A DYNAMIC MODEL OF AN EARTH FAULT RELAY FOR ONE PHASE POWER SYSTEM
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The single-phase earth fault is the most common fault type on high voltage transmission line. But the sensitivity of single-phase distance relays can’t satisfy the requirement of power system for such reason a dynamic model type of earth was introduced to achieve that security required. Very high levels of faulty current in electrical power systems are usually caused by short circuit faults between phases or between phases and earth. Measurement of earth fault current setting can be used as an indicator of such faults. Co-ordination of overcurrent devices uses a combination of current settings and time delayed operation. Where fault current can flow in both directions then directional earth fault relays can be applied.
Earth fault relay is a relay which is sense the faults
between the phase and Earth (not b/w neutral to earth). An Earth fault relay will kick out when sensing a ground fault, or a passage of electricity between a phase and ground.
A dynamic model relay will trip when a current exceeds a set limit within a phase conductor, or multiple phases in the case of a substation. Such earth fault relay works in the way of sensing and control devices to accomplish its function. Under normal power system operation, a dynamic earth fault relay remains idle and serves no active function. But when fault or undesirable condition arrives Protective Relay must be operated and function correctly.
This work is on a new dynamic model of earth fault relay for single phase power system.
1.0 INTRODUCTION
A Power System consists of various electrical components like Generator, transformers, transmission lines, isolators, circuit breakers, bus bars, cables, relays, instrument transformers, distribution feeders, and various types of loads.
Faults may occur in any part of power system as a short circuit and earth fault. Fault may be Single Line to Ground, Double Line to Ground, Line to Line, three phase short circuit etc. This results in flow of heavy fault current through the system.
Fault level also depends on the fault impedance which depends on the location of fault referred from the source side. To calculate fault level at various points in the power system, fault analysis is necessary.
The protection system operates and isolates the faulty section. The operation of the protection system should be fast and selective i.e. it should isolate only the faulty section in the shortest possible time causing minimum disturbance to the system. Also, if main protection fails to operate, there should be a backup protection for which proper relay co-ordination is necessary.
Earth fault relay is a relay which is sense the faults
between the phase and Earth (not b/w neutral to earth). An Earth fault relay will kick out when sensing a ground fault, or a passage of electricity between a phase and ground.
A dynamic model relay will trip when a current exceeds a set limit within a phase conductor, or multiple phases in the case of a substation. Such earth faults relay works in the way of sensing and control devices to accomplish its function. Under normal power system operation, a dynamic earth fault relay remains idle and serves no active function. But when fault or undesirable condition arrives Protective Relay must be operated and function correctly.
1.1 BACKGROUND OF THE STUDY
The primary purpose of grounding electrical systems is to provide protection against electrical faults. However, this was not realized until the 1970’s. Until then, most commercial and industrial systems were ungrounded. Although ungrounded systems do not cause significant damage during the first ground fault, the numerous disadvantages associated with ground faults resulted in a change to the grounding philosophy. There are other advantages for a grounded system, such as reduction of shock hazards and protection against lightning.
Electrical faults can be broken down into two categories: phase-to-phase faults and ground faults. Studies have shown that 98% of all electrical faults are ground faults (Source: Woodham, Jack, P.E. “The Basics of Grounding Systems” May 1, 2003). Where fuses can protect against phase-to-phase faults, additional protection, such as protection relays, are typically required to protect against ground faults.
1.2 AIM OF THE STUDY
The aim of this study is to discuss the about the dynamic model of earth fault relay, that is, its functions, features and specification – the uniqueness.
1.3 SIGNIFICANCE OF THE STUDY
Important thing about this study is that, this study exposes me to the functions of earth fault relay, different kinds of earth fault relay, and different model of earth fault relay. By being able to detect electrical problems in the early stages, ground fault relays can significantly reduce damage and speed up the repair process. Sensitive ground fault relays with advanced filtering capabilities will detect the breakdown in insulation caused by moisture, vibration, chemicals, and dust.
1.4 APPLICATION OF THE STUDY
Ground or earth fault relays are commonly used in industrial and manufacturing facilities on generators, transformers, switchgear, motor control centers (MCC), panel boards, variable frequency motor drives , welders and heating cables.
1.5 DEFINITION OF EARTH FAULT
A earth fault is an inadvertent contact between an energized conductor and ground or equipment frame. The return path of the fault current is through the grounding system and any personnel or equipment that becomes part of that system. Ground faults are frequently the result of insulation breakdown. It’s important to note that damp, wet, and dusty environments require extra diligence in design and maintenance. Since water is conductive it exposes degradation of insulation and increases the potential for hazards to develop.
