What are the requirements of protection of transmission lines?

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The protection scheme must meet the following requirements: a) Under normal conditions, the breaker will not trip. (b) Under fault conditions, only the breaker closest to the source-side fault is tripped. (c) If the closest breaker fails to operate, the next breaker closer to the source must trip.

What are the primary requirements of the transmission lines?

Transmission line grounding The secondary functional requirements of the transmission grounding system for the design life are: a) to maintain electrical safety and minimize adverse environmental effects. b) Provide effective technical solutions. c) provide cost-effective overall service for life.

What are the different types of protection of transmission line?

Considering the protection of transmission lines, three types of protection are used to safeguard these lines

  • Differential protection.
  • Phase comparison.
  • Overcurrent protection.
  • Earth fault overcurrent protection (used to protect against large residual currents)
  • Distance protection.

What is transmission protection?

The transmission protection system actively identifies the location of faults and isolates fault sections. Weather events such as lightning, storms, snowstorms, and high winds can affect a small portion of the distribution system or a single distribution circuit.

What are the 4 basic parameters of transmission line?

Transmission lines have four main parameters: resistance, inductance, capacitance, and shunt conductance. These parameters are uniformly distributed along the line. Therefore, they are also called distributed parameters of the transmission line. …

What are the four types of transmission lines?

Types of transmission lines include parallel lines (ladder lines, twisted pair), coaxial cables, and planar transmission lines such as striplines and microstrips.

What are the two types of transmission lines?

Two types of transmission lines are coaxial lines (Figure 3.2. 1) and microstrip lines (Figure 3.2. 2).

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Which type relays are used for transmission line protection?

Distance relays are a type of protective relay most often used for transmission line protection. Distance relays measure the impedance from the installation side to the fault location and operate according to the change in the ratio of the measured current to voltage.

Which protection used for protection of transmission line is unit type protection?

1. Transformer unit protection. Transformers at the low and high voltage and neutral ends of the winding are connected in parallel to form a circulating current scheme.

What are the factors to consider in the selection of protective relays in transmission lines?

The high-level factors affecting line protection are the system supplying the line, the configuration of the line (number of terminals, physical structure of the line, presence of parallel lines), the load on the line, the type of communication available, and

Why is speed of protection so important?

Faults must be cleared faster than critical clearing times or systems losing temporary stability. Faster protection also allows for better power transfer capability, reduces equipment damage, and improves power quality.

What are the properties of transmission line?


  • Inductance – Alternating current creates a changing magnetic flux, which interferes with current changes.
  • Resistance – This is the opposite of current flow.
  • Capacitance – A capacitance exists between two conductors as long as they are separated by a dielectric medium.

What is the purpose of transmission lines?

Transmission lines, consisting of heavy cables strung between tall towers, carry power from the generated location to the required area. The transmission network allows the movement of large amounts of power over long distances.

What is the range of transmission line?

Permissible voltages range from 20 to 100 kV. Analysis of medium transmission systems considers three lumped line constants: resistance, inductance, and capacitance. Long transmission lines – lengths exceeding 150 km and voltages exceeding 100 kV form long transmission lines.

Which conductor is used for transmission line?

Type of conductor:. In the early days, the conductor used in transmission lines was usually copper, but aluminum conductors have completely replaced copper due to the much lower cost and much lower weight of aluminum conductors compared to copper conductors of the same resistance.

What is the efficiency of transmission line?

An ideal transmission line would have 100% efficiency (i.e., zero losses), but this is not possible in practice. If the full load at the specified power factor is off, i.e..

What is power factor in transmission line?

The power factor describes the amount of actual power transmitted along a transmission line compared to the total apparent output flowing in the line. The power factor can also be calculated as the cosine of the angle θ at which the current waveform lags or leads the voltage waveform.

Where is MHO relay used?

MHO distance relays are widely used in the protection of uncompensated and compensated transmission lines to determine the presence and location of faults.

What is MHO relay?

MHO relays are voltage-suppressed directional relays. Important point: Reactance relays are suitable for the protection of short transmission lines because their operation is independent of arc resistance. Relays selected for longer transmission lines must be less susceptible to power swings.

What are the 5 different types of relay?

What are the different types of electrical relays?

  • Electromagnetic Relay. Electromagnetic relays are the simplest, oldest, and most widely used relays.
  • Latching relay.
  • Thermal relays.
  • Reed relays.
  • High voltage relays.
  • Time relays.
  • Current and voltage relays.
  • Differential relays.

What is used for protection over a short transmission line?

Reactance relays are suitable for protection of short transmission lines because their operation is independent of arc resistance. Impedance relays are suitable for medium capacity transmission lines.

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What are the different types of protection?

Types of Protection

  • High-voltage transmission networks.
  • Generator sets.
  • Distance overloads and backups (overcurrents)
  • Earth Fault / Ground Fault.
  • Distance (impedance relay)
  • Backup.
  • Low voltage networks.
  • Cyber security.

What are the fundamental requirements of protective relaying?

The seven basic requirements for protective relaying are

  • Selectivity.
  • Sensitivity.
  • Speed.
  • Discrimination.
  • Stability.
  • Reliability.
  • Economy.

Why do we need distance protection of a transmission line besides overcurrent protection?

What are the advantages of distance relays over overcurrent relays? Due to the disadvantages of variable reach and the source impedance variations and types of faults, they cannot be used for distance protection over distance protection.

What is 3 zone distance relay?

The third zone protection on distance relays serves as a backup for faults on the longest transmission line adjacent to the line being protected. For accurate detection of failures, its reach setting is reduced to 100% of the primary line plus 100% of the longest adjacent line.

