, and load-encroachment and directional power elements. Also take advantage of the vector shift elements to aid in islanding detection.

➤ Optional Directional Control. Use overcurrent elements with directional control to optimize radial and looped network protection for lines and equipment. Best Choice Ground Directional Element® logic optimizes directional element performance and eliminates the need for many directional settings.

➤ Optional High-Impedance Fault Detection. Use the high-impedance fault (HIF) detection element to detect small current ground faults typically resulting from downed conductors on ground surfaces, such as earth, reinforced concrete, or other poorly conductive materials. HIF event data are available in COMTRADE or Compressed ASCII format.

➤ Optional Arc-Flash Protection. Reduce or eliminate damage from arc-flash events with the optional four- or eight-channel fiber-optic arc-flash detector inputs and protection elements. Settable arc-flash phase and neutral overcurrent elements, combined with arc-flash light detection elements, provide secure, reliable, and fast arc-flash event protection.

➤ Optional Broken Conductor Detection. The broken conductor detection (BCD) element identifies high-impedance downed conductors when combined with the Arc Sense™ technology (AST) option on wye-connected services. This detector operates on three-phase and single-conductor services and can help reduce the possibility of a public hazard, including fire.

➤ Optional Low-Energy Analog (LEA) Voltage Sensor Inputs, Rogowski Coil/LPCT Currents Inputs, and Conventional 200 mA Sensitive Neutral Input. The LEA input range for voltages is as high as 8 Vac rms. Based on the nominal feeder current, the relay automatically sets the gain for the LEA current channel inputs, which allows for a wide range of primary currents.

SEL-751 Data Sheet Schweitzer Engineering Laboratories, Inc.

➤ Optional Synchronism Check and DC Station Battery Monitor. Check single-phase voltage across a circuit breaker, measure dc voltage levels in the substation battery, or use as an additional ac voltage measurement with over- and undervoltage elements.

➤ Operator Controls and Reclosing. Trip and close the breaker easily with four or eight programmable front-panel pushbuttons, each with two tricolor LEDs. Implement remote and local control functions, and selectively reclose with synchronism and voltage checks.

➤ Integrated Web Server. View settings and metering and monitoring data, download event reports, and upgrade relay firmware with an intuitive password-protected web server.

➤ Relay and Logic Settings Software. Reduce engineering costs by using ACSELERATOR QuickSet® SEL-5030 Software for relay settings and logic programming and to simplify development of SELOGIC control equations.

➤ Metering and Monitoring. Use built-in metering functions to eliminate separately mounted metering devices.

Analyze Sequential Events Recorder (SER) reports and oscillographic event reports for rapid commissioning, testing, and post-fault diagnostics. Unsolicited SER protocol allows station-wide collection of binary SER messages.

➤ Optional Fault Location. Reduce fault location and repair time with built-in impedance-based fault location and faulted phase indication.

➤ Wye or Delta Voltage Inputs. Connect voltage inputs that are wye-connected, open-delta-connected, or single voltage.

➤ Additional Standard Features. Improve your feeder protection with these additional standard features in every SEL-751: Modbus RTU, Event Messenger support and MIRRORED BITS® communications, load profile and breaker wear monitoring, support for 12 external RTDs (SEL-2600), IRIG-B input, advanced SELOGIC, and IEEE C37.118-2005-compliant synchrophasor protocol to provide real-time measurement data.

➤ Optional Communications Protocols. Optional communications protocols include IEC 61850 Edition 2.1, Modbus TCP/IP, Simple Network Time Protocol (SNTP), IEEE 1588-2008 firmware-based PTP, IEEE 1588-2008 hardware-based PTP when in PRP mode, PRP, EtherNet/IP, DNP3 LAN/WAN, DNP3 serial, IEC 60870-5-103, and RSTP. With an Ethernet equipped relay, use the integrated web server to view settings and metering and monitoring data, download reports, and upgrade firmware.

➤ Optional Communications Ports. Elective communications ports include EIA-232 or EIA-485 multimode fiber-optic serial port and single or dual, copper or fiber-optic Ethernet ports.

➤ Optional I/O Cards. Digital and analog I/O options include 4 AI/4 AO, 4 DI/4 DO, 8 DI, 8 DO, 8 AI, 3 DI/4 DO/ 1 AO, 4 DI/3 DO, and 14 DI. An optional 10 internal RTD card is also available for the SEL-751. Conformal coating for chemically harsh and/or high moisture environments is also available as an option.

➤ Supported Languages. Choose English or Spanish for your serial ports, including the front-panel serial port. The standard relay front-panel overlay is in English; a Spanish overlay is available as an ordering option.

Model Comparison Guide: Exploring the SEL-751 Options The SEL-751 protection features depend on the model selected. The models are configured with specific current/voltage input cards. The SEL-751 supports both conventional current and potential transformer inputs and low-energy analog sensor inputs. Table 1 shows current (ACI) and voltage (AVI) card selections for the SEL-751 models.

Table 1 Current (ACI) and Voltage (AVI) Card Selection for SEL-751 Models (Sheet 1 of 2)

Model Description Slot Z Card Option (MOT String Digits Number 14, 15)

Slot Z Inputs Slot E Card Option (MOT String Digits Number 12, 13)

Slot E Inputs

Base SEL-751 AC Currents Only 4 ACI (A1, A2, A3, A5, A6, A7)

IA, IB, IC, IN None (0X) None

SEL-751 With AC Voltages (300 Vac) 4 ACI/3 AVI (81, 82, 83, 85, 86, 87)

IA, IB, IC, IN,

VA, VB, VC

None (0X) None

SEL-751 With LEA AC Voltages (8 Vac) 4 ACI/3 AVI (L1, L2, L3, L5, L6, L7)

IA, IB, IC, IN,

VA, VB, VC

None (0X) None

For the LEA option, the current sensors are based on Rogowski coils/low-power current transformers (LPCT), and the voltage sensors are based on resistive or capacitive voltage dividers.

