Tricky but Easy Electrical Engineering!
Programmable Scheme Logic or PSL is a kind of feature provided in Numerical Relays to implement the protection scheme of a particular type. This feature of Numerical Relays makes it easier to implement many protection schemes in a single Numerical Relay for example, in Distance Relay we can configure Distance protection, over voltage protection, Over … Read more
I would suggest to read Transformer Inrush Current before reading this article for better understanding. Any event on the power system that causes a significant increase in the magnetizing voltage of the transformer core results in magnetizing inrush current flowing into the transformer. The three most common events are as follows: Energization of the Transformer. … Read more
Before going into the calculation part of Stabilizing Resistor, I will first explain the purpose of Stabilizing Resistor in High Impedance Differential Protection. Stabilizing Resistor in High Impedance Differential Protection is used to prevent the operation of Relay in case of through fault. Through fault is a fault outside the zone of protection. Lets us … Read more
The concept of Subtransient, Transient and Steady State arises in case of fault in an Alternator. Let us assume a sudden short circuit in three phase of alternator. The fault current will flow in all the three phases of alternator and its waveform will be as shown in figure below. When the alternator is short-circuited, … Read more
We know that Relay is a switch which senses fault in a system and once fault is sensed by the Relay, it issues trip command to the Circuit Breaker, CB to isolate the faulty section of the network from the healthy section. The Relay detects the abnormal condition by continuously monitoring electrical quantities which are … Read more
The protection provided by the protective relaying equipment can be categorized into two types as: a) Primary protection b) Back-up protection The primary protection is the first line of defense and is responsible to protect all the power system elements from all the types of faults. The backup protection comes into play only when the primary protection … Read more
Protection schemes can be divided into two major groupings: a) Unit schemes b) Non-unit schemes a) Unit Protection Scheme: Unit type schemes protect a specific area of the system i.e. a transformer, transmission line, generator or bus bar. The unit protection schemes are based on Kirchhoff’s Current Law – the sum of the currents entering … Read more
Zoning in Power system Protection is an important philosophy and must be done carefully so that no part of the system remains unprotected in any condition. To limit the extent of the power system that is disconnected when a fault occurs, protection is arranged in zones. The principle is shown in figure below. … Read more
According IEC, Knee Point Voltage of a Current Transformer is defined as the voltage at which 10 % increase in voltage of CT secondary results in 50 % increase in secondary current. If you carefully read the definition, you will notice that it is something related to saturation of Current Transformer CT. Never mind, I will … Read more
An Earth Leakage Circuit Breaker (ELCB) is a safety device used to directly detect the leakage current to the Earth from an installation and cut the power supply. Basically ELCB is used where the earth impedance is high. Because of high earth impedance, the voltage difference between the Metallic part of the Installation and Earth … Read more