Sel SEL-400 Series - User Manual

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Date Code 20200326 SEL Application Guide 2020-04

Use SEL-300 and SEL-400 Series Relays to

Set Up POTT and DCB Schemes

Jared Candelaria, Hardesh Khatri, and Avinash Maddela

INTRODUCTION

The first SEL-300 series relay, the SEL-321-1 Phase and Ground Distance Relay, was introduced

in 1993 and has been used to provide pilot protection on transmission lines ever since. Now, more

than 20 years later, SEL-300 series relays are still widely used. However, as utilities upgrade their

systems, SEL-300 series relays are being replaced by relays with additional functionality, such as

SEL-400 series relays. It is not uncommon for these upgrades to occur on a tie line, where each

end of the line is owned by a different utility. Occasionally, one utility will upgrade its terminal to

match a new standard relaying package, while the other utility will choose to keep their existing

protection. Dissimilar relays on either end of the line do not maintain conventional pilot protec-

tion; however, it is possible to maintain pilot protection. SEL does not recommend connecting dis-

similar relays for pilot protection.

This application guide details how to program SEL-300 and SEL-400 series relays to maintain

pilot protection coordination by using either a permissive overreaching transfer trip (POTT) or a

directional comparison blocking (DCB) scheme. The SEL-400 series relay covered in this applica-

tion guide is the SEL-421-5 Protection, Automation, and Control System. The SEL-300 series

relays covered in this application guide include the SEL-311C-1 Transmission Protection System,

the SEL-311L Line Current Differential Protection and Automation System, and the SEL-321-1

Phase and Ground Distance Relay.

For the examples in this guide, we use the SEL-421-5 to represent all the SEL-400 series relays.

For the SEL-300 series relays, we consider two cases, one with the SEL-311C-1 representing all

variations of the SEL-311 relays and the other with the SEL-321-1. The reason for considering the

SEL-321-1 relay separately than the other SEL-300 series relays is that the internal logic of the

SEL-321-1 is different compared to the other SEL-300 series relays. This guide shows two pilot

protection scheme examples, one between the SEL-421-5 and SEL-311C-1 relays, and the other

between the SEL-421-5 and SEL-321-1 relays.

We assume the reader of this guide has a basic understanding of pilot protection, so this application

guide does not go into detail on the schemes. For an in-depth discussion of POTT and DCB

schemes, refer to [1] and [2].

NOTE: POTT and DCB schemes are not available on the SEL-311A Phase and Ground Distance Relay and the

SEL-311B Distance Relay With Recloser.

SAMPLE SYSTEM

Figure 1 shows a typical two-terminal system. Relay 1 is an SEL-421-5 and Relay 2 can be an

SEL-311C-1 or an SEL-321-1. The two relays communicate through a fiber-optic connection to

implement a POTT or DCB scheme.

Application Guide Volume I AG2020-04

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Summary

Permissive Overreaching Transfer Trip (POTT) Overview

POTT Scheme Operation Principle

Explains POTT scheme operation using overreaching and reverse-looking elements.

POTT Setup and Logic

POTT Logic Configuration

Details how to set up POTT logic in SEL relays.

SEL-321-1 POTT Settings and Logic

Programming POTT Communications-Assisted Trip

Programs elements for communications-assisted trips in POTT schemes.

SEL-421-5 POTT Logic Details

SEL-311 C-1 POTT Logic Details

Outlines POTT logic settings and equations for the SEL-311C-1.

DCB Setup for SEL-421-5

DCB Scheme Operation Principle

Explains DCB scheme operation using blocking signals.

DCB Setup for SEL-311 C-1

DCB Setup for SEL-321-1

Summarizes DCB logic settings for the SEL-321-1.

Dissimilar Relay Coordination Issues

Considerations for Dissimilar Relays

Discusses issues and considerations for pilot protection between dissimilar relays.

Sensitivity Miscoordination Example

Summary

Permissive Overreaching Transfer Trip (POTT) Overview

POTT Scheme Operation Principle

Explains POTT scheme operation using overreaching and reverse-looking elements.

