ieee c37.234 guide for protective relay application to...

IEEE C37.234 Guide for Protective

Relay Application to Power

System Buses

B.Kasztenny (Chairman), S.Conrad (Vice-Chairman),

P.Beaumont, K.Behrendt, O.Bolado, J.Boyle, G.Brunello,

J.Burger, F.Calero, S.Chano, G.Dalke, A.Darlington, H.DoCarmo,

D.Fontana, Z.Gajic, J.Holbach, L.Kojovic, F.Lopez, D.Lukach,

D.McGinn, J.Miller, P.Mysore, J.O'Brien, B.Pickett,

S.Sambasivan, G.Sessler, V.Skendzic, J.Smith, D.Tholomier,

M.Thompson, J.Uchiyama, D.Ware, D.Weers, R.Whittaker,

R.Young, S.Zocholl

Presentation to the Main Committee of PSRC, January 14, 2010, Orlando, FL

Table of Contents

• Definitions

• Bus configurations

• Introduction to bus protection

• Relay input sources

• Bus protection methods

• Application of bus protection schemes

• Annexes

Definitions

• 23 new terms defined

• Bus protection and primary equipment

breaker substitution – Temporary usage of a bus tie breaker in a

multiple bus configuration to substitute for one of the network

element’s circuit breakers, typically for the maintenance of the latter;

also known as breaker transfer

breaker substitution – Temporary usage of a bus tie breaker in a

multiple bus configuration to substitute for one of the network

element’s circuit breakers, typically for the maintenance of the latter;

