protection basics r3

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1GE Consumer & Industrial

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Protection BasicsPresented by

John S. Levine, P.E.

Levine Lectronics and Lectric, Inc.

770 565-1556

[email protected]


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Protection Fundamentals

By

John Levine


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Outline

Introductions Tools

Enervista Launchpad

OnLine Store Demo Relays at Levine

ANSI number

Training CDs Protection Fundamentals


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Objective

We are here to help make your job easier.This is very informal and designed around

Applications. Please ask question. We

are not here to preach to you. The knowledge base in the room varies

greatly. If you have a question, there is agood chance there are 3 or 4 other peoplethat have the same question. Please askit.


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Tools


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Demo Relays at L-3


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8GE Consumer & Industrialultilin

Relays at L-3


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GE Multilin Training CDs


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ANSI Symbols


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Conversion of Electro-Mechanical

to Electronic sheet

P P i t t ti t


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PowerPoint presentations at:

http://l-3.com/private/ieee/
http://l-3.com/private/ieee/http://l-3.com/private/ieee/http://l-3.com/private/ieee/http://l-3.com/private/ieee/


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Desirable Protection Attributes

Reliability: System operate properly Security: Dont trip when you shouldnt

Dependability: Trip when you should

Selectivity: Trip the minimal amount to clear thefault or abnormal operating condition

Speed: Usually the faster the better in terms ofminimizing equipment damage and maintaining

system integrity Simplicity: KISS

Economics: Dont break the bank


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Selection of protective relays requires compromises: Maximum and Reliable protection at minimum

equipment cost

High Sensitivity to faults and insensitivity to maximum

load currents

High-speed fault clearance with correct selectivity

Selectivity in isolating small faulty area

Ability to operate correctly under all predictable power

system conditions

Art & Science of Protect ion


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Cost of protective relays should be balancedagainst risks involved if protection is not

sufficient and not enough redundancy.

Primary objectives is to have faulted zonesprimary protection operate first, but if there are

protective relays failures, some form of

backup protection is provided.

Backup protection is local (if local primary

protection fails to clear fault) and remote (if

remote protection fails to operate to clear

fault)

Art & Science of Protect ion


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Primary Equipment & Components

Transformers - to step up or step down voltage level

Breakers - to energize equipment and interrupt fault current

to isolate faulted equipment

Insulators - to insulate equipment from ground and other

phases

Isolators (switches) - to create a visible and permanent

isolation of primary equipment for maintenance purposes

and route power flow over certain buses.

Bus - to allow multiple connections (feeders) to the same

source of power (transformer).


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Primary Equipment & Components Grounding - to operate and maintain equipment safely

Arrester - to protect primary equipment of sudden

overvoltage (lightning strike).

Switchgearintegrated components to switch, protect,

meter and control power flow

Reactors - to limit fault current (series) or compensate for

charge current (shunt)

VT and CT - to measure primary current and voltage and

supply scaled down values to P&C, metering, SCADA, etc.

Regulators - voltage, current, VAR, phase angle, etc.


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Types of Protection

Overcurrent Uses current to determine magnitude of fault Simple

May employ definite time or inverse time curves

May be slow Selectivity at the cost of speed (coordination stacks)

Inexpensive

May use various polarizing voltages or ground current

for directionality Communication aided schemes make more selective

I t t O t P t ti (IOC) &


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Instantaneous Overcurrent Protection (IOC) &

Definite Time Overcurrent

Relay closest to fault operates

first Relays closer to source

operate slower

Time between operating forsame current is called CTI(Clearing Time Interval)

Distribution

Substation


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(TOC) Coordination

Relay closest to fault operates

first Relays closer to source

operate slower

Time between operating forsame current is called CTI

Distribution

Substation


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Selection of the curves

uses what is termed as a

time multiplier or

time dial to effectively

shift the curve up or

down on the time axis

Operate region lies

above selected curve,

while no-operate region

lies below it

Inverse curves can

approximate fuse curve

shapes

Time Overcurrent Protection (TOC)


