Power System Protection - UPRMlorama/Week8b.pdf · Power System Protection Dr. Lionel R. Orama...

Power System Protection

Dr. Lionel R. Orama Exclusa, PEWeek 8

Copyright L.R. Orama 2006 2

Distance Relays

• Mason– Chapter 4, pgs. 61-76


Objectives

• R-X Diagrams• Operating Principles of:

– Impedance– Admittance (Mho)– Reactance

• Memory Action


Distance Relays

• Respond to phasor ratio of input voltage & input current to relay (V/I)

• They are directional• They have high speed• Used to protect transmission lines• Usually induction cup design


Construction


R-X Diagram

• Can use impedance or R-X diagram to analyze relay operation

1. Plot relay characteristic

2. Plot impedance “seen” by the relay (Z relay)


Impedance Relay


Admittance (Mho) Relay


Offset Mho


Angle Impedance Relay

Non-Directional

Not appropriate to work alone


Reactance Relay

Non-Directional


Distance Relays• Operating Time

– Induction Cup: High Speed

• Adjustments– Reach: Tapped

Transformer• Rises or lowers voltage on

restraining coil• Range of Z to cover down

the line

– Offset: Tapped Reactor• For offset Mho, adjust ZT


Application of Distance Relays to Transmission Line Protection

• Phase distance relays• Ground distance relays (will not be

covered)• Step distance relays

– Usually 3 zones

• Distance better than overcurrent– Faster– Easier coordination– Permit higher line loading


System Impedance on Relay Base


PT Connections-Phase Distance Relays

600577115

4.66

10115

115 3

→===

===

V

kV

V

VPTR

V

kV

V

VPTR

LGout

LGinLG

LLout

LLinLL


CT Connection to Op Coils


Impedances Detected by Phase Relays

3 Phase Fault

Phase-Phase Fault

Relay setting based on Positive Sequence Impedance (Z1)


Step Distance Relaying

Objectives• Zones of protection• Effect of arc resistance• Effect of infeed• Methods to reduce size of distance relay

characteristic


Zones of Protection-3 Zones

• 3 zones (Primary & Backup)Purpose: Provide high speed tripping for internal faults• Relay must be set to underreach• Does not cover entire line• Zone 1 settings:

– Reach:80-90%– Time: No time delay

Zone 1


Zones of Protection

Purpose: Cover remaining 10-20% of AB segment• Zone 2 must reach beyond B• Will detect faults on CD segment• Must have time delay• Zone 2 settings:

– Reach:120%– Time: 0.2-0.4 seconds

Zone 2


Zones of Protection

Purpose: Provides Backup protection for faults on adjacent line

• Do not set such that load can cause a trip• Zone 3 settings:

– Reach:120% of ZAB+ZCD

– Time: 0.4-1.0 seconds

Zone 3

Equivalent Relays at B and D looking on the other direction


Three Zones of Protection Using Mho Relays

• Advantage– Lots of fault coverage

• Disadvantage– Characteristic gets

close to ZLOAD

GCY - GE Mho


Relay Characteristic Vs Arc Resistance

• illustrates increase RF coverage with mho relay (GCY) & reactance relay (GCX)– O1 & M3 operate - Zone 1– O2 & M3 operate – Zone 2– M3 operate – Zone 3– M1 – Zone1 using mho


Zone 3 Setting with Infeed


Zone 3 Setting with Infeed

danger


Use of Blinders where Impedance may cause incorrect tripping

Zone 3 so big that ZLOAD gets inside of it

Angle Impedance relays to blind


Reverse Third ZoneZAB+ZCDIF/IA


Reverse Third Zone

Load


Admittance Relay Settings• Reach: Diameter of Mho

Circle– Maximum Z that makes

relay operate


Admittance Relay Settings

• t varies from 0.10 to 1.00 (t higher, smaller circle)• k is called Basic Minimum Reach is adjustable• Angle of maximum torque is adjustable• Offset is adjustable


Impedances Detected by all Relays During B-C Fault

B-C Relay

A-B Relay

C-A Relay


Impedances Detected by all Relays During B-C Fault

Power System Protection - UPRMlorama/Week8b.pdf · Power System Protection Dr. Lionel R. Orama...

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