There are many different types of electronic fuses and every manufacturer has their own solution. The principle is the same though; a sensor measures the current and some kind of controller or comparator, often a micro processor, controls a transistor, typically of a MOSFET kind. By master the opening and
As mentioned previously, circuit breakers can detect a fault either thermally or magnetically. The magnetic hydraulic circuit breaker is an all round device and can operate in many different areas. The magnetic hydraulic circuit breaker can be divided into two different categories; sealed and unsealed breakers. Sealed breakers, made for
A simple circuit breaker was developed by Edison as early as 1878 when he worked on his electric light circuit. Even though he did not use his mechanical breaker in his commercial circuit, the function was based on the same principle that is used in a modern circuit breaker. The
The first type of fuse developed was of a melting kind. The word fuse comes from the Latin word to melt, “fusus”. As Thomas Edison developed his electric light circuit in the late 1870’s, he needed a protective mechanism “to provide against accidental crossing of the conductors leading from the
ELECTROMECHANICAL RELAYS: Early relay designs utilized actuating forces that were produced by electromagnetic interaction between currents and fluxes, much as in a motor. These forces were created by a combination of input signals, stored energy in springs, and dash pots. The plunger type relays are usually driven by a single
As can be seen from Fig. 3.8, step distance protection does not offer instantaneous clearing of faults over 100% of the line segment. In most cases this is unacceptable due to system stability considerations. To cover the 10–20% of the line not covered by Zone 1, the information regarding the
Distance relays respond to the voltage and current, i.e., the impedance, at the relay location. The impedance per mile is fairly constant so these relays respond to the distance between the relay location and the fault location. As the power systems become more complex and the fault current varies with
Figure 3.5 also shows why the TDOC relay cannot be used without additional help. The closer the fault is to the source, the greater the fault current magnitude, yet the longer the tripping time. The addition of an instantaneous over current relay makes this system of protection viable. If an
The principal application of time delay over current relays (TDOC) is on a radial system where they provide both phase and ground protection. A basic complement of relays would be two phase and one ground relay. This arrangement will protect the line for all combinations of phase and ground faults
The most commonly used protective device in a distribution circuit is the fuse. Fuse characteristics vary considerably from one manufacturer to another and the specifics must be obtained from their appropriate literature. Figure 3.3 shows the time-current characteristics which consist of the minimum melt and total clearing curves. FIGURE 3.3