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Multiples of pick-up

Time Overcurrent Protection

(51, 51N, 51G)


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Types of Protection

Differential current in = current out

Simple

Very fast

Very defined clearing area

Expensive

Practical distance limitations Line differential systems overcome this using

digital communications


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Differential

Note CT polarity

dots

This is athrough-current

representation

Perfect

waveforms, nosaturation


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Differential

Note CT

polarity dots

This is aninternal fault

representation

Perfectwaveforms, no

saturation


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Types of Protection

Voltage Uses voltage to infer fault or abnormal

condition

May employ definite time or inverse time

curves May also be used for undervoltage load

shedding Simple

May be slow

Selectivity at the cost of speed (coordinationstacks)

Inexpensive


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Types of Protection

Frequency Uses frequency of voltage to detect power

balance condition

May employ definite time or inverse time

curves Used for load shedding & machinery

under/overspeed protection Simple

May be slow

Selectivity at the cost of speed can be expensive


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Types of Protection

Power Uses voltage and current to determine

power flow magnitude and direction

Typically definite time Complex

May be slow

Accuracy important for many applications

Can be expensive


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Types of Protection

Distance (Impedance) Uses voltage and current to determine impedance of

fault

Set on impedance [R-X] plane

Uses definite time Impedance related to distance from relay

Complicated

Fast

Somewhat defined clearing area with reasonableaccuracy

Expensive

Communication aided schemes make more selective


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Impedance

Relay in Zone 1 operates first

Time between Zones is calledCTI

Source

A B

21 21

T1

T2

ZA

ZB

R

X ZL


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Generation-typically at 4-20kV

Transmission-typically at 230-765kV

Subtransmission-typically at 69-161kV

Receives power from transmission system and

transforms into subtransmission level

Receives power from subtransmission system

and transforms into primary feeder voltage

Distribution network-typically 2.4-69kV

Low voltage (service)-typically 120-600V

Typical

Bulk

PowerSystem



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1. Generator or Generator-Transformer Units

2. Transformers

3. Buses

4. Lines (transmission and distribution)5. Utilization equipment (motors, static loads, etc.)

6. Capacitor or reactor (when separately protected)

Unit Generator-Tx zone

Bus zone

Line zone

Bus zone

Transformer zone Transformer zone

Bus zone

Generator

~

XFMR Bus Line Bus XFMR Bus Motor

Motor zone

ProtectionZones


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1. Overlap is accomplished by the locations of CTs, the key source forprotective relays.

2. In some cases a fault might involve a CT or a circuit breaker itself, which

means it can not be cleared until adjacent breakers (local or remote) are

opened.

Zone A Zone B

Relay Zone A

Relay Zone B

CTs are located at both sides of CB-fault between CTs is cleared from both remote

sides

Zone A Zone B

Relay Zone A

Relay Zone B

CTs are located at one side of CB-fault between CTs is sensed by both relays,

remote right side operate only.

Zone Overlap


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1. One-line diagram of the system or area involved

2. Impedances and connections of power equipment, system

frequency, voltage level and phase sequence

3. Existing schemes

4. Operating procedures and practices affecting protection

5. Importance of protection required and maximum allowed

clearance times

6. System fault studies

7. Maximum load and system swing limits

8. CTs and VTs locations, connections and ratios

9. Future expansion expectance

10. Any special considerations for application.

What Info is Required to Apply Protection


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C37.2:

Device

Numbers

Partial listing



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One Line Diagram

Non-dimensioned diagram showing how

pieces of electrical equipment are

connected

Simplification of actual system

Equipment is shown as boxes, circles and

other simple graphic symbols

Symbols should follow ANSI or IEC

conventions


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1-Line Symbols [1]


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1-Line Symbols [2]


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1-Line Symbols [3]


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1-Line Symbols [4]


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1-Line [1]


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1-Line [2]


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3-Line


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CB Trip Circuit (Simplified)


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Lock Out Relay

86b

PR

86b

Shown in RESET position

86

TC 86a

CB C il Ci it M it i


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CB Coil Circuit Monitoring:

T with CB Closed; C with CB Opened

CB C il Ci it M it i


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CB Coil Circuit Monitoring:

Both T&C Regardless of CB state

Current Transformers


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Current transformers are used to step primary system currents

to values usable by relays, meters, SCADA, transducers, etc.

