Power System Protection Dr. Lionel R. Orama Exclusa, PE Week 9
Pilot Relaying Communication channels & signals Pilot wire schemes Opposed voltage Circulating current Blocking schemes Directional comparison Phase comparison Tripping schemes DUTT, PUTT, POTT Hybrid schemes Copyright L.R. Orama 2006 2
Suggested Reading Mason Chapter 5, pgs. 77-88 Chapter 6, pgs. 79-98 Copyright L.R. Orama 2006 3
Pilot Relaying Zone 1- under-reach For F2, R1 send signal to R2 to open No intentional time delay, Op time for signal to get to the remote station Copyright L.R. Orama 2006 4
Blocking & Tripping Schemes Blocking Schemes When a signal is received from remote terminal, tripping is not permitted (blocked) at local terminal Tripping Schemes When a signal is received from a remote terminal, tripping occurs at local terminal Copyright L.R. Orama 2006 5
Blocking & Tripping Schemes Fault Internal External Scheme Tripping Blocking Tripping Blocking Signal Signal sent Signal not sent Signal not sent Signal sent Copyright L.R. Orama 2006 6
Blocking & Tripping Schemes Channel failure Blocking (security) Internal fault not a problem External fault, signal not sent problems Tripping (dependability) Internal fault, signal not sent problems External fault - not a problem Copyright L.R. Orama 2006 7
Channels & Signals for Pilot Relaying Types of Channels for line protection Wire lines & cables Fiber optic cables Power line carrier Microwave Copyright L.R. Orama 2006 8
Wire lines (Pilot Wire) Wire line twisted pair of wires between terminals Usually telephone circuit is rented Open wire or buried cable Can be used as channel for: AC pilot relay, up to 10 miles Frequency shift audio tone signal (850-3200Hz), up to 30 miles Copyright L.R. Orama 2006 9
Wire Line & Cables Advantages Simple Economical for short distances Disadvantages Susceptible a natural hazards (lightning) Susceptible to electromagnetic interference, EMI (noise) Copyright L.R. Orama 2006 10
Fiber Optic Cable Glass rather that conductor Advantages Immune to EMI (noise) Limitations Expensive Special termination equipment Copyright L.R. Orama 2006 11
Copyright L.R. Orama 2006 12
Power Line Carrier Advantages Most reliable form of communication Most economical for few channels over long distance Repeaters not require for long distance Disadvantages Susceptible to line noise and fault attenuation Limited frequency spectrum Copyright L.R. Orama 2006 13
Microwave Copyright L.R. Orama 2006 14
Microwave Advantages Independent path not affected by line noise or faults Accommodates a large number of channels Large frequency spectrum available Disadvantages Very expensive for low channel density Interim sites required for repeaters Subject to propagation fades Copyright L.R. Orama 2006 15
Pilot Relaying Schemes Pilot wire schemes Blocking schemes When signal is received from remote terminal, tripping is not permitted at local terminal Tripping schemes When signal is received from remote terminal, tripping occurs at local terminal Copyright L.R. Orama 2006 16
Pilot Wire Schemes Opposed voltage Circulating current Basically current differential schemes Application considerations Loop R < 2000 Ohms Shunt C < 1.5uF (20-30 miles) Copyright L.R. Orama 2006 17
Opposed Voltage AC Pilot Wire Scheme External Fault Copyright L.R. Orama 2006 18
Opposed Voltage AC Pilot Wire Scheme Internal Fault Copyright L.R. Orama 2006 19
Opposed Voltage AC Pilot Wire Scheme Open Pilot Wire Copyright L.R. Orama 2006 20
Opposed Voltage AC Pilot Wire Scheme Short Circuited Pilot Wire Copyright L.R. Orama 2006 21
Circulating Current AC Pilot Wire Scheme External Fault Copyright L.R. Orama 2006 22
Circulating Current AC Pilot Wire Scheme Internal Fault Copyright L.R. Orama 2006 23
Circulating Current AC Pilot Wire Scheme Open Pilot Wire Copyright L.R. Orama 2006 24
Circulating Current AC Pilot Wire Scheme Short Circuited Wire Copyright L.R. Orama 2006 25
Comparison of Failure Modes Copyright L.R. Orama 2006 26