What are the two types of protection?

It is normal practice to divide protection scheme types into two classes. Primary protection and backup protection.

What are the essential qualities of protection?

The essential quality of the protection system: the

  • Reliability.
  • Selectivity.
  • Robustness of operation.
  • Discrimination.
  • Sensitivity.
  • Stability.
  • Simplicity.
  • Relevance.

What is corona effect in transmission line?

Corona Effects in Overhead Transmission Lines The phenomenon of violet glow, a sizzling sound, and the production of ozone gas in overhead transmission lines is known as corona. When very high voltages are applied to two conductors in an overhead transmission line that have a large spacing compared to their diameters.

What is G in transmission line?

G = Shunt conductance per unit length (S/M) of medium between transmission line conductors. C = Shunt capacitance per unit length (f/m) of the transmission line conductor. By writing the KVL and KCL equations for the equivalent circuit, we can relate the values of voltage and current at Z and Z+ΔZ KVL.

Why is a 50 ohm transmission line standard?

Since 50 ohms is more or less in the middle between these two values, we have settled on 50 ohms as the standard characteristic impedance. It really is as simple as that. Thus, in the RF and microwave fields, where there is a tradeoff between loss and power, the transmission line is chosen with an impedance value of 50 ohms.

How many kV is high voltage?

In the United States, the American National Standards Institute (ANSI) has established a nominal voltage rating for 60 Hz power systems above 100 V. In particular, ANSI C84. 1-2020 defines high voltage as 115 kV to 230 kV, extra high voltage as 345 kV to 765 kV, and extra high voltage as 1,100 kV.

What is the voltage level on 11kV line?

For example, in an 11 kV 3-phase system, the voltage between any two live conductors gives a line voltage of 11 kV, and the voltage between the live conductors and the neutral (or earth) gives a phase voltage of 6.35 kV.

What material is used in transmission lines?

Copper, aluminum, and steel are the primary conductor materials used in power systems. Other types of conductors, such as silver and gold, are actually better conductors of electricity. However, cost prohibits the wide use of these materials.

Why is high voltage used in transmission lines?

High-voltage transmission lines provide power over long distances. High voltages are necessary to reduce the amount of energy lost during the distance. Unlike other energy sources, such as natural gas, electricity cannot be stored when not in use. When demand exceeds supply, power outages occur.

What are the types of transmission lines?

Types of transmission lines include parallel lines (ladder lines, twisted pair), coaxial cables, and flat transmission lines such as striplines and microstrips. The higher the frequency of the electromagnetic waves traveling through a particular cable or medium, the shorter the wavelength of the waves.

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How we can reduce transmission loss?

How to Reduce Transmission Line Losses

  • Reduce ohm losses by using good electrical conductors with minimum resistance and maximum conductivity.
  • Reduce dielectric losses and losses due to leakage currents by using low-loss tangents and high dielectric substrates.

What is the range of power factor?

The ratio of actual power to total power is your power factor, between 0 and 1. Acceptable power factor.

Supply Voltage (nominal) Power Factor Range
1 kV 0.90 Leading 0.90 lagging behind

What is a 69 kV line?

The transmission network of 69 kV transmission lines serves as the backbone of SRP’s neighborhood electric system. These transmission lines interconnect local substations and provide system redundancy and reliability. From the substations, 69 kV is converted to 12 kV to supply homes, schools, and businesses.

What is a good power factor?

The ideal power factor is unity, or one. Anything less than one means that extra power is needed to accomplish the actual task at hand. All current flow causes losses in both the supply and distribution systems. A load with a power factor of 1.0 yields the most efficient load in the supply.

What is the unit of power factor?

Power Factor (PF) is the ratio of working power measured in kilowatts (kW) and apparent output measured in kilovolt-amperes (KVA).

What is difference between OLR and relay?

Thermal OLR is based on the principle of bimetallic strip deformation over heating. Electronic overload relays are microprocessor-based devices with a wide range of functionality. OLRs are used in combination with contactors. Whenever a fault is sensed, the contactor is opened.

Which relay is commonly used?

Current relays are the most commonly used component in power system relay protection.

What is the purpose of Buchholz relay?

A typical Buchholz relay has two sets of contacts. One is arranged to operate for slow buildup of gas and the other for bulk displacement of oil in the event of a heavy internal fault. The former generates an alarm, while the latter is usually wired directly to a circuit breaker trip relay.

What is Idmt relay?

The IDMT relay is a reverse clear minimum time relay. This means that the operating time is inversely proportional to the magnitude of the fault current near the pickup value, which will be slightly slightly above the relay’s pickup value.

Why is Buchholz relay tripped?

Nuisance tripping of Buchholz relays is common enough. It is possible if the level of guardian oil is allowed to fall below the outlet of the Buchholz relay, especially if the transformer has not been monitored for a long time.

What is RX diagram?

The R-X graph shows the apparent impedance in a complex relationship to the actual RF depending on the power system conditions. Fault location and true RF graphs can remove all these effects and show true performance whatever the power system conditions.

Which protection used for protection of transmission line is unit type protection?

1. Transformer unit protection. Transformers at the low and high voltage and neutral ends of the winding are connected in parallel to form a circulating current scheme.

What’s the difference between AC and DC relay?

The DC relay coil has a resistor that limits the DC current. The AC coil relies on impedance to govern the current. The AC relay remains in contact closure due to mechanical inertia and little mechanical hysteresis, and the fact that both the alternating north and south poles attract the relay armature.