CT ratios are expressed as primary to secondary; 2000:5, 1200:5,

600:5, 300:5

A 2000:5 CT has a CTR of 400

Current Transformers

St d d IEEE CT R l


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IEEE relay class is defined in terms of the voltage a CT

can deliver at 20 times the nominal current rating

without exceeding a 10% composite ratio error.

For example, a relay class of C100 on a 1200:5 CT means that

the CT can develop 100 volts at 24,000 primary amps

(1200*20) without exceeding a 10% ratio error. Maximum

burden = 1 ohm.

100 V = 20 * 5 * (1ohm)

200 V = 20 * 5 * (2 ohms)

400 V = 20 * 5 * (4 ohms)

800 V = 20 * 5 * (8 ohms)

Standard IEEE CT Relay

Accuracy

Standard IEEE CT B rdens (5 Amp)


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Standard IEEE CT Burdens (5 Amp)(Per IEEE Std. C57.13-1993)

Voltage Transformers


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VP

VS

Relay

Voltage (potential) transformers are used to isolate and step

down and accurately reproduce the scaled voltage for the

protective device or relay

VT ratios are typically expressed as primary to secondary;

14400:120, 7200:120

A 4160:120 VT has a VTR of 34.66

Voltage Transformers

T i l CT/VT Ci it


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Typical CT/VT Circuits

Courtesy of Blackburn, Protective Relay: Principles and Applications

CT/VT Ci it C i G d


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CT/VT Circuit vs. Casing Ground

Case ground made at IT location

Secondary circuit ground made at first point of

use

Case

Secondary Circuit


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Equipment Grounding

Prevents shock exposure of personnel

Provides current carrying capability for the

ground-fault current

Grounding includes design and construction ofsubstation ground mat and CT and VT safety

grounding


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System Grounding

Limits overvoltages

Limits difference in electric potential through local

area conducting objects

Several methods

Ungrounded

Reactance Coil Grounded

High Z Grounded Low Z Grounded

Solidly Grounded


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1. Ungrounded: There is no intentional

ground applied to the system-

however its grounded through

natural capacitance. Found in 2.4-

15kV systems.

2. Reactance Grounded: Total system

capacitance is cancelled by equal

inductance. This decreases thecurrent at the fault and limits voltage

across the arc at the fault to decrease

damage.

X0


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3. High Resistance Grounded: Limitsground fault current to 10A-20A.

Used to limit transient overvoltages

due to arcing ground faults.

R0= 2X0

System Grounding


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5. Solidly Grounded: There is a

connection of transformer orgenerator neutral directly to station

ground.

Effectively Grounded: R0


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Basic Current Connections:How System is Grounded

Determines How Ground Fault is Detected

Medium/High

Resistance

Ground

Low/No

Resistance

Ground


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Substation Types

Single Supply

Multiple Supply

Mobile Substations for emergencies

Types are defined by number of

transformers, buses, breakers to provide

adequate service for application

Industrial Substation Arrangements


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Industrial Substation Arrangements(Typical)

Industrial Substation Arrangements


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Industrial Substation Arrangements(Typical)

Utility Substation Arrangements


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Single Bus, 1 Tx, Dual supply Single Bus, 2 Tx, Dual

Supply

2-sections Bus with HS Tie-Breaker,

2 Tx, Dual Supply

(Typical)



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Breaker-and-a-halfallows reduction of

equipment cost by using 3 breakers for

each 2 circuits. For load transfer and

operation is simple, but relaying is

complex as middle breaker is responsible

to both circuits


Bus

1

Bus 2

Ring busadvantage that one

breaker per circuit. Also each

outgoing circuit (Tx) has 2 sources

of supply. Any breaker can be taken

from service without disrupting

others.