Figure 1 shows Slot Z, LEA current input, with Rogowski coil connection.

The SEL-751 offers an extensive variety of protection features, depending on the model and options selected. Table 2 lists the protection features available in each model.

SEL-751 With AC Phase Voltages (300 Vac), Vsync (300 Vac), Vbat (300 V) Input, and 4 Arc-Flash Detection Inputs

4 ACI/3 AVI

(81, 82, 83, 85, 86, 87)

IA, IB, IC, IN,

VA, VB, VC

2 AVI/4 AFDI (70) VS, VBAT, AF1,

AF2, AF3, AF4

SEL-751 With LEA AC Phase Voltages (8 Vac), LEA Vsync (8 Vac), Vbat (300 V) Input, and 4 Arc-Flash Detection Inputs

4 ACI/3 AVI

(L1, L2, L3, L5, L6, L7)

IA, IB, IC, IN,

VA, VB, VC

2 AVI/4 AFDI (L0) VS, VBAT, AF1,

AF2, AF3, AF4

SEL-751 With LEA Voltage Sensor Inputs, Rogowski Coil or Low Power Current Inputs, 200 mA Neutral Inputs, and 7 Digital Inputs

4 ACI/3 AVI (7L) IA, IB, IC, IN,

VA, VB, VC

2 AVI/7 DI (LA, LB,

LC, LD, LG, LH)

VS, VBAT, 7 DI

Figure 1 Slot Z LEA Card With Rogowski Coil Connection for Current Input

Table 1 Current (ACI) and Voltage (AVI) Card Selection for SEL-751 Models (Sheet 2 of 2)

Model Description Slot Z Card Option (MOT String Digits Number 14, 15)

Slot Z Inputs Slot E Card Option (MOT String Digits Number 12, 13)

Slot E Inputs

Table 2 SEL-751 Protection Elements (Sheet 1 of 2)

Protection Element

Slot Z 4 ACI Card (Current

Only Model) With 1 A or 5 A

Neutral Channel

Slot Z 4 ACI/ 3 AVI Card With

1 A or 5 A Neutral Channel

Slot Z 4 ACI/ 3 AVI Card With 200 mA Neutral

Channel

Slot Z 4 ACI/ 3 AVI LEA Card With 200 mA

Neutral Channel

50P Max. Phase Overcurrent X X X X

67P Max. Phase Overcurrent With Directional Control

Xa Xb Xb

50Q Neg.-Seq. Overcurrent X X X X

67Q Neg.-Seq. Overcurrent With Directional Control

Xa Xb Xb

50G Residual Overcurrent X X X X

67G Residual Overcurrent With Directional Control

Xa Xb Xb

50N Neutral Overcurrent X X X X

67N Neutral Overcurrent With Directional Control

Xb Xb

50INC Incipient Cable Fault Detection X X X X

51mP Phase Time Overcurrent (m = A, B, C) X X X X

51P Max. Phase Time Overcurrent X X X X

51P Max. Phase Time Overcurrent With Directional Control

Xa Xb Xb

51G Residual Time Overcurrent X X X X

51G Residual Time Overcurrent With Directional Control

Xa Xb Xb

51Q Neg.-Seq. Time Overcurrent X X X X

51Q Neg.-Seq. Time Overcurrent With Directional Control

Xa Xb Xb

51N Neutral Time Overcurrent X X X X

51N Neutral Time Overcurrent With Directional Control

Xb Xb

SEF Sensitive Earth Fault X X

HBL Second- and Fifth-Harmonic Blocking X X X X

FLOC Fault Locator X X X

27 Undervoltage (Phase, Phase-to-Phase, Vsync)

X X X

59 Overvoltage (Phase, Phase-to-Phase, Seq., Vsync)

X X X

27I Inverse Time Undervoltage X X X

59I Inverse Time Overvoltage X X X

60LOP Loss of Potential X X X

32 Directional Power X X X

49T IEC Thermal (Line/Cable) X X X X

55 Power Factor X X X

78VS Vector Shift X X X

81 Over- and Underfrequency X X X X

81R Rate-of-Change of Frequency X X X

81RF Fast Rate-of-Change of Frequency X X X

25 Synchronism Check Xc Xc Xc

BF Breaker Failure X X X X

49RTD Resistance Temperature Detectors (RTDs)

Xd Xd Xd Xd

79 Reclosing Xd Xd Xd Xd

HIF AST High-Impedance Fault Detection With Arc Sense Technology

Xd Xd Xd

AFT Arc-Flash Detection Xd Xd Xd Xd

PPD Phase Discontinuity Detection X X X

BCD Broken Conductor Detection Xd, e Xd, e Xd, e

CLPU Cold-Load Pickup Element X X X X

97FM Frequency Component Detection X X X a Available when ordered with the directional option. The 1 A/5 A neutral channel is suitable for solidly grounded systems and also impedance-grounded systems, depending on the available fault current level.

b Available when ordered with the directional option. The 200 mA neutral channel is suitable for ungrounded, low-impedance grounded, high-impedance grounded, and Petersen coil-grounded applications.

c Available with the 2 AVI/4 AFDI or 2 AVI/7 DI card in Slot E.

d Available as ordering options.

e Available only for models with Arc Sense technology.

Table 3 SEL-751 Front-Panel Options

Model/Display Descriptiona a For ordering options, refer to the SEL-751 MOT.

