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.
In what way is distance protection superior to over current protection of transmission lines?
The reach of the relay is the corresponding distance or the preset impedance. The distance relay can provide better protection than the overcurrent relay, basically, it can overcome the problems related to the overcurrent relay.
Why distance protection is used in transmission line?
A distance relay is a type of protection relay most often used for transmission line protection. Distance relays measure the impedance from the installation side to the fault location and operates in response to changes in the ratio of measured current and voltage.
What are the advantages of distance protection over other type of protection of feeders?
Unlike phase and neutral overcurrent protection, the key advantage of distance protection is that its fault coverage of the protected circuit is virtually independent of source impedance variations.
What are the protection methods used for transmission lines?
System earthing-whether the neutral is grounded or insulated.
- Overload Protection of Transmission Lines:
- Overcurrent and Earth-Fault Protection of Transmission Lines:
- Current-Graded Protection of Transmission Lines:
- Differential Pilot-Wire Protection of Transmission Lines:
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).
What are different types of distance protection?
There are two types of distance relays in use for the protection of power supply, namely ; Definite-Distance relay which operates instantaneously for fault up to a pre-determined distance from the relay. Time-Distance relay in which the time of operation is proportional to the distance of fault from the relay point.
What are the various methods of overvoltage protection of overhead transmission lines?
Lighning arrester or surge dividers.
- Earthing Screen. Earthing screen is generally used over electrical substation.
- Overhead Earth Wire. This method of over voltage protection is similar as earthing screen.
- Lightning Arrester.
Which type of back up protection is widely used for protection of transmission lines?
Distance relay: Distance relay is widely used for the protection of high-voltage AC transmission line and distribution lines.
Why three units of distance relay are used for transmission line protection?
It uses a number of distance relays associated with timing relays, such that the power system is divided into a number of zones with varying tripping times associated with each zone. At a particular location for three zones of protection, three units of distance relays are required.
How many types of protection zones are there in power system?
Protection Zones in Power System
Therefore, only a faulty element is disconnected without affecting the rest of the system. Following six categories of protection zones are possible in a system, we apply here a concept of selective coordination.
What is step distance protection?
Step Distance Relaying is a setting philosophy that utilizes zones of protection and tripping time intervals to determine when a relay operates. This protection scheme is used for both phase and ground faults, but it uses separate relays for each.
What are the different protection schemes of alternator?
Reverse-power protection; Earth-fault protection, using an overcurrent relay; Protection against overloads by means of thermal relays.
What are the basic distance protection zones?
Zones of distance protection
The zone and time grading set-up provide protection of the power line through zone 1 and the adjacent line through zones 2 and 3. The impedance reach of each zone is set with a certain overreach and underreach with respect to the protected line.
What are main problems with distance relaying scheme?
The major problem to the distance relay is to measure correct impedance from relaying point to fault point when series capacitor remains in fault path.
How can you protect against overvoltage?
There are many different ways to protect your circuit from overvoltage. The simplest way is to connect the fuse at the input supply side. But the problem is that it’s a one-time protection, because as the voltage exceeds the preset value, the wire inside the fuse will burn and break the circuit.
Which of these are the devices for overvoltage protection?
Here, the list of overvoltage protection devices, Arcing Horns. Lightning Rod. Spark Gap.
Which among these is the least expensive protection for over current in low voltage system?
Among these, the least expensive protection for over current inlow voltage system is (a)Rewirable fuse. It is likewise called a Kit-Kat fuse. It is most regularly utilized in houses and little circuits.
What’s the percentage of line protection in distance Zone 1?
Zone-1 is meant for protection of the primary line. Typically, it is set to cover 80% of the line length. Zone-1 provides fastest protection because there is no intentional time delay associated with it.
Which is the type of distance relay Mcq?
Types of distance relays are impedance relays, reactance relays, and the mho relays.
What is the tendency of the distance relay to operate at impedance larger than its setting value?
The tendency of a Reach of Distance Relay to operate at impedance larger than its setting value is known as overreach and similarly the tendency to restrain at the set value of impedance or impedances lower than the set value is known as underreach.
Which distance relay is most affected due to power swing Mcq?
The relay which is selected for a long transmission line should be less affected due to power swings. Hence Mho relay is preferred.
Which relay is preferred for distance protection scheme for long transmission line?
Mho Relay: The relay which is selected for long transmission lines should be less affected due to power swings. Hence Mho relay is preferred.
What is an over current relay?
An overcurrent relay is a type of protective relay which operates when the load current exceeds a pickup value. It is of two types: instantaneous over current (IOC) relay and definite time overcurrent (DTOC) relay. The ANSI device number is 50 for an IOC relay or a DTOC relay.
Which type of protection scheme is used against loss of field fault?
There are mainly two schemes available for protection against loss of field or excitation of a generator. In 1st scheme, we use an undercurrent relay connected in shunt with main field winding circuit. This relay will operate if the excitation current comes below its predetermined value.
Which are the reasons of not providing automatic over current protection in an alternator?
Overcurrent protection for alternators is considered unnecessary because of the following reasons : The modern tendency is to design alternators with very high values of internal impedance so that they will stand a complete short-circuit at their terminals for sufficient time without serious overheating.
Why is it called distance relay?
A form of protection against faults on long-distance power lines is called distance relaying, so named because it is actually able to estimate the physical distance between the relay’s sensing transformers (PTs and CTs) and the location of the fault.
What is working principle of distance relay?
The distance relay working principle is very simple and it is based on the ratio of voltage and current i.e, impedance. This relay contains a potential transformer to supply voltage and current transformer for the current element, which is connected in series with the entire circuit.
What is power swing in distance protection?
Abstract. Power swing leads to mis-operation of distance relays due to variations in system current (I) and voltage (V) magnitudes. PSB function is crucial to distinguish power swing and fault properly and prevent relay pickup during power swings to avoid unintended outage of the transmission lines.
What is overreach condition of a distance relay?
This is called Over Reach. Mind the word over reach, the word itself means that the relay has actuated beyond its reach setting. “Thus a distance relay is said to over reach if the impedance measured by the relay is less than the apparent fault impedance.” Over reach is often expressed in percentage as below.
What is overvoltage and its causes?
November 03, 2021. The overvoltage or transients or surge voltages are the voltages whose values are much more than the normal voltages. These are of short duration which can cause malfunction or failure of equipment in the system depending upon the severity of the voltage level.
What are the sources of overvoltage?
Transient overvoltages have four main causes :
- Industrial and switching surges.
- Electrostatic discharges (ESD)
- Nuclear electromagnetic pulses (NEMP) Overvoltages differ in amplitude, duration and frequency.
How do you protect an overcurrent circuit?
Fuses, circuit breakers, or fusible links are the most commonly used methods to provide overcurrent protection to a circuit or the internal wiring of a piece of equipment. Breakers, fuses, and fusible links generally function as conductors and add a negligible amount of resistance to the total circuit.
What does overvoltage protection mean?
Overvoltage Protector (OVP) refers to a circuit that protects downstream circuitry from damage due to excessive voltage.
What are the causes of overvoltage in transmission line?
The main cause of these voltage surges in power system are due to lightning impulses and switching impulses of the system. But over voltage in the power system may also be caused by, insulation failure, arcing ground and resonance etc.
Which of the following relay is provided as the primary protection of transmission lines IDMT relay distance relay overcurrent relay Buchholz relay?
It is the gas actuated relay.
Which of the following is the best expensive protection for overcurrent is low voltage system?
ANSWER: Rewirable fuse.