CAUSES OF LONG INTERRUPTIONS

Long interruptions are always due to component outages. Component outages are due to three different causes:

I. A fault occurs in the power system which leads to an intervention by the power system protection. If the fault occurs in a part of the system which is not redundant or of which the redundant part is out of operation the intervention by the protection leads to an interruption for a number of customers or pieces of equipment. The fault is typically a short-circuit fault, but situations like overloading of transformers or under frequency may also lead to long interruptions. Although the results can be very disturbing to the affected customers, this is a correct intervention of the protection. Would the protection not intervene, the fault would most likely lead to an interruption for a much larger group of customers, as well as to serious damage to the electrical equipment.

As distribution systems are often operated radially (i.e., without redundancy) and transmission systems meshed (with redundancy), faults in transmission systems do not have much influence on the reliability of the supply, but faults in distribution systems do.

2. A protection relay intervenes incorrectly, thus causing a component outage, which might again lead to a long interruption. If the incorrect tripping (or maltrip) occurs in a part of the system without redundancy, it will always lead to an interruption. If it occurs in a part of the system with redundancy the situation is different. For a completely random maltrip, the chance that the redundant component is out of operation is rather small. Random maltrips are thus not a serious reliability concern in redundant systems. However maltrips are often not fully random, but more likely when the system is faulted. In that case there will be two trips by the protection: a correct intervention and an incorrect one. The maltrip trips the redundant component just at the moment that redundancy is needed. Fault-related maltrips are a serious concern in redundant systems.

3. Operator actions cause a component outage which can also lead to a long interruption. Some actions should be treated as a backup to the power system protection, either correct or incorrect. But an operator can also decide to switch off certain parts of the system for preventive maintenance. This is a very normal action and normally not of any concern to customers. There is in most cases at least some level of redundancy available so that the maintenance does not lead to an interruption for any of the customers. In some low voltage networks there is no redundancy present at all, which implies that preventive maintenance and repair or changes in the system can only be performed when the supply to a part of the customers is interrupted. These interruptions are called "scheduled interruptions" or "planned interruptions."

The customer can take some precautions that make the consequences of the interruption less than for a nonscheduled interruption. This of course assumes that the utility informs the customer well in advance, which is unfortunately not always the case.

Comments

PRIMARY SECONDARY AND TERTIARY FREQUENCY CONTROL IN POWER SYSTEMS

Primary, Secondary and Tertiary Frequency Control in Power Systems Author: Engr. Aneel Kumar Keywords: frequency control, primary frequency control, automatic generation control (AGC), tertiary control, load-frequency control, grid stability. Frequency control keeps the power grid stable by balancing generation and load. When generation and demand drift apart, system frequency moves away from its nominal value (50 or 60 Hz). Grids rely on three hierarchical control layers — Primary , Secondary (AGC), and Tertiary — to arrest frequency deviation, restore the set-point and optimize generation dispatch. Related: Power System Stability — causes & mitigation Overview of primary, secondary and tertiary frequency control in power systems. ⚡ Primary Frequency Control (Droop Control) Primary control is a fast, local response implemented by generator governors (dro...

CASCADED TRANSFORMERS METHOD FOR GENERATING AC HIGH VOLTAGE

High-Frequency AC High Voltage Generation Using Cascaded Transformers Author: Engr. Aneel Kumar Figure 1: Infographic representation of cascaded transformers method for generating high AC voltages. Introduction In high voltage engineering , generating very high alternating current (AC) voltages is essential for testing equipment like insulators, circuit breakers, power cables, and other apparatus. One common and effective method for producing such voltages is the cascaded transformers method . This technique uses a series connection of specially designed test transformers , where the secondary of one transformer feeds the primary of the next. In this way, voltages are built up step by step, achieving levels in the range of hundreds of kilovolts (kV) or even megavolts (MV). Working Principle The principle of cascaded connection relies on the fact that each...