Front-Panel Option (MOT String Digit

Number 16) Number of Pushbuttons LED Type

SEL-751With Two-Line Display (2 x 16 characters)

0 8 Tricolor

SEL-751 With Two-Line Display (2 x 16 characters)

1 4 Tricolor

SEL-751 With Touchscreen Display (5-inch, color, 800 x 480 pixels)

A 8 Tricolor

SEL-751With Touchscreen Display (5-inch, color, 800 x 480 pixels)

B 4 Tricolor

Table 2 SEL-751 Protection Elements (Sheet 2 of 2)

Protection Element

Slot Z 4 ACI Card (Current

Only Model) With 1 A or 5 A

Neutral Channel

Slot Z 4 ACI/ 3 AVI Card With

1 A or 5 A Neutral Channel

Slot Z 4 ACI/ 3 AVI Card With 200 mA Neutral

Channel

Slot Z 4 ACI/ 3 AVI LEA Card With 200 mA

Neutral Channel

Functional Overview

Figure 2 Functional Diagram

Bus

Line

EIA-232

EIA-485

Ethernet*, 1

IRIG-B

2551N50N

27 59I78VS

59P G Q

P G Q

BF

R

F81OUR

51PGQ 49

BW DFR HIZ HMI LGC LOC LEA

HBLMET

Breaker

AFD 27S

67P G Q

50P

AF

50N

AF

27I

59S

RIO PMU SBMRTU

ENVSER WEB

49R

67N

SEL-751

52PB

INC

PDDBCD CLPU 97FM

Protection Features Overcurrent Elements The SEL-751 includes a robust set of phase, negative-sequence, residual, and neutral overcurrent elements.

Each element type has four levels of instantaneous pro-tection with individual torque control and definite-time delay settings. Each element type has two inverse-time overcurrent elements (except negative-sequence, which has one time-overcurrent element). Table 4 lists the curves available in the SEL-751.

The SEL-751 has two reset characteristic choices for each time-overcurrent element. One choice resets the elements if current drops below pickup for at least one cycle. The other choice emulates electromechanical induction disc elements, where the reset time depends on the time dial setting, the percentage of disc travel, and the amount of current.

Overcurrent Elements for Phase Fault Detection The SEL-751 provides the tools necessary for sensitive fault protection while accommodating heavily loaded circuits. Where heavy loading prevents sufficiently sensitive setting of the phase overcurrent elements to detect lower magnitude phase-to-ground faults, residual-ground overcurrent elements are available to provide sensitive ground fault protection without tripping under balanced heavy load conditions. Similarly, when heavy loading prevents sufficiently sensitive setting of the phase overcurrent elements to detect lower magnitude

Figure 2 Functional Diagram (Continued)

➤ Low-Energy Analogs (LEA) for AC Voltage Inputs (8 Vac RMS)*

➤ LEA Voltage Sensor Inputs, Rogowski Coil/LPCT Current Inputs, and Conventional 200 mA Sensitive Neutral Input

➤ Sequential Events Recorder ➤ Event Reports and Load Profile ➤ Web Server ➤ SEL ASCII, Modbus RTU, Ethernet*, Modbus TCP*, IEC 61850 Edition 2.1*, DNP LAN/WAN*, DNP3 Serial*, SNTP*, IEEE 1588-2008 Firmware-Based PTP*, Hardware-based PTP* with PRP*, PRP*, Telnet*, IEC 60870-5-103*, EtherNet/IP*, RSTP*, FTP*, and DeviceNet Communications*

➤ Event Messenger Compatible ➤ Two Inputs and Three Outputs Standard ➤ I/O Expansion*—Additional Contact Inputs/

Outputs, Analog Inputs/Outputs, and RTD Inputs ➤ ST Fiber-Optic Communication Port* ➤ Single or Dual Ethernet, Copper or Fiber-Optic

Communications Port* ➤ Battery-Backed Clock, IRIG-B Time

Synchronization ➤ Instantaneous Metering

➤ Four or Eight Programmable Front-Panel Pushbuttons and Tricolor LED Indicators

➤ Advanced SELOGIC® Control Equations ➤ 32 Programmable Display Messages ➤ Station Battery Monitor* ➤ Breaker Wear Monitoring ➤ Synchrophasor Protocol (IEEE C37.118-2005) ➤ Arc-Flash Protection* ➤ Peak Demand, Demand Metering ➤ Cold-Load Pickup ➤ Load Encroachment ➤ High-Impedance Fault Detection* ➤ Phase Discontinuity Detection ➤ Broken Conductor Detection* ➤ Fault Locator ➤ Directional Protection* ➤ MIRRORED BITS Communications ➤ Front-Panel Tricolor LED Programmable Targets ➤ Front-Panel HMI with 2 x 16 Character LCD ➤ 5-Inch, Color, 800 x 480 Touchscreen Display* ➤ Frequency Component Detection (97FM)

*Optional

Table 4 Inverse-Time Overcurrent Curves

US IEC IEEE

Moderately Inverse Standard Inverse Moderately Inverse

Inverse Very Inverse Very Inverse

Very Inverse Extremely Inverse Extremely Inverse

Extremely Inverse Long-Time Inverse

Short-Time Inverse Short-Time Inverse phase-to-phase faults, negative-sequence overcurrent elements are available to provide more sensitive phase-to-phase fault detection without tripping under balanced heavy load conditions. You can set phase overcurrent element pickup sufficiently high to accommodate heavy load while retaining sensitivity to higher magnitude three-phase faults.

On extremely heavily loaded feeders, SEL-751 load-encroachment logic adds security in cases when you cannot set phase overcurrent elements to provide ade-quate three-phase fault sensitivity while also accommo-dating load. With this logic, you can set the phase overcurrent elements below peak load current so that the relay can detect end-of-line phase faults in heavily loaded feeder applications. This load-encroachment logic uses positive-sequence load-in and load-out ele-ments to discriminate between load and fault conditions based on the magnitude and angle of the positive-sequence impedance. When the measured positive-sequence load impedance (Z1) is within a region the load-encroachment settings define, load-encroachment logic blocks the phase overcurrent elements. As Figure 3 shows, a phase fault causes Z1 to move from a load region to the line angle and leads to operation of the phase overcurrent elements.

