Overcurrent and Earth-Fault Protection of Transmission Lines: The general practice is to employ a set of two or three overcurrent relays for protection against phase-to-phase faults and a separate overcurrent relay for single line-to-ground faults.
Which relay is used for protection of long transmission lines?
There are several types of circular impedance relay: full impedance circle, directional impedance circle, and offset impedance circle. It is the most widely used impedance relay in traditional relay protection.
What is transmission line protection system?
Transmission Line Protection. Distance Protection. A distance relay measures the impedance of a line using the voltage applied to the relay and the current applied to the relay. When a fault occurs on a line, the current rises significantly and the voltage collapses significantly.
What is distance protection of transmission lines?
Distance Protection is a Non-unit System of Protection, which measures the Impedance between the Relay Location and the point where the fault is incident and compares it with the Set Value. If the measured Impedance is less than the Set Value , the Relay operates and Isolates the Faulty Section.
Why Mho relay is used in long transmission line?
The working principle of Mho relay is, it used for long-distance transmission lines because these lines generally experience power swinging transients as well as load shedding problems. Thus, mho relays are used in practice to provide improved accuracy whenever these transients occur.
Which relay is preferred for distance protection scheme for long transmission line?
The relay which is selected for a long transmission line should be less affected due to power swings. Hence Mho relay is preferred.
Which are different types of protection of transmission line?
If we consider about the protection of transmission line there are three protection types are used to protect these lines .
- Differential Protection.
- Phase Comparison.
- Over Current Protection.
- Earth fault overcurrent protection (Use for protect from large residual current)
- Distance Protection.
Which protection used for protection of transmission line is a unit type protection?
1. Transformer Unit Protection. transformers in the low and high voltage and neutral ends of the windings are connected in parallel to form a circulating current scheme.
Which is a line protection device?
Surge Protection Devices (SPDs) have become increasingly important in recent years and has got wide presence across industries. … SPDs are used for protection against surges from power lines, signal lines, feeder lines and other various line voltage surges, and can be used as class 1, 2 & 3 levels of protection.
What are the three zones of protection?
As the figure above shows, there is a zone of protection covering from each feeder breaker (Blue dotted lines), a zone covering each low-side bus, a zone covering each transformer (Green dotted lines), a zone covering each high-side bus and a zone covering each incoming transmission Line (Yellow Dotted lines).
In what way is distance protection superior to over current protection of transmission line?
Distance relays are preferred to overcurrent reIays because they are not nearly so much affected by changes in short-circuit-current magnitude as overcurrent relays are, and, hence, are much less affected by changes in generating capacity and in system configuration.
What is stub protection?
STUB Protection is simple overcurrent protection it is used to protect the power system transmission line when the line isolator is in open condition. STUB protection is mainly required in one and half breaker busbar schemes. … For the system stability, line should be connected to both the buses.
How does distance protection relay work?
Distance relays are the protecting equipment that functions based on the distance of the fault point on the transmission line. The distance is calculated from the generating unit. Based on the distance, the impedance is calculated by evaluating the fault voltage and fault current.
Why is PLCC used in a substation?
PLCC in modern electrical power system substation is mainly used for following purpose: Carrier protection relaying of transmission line so that: Inter trip command can be issued by relay due to tripping of circuit breaker at any one end.
What is pilot wire protection?
Whenever a transmission line or equipment is to be protected by using distance relay or differential relay or Merz-price protection. … This wire provides the path for the circulating current produce in an abnormal condition, which is sensed by the relay and therefore is tripped; this wire is known as pilot wire.