S E L - 7 0 0 G P r o t e c t i o n , C o n t r o l a n d A u t o m a t i o n

L e o G a g h a n , C a s c o S y s t e m s

J a n u a r y 2 4 , 2 0 1 9

Table of Contents

Device Overview………………………………………………………….… 3Sample System………………………………………………………………. 4Logic Diagram………………………………………………………………… 5Example Protection Elements………………………………………… 9

Loss-of-Field (40)………………………………………………….…… 9Voltage-Controlled Overcurrent (51C)……………….…….. 12Ground Over Voltage (59G)…………………………….……..… 14100% Stator Protection (64G)………………………….….…… 16

Event Reporting………………………………………………….….……. 19References…………………………………………………………….….…. 24

Device Overview

Sam

ple

Sys

tem

Logi

c D

iagr

am

Example Protection Elements

Loss of Field (40)

The source of excitation for a generator may be completely or partially

removed through such incidents as accidental tripping of a field breaker, field

open circuit, field short circuit (flash over of the slip rings), voltage regulation

system failure, or the loss of supply to the excitation system. Partial or total

loss-of-field on a synchronous generator is detrimental to both the generator

and the power system which it is connected.

Sample System

Loss of Field (40)

The SEL-700G uses a pair of offset mho circles to detect loss-of-field.

Loss of Field (40)

Mho circles plotted against generator capability curve.

Voltage-Controlled Overcurrent (51C)

The differential relay generally provides primary fault protection for the

generator. Backup fault protection is also recommended to protect the

generator from the effects of faults that are not cleared because of failures

within the normal protection scheme. The backup relaying can be applied to

provide protection in the event of a failure at the generation station, on the

transmission system, or both.

Sample System

Voltage-Controlled Overcurrent (51C)

Ground Overvoltage (59G)

When a SLG fault occurs on an ungrounded system the effected phase

potential to ground goes to zero but the potential from that phase to the other

two phases does not change. The result is the un effected phases potential to

ground being increased by a square root of three and having a phase angle

difference of 60 degrees between each other. This phase arrangement creates

a zero-sequence voltage.

Sample System

Ground Overvoltage (59G)

100% Stator Protection (64G)

The SEL-700G provides a two-zone function designed to detect stator winding

ground faults on high-impedance grounded generators. The Zone 1 element

uses a fundamental-frequency neutral overvoltage element that is sensitive to

faults in the middle and upper portions of the winding. The Zone 2 element

uses a third-harmonic neutral undervoltage scheme to detect ground faults on

the lower portions of the winding

Sample System

100% Stator Protection (64G)

100% Stator Protection (64G)

No Load Full Load

Event Reporting

Event reporting can be triggered from any predefined logic or protection

element. Reports can be as long as 180 cycles (3 seconds) and can record

defined pre and post event lengths

Event reporting give's three phase oscillography as well as word bit status

during the duration of the event.

Can be remotely accessed with proper network configuration

Very helpful tool for troubleshooting

Event Reporting (Differential Trip)

Event Reporting (Lightning Arrestor Fail)

Event Reporting (Sync Capture)

Sync Report

References- Protective Relaying: Principles and Applications, 4th Edition by

Blackburn and Domin

- Protective Relaying for Power Generation Systems by Donald

Reimert

- IEEE Tutorial on Synchronous Generators: Cat. Number 95 TP 102

- IEEE Guide for AC Generator Protection, Standard C37.102-2006

- IEEE 1547 Standard for Interconnecting Distributed Resources with

Electric Power Systems

- SEL-700G Instruction Manual, Date Code 20180629

- Paul Shea and Todd Ward

THANK YOU !