ADVANTAGES AND DISADVANTAGES OF CORONA EFFECT IN TRANSMISSION LINES | ELECTRICAL ENGINEERING GUIDE

Advantages and Disadvantages of Corona Effect in Power Systems In high-voltage overhead transmission lines , the corona effect plays a critical role in system performance. Corona occurs when the air around a conductor becomes ionized due to high electric stress. While often seen as a drawback because of power losses and interference , it also provides certain engineering benefits . This article explains the advantages and disadvantages of corona effect in detail, with examples relevant to modern electrical power systems. ✅ Advantages of Corona Effect Increase in Virtual Conductor Diameter Due to corona formation, the surrounding air becomes partially conductive, increasing the virtual diameter of the conductor. This reduces electrostatic stress between conductors and minimizes insulation breakdown risks. Related Reading: Electrostatic Fields in High Voltage Engineering Reduction of Transient Surges Corona acts like a natural cushion for sudden ...

REVERSING DIRECTION OF ROTATION OF UNIVERSAL MOTOR

The direction of rotation of a universal motor can be changed by either: (i) Reversing the field connection with respect to those of armature; or (ii) By using two field windings wound on the core in opposite directions so that the one connected in series with armature gives clockwise rotation, while the other in series with the armature gives counterclockwise rotation. The second method, i.e, the two field method is used in applications such as motor operated rheostats and servo systems. This method has somewhat simpler connections than the first method. For simple applications like portable drills etc. manual switches are frequently used for reversing the direction of rotation of the motor. Figure 1 (a and b) shows how a DPDT (Double Pole Double Throw) switch and a three position switch may be used for reversing the direction of rotation of single field and double field type of motors respectively. Figure 1 Reversing of a universal motor (a) Armature re...

Advantages of Per Unit System in Power System Analysis | Electrical Engineering

Advantages of Per Unit System in Power System Analysis In electrical power engineering, the per unit (p.u.) system is one of the most widely used techniques for analyzing and modeling power systems. It is a method of expressing electrical quantities — such as voltage, current, power, and impedance — as fractions of chosen base values rather than their actual numerical magnitudes. This normalization technique provides a universal language for system calculations, minimizing errors, simplifying transformer modeling, and enabling consistency across multiple voltage levels. Because of these benefits, the per unit system is essential in fault analysis, load flow studies, transformer testing, and short-circuit calculations . ⚡ What is the Per Unit System? The per unit system is defined as: Q u a n t i t y ( p u ) = A c t u a l V a l u e B a s e V a l u e Quantity_{(pu)} = \dfrac{Actual \ Value}{Base \ Value} Q u an t i t y ( p u ) = B a se ...

PRINCIPLE OF OPERATION OF UNIFIED POWER FLOW CONTROLLER UPFC

UPFC consist of two back to back converters named VSC1 and VSC2, are operated from a DC link provided by a dc storage capacitor. These arrangements operate as an ideal ac to ac converter in which the real power can freely flow either in direction between the ac terminals of the two converts and each converter can independently generate or absorb reactive power as its own ac output terminal. Figure: Basic UPFC scheme One VSC is connected to in shunt to the transmission line via a shunt transformer and other one is connected in series through a series transformer. The DC terminal of two VSCs is coupled and this creates a path for active power exchange between the converters. VSC provide the main function of UPFC by injecting a voltage with controllable magnitude and phase angle in series with the line via an injection transformer. This injected voltage act as a synchronous ac voltage source. The transmission line current flows through this voltage source resulting in reactive an...

Types of Transmission Towers in Saudi Electricity Company (SEC) – NGSA Standards

The Kingdom of Saudi Arabia (KSA) is rapidly expanding its energy infrastructure projects to meet the growing demand for electricity. At the heart of this growth lies the high voltage transmission network , which delivers reliable power from generation plants to cities, industries, and remote areas. To ensure safety and efficiency, the Saudi Electricity Company (SEC) follows strict NGSA (National Grid Saudi Arabia) standards for designing and selecting transmission towers . These lattice steel towers are engineered to withstand extreme desert conditions, high wind loads, and long transmission spans. In this article, we will explore the different types of transmission towers in Saudi Arabia , their applications, and how they contribute to the power transmission system design . Why Transmission Towers Are Crucial in Power Grid Development Every kilometer of transmission line construction requires careful planning. The right tower design ensures: Stable support for 69k...

ENGINEERING ARTICLES

Search This Blog