Overcurrent Elements for Ground Fault Detection Residual-ground (IG) and neutral (IN) overcurrent elements detect ground faults. Increase security by controlling these elements using optoisolated inputs or the internal ground directional element. The SEL-751 protection system includes patented Best Choice Ground Directional Element logic, providing a selection of nega-tive-sequence impedance, zero-sequence impedance, and zero-sequence current polarizing techniques for optimum directional ground element control.

Directional Elements Increase Sensitivity and Security Phase and ground directional elements come standard in an SEL-751 with the directional control option. An automatic setting mode (EDIR = AUTO or AUTO2) sets all directional threshold settings according to replica positive-sequence and zero-sequence line impedance settings (Z1MAG, Z1ANG, Z0MAG, and Z0ANG) for line protection applications. For all non-line protection applications, set EDIR = Y to enable and set appropriate directional element thresholds. Phase directional elements provide directional control to the phase- and negative-sequence overcurrent elements.

Phase directional characteristics include positive-sequence and negative-sequence directional elements working together. The positive-sequence directional element memory provides a reliable output for close-in, forward, or reverse three-phase faults where each phase voltage is zero.

Ground directional elements provide directional control to the residual-ground and neutral overcurrent elements.

Patented negative-sequence, zero-sequence impedance directional elements, and the zero-sequence current directional element use the same principles proven in our SEL transmission line relays. Our patented Best Choice Ground Directional Element logic selects the best available ground directional element for the ORDER setting you provide.

Figure 3 Load Encroachment Characteristics

Fault LineX1

SEL-751

Line

3f Fault

Positive-Sequence Impedance Plane Maximum Load-Out

Minimum Load Impedance (Z1)

Load-In Region

Load-Out Region

Directional Protection for Various System Grounding Practices Current channel IN, ordered with an optional 0.2 A secondary nominal rating, provides directional ground protection for the following systems:

➤ Ungrounded systems ➤ High-impedance grounded systems ➤ Petersen coil-grounded systems ➤ Low-impedance grounded systems

This optional directional control allows the faulted feeder to be identified on a multifeeder bus with an SEL-751 on each feeder (Figure 4). Alarm or trip for the ground fault condition with sensitivity down to 5 mA secondary.

Line/Cable Thermal Elements Power lines and cables are designed to operate under a certain temperature range. Because equipment is often used as close to the operating limits as possible, the importance of protecting equipment against thermal overloads becomes more critical. The thermal overload protection element is used to protect the overhead lines and cables against thermal damage (including insulation degradation and loss of equipment life) and to monitor the thermal state of the overhead lines and cables. The temperature is calculated using a thermal model according to IEC 60255-149.

Incipient Cable Fault Detection Cable insulation degrades over time. The incipient cable fault detection element can monitor for self-extinguish-ing, half-cycle overcurrent events that precede typical cable insulation failure. Monitoring the number of incipient faults can provide an early warning of cable insulation breakdown. This information can be used for preventative maintenance.

Cold-Load Pickup Element Cold-load pickup is the phenomenon that takes place when a distribution circuit is re-energized following an extended outage of that circuit. It can result in current levels that are significantly higher than normal peak load levels. This excess amount of current draw could be falsely identified as an overcurrent condition by the relay. The cold-load pickup element identifies possible cold-load pickup events as per the settings in a distribu-tion line after an outage. The logic provides Relay Word bits that can be used in programmable torque-control equations of the overcurrent element to enable new trip level settings for the cold-loading period.

Wye or Open-Delta Voltages You can apply wye-connected (four-wire) voltages or open-delta-connected (three-wire) voltages to three-phase voltage inputs VA, VB, VC, and N, as shown in Figure 5. You only need to make a setting change (DELTA_Y = WYE or DELTA_Y = DELTA) and an external wiring change—no internal relay hardware changes or adjustments are necessary. Thus, a single SEL-751 model meets all your distribution protection needs, regardless of available three-phase voltages.

Figure 4 Apply SEL-751 Relays to Petersen Coil-Grounded, Impedance-Grounded, and Ungrounded Systems for Directional Control

Core-Balance CT

NABC3

Core-Balance CT

ABC

3 N

Forward

Reverse

Ground Fault

Petersen Coil Impedance Ungrounded

SEL-751

SEL-751

Figure 6 shows the connections for a 3V0 broken delta input.

In addition, the SEL-751 supports single voltage input.

For customers with a single PT input, the SEL-751 assumes balanced voltage input for all protection and metering functions.

Loss-of-Potential Logic The SEL-751 includes loss-of-potential (LOP) logic that detects one, two, or three blown potential fuses. This patented LOP logic is unique because it does not require settings and is universally applicable. The LOP feature allows the blocking of protection elements to add security during fuse failure.

Synchronism Check When you order the Vsync, Vbat Voltage Input and 4 Arc-Flash Detection Inputs card (SELECT 2 AVI/ 4 AFDI), single-phase voltage (phase-to-neutral or phase-to-phase) is connected to voltage input VS/NS for synchronism check across a circuit breaker (or hot/dead line check). You can use synchronism-check voltage to coordinate reclosing with the optional recloser control.

Voltage and Frequency Elements for Extra Protection and Control Over- and Undervoltage Elements Phase-to-ground, phase-to-phase, negative-sequence, and residual overvoltage (59) and phase-to-ground or phase-to-phase undervoltage (27) elements in the SEL-751 can be used to create the following protection and control schemes.

➤ Trip/alarm or event report triggers for over- and undervoltage conditions.

➤ Undervoltage (27) load shedding scheme (having both 27 and 81U load shedding schemes allows detection of system MVAR- and MW-deficient conditions).

Inverse-Time Over- and Undervoltage Elements Custom programmable, IEC equation-based inverse-time overvoltage (59I) and undervoltage (27I) elements in the SEL-751 add flexibility in voltage protection and control schemes.