(Typical)



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Double Bus:Upper Main and

Transfer, bottom Double Main bus

Main bus

Aux. bus

Bus 1

Bus 2

Tie

breaker


Main

ReserveTransfer

Main-Reserved and Transfer

Bus: Allows maintenance of any

bus and any breaker

(Typical)

Switchgear Defined


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Switchgear Defined Assemblies containing electrical switching,

protection, metering and management devices Used in three-phase, high-power industrial,

commercial and utility applications

Covers a variety of actual uses, including motor

control, distribution panels and outdoorswitchyards

The term "switchgear" is plural, even whenreferring to a single switchgear assembly (never

say, "switchgears") May be a described in terms of use:

"the generator switchgear"

"the stamping line switchgear"

Switchgear Examples


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Switchgear Examples

A Good Day in System


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A Good Day in System

Protection

CTs and VTs bring electrical info to relays

Relays sense current and voltage and declare

fault

Relays send signals through control circuits tocircuit breakers

Circuit breaker(s) correctly trip

What Cou ld Go Wrong Here????

A Bad Day in System


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y y

Protection

CTs or VTs are shorted, opened, or their wiring is Relays do not declare fault due to setting errors,

faulty relay, CT saturation

Control wires cut or batteries dead so no signal issent from relay to circuit breaker

Circuit breakers do not have power, burnt trip coil

or otherwise fail to trip

Protect ion Systems Typ ical ly are

Designed for N-1


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Protection Performance Statistics

Correct and desired: 92.2%

Correct but undesired: 5.3% Incorrect: 2.1%

Fail to trip: 0.4%

Contribution to Faults


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Contribution to Faults


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Fault Types (Shunt)

AC & DC Current Components


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AC & DC Current Components

of Fault Current

Useful Conversions


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Useful Conversions


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Per Unit System

Establish two base quantities:

Standard practice is to define

Base power3 phase

Base voltageline to line

Other quantities derived with basic powerequations

Per Unit Basics


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Per Unit Basics

Short Circuit Calculations


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Per Unit System

Per Unit Value = Actual QuantityBase Quantity

Vpu

= Vactual

Vbase

Ipu = Iactual

Ibase

Zpu = ZactualZbase

Sh t Ci it C l l ti


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Per Unit System



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Per Unit SystemBase Conversion

Zpu = ZactualZbase

Zbase = kV2base

MVAbase

Zpu1= MVAbase1kV 2base1

XZactual

Zpu2= MVAbase2kV 2base2

XZactual

Zpu2 =Zpu1 x kV2base1 xMVAbase2

kV 2base2 MVAbase1

A St d f F lt


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A Study of a Fault.

A Fl h H d


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Arc Flash Hazard

Protective Relaying Methods


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of Reducing Arc Flash Hazard

Bus differential protection (thisreduces the arc flash energy by

reducing the clearing time

Zone interlock schemes where

bus relay selectively is allowed

to trip or block depending onlocation of faults as identified

from feeder relays

Temporary setting changes to

reduce clearing time during

maintenance

Sacrifices coordination

FlexCurve for improvedcoordination opportunities

Employ 51VC/VR on feeders

fed from small generation to

improve sensitivity and

coordination Employ UV light detectors with

current disturbance detectors

for selective gear tripping

Arc Flash Hazards


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Arc Flash Hazards


Arc Pressure Wave


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Arc Pressure Wave


Copy of this presentation are at:


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www.L-3.com\private\IEEE


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protection basics r3

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