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Application Guide Volume I AG98-07

Implementing a Breaker Failure Function in the SEL-351 Relay

Bill Fleming

INTRODUCTION

The SEL-351 Relay is an extremely flexible device. This flexibility is a result of Enhanced SELOGIC® control equations and allows the SEL-351 Relay to provide many useful functions in addition to its pre-assigned tasks. This application guide details how to build a complete breaker failure relay function into the SEL-351 Relay using SELOGIC control equations.

SV2

IN1(52A)50P150G1

IN2(BFI)

SV4

SV7

SV3

SV1

SV5PU

SV5DO

SV6PU

SV6DO

SV5

SV6

SV5T

SV6T Retrip

BreakerFailure

DWG: AG980008.vsd

SV1 = 0 or 1 (disable or enable 52a supervision)SV2 = 0 or 1 (disable or enable BFI seal-in)SV3 = 0 or 1 (disable or enable retrip)SV4 = 0 or 1 (retrip is supervised or unsupervised)

Figure 1: Logic Diagram of Breaker Failure Scheme

INPUTS

Two inputs are used for the breaker failure relay. One input monitors the 52a breaker auxiliary contact for use in supervision and the other input is used as an external breaker failure initiate input.

2 SEL Application Guide 98-07 Date Code 991221

Input Function IN1 52a IN2 BFI

The programming required for input assignments consists of the one following setting:

SET L 52A • 52A = IN1

CURRENT DETECTORS

Two overcurrent elements are used to supervise breaker failure operations. One phase instantaneous overcurrent element (50P1) is used for three-phase and phase-to-phase faults and one residual ground instantaneous overcurrent element (50G1) is used for faults involving ground. Settings required for the overcurrent detectors are:

SET E50P • E50P = 1 (or more, to enable at least one phase overcurrent element) • E50G = 1 (or more, to enable at least one residual ground overcurrent element) • 50P1P = phase current detector pickup in secondary amps • 50G1P = residual ground current detector pickup in secondary amps

CONTROL VARIABLES

To make this breaker failure scheme universal, four SELOGIC control equation variables are used to modify the operating characteristics of the scheme. The SELOGIC control equation variables and their functions are shown below:

SELOGIC Logical Variable Value Function

SV1 0 Disable 52a supervision 1 Enable 52a supervision

SV2 0 Disable BFI seal-in 1 Enable BFI seal-in

SV3 0 Disable Retrip 1 Enable Retrip

SV4 0 Retrip, if enabled by SV3 above, is supervised 1 Retrip, if enabled by SV3 above, is not supervised

Since these characteristics are not likely to change for individual schemes, they are controlled by relay settings directly. SV1 through SV4 are “hardcoded” as a logical one or logical zero via the following settings:

SET L SV1 • SV1 = 0 or 1 • SV2 = 0 or 1 • SV3 = 0 or 1 • SV4 = 0 or 1

Date Code 991221 SEL Application Guide 98-07 3

INTERMEDIATE VARIABLES

Three SELOGIC control equation variables are used as intermediate variables. These variables appear in the central portion of the logic diagram and are used to simplify the overall SELOGIC control equations. The programming required for these three intermediate variables is:

SET L SV5 • SV5 = SV5*SV2*SV7 + IN2*SV7 • SV6 = (SV7 + SV4)*SV3*IN2 • SV7 = SV1*IN1 + 50P1 + 50G1

BREAKER FAILURE AND RETRIP TIMERS

The timed SELOGIC control equation variables SV5T and SV6T are used for breaker failure and retrip logic respectively. The breaker failure time delay is set using the SV5PU setting and the retrip time delay, if required, is set using the SV6PU setting.

SET SV5PU • SV5PU = breaker failure time in cycles • SV6PU = retrip time in cycles

The dropout timers for the above two SELOGIC control equation variables may be used to provide minimum trip duration timers to assure that the appropriate action (such as tripping a lockout relay) has occurred before attempting to open the breaker failure or retrip output contacts.

SET SV5DO • SV5DO = 9 cycles typical • SV6DO = 9 cycles typical

OUTPUTS

Program an output contact to SV5T for a breaker failure output contact and use SV6T for a retrip output contact. As an example:

SET L OUT1 • OUT1 = SV5T • OUT2 = SV6T

CONCLUSION

A fully functional and flexible breaker failure function may be easily implemented in the SEL-351 Relay using SELOGIC control equations.

4 SEL Application Guide 98-07 Date Code 991221

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