POTT Setup and Logic

POTT Logic Configuration

Details how to set up POTT logic in SEL relays.

SEL-321-1 POTT Settings and Logic

Programming POTT Communications-Assisted Trip

Programs elements for communications-assisted trips in POTT schemes.

SEL-421-5 POTT Logic Details

SEL-311 C-1 POTT Logic Details

Outlines POTT logic settings and equations for the SEL-311C-1.

DCB Setup for SEL-421-5

DCB Scheme Operation Principle

Explains DCB scheme operation using blocking signals.

DCB Setup for SEL-311 C-1

DCB Setup for SEL-321-1

Summarizes DCB logic settings for the SEL-321-1.

Dissimilar Relay Coordination Issues

Considerations for Dissimilar Relays

Discusses issues and considerations for pilot protection between dissimilar relays.

Sensitivity Miscoordination Example

This application guide, titled "Use SEL-300 and SEL-400 Series Relays to Set Up POTT and DCB Schemes," details the configuration and settings required for Schweitzer Engineering Laboratories (SEL) 300 and 400 series relays to implement Permissive Overreaching Transfer Trip (POTT) and Directional Comparison Blocking (DCB) pilot protection schemes. It specifically addresses scenarios where dissimilar SEL relays are used at different ends of a transmission line, although SEL generally does not recommend such connections.

Function Description:

The guide focuses on enabling and configuring pilot protection schemes, POTT and DCB, between SEL-300 and SEL-400 series relays. POTT schemes rely on an asserted overreaching element at the local terminal receiving permission to trip from the remote terminal. A reverse-looking zone (Zone 3) at the local terminal blocks permission to the remote terminal. DCB schemes, conversely, use an asserted overreaching element at the local terminal that trips at high speed unless it receives a blocking signal from the remote end, typically sent by a reverse-looking zone (Zone 3) at the remote terminal.

The SEL-400 series relay covered is the SEL-421-5 Protection, Automation, and Control System. The SEL-300 series relays include the SEL-311C-1 Transmission Protection System, the SEL-311L Line Current Differential Protection and Automation System, and the SEL-321-1 Phase and Ground Distance Relay. The guide provides specific settings for communications, logic elements, and coordination timers for various combinations of these relays (e.g., SEL-421-5 with SEL-311C-1, and SEL-421-5 with SEL-321-1).

Important Technical Specifications:

Communication Protocols: The relays utilize MIRRORED BITS® communications. For direct fiber communications, fiber-optic transceivers like the SEL-2800 or SEL-2812 are used to convert serial to fiber.
Communication Channels: SEL-311C-1 and SEL-421-5 support two MIRRORED BITS channels (A and B), while SEL-321-1 supports one channel, compatible with either of the SEL-421-5 channels.
Baud Rates: The maximum baud rate for the SEL-421-5 is 38400. The SEL-311C-0 is limited to 38400, and the SEL-311C-1, -2, -3 are limited to 57600. The SEL-321-3, -4, and -5 are limited to 9600. Higher baud rates are generally recommended for direct fiber-optic connections due to faster data transfer capabilities.
MIRRORED BITS Transmit/Receive Identifiers: These settings must match between local and remote relays for proper communication.
TXMODE Setting (SEL-421-5): Set to 'P' (Paced mode) for compatibility with SEL devices that are not SEL-400 series relays. This ensures the SEL-421-5 sends messages at a slower rate (every 3 ms) that older SEL-300 series relays can process, preventing data loss.
Default Status (RXDFLT): For POTT schemes, the default state of the permissive receive bit (RMB1A) should be 0 (XXXXXXX0) for security during communication loss. For DCB schemes, the default state of the block bit (RMB1A) should be 1 (XXXXXXX1).
Relay Elements for Pilot Schemes: Common elements include Zone 2 mho-phase/ground forward-distance (M2P, Z2G), Level 2 residual-ground/negative-sequence forward-overcurrent (67G2, 67Q2), Zone 3 mho-phase/ground reverse-distance (M3P, Z3G), and Level 3 residual-ground/negative-sequence reverse-overcurrent (67G3, 67Q3).
Directional Element Polarization: SEL-321-0, -1, -2, -3, -4 relays only have negative-sequence voltage (Q) polarization. SEL-321-5 has both negative-sequence voltage (Q) and zero-sequence voltage (V) polarization. SEL-421-5, SEL-311L, and SEL-311C-1 allow combinations of Q, V, or zero-sequence current (I) polarization. For miscoordination prevention, the SEL-421-5 should use the same directional elements as the SEL-300 series relay at the other end.
Coordination Time Delay (CTD): Critical for DCB schemes. The CTD must be greater than the communications channel delay and accounts for control input recognition time, remote Zone 3 distance protection maximum operating time, and maximum communications channel time.
Processing Intervals: SEL-400 series relays have a 1/8-cycle processing interval, while most other SEL relays have a 1/4-cycle processing interval. This difference impacts data delay calculations.
Zone 3 Overreach Setting: For two-terminal lines, Zone 3 of the local relay should overreach the remote Zone 2 by a margin of 25 percent, compensating for differences in CT and PT ratios.