Figure 5 Connect Wye or Open-Delta Voltages to SEL-751 Three-Phase Voltage Inputs

Figure 6 Broken-Delta Connections

A CB

(Setting DELTA_Y = WYE)

SEL-751 Relay

SEL-751 Relay

VA

VB

VC

N

Z09

Z10

Z11

Z12

Z09

Z10

Z11

Z12

VA

VB

VC

N

(Setting DELTA_Y = DELTA)

Open-Delta and Broken-Delta (3V0) VT Connections (Set DELTA_Y := DELTA and VSCONN := 3V0)

A B C Z09

Z10

Z11

Z12

F2

F3

Broken-Delta

VA

VB

VC

E02

E01

N

VA

VB

VC

VS

NS

F4

SEL-751 Relay

Over- and Underfrequency Protection Six levels of secure overfrequency (81O) or underfrequency (81U) elements detect true frequency disturbances. Use the independently time-delayed output of these elements to shed load or trip local generation.

The SEL-751 uses the voltage input to make frequency measurements; it switches automatically to current input when voltages are insufficient.

Implement an internal multistage frequency trip/restore scheme at each breaker location using the multiple over-and underfrequency levels. This method avoids the cost of wiring a complicated trip and control scheme from a separate frequency relay.

Rate-of-Change-of-Frequency Protection Four independent rate-of-change-of-frequency elements are provided with individual time delays for use when frequency changes occur (e.g., when there is a sudden unbalance between generation and load). The elements can call for control action or switching action such as network decoupling or load shedding. Each element includes logic to detect either increasing or decreasing frequency and above or below nominal frequency.

Fast Rate-of-Change-of-Frequency Protection for Aurora Vulnerability Mitigation The fast rate-of-change-of-frequency protection, 81RF, provides a faster response compared to frequency (81) and rate-of-change-of-frequency (81R) elements. Fast operating speed makes the 81RF element suitable for detecting islanding conditions. The element uses a char-acteristic (see Figure 7) based on the frequency deviation from nominal frequency (DF = FREQ – FNOM) and the rate-of-change of frequency (DF3C) to detect islanding conditions.

A time window of three cycles is used to calculate the value of DF3C. Under steady state conditions, the operating point is close to the origin. During islanding conditions, depending on the islanded system acceleration, the operating point enters Trip Region 1 or Trip Region 2 of the characteristic. 81RFDFP (in Hz) and 81RFRP (in Hz sec) are the settings used to configure the characteristic.

Frequency Component Detection With the 97FM Element The 97FM elements monitor the magnitude of a user-selected frequency component in different analog signals by evaluating an individual term of the discrete Fourier transform (DFT). You can use 97FM elements to detect low-frequency power oscillation resulting from sub-synchronous resonance or load oscillations.

Vector Shift (78VS) Protection When distributed generators (DG) are connected to a utility network, the vector shift (78VS) element is used to detect islanding conditions and trip the DG. Failure to trip islanded generators can lead to problems such as personnel safety, out-of-synchronization reclosing, and degradation of power quality. Based on the change in the angle of the voltage waveform, the islanding condition can be detected by the vector shift function.

Use the vector shift element with the 81RF element as a backup for fast and secure islanding detection. The vector shift element operates within three cycles, which is fast enough to prevent reclosing out-of-synchronism with the network feeders to avoid generator damage.

Harmonic Blocking Elements Secure Protection During Transformer Energization Transformer inrush can cause sensitive protection to operate. Use the second- and fifth-harmonic blocking feature to detect an inrush condition and block selected tripping elements until the inrush subsides. Select the blocking threshold as a percentage of fundamental current, and optimize security and dependability with settable pickup and dropout times. Use the programma-ble torque control equation only to enable the blocking element immediately after closing the breaker.

Figure 7 81RF Characteristic Power Element Protection

DF3C Hz/s (df/dt calculated over 3-cycle window)

0.2

–0.2 0.1

–0.1

Trip Region 2

Trip Region 1

DF (FREQ – FNOM) Hz

+81RFDFP

+81RFPR

–81RFDFP

–81RFPR

Power Element Protection The SEL-751 provides two power elements for detecting real (watts) or reactive (VARS) positive- or negative-power flow levels for the feeder application. Each power element has a definite-time delay setting.

High-Impedance Fault (HIF) Detection High-impedance faults are short-circuit faults with fault currents smaller than what a traditional overcurrent protective relay can detect. The main causes of HIFs are tree branches touching a phase conductor; dirty or failing insulators that cause flashovers between a phase conduc-tor and the ground; or downed conductors touching the ground. The SEL-751 with the Arc Sense™ technology (AST) option includes logic that can detect HIF signa-tures without being affected by loads or other system operation conditions. A running average provides a stable prefault reference, and adaptive tuning learns and tunes out feeder ambient noise conditions. Decision logic differentiates an HIF condition from other system conditions such as switching operations and noisy loads.

The relay stores as many as 20 minutes of HIF activity in 2-cycle resolution Compressed ASCII and COMTRADE formats and it stores a summary of HIF activity that you can access through the use of ASCII commands.

Phase Discontinuity Detection (PDD) Element The PDD element uses current unbalance to detect an open conductor. The PDD logic detects a phase disconti-nuity only for cases that result in an open-phase condi-tion for a minimum of eight power system cycles.

Broken Conductor Detection (BCD) Element The BCD algorithm is only available for SEL-751 models with the Arc Sense technology (AST) option included. BCD uses the charging current of the line to reliably detect and estimate the location of broken conductors. It can be used to trip the breakers before the conductor touches the ground and creates a shunt fault.

Thus, the algorithm can prevent such faults and block any attempt to reclose the line. The BCD function is designed for single-conductor line configurations and can help in mitigating a possible fire or other public hazard.

Arc-Flash Protection An arcing short circuit or a ground fault in low- or medium-voltage switchgear can cause serious equipment damage and personal injury, resulting in prolonged and expensive downtime.

