INTRODUCTION
PROTECTIVE ZONE PACKAGES
Introduction
Basic Concepts
Types of Distress
Detection Modes
Protection Characteristics
Generators
Motors
Feeders
Transformers
Buses
Incoming Lines
GE Relay Index
References
INTRODUCTION
Power distribution systems serving industrial or commercial facilities represent a variety of costs to the owner. Obviously, the capital cost of the equipment is a concern, as is the cost of the energy which that power system delivers to the loads which convert electrical energy to a saleable product or service. There are some less obvious costs - the cost or reliability, measured in products or services which cannot be sold because power
is unavailable, or an even more illusive concept, the cost of quality, which relates to customer satisfaction. Ultimately, as the designer of the system struggles with devising a system arrangement and choosing equipment, he must face the reality that no matter how clever he is, no matter how much redundancy he builds into the system, and no matter how much he pays for premium quality components, he simply cannot build a system which will never fail.
This is where system protection, and protective relays become important. If component failure is inevitable, then it is necessary to provide a means
of detecting these failures. Better and faster Protection afford a number of desirable attributes, all of which ultimately result in saving the owner
of the system money through cost avoidance.
When component distress is detected and
corrected earlier, the damage associated with the failure is minimized, which results in lower repair costs (or even the ability to repair versus the need to replace). At the same time, faster and more sensitive detection of problems means that the cause of the problem can be corrected while it is still a minor problem, and before it escalates into a major catastropheProtection is applied on a component basis.
Relays are associated with each major
component of the power distribution system to detect various forms of distress associated with those components. If one of those relays
operates (which means that an output contact closes because the relay detects a level of distress in excess of its calibration or setting), it initiates tripping of circuit breakers or other protective devices which then isolates the defective system components. It may be
convenient to think of the circuit breaker as the muscle that does the work of isolating the component , while the relay is the brain which decides that isolation is required
Because protection is associated with
components, it has become customary to talk about relays which protect the component with which they are paired. While it is true that faster and more sensitive protection does reduce the amount of damage at the point of the actual fault or distress, and in this sense, relays which detect and de-energize defective equipment do protect their associated components, the value of relay protection on system continuity is even greater.
In the limit, a failed motor may have to be
replaced, but good relaying on the motor will isolate the motor from the remainder of the power distribution system, allowing it to continue to function and permitting the facility to continue in-service. Ultimately, therefore, it is system protection and service continuity that are the justification for good relay protection
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