PROTEKSI PILOT SALURAN TRANSMISI

PENDAHULUAN

Penggunaan proteksi non pilot (relay distance,diferensial dan directional overcurent) pada salurantransmisi memiliki kelemahan yaitu pemutusangangguan tidak dapat dilakukan secara instant darikedua ujung saluran apabila terjadi gangguan padaujung saluran terdekat. Pada proteksi non pilot,koordinasi dicapai dengan mengatur tundaan waktudari relay yang terpasang pada saluran yangberdekatan dengan konsep main dan backupprotection. Akibatnya pemutusan gangguan akanberlangsung lambat sesuai dengan tundaan waktu darirelay yang bekerja pada masing – masing zonaproteksi.

Untuk mengatasi hal ini, proteksi pada salurantransmisi dapat dilakukan dengan cara:

Penerapan proteksi diferensial (untuktransmisi jarak pendek)

Penerapan proteksi pilot (menggunakan pilot relay) untuk jarak transmisi yang jauh.

PROTEKSI PILOT

Proteksi pilot merupakan mekanisme proteksipada sistem tenaga yang dilengkapi denganperalatan komunikasi, sehingga masing – masingrelay proteksi yang terpasang dapat salingberkomunikasi satu sama lain. Proteksi pilot inisering disebut juga Tele Proteksi

PERALATAN KOMUNIKASI PROTEKSI PILOT

• power line carrier • microwave • fiber optics • communication cable.

POWER LINE CARRIER

POWER LINE CARRIER

PLC systems operate in an on–off mode by transmitting radio frequency signals in the 10 to 490

kHz band over transmission lines. PLC systems with power outputs of 10 W are reliable up to

about 100 miles and those with 100 W outputs are effective at over 150 miles. Coupling

capacitors are used to couple the carrier equipment to the high-voltage transmission line. They

are low-impedance paths to the high frequency of the carrier current but high-impedance paths

to the 60 Hz power frequency. In conjunction with the coupling capacitors, line tuners and wave

traps are used which present low impedance to the power frequency and high impedance to the

radio frequency. The signal is thus trapped between the ends of the line. Normally only one 4

kHz bandwidth channel is provided exclusively for protection. The transmission time is

approximately 5 ms.

MICROWAVE

Microwave operates at frequencies between 150 MHzand 20 GHz. This bandwidth can be put at the disposalof protection systems with many 4 kHz channelsoperating in parallel. Protection, however, is usually asmall part of the total use of a microwave system. Thelarge bandwidth allows a wide variety of information tobe sent, such as voice, metering, alarms, etc.Microwave is not affected by problems on thetransmission line but is subject to atmosphericattenuation and distortion. The transmission length islimited to a line-of-sight path between antennas but canbe increased through the use of repeaters for increasedcost and decreased reliability.2

FIBER-OPTIC LINKS

The use of fiber cable, however, is rarely justified just for protection but, with its

large data transmission capacity, it is used for dispatching and telemetering. Once

available, however, it makes an excellent communication channel for relaying. Many

utilities are installing multiple paths of fiber-optic cable, using sophisticated

computer programs to monitor the integrity of the cable and to reroute the signals in

the event of difficulty on any path. Figure 6.4 shows several methods of stringing

fiber-optic cable. Two of the most common methods are to embed the fiber cable

within the aluminum conductors of the overhead ground wire (Figure 6.4(d)) or to

wrap the fiber cable around one of the phase or ground conductors. The channel

capacity is virtually unlimited, providing as many as 8000 4 kHz channels per fiber.

FIBER-OPTIC LINKS

PILOT WIRE

Telephone cable consists of shielded copper conductors, insulated

up to 15 kV, and is the most popular form of pilot protection using a

separate communication medium for short distances (up to 10–15

miles). This type of communication channel has a bandwidth from 0

kHz (DC) to 4 kHz. Attenuation is a function of cable type, cable

length and frequency. Overhead cable is vulnerable to induced

voltages by power line faults and lightning. Buried cable is subject to

damage by digging or animals.

PILOT WIRE

MODEL OPERASI PROTEKSI PILOT

A blocking mode is one in which the presenceof a transmitted signal prevents tripping of acircuit breaker. The use of a blocking signal ispreferred if the communication medium is anintegral part of the protected line section, suchas PLC.

A tripping mode is one in which the signalinitiates tripping a circuit breaker. Used in aseparate transmission medium such asmicrowave, fiber-optic cable or a pilot cable

MEKANISME PROTEKSI PILOT

Directional comparison blocking Directional comparison unblocking Underreaching transfer trip Permissive overreaching transfer trip Permissive underreaching transfer trip Phase comparison relaying Current differential Pilot wire relaying

DIRECTIONAL COMPARISON BLOCKING

The fundamental principle upon which this scheme is based utilizes the fact that, at

a given terminal, the direction of a fault, either forward or backward, is easily

determined. a directional relay can differentiate between an internal or an external

fault. By transmitting this information to the remote end, and by applying the

appropriate logic, both ends can determine whether a fault is within the protected

line, or external to it. For phase faults, a directional or nondirectional distance relay

can be used as a fault detector to transmit a blocking signal, i.e. a signal that, if

received, will prevent the circuit breaker from tripping. Tripping is allowed in the

absence of the signal, plus other supervising relay action.