The best way to minimize the impact of an arc-flash event is to reduce the detection and circuit breaker trip-ping times. Conventional protection may need several cycles to detect the resulting overcurrent fault and trip the breaker. In some cases, there may not be sufficient current to detect an overcurrent fault. Tripping may be delayed hundreds of milliseconds for sensitivity and selectivity reasons in some applications.

The arc-flash detection-based (AFD) protection can act on the circuit breaker in a few milliseconds (2–5 ms).

This fast response can limit the arc-flash energy, thus preventing injury to personnel and limiting or eliminat-ing equipment damage.

The arc-flash protection option in the SEL-751 adds four- or eight-channel fiber-optic AFD inputs and protec-tion elements. Each channel has a fiber-optic receiver and an LED-sourced fiber-optic transmitter that continuously self-tests and monitors the optical circuit to detect and alarm for any malfunction. There are two types of applications supported by the SEL-751: point sensor applications and fiber sensor applications.

Point Sensor Application The arc is detected by transmitting the arc-flash light captured by the optical diffuser (located appropriately in the switchgear) over a 1000 µm plastic fiber-optic cable to the optical detector in the relay. The relay performs sensor loopback tests on the optical system using an LED-based transmitter to transmit light pulses at regular intervals to the point-sensor assembly (through a second fiber-optic cable). If the relay optical receiver does not detect this light, the relay declares a malfunction and alarms. Figure 8 (top) shows a diagram for the point sensor application.

Fiber Sensor Application Fiber sensor AFD uses a clear-jacketed 1000 µm plastic fiber-optic cable located in the switchgear equipment.

One end of the fiber is connected to the optical detector in the relay and the other end is connected to the LED transmitter in the relay. The LED transmitter injects peri-odic light pulses into the fiber as a sensor loopback test to verify the integrity of the loop. The relay detects and alarms for any malfunction. Figure 8 (bottom) shows a diagram for the clear-jacketed fiber sensor application.

The SEL-751 AFD system provides four or eight channels per relay that can be configured for the point sensor or the clear-jacketed fiber sensor applica-tions. The optional fast hybrid outputs (high-speed and high-current) of the relay provide fast-acting trip outputs to the circuit breaker (less than 50 µs). The fast breaker tripping can prevent serious damage or personal injury in case of an arc-flash event. The relay also provides light metering and light event capture to aid in setting the relay and capturing the arc-flash event for records and analysis.

Settable arc-flash phase and neutral overcurrent elements are combined with arc-flash light detection elements to provide secure, reliable, and fast acting arc-flash event protection.

RTD Thermal Protection When the SEL-751 is equipped with either an optional 10 RTD input expansion card or an external SEL-2600 RTD Module with as many as 12 RTD inputs, you can program as many as 12 thermal elements in the relay for two levels of thermal protection per element. Each RTD input provides an alarm and trip thermal pickup setting in degrees Celsius, open and shorted RTD detection, and is compatible with the following three-wire RTD types:

➤ PT100 (100 platinum) ➤ NI100 (100 nickel) ➤ NI120 (120 nickel) ➤ CU10 (10 copper)

Figure 8 SEL-751 Arc-Flash Detection System

Optical Arc-Flash Detector LED Circuit for Continuous Self-testing

Ch. 2

Ch. 3

Ch. 4

Point Sensor (SEL-C804) Application

Diffuser

Sw itc hg ea r

Clear-Jacketed Fiber Black-Jacketed Fibers

ST—ST Connector

V-pi n Te rm in at io ns

SEL-751

Ch. 1Black-Jacketed Light Fibers

SE

LE

CT

A

VI

/4 A

FD

I C ar d

1000 μm1000 μm

1000 μm

ARC

ARC

Fiber Sensor (SEL-C804) Application

Operator Controls and Reclosing Operator controls eliminate traditional panel control switches. Four or eight conveniently sized operator controls, each with two programmable tricolor LEDs, are located on the relay front panel (see Figure 9). You can set the SER to track operator controls. Use SELOGIC control equations to change operator control functions.

Use configurable labels to change all of the text shown in Figure 9.

In the non-reclosing control SEL-751, you can program the top right operator control and its corresponding two LEDs. When the SEL-751 is ordered with optional reclosing, the two LEDs are programmed to give the sta-tus of the reclosing. The two LEDs, RECL RESET and RECL LOCKOUT, indicate whether the recloser is in the Reset or Lockout state.

The following operator control descriptions are for factory-set logic.

LOCK: The LOCK operator control blocks selected functions. Press it for at least three seconds to engage or disengage the lock function. When the LOCK pushbutton is engaged, the TRIP and CLOSE operators are blocked.

CLOSE and TRIP: Use the CLOSE and TRIP operator controls to close and open the circuit breaker. You can program these controls with intentional time delays to support operational requirements for breaker-mounted relays.

This allows you to press the CLOSE or TRIP pushbutton, then move to an alternate location before the breaker command is executed.

AUXn: You can program the AUXn (n = 1, 2, 3, or 4) pushbuttons for additional control of your specific application.

In the SEL-751 with the touchscreen display, you can use the front-panel operator control pushbuttons to jump to a specific screen while also using them for LOCK/TRIP/ CLOSE operations, etc. You can program the selectable operator pushbutton screen settings under the Touchscreen settings category in QuickSet to map the button to the specific screen.

Programmable Autoreclosing When ordered with optional reclosing, the SEL-751 can autoreclose a circuit breaker as many as four times before lockout. Use SELOGIC control equations to pro-gram the SEL-751 to perform the following reclosing functions.

➤ Allow closing, e.g., when the load-side line is dead, or when the two systems are in synchronism (optional).

➤ Advance the shot counter without tripping, e.g., when another protective relay clears a fault, also known as sequence coordination.

➤ Initiate reclosing, e.g., for particular protection trip operations.

➤ Drive-to-lockout, e.g., when an optoisolated input is deasserted.

➤ Delay reclosing, e.g., after a trip caused by a close-in, high-current fault.

➤ Flexible reclose supervision failure scheme that allows going to lockout or moving to the next available shot.

The reclosing shot counter controls which protective ele-ments are involved in each reclose interval. Applications include fuse- and trip-saving schemes. The front-panel LEDs (RECL RESET and RECL LOCKOUT) track the reclosing state.

Figure 9 Operator Controls for Standard Model and Optional Reclosing Control Model

Without Reclosing Control

With Reclosing Control

Only available in models with 8 pushbuttons

(PB05–PB08)

Built-In Web Server Every Ethernet-equipped SEL-751 includes a built-in web server. Interface with the relay by using any stan-dard web browser to perform the following actions:

➤ Log in with password protection.

➤ Safely read the relay settings.

➤ Verify the relay self-test status and view the relay configuration.

➤ Inspect meter reports.

➤ Download SER and event reports.

➤ Upload new firmware (firmware upgrade).

Figure 10 shows the fundamental metering screen that can be accessed by clicking Meter > Fundamental. Use the Meter menu to view all the available relay metering statistics.

Figure 11 shows the Group 1 settings webpage. You can view the settings of each relay settings class by selecting Settings and the respective relay settings class.

You can upgrade the relay firmware through the relay web server by clicking System > File Management (available at Access Level 2) and selecting the firmware upgrade file. Figure 12 shows the firmware upgrade webpage.

Relay and Logic Settings Software QuickSet simplifies settings and provides analytical sup-port for the SEL-751. There are several ways to create and manage relay settings with QuickSet.

➤ Develop settings offline with an intelligent settings editor that only allows valid settings.

➤ Create SELOGIC control equations with a drag-and-drop text editor.

➤ Configure proper settings using online help.

➤ Organize settings with the relay database manager.

➤ Load and retrieve settings using a simple PC communications link.

With QuickSet, you can verify settings and analyze power system events with the integrated waveform and harmonic analysis tools.

Use the following features of QuickSet to monitor, com-mission, and test the SEL-751.

➤ Use the HMI to monitor meter data, Relay Word bits, and output contact statuses during testing.

➤ Use the PC interface to remotely retrieve power system data.

➤ Use the Event Report Analysis tool for easy retrieval and visualization of ac waveforms and digital inputs and outputs the relay processes.

➤ Use the graphical current phasor display in the HMI to visualize differential current relationships.

➤ Use bay control to design new bay screens and edit existing bay screens by launching ACSELERATOR Bay Screen Builder SEL-5036 Software for SEL-751 relays with the touchscreen display.

Figure 10 Fundamental Meter Report Webpage

Figure 11 Group 1 Settings Webpage

Figure 12 Upgrade the Relay Firmware From the File Management Webpage

ACSELERATOR Bay Screen Builder SEL-5036 Software The SEL-751 with the touchscreen display option pro-vides you with the ability to design bay configuration screens to meet your system needs. You can display the bay configuration as a single-line diagram (SLD) on the touchscreen. You can use ANSI and IEC symbols, along with analog and digital labels, for the SLD to indicate the status of the breaker and disconnects, bus voltages, and power flow through the breaker. In addition to SLDs, you can design the screens to show the status of various relay elements via Relay Word bits or to show analog quanti-ties for commissioning or day-to-day operations. You can design these screens with the help of Bay Screen Builder in conjunction with QuickSet. Bay Screen Builder provides an intuitive and powerful interface to design bay screens to meet your application needs.

Metering and Monitoring The SEL-751 provides extensive metering capabilities.

See Specifications on page 36 for metering and power measurement accuracies. As shown in Table 5, metered quantities include phase voltages and currents; neutral current, sequence voltages and currents; power, frequency, and energy; and maximum/minimum logging of selected quantities. The relay reports all metered quantities in primary quantities (current in A primary and voltage in V primary).

Figure 13 Bay Screen Builder

Load Profile The SEL-751 features a programmable Load Data Pro-file (LDP) recorder that records as many as 17 metering quantities into nonvolatile memory at fixed time intervals. The LDP saves several days to several weeks of the most recent data depending on the LDP settings (6500 entries total).

Synchrophasor Measurements Combine the SEL-751 with an SEL-IRIG-B time source to measure the system angle in real time with a timing accuracy of ±10 µs. Measure instantaneous voltage and current phase angles in real time to improve system operation with synchrophasor information. Replace state measurement, study validation, or track system stability.

Use SEL-5703 Synchrowave Monitoring software to view system angles at multiple locations for precise system analysis and system-state measurement (see Figure 14).

Use IEEE C37.118-2005 protocol to send synchrophasor data to SEL synchrophasor applications. These include the SEL-3378 Synchrophasor Vector Processor (SVP), SEL-3530 Real-Time Automation Controller (RTAC), and the SEL-5078-2 SYNCHROWAVE® Central Visualization and Analysis Software suite.

Table 5 SEL-751 Metered Values (Model Dependent)

Types of Metering

Instantaneous Light Analog Inputs Energy Math Variables RMS Remote Analogs Thermal Demand and Peak Demand Synchrophasors Max/Min HIF (High-Impedance Fault)

Quantities Description

Currents IA, IB, IC Phase current magnitude and angle, primary A IN Neutral current magnitude and angle, primary A IG Residual-ground fault current and angle, primary A (IG = 3I0 = IA + IB + IC) Currents IAV, UBI Average current magnitude, current unbalance Voltages VA, VB, VC Phase voltage and angles, primary volts, for wye-connected voltage inputs Voltages VAB, VBC, VCA Phase-to-phase voltages and angles, primary volts, for delta-connected voltage inputs Voltages VAVE, UBV Average voltage magnitude, voltage unbalance Voltage VS Synchronism-check voltage magnitude and angle, primary volts Power kVA, kW, kVAR a a Single-phase power and power factor quantities are not available when delta-connected PTs are used.

Calculated apparent, real, and reactive power scales to primary values (single and three-phase) Energy MWh, MVARh, MVAh Three-phase positive and negative megawatt-hours, megavar-hours, and megavolt-amp-hours Power Factor PFa Single and three-phase power factor (leading or lagging) Sequence I1, 3I2, 3I0, V1, 3V2, 3V0 Positive-, negative-, and zero-sequence currents and voltages Voltage VDC Station battery voltage or VBAT channel ac voltage depending on the Global setting

EDCMON

Frequency FREQ Instantaneous system frequency (Hz) Frequency FREQS Instantaneous frequency (Hz) of synchronism-check voltage channel Light Intensity (%) LS1–LS8 Arc-flash light inputs in percentage of full scale AIx01–AIx08 (x = 3, 4, or 5) Analog inputs MV01–MV64 Math variables RA001–RA128 Remote analogs Thermal Element x

Current THIEQx pu TCU THTCUx% Trip Time THTRIPx s Release Time THRLSx s

Element x pu current level, thermal capacity, time to trip, and time to reset values, where x = 1, 2, or 3

RTD1–RTD12 RTD temperature measurement (degrees C)

Figure 14 View of System Angle at Multiple Locations

View system angle at multiple locations.

59.996 Hz 60.003 Hz 59.996 Hz

60.015 Hz 60.0 Hz 60.007 Hz

Pullman, WA Chicago, IL Philadelphia, PA

Monterrey, Mexico San Antonio, TX Tampa, FL

Pullman

MonterreySan Antonio

Phi lade lph ia

Tampa

Chicago

The SEL-3373 Station Phasor Data Concentrator (PDC) and the SEL-5073 SYNCHROWAVE PDC software correlate data from multiple SEL-751 relays and concentrate the result into a single output data stream.

These products also provide synchrophasor data archiving capability. The SEL-3378 SVP enables control applications based on synchrophasors. Directly measure the oscillation modes of your power system and then act on the result. Use wide-area phase angle slip and acceleration measurements to properly control islanding of distributed generation. With the SVP, you can customize a synchrophasor control application according to the unique requirements of your power system.

The data rate of SEL-751 synchrophasors is selectable with a range of 1–60 messages per second. This flexibil-ity is important for efficient use of communication capacity.

The SEL-751 phasor measurement accuracy meets the highest IEEE C37.118-2005 Level 1 requirement of 1 percent total vector error (TVE). This means you can use any SEL-751 model in an application that otherwise would require purchasing a separate dedicated phasor measurement unit (PMU).

Use the SEL-751 with SEL communications processors or RTACs to change nonlinear state estimation into lin-ear state estimation. If all necessary lines include syn-chrophasor measurements then state estimation is no longer necessary. The system state is directly measured.

Improve Situational Awareness Provide improved information to system operators.

Advanced synchrophasor-based tools produce a real-time view of system conditions. Use system trends, alarm points, and preprogrammed responses to help operators prevent a cascading system collapse and maxi-mize system stability. Awareness of system trends pro-vides operators with an understanding of future values based on measured data.

➤ Increase system loading while maintaining adequate stability margins.

➤ Improve operator response to system contingencies such as overload conditions, transmission outages, or generator shutdown.

➤ Advance system knowledge with correlated event reporting and real-time system visualization.

➤ Validate planning studies to improve system load balance and station optimization.

Figure 15 Synchrophasor Measurements Turn State Estimation Into State Measurement d1 d2

V1

V2

V1

V2

P12

Q12

= h (V,q) State

= h (V,q) + error State

MeasurementsMeasurements

1 Second10 Minutes

Figure 16 Visualization of Phase Angle Measurements Across a Power System

Event Reporting and SER Event reports and the SER simplify post-fault analysis and improve understanding of simple and complex pro-tective scheme operations. In response to a user-selected trigger, the voltage, current, frequency, and element sta-tus information contained in each event report confirms relay, scheme, and system performance for every fault.

Decide how much detail is necessary when you request an event report (e.g., 1/4-cycle or 1/32-cycle resolution, filtered or raw analog data, respectively).

The relay stores as many as 5 of the most recent 300-cycle event reports, 8 of the most recent 180-cycle event reports, 20 of the most recent 64-cycle event reports, or 40 of the most recent 15-cycle event reports in nonvolatile memory. The relay always appends relay settings to the bottom of each event report.

The following analog data formats are available:

➤ 1/4-cycle or 1/32-cycle resolution, filtered or unfiltered analog, ASCII or Compressed ASCII reports

➤ 1/32-cycle resolution COMTRADE reports

The relay SER feature stores the latest 1,024 entries. Use this feature to gain a broad perspective at a glance. An SER entry helps to monitor input/output change-of-state occurrences and element pickup/dropout.

Synchronized Measurements The IRIG-B time-code input synchronizes the SEL-751 internal clock time to within ±1 µs of the time-source input. Convenient sources for this time code are an SEL-2401 Satellite-Synchronized Clock, an SEL communications processor, or an SEL RTAC (via Serial Port 2 or 3 on the SEL-751). For time accuracy specifications for metering, synchrophasors, and events, see Specifications on page 36.

Substation Battery Monitor The SEL-751 relays that include the enhanced voltage option with the monitoring package measure and report the substation battery voltage connected to the VBAT terminals. The relay includes two programmable thresh-old comparators and associated logic for alarm and con-trol. For example, if the battery charger fails, the measured dc falls below a programmable threshold. The SEL-751 alarms to alert operations personnel before the substation battery voltage falls to unacceptable levels.

Monitor these thresholds with an SEL communications processor and trigger messages, telephone calls, or other actions.

The measured dc voltage appears in the meter display and the Vdc column of the event report. Use the event report column data to see an oscillographic display of the battery voltage. This display shows how much the substation battery voltage drops during trip, close, and other control operations.

Circuit Breaker Contact Wear Monitor…