Power System Protection Dr. Lionel R. Orama Exclusa, PE Week 8
Distance Relays Mason Chapter 4, pgs. 61-76 Copyright L.R. Orama 2006 2
Objectives R-X Diagrams Operating Principles of: Impedance Admittance (Mho) Reactance Memory Action Copyright L.R. Orama 2006 3
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 Copyright L.R. Orama 2006 4
Construction Copyright L.R. Orama 2006 5
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) Copyright L.R. Orama 2006 6
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Impedance Relay Copyright L.R. Orama 2006 12
Admittance (Mho) Relay Copyright L.R. Orama 2006 13
Offset Mho Copyright L.R. Orama 2006 14
Offset Mho Copyright L.R. Orama 2006 15
Angle Impedance Relay Non-Directional Not appropriate to work alone Copyright L.R. Orama 2006 16
Reactance Relay Non-Directional Copyright L.R. Orama 2006 17
Operating Time Induction Cup: High Speed Adjustments Reach: Tapped Transformer Distance Relays Rises or lowers voltage on restraining coil Range of Z to cover down the line Offset: Tapped Reactor For offset Mho, adjust Z T Copyright L.R. Orama 2006 18
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 Copyright L.R. Orama 2006 19
System Impedance on Relay Base Copyright L.R. Orama 2006 20
System Impedance on Relay Base Copyright L.R. Orama 2006 21
PT Connections-Phase Distance Relays PTR LL = V V LLin LLout 115 kv = = 10 3 115V PTR LG = V V LGin LGout = 66.4kV 115V = 577 600 Copyright L.R. Orama 2006 22
CT Connection to Op Coils Copyright L.R. Orama 2006 23
Impedances Detected by Phase Relays 3 Phase Fault Phase-Phase Fault Relay setting based on Positive Sequence Impedance (Z 1 ) Copyright L.R. Orama 2006 24
Step Distance Relaying Zones of protection Objectives Effect of arc resistance Effect of infeed Methods to reduce size of distance relay characteristic Copyright L.R. Orama 2006 25
Zones of Protection-3 Zones Zone 1 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 Copyright L.R. Orama 2006 26
Zones of Protection Zone 2 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 Copyright L.R. Orama 2006 27
Zones of Protection Zone 3 Equivalent Relays at B and D looking on the other direction 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 Z AB +Z CD Time: 0.4-1.0 seconds Copyright L.R. Orama 2006 28
Three Zones of Protection Using Mho Relays GCY - GE Mho Advantage Lots of fault coverage Disadvantage Characteristic gets close to Z LOAD Copyright L.R. Orama 2006 29
Relay Characteristic Vs Arc Resistance illustrates increase R F 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 Copyright L.R. Orama 2006 30
Zone 3 Setting with Infeed Copyright L.R. Orama 2006 31
Zone 3 Setting with Infeed danger Copyright L.R. Orama 2006 32
Use of Blinders where Impedance may cause incorrect tripping Zone 3 so big that Z LOAD gets inside of it Angle Impedance relays to blind Copyright L.R. Orama 2006 33
Reverse Third Zone Z AB +Z CD I F /I A Copyright L.R. Orama 2006 34
Reverse Third Zone Load Copyright L.R. Orama 2006 35
Admittance Relay Settings Reach: Diameter of Mho Circle Maximum Z that makes relay operate Copyright L.R. Orama 2006 36
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 Copyright L.R. Orama 2006 37
Impedances Detected by all Relays During B-C Fault B-C Relay A-B Relay C-A Relay Copyright L.R. Orama 2006 38
Impedances Detected by all Relays During B-C Fault Copyright L.R. Orama 2006 39