DIRECTIONAL COMPARISON BLOCKING

DIRECTIONAL COMPARISON BLOCKING

DIRECTIONAL COMPARISON BLOCKING

If we assume an internal fault at F1, since the tripping relays Dab and Dba are directional and are set to see faults

from the bus into and beyond the line, contact 21-1 (Figure 6.7) will close. If the fault detector starting relays FDab

and FDba are directional, they are set with reversed reach, i.e. to see behind the protected line, and they will not

see the fault at F1 and will not send a blocking signal (contact 85-1 in Figure 6.7 will remain closed). If they are

nondirectional, they will start transmission but the directional relays will stop it. In either case, since the receiver

relay contacts 85-1 will be closed due to the absence of a carrier signal, and the directional relays have operated,

both ends will trip their associated breakers. An external fault, F2, will result in the operation of the directional relay

Dab at breaker 1, but if fault detector FDab is directional it will not operate for the fault at F2. If FDab is

nondirectional, it will start transmitting a blocking signal but Dab will stop it. At breaker 2, however, FDba will operate

whether it is directional or not, and the tripping relay Dba will not operate to stop transmission. Breaker 1 will not trip

since it is receiving a blocking signal from terminal B, opening its receiver relay contact, and breaker 2 will not trip

for two reasons: it is receiving its own blocking signal and relay Dba did not operate.

SETTING DIRECTIONAL COMPARISON BLOCKING

A major advantage in applying distance relays in a directional comparison scheme

is the relative ease and consistency of the settings. Since the distance relay

operates on the ratio of V /I, load is not usually a concern. The major criteria are

that the blocking signal must be present for all external faults and the tripping relay

must operate for all internal faults. The usual setting for the carrier trip relay is 175–

200% of the protected line section. For the reversed mho carrier start relay, the

carrier start at one terminal must overreach the carrier trip relay at the other

terminal. If this relay is a directional, reversed mho-type relay, it is set at 125–160%

of (Mtrip − Zline). If it is a nondirectional impedance-type relay, it is set at 150%

beyond the longest tripping zone.

EXAMPLE 1

(a) Consider the transmission line shown in Figure 6.8. The line impedance is shown with a

resistance component of 0 ohms. This is acceptable since the resistance is small compared to

the inductance. However, the line angle is assumed equal to the relay angle of maximum

torque to simplify the diagram, as if there were a resistance component. Both of these

conventions are commonly used despite the seeming contradiction. Line section AB is

protected by a directional comparison blocking scheme using, at each end, an admittance-type

tripping relay (Mtrip) and a reverse admittance-type blocking relay (Mblock) without any offset.

Calculate the settings of the tripping relay at A and the blocking relay at B. Draw the relay

characteristics on an R–X diagram. Assume the line angle and the angle of maximum torque

of each relay is 75.

(b) (Repeat (a) for a nondirectional impedance blocking relay. Assume the line angle and the

angle of maximum torque of each relay is 60.

SOLUTION

(a) Set Mtrip at bus A between 175 and 200% of Zline: Mtrip = 17.520 Ω. Set Mblock at bus B between 125 and 160% of (Mtrip − Zline) so it will overreach Mtrip at bus A. If Mtrip = 17.5: Mblock at bus B = 1.25(17.5 − 10) = 9.375 Ωor Mblock at bus B = 1.60(17.5 − 10) = 12.0 Ω.If Mtrip = 20: Mblock at bus B = 1.25(20 − 10) = 12.5 Ωor Mblock at bus B = 1.6(20 − 10) = 16 ΩAll of these settings are acceptable.

SOLUTION

(b) In (a) the blocking relay at A mustoverreach the tripping relay at B, and viceversa. However, if the blocking relay is animpedance type, the blocking relays atboth terminals must coordinate with bothtripping relays. For the system shown inthis example, the relays at both terminalsare set the same.

SOLUTION

Mtrip can be 17.5 or 20.0 . Use the smaller number.

Zblock = 1.5(17.5) = 26.25.

These settings must be checked against loadability. For the system shown, the parameters are E = 20

kV, ni = 100, nv = 288.6 and (θ + ϕ) = 45.49. Loadability is checked for the largest characteristic that

might encompass the load at a reasonable load power factor.

These values must be compared against the maximum reasonable load beforedetermining the finalrelay settings.

R – X DIAGRAM SOLUTION

PILOT WIRE RELAYING

PILOT WIRE RELAYING