Transformer Protection by Digital Relays - Research Paper Example

The purpose of this project report is to explore the possibility of protecting transformer devices by means of digital relays. In several instances, electrical equipment has ended up malfunctioning due to a lack of proper measures to prevent them from such situations. In the long run, malfunctioning of such equipment may lead to great losses especially with regard to the financial implications in the event that such equipment needs replacement or repairs. Transformers are some of the most common machines that have a significant effect on both high voltage transmission systems as well as electronic devices.

Considering the fact that these devices find applications in virtually all spheres of the electrical world, it would be rather illogical not to consider assessing the possibility of improving their performance to enable them to be of better service. As stated, high voltage transformers find applications in high voltage transmission lines, which are essentially three-phase systems. However, as per the scope of this project, implementation of this project using the three-phase model may not fall within the constraints of the project.

As a result, the proposed model will involve the use of a single-phase transformer to demonstrate the protection mechanisms of digital relays as far as transformers are concerned. This model will provide a basis that may be modified in the future for use in high voltage applications. Protection of transformers using digital relays may take quite a number of dimensions. However, in this case, only a few of these will be explored as the scope of the project will allow just a basis by which further modification can be done to achieve the intended purpose, whether it is related to false tripping or any other aspect that may be useful in the particular choice of application.

This project will therefore offer a heads up for scholars and individuals in the engineering profession to appreciate the need of protecting transformer devices for effectiveness in their various applications.It is a mandatory electrical practice to ensure the protection of electrical equipment in electrical substations so as to minimize damages, and at the same time control malfunctioning that may arise as a result of unwanted voltages and currents.

Every kind of equipment thus used is required to have standard short-time ratings which are indicative of limits that the equipment is able to withstand. Given this situation, it becomes inevitable that the fault conditions be done away with as soon as possible in order to see to it that coordination of protective devices at any point in the system is maintained. It is, therefore, required that though more than one protective device may detect a fault, only one is supposed to respond. There are two generally accepted means that can be used to achieve this purpose.

One can opt to use fuses, which in most cases acts either directly, or by means of a device that causes mechanical tripping, attached to it. Such a device works by opening a 3-phase load-break switch which is attached to it. On the other hand, the methods that is progressively gaining popularity and acceptance is the use of relays, which, as opposed to fuses, are independent from the circuit breaker coil, and hence, act indirectly to the coil of the circuit breaker. When it comes to transformers, there are quite a number of faults from which the transformer needs to be protected to make it achieve its proper functioning capacity.

To begin with, transformers face stresses which may emanate from the supply network. These are usually in form of voltage surges, which may either be atmospheric or operating voltage surges. Atmospheric ones in most cases occur from natural sources such as lightening strokes that occur close to transmission lines. In the case of operating surges, they mainly result from spontaneous changes in the normal functional conditions of given electrical networks leading to transients within the system.

The high frequency voltage surge wave that occurs in this scenario hampers the normal functioning of the transformer. The most effective methods of protecting transformers from such kinds of surges have been found to be the use of varistors and they do not affect the switchgear much. A part from voltage surges, there may also be stresses that arise from the load itself. In most cases, the reason for overloading is usually as a result of simultaneous power need of small loads connected to the network (Paithankar & Bhide, 2013).

At times, it arises when the need for apparent power (kVA) increases; especially when the facility (in this case the factory) grows and expands leading to an extension that causes an increase in the power of demands. An increase in the load leads to a subsequent increase in the temperatures of the wirings and insulations. These eventually reduce the lifespan of the equipment. There are no specific place to place overload protection devices as they can always be either on the low voltage or high voltage side of the transformer.

The most effective way of protecting a transformer against overloading is by means of a digital relay, which serves to trip the circuit-breaker located on the secondary side. The term ‘thermal relay’ is interchangeably used with the digital relay considering its function on the transformer (Horowitz & Phadke, 2008). Their mode of working usually involves the artificial simulation of temperature based on the time constant of the particular transformer in use, with some of them having the ability to incorporate the impact of harmonic currents resulting from non-linear loads.

Such loads are the likes of variable speed drives and computer drives among others. The relays are useful in projecting and estimating the time required for overload tripping as well as the wait time required in the event that tripping has occurred. Such a control measure is a very useful step in the control of the shedding operations, which can either be coordinated with thermostats or heat sensors depending on whether they are being used for oil-immersed or dry-type transformers respectively. 1.1 Objectives To explore the possibilities of protecting transformers by employing digital relay systems 1.

2 Problem statement In order to curb the various challenges affect conventional methods of protection of transformers, this project proposal delves in a direction that will be used to improve the protection of transformers using digital relay systems.