also known as breaker transfer

check zone – Nonselective part of a multi-zone bus protection

system measuring current flows around the entire station and

supervising selective tripping from individual bus zones of protection

check zone – Nonselective part of a multi-zone bus protection

system measuring current flows around the entire station and

supervising selective tripping from individual bus zones of protection

stub bus – Area of a bus or line that becomes isolated from the

original zone of protection or an area that loses protection due to the

loss of sensing to zone protection relays

stub bus – Area of a bus or line that becomes isolated from the

original zone of protection or an area that loses protection due to the

loss of sensing to zone protection relays

Bus design considerations

• Continuity of service for the bus and essential network elements

• Equipment maintainability and network switching flexibility

• Economical and footprint constraints

• Sectionalizing requirements to avoid exceeding breaker fault duties

• Ease of future bus expansion

Bus arrangements

• Single bus

• Main and transfer bus

• Double-bus double-breaker

• Double-bus single-breaker

• Breaker-and-a-half

• Ring bus

Main and transfer bus

Bus zone

Transfer bus

TB

Introduction to bus protection

• Zones of protection

• Bus protection methods

• Scheme selection guidelines

Zones of protection

Bus zone

Dynamic zones of protection

Zones of protection

Over-tripping spot for bus protection

Blind spot for network

element protection

Bus

Over-tripping spot for network element protection

Blind spot for bus protection

Bus

Bus protection methods

• Differential

– Differentially-connected overcurrent

• Instantaneous

• Time-delayed

– Percentage-restrained differential

• Restrained

• Advanced microprocessor based

– High-impedance differential

• Resistor-stabilized overcurrent

• High-impedance

– Partial differential overcurrent

– Fault bus

Bus protection methods

• Zone-interlocked schemes

– Simple blocking

– Directional blocking

• Time-coordinated relays overlapping the bus

• Protection (sensors) built into the gas isolated

switchgear*

* Not covered in the Guide

Scheme selection criteria

• Bus arrangement and flexibility

– Fixed vs. switchable buses

• Availability and characteristics of CTs

• For reconfigurable buses, availability of

auxiliary contacts of disconnect switches

• Performance requirements

– Security, Selectivity, Speed, Sensitivity

• Cost and complexity

Scheme

selection

Dif

fere

nti

ally

co

nn

ect

ed

ov

erc

urr

en

t

Pe

rce

nta

ge

-re

stra

ine

d

dif

fere

nti

al

Ad

van

ce

d p

erc

en

tage

-

rest

rain

ed

dif

fere

nti

al

Hig

h-i

mp

ed

an

ce d

iffe

ren

tia

l

Pa

rtia

l

dif

fere

nti

al

ov

erc

urr

en

t

Zon

e in

terl

ock

ed

sim

ple

blo

ckin

g

Zon

e i

nte

rlo

cke

d d

irec

tio

na

l

blo

ckin

g

Tim

e c

oo

rdin

ate

d r

ela

ys

tha

t

ov

erl

ap

th

e b

us

zon

e

Breaker/Bus Arrangements

Fixed bus arrangements R R R

Switchable bus arrangements R1 N

1

Bus Sectionalized with switches R R R

Buses with low short circuit levels R R R

Available CTs

Dedicated CTs available R R R

Shared CTs with other protection R R N R R

Unmonitored network elements N N N R R R R

CTs with unmatched ratios N R R N2 R R

CTs with low accuracy class N R3 R

4

Performance

Selectivity H H H H L H H L

Speed H5 M H H L

6 M M L

Sensitivity H5 M M H L M M M

Security L M H H L M M H7

Relay input sources

• Current transformers

– Types

– Accuracy classes

– Equivalent circuit & time to saturation

– No universal CT requirements

• Voltage Transformers

– Voltage trip supervision

– Directional blocking schemes

• Position of switches and breakers

Detailed scheme review

• Section 7 gives in-depth review of each

method following a consistent pattern

– Theory of operation

– Setting considerations

– CT requirements

–Application considerations

Example – High-impedance scheme

Voltage setting:

• Above the maximum voltage for an

external fault assuming that one CT

saturates completely

• High enough so that pickup current is

above the short circuit current on the

secondary of any PT or station service

transformer inside the bus zone

• Below the accuracy class voltage

rating of the lowest accuracy class CT

in the differential circuit

• Low enough so that pickup current is

below the minimum fault current for

the bus

ZSR50

59

MOV

86

87

Example – High-impedance scheme

CT requirements:

• CTs dedicated to bus protection

(cannot be shared)

• Equal CT ratios*

• The accuracy class voltage rating of

the CT with the lowest accuracy class

above the selected voltage setting,

with margin

ZSR50

59

MOV

86

87

* Ratio matching covered but discouraged

Application of bus protection

• Partial differential

– Loads

– Capacitor banks

– Application with overcurrent and distance relays

• Combined bus and transformer zone

• Buses with directly connected grounding

transformers

• Application of auxiliary transformers

– Generally discouraged


• Applications with paralleled CTs

– Generally discouraged

– Guidelines included


• Application of auxiliary tripping relays

– Lockout relays

– Non-lockout relays

– Ratings

• Automatic reclosing after bus faults

• Dynamic bus replica

• Check-zone

• Voltage trip supervision

Dynamic bus replica

Position of switches and breakers

89a 89b

Position

Filtering

Logic

Switch

Position

Discrepancy

Alarm

Bus Protection System

Binary Inputs

Auxiliary contacts Scheme output

89a 89b Declared position Discrepancy alarm

On Off Closed Normal

Off On Opened Normal

On On Closed Alarm

Off Off Closed Alarm

“If not opened, then closed” logic

In-service transfer

Check zoneCheck zone


• Application of CT trouble detection

– Detection methods

– Fallback strategies

• Reliable, selective tripping at the

differential zone boundary

– Line-side CT

– Bus-side CT

– Bus coupler considerations

– The role of Breaker Failure protection

Line-side CT

CB close command

Trip Network

Element

Instantaneous Overcurrent (50/CT-2)

Bus coupler considerations


• CT column ground fault protection

• In-zone grounds

– Surge arresters

– Safety grounds and circulating current while

testing

– In-zone grounding of out-of-service elements

• In-service transfer of network elements

and breaker substitution

Breaker substitution

C-1

CT-1

CB-1

BSw-1

CT-5

CB-4

CT-4

DSw-2DSw-1

C-2

CT-2

CB-2

BSw-2

DSw-4DSw-3

C-3

CT-3

CB-3

BSw-3

DSw-6DSw-5

BUS 1

BUS 2


• Stub bus considerations

• Breaker Failure considerations

• Backup protection

– Local backup

• Duplicated relays

• BF, batteries, wiring

• Reverse-looking distance relays

• Overcurrent relays

–Remote backup

Annexes

• Setting example for a high-impedance

scheme (Annex A)

• Logic example for double-bus single-

breaker configuration (Annex B)

– Bus and Breaker Failure protection

– Two zones, check zone and voltage supervision

– In-service transfers and breaker substitution

• Setting guidelines for differentially

connected OC schemes (Annex C)

C37.234 Highlights

• Complex bus arrangements and switching

• Advanced bus protection topics

(reconfigurable buses, µP relays)

• Balanced coverage of high- and low-

impedance schemes

• Protection scheme selection guidelines

• CT requirements given per scheme

• List of application considerations

• Detailed examples for most common schemes

ieee c37.234 guide for protective relay application to...

Documents