Protective relays Electronic

Our strategy here was to develop Pt colloids of minimum particle size which would render the water reduction by the electron relay R peirticularly effective. The goal was to obteiin hydrogen evolution rates in the microsecond time domain which would compete with beick electron transfer. First a centrifuged Pt sol protected by polyvinyl alcohol weis employed which gave clear and almost colorless aqueous suspensions even at hi Pt concentrations ( 28). Flash photolysis technique was applied for the first time to study the dynamics of intervention of the Pt particles in the water reduction process. Methylviologen (MV ) wets reduced... 

Some similar components may be left behind if a purely electronic timer is involved. In this instance a metal chassis may not be used, since amateur builders and experimenters often bread-board their layouts that is, they build them on the surface of an ordinary piece of wood in order to speed construction and to hold costs to a minimum. In this case, the wood might burn completely and this would be advantageous to the arsonist. Resistors and capacitors would also be used in this type of circuit, although they would not be as well protected as they would be in a regular commercial unit- Parts of the relays might be in evidence, and the toggle switch may be expected to retain most of its original characteristics. 

Such units will usually be found in close proximity to a telephone, but in some applications of the sound operated relay, this may not be true. The circuitry is miniaturized for the most part, and the remains will be difficult to spot after a disaster. Aside from the conventional electronic debris that might be expected, look for a metal shell of a microphone, or for the inductive loop that may have been protected from destruction by being hidden under the telephone. 

These data are corroborated by results obtained from continuous photolysis experiments. Cabowax-20M protected Pt catalyst when coupled to Ru02 fails to split water under illumination of a cyclic system containing Ru(bipy)3+ as a sensitizer and methylvio-logen as an electron relay. By contrast, if the Pt microspheres are protected by PVP-Ci6 simultaneous H2 and 02 productions are observed. The lack of specificity of the Carbo-wax 20 M protected particles is attributed to the strongly hydrophylic nature of this protective polymer providing facile access of the Ru(bipy)3+ cation to the platinum surface. Uncharged hydrophylic polymers appear thus unsuitable for Pt protection in this cyclic water decomposition system. 

When the first programmable electronic equipment, called programmable logic controllers (PLCs), were created as an alternative to relay logic, many engineers immediately believed these new devices would be perfect for automatic protection applications. They felt that the functionality of these electronic devices encompassed aU that would be needed and more. 

Critical interlock While identifying the hazards it is important to categorize critical interlocks (for new plants, data/experience from similar plants may be helpful) for which sufficient backup may have to be arranged as a safety measure. In many of these cases, in addition to software interlock, hardware interlocks are also provided. In some cases, even mechanical protection is provided. A critical trip interlock pertinent to a turbine is an example. For turbine overspeed, condenser vacuum, etc., in addition to electronic interlock (with sufficient hardware/software redundancy), mechanical interlocks are provided so that the equipment is saved. Choke and kill in offshore is also an example of this. Regulations To meet the requirement of a regulatory board or company standards, measures are taken to enhance overall safety. Incorporation of these safety measures does not always mean that risk is adequately reduced. These measures could make the system acceptable for use, and a local regulatory board may require additional precautions. An example will elaborate the situation. Many turbine manufacturers give low forward power relays or reverse power... 

The Berlin technical centre of Tyco Electronics has developed an especially silent relay with a completely redesigned electromechanical system. The minimal noise it emits is attenuated to an inaudible level by a protective housing made from a specially developed blend of DuPont s Crastin polybutylene terephthalate (PBT). As in other similar devices the device is encapsulated in a thermoset resin. 

Motor starters can be divided into three basic types (manual, magnetic, and electronic operation) and three categories (full voltage/across the line, reduced voltage, and multispeed). Starters consist of a contactor to switch the electrical load and an overload relay which provides protection for the motor. 

Solid-State Overload Relays. These overload relays are of two types, self-powered and externally powered.The self-powered relay (Fig. 5.137) uses