Usage Features:

Port Setup: Detailed tables provide example settings for Port 2 on SEL-421-5, SEL-311C-1, and SEL-321-1 relays, including EPORT (Enable Port), PROTO (Communications Protocol), SPEED (Baud Rate), TX_ID (Transmit Identifier), RX_ID (Receive Identifier), RBADPU (Receive Bad Pickup Time), CBADPU (Channel Bad Pickup), and TXMODE (Transmission Mode).
Channel Verification: After port setup, users can verify channel status using TAR ROKA (for SEL-421-5 and SEL-311C-1) or TAR 20 (for SEL-321-1) commands.
POTT Logic Setup: Involves enabling the POTT scheme (ECOMM = POTT or EPOTT = Y), configuring Zone 3 Reverse Block Time Delay (Z3RBD), Echo Block Time Delay (EBLKD), Echo Time Delay Pickup (ETDPU), Echo Duration Time Delay (EDURD), and Weak-Infeed Enable (EWFC).
DCB Logic Setup: Involves enabling the DCB scheme (ECOMM = DCB or EDCB = Y), configuring Zone 3 Reverse Pickup Time Delay (Z3XPU), Zone 3 Pickup Extension Time Delay (Z3XD), Block Trip Receive Extension Delay (BTXD), Zone 2 Phase and Ground Coordination Time Delay (21SD), and 67G and 67Q Coordination Time Delay (67SD).
Logic Programming: Requires programming elements for communications-assisted trip (TRCOMM or MTCS), transmitting permissive/block signals (TMB1A or TMB1 to KEY or DSTRT), mapping received signals (PT1 to RMB1A or RMB1 to PT/BT), and assigning tripping outputs (OUT201/OUT101/OUT1 to TRIP/3PT).
Breaker Contact Status: Wiring a breaker contact status (52A) to an input (IN201/IN101/IN1) is recommended for other relay elements, though not strictly required for DCB and POTT.
Coordination for Dissimilar Relays: Emphasizes matching directional and protective element sensitivities, using the same protective elements where possible, and setting reverse-reaching elements with greater sensitivity than remote overreaching elements. Disabling echo keying logic at the least-sensitive terminal is a consideration if other coordination steps cannot be met.

Maintenance Features:

Communication Delay Considerations: The guide highlights the importance of understanding communication delays, which depend on baud rate and relay processing speed. Choosing appropriate baud rates and accounting for these delays in coordination settings is crucial.
Fault Study: When coordinating SEL-400 series relays with SEL-300 series relays, a fault study is recommended to ensure adequate operating quantities for all internal and external faults.
Instruction Manuals: Users are advised to refer to respective instruction manuals for detailed information on Zone 3 distance protection maximum operating times and operating curves for specific relays.
Troubleshooting: The TAR ROKA and TAR 20 commands provide a quick way to check the operational status of the MIRRORED BITS communication channel, aiding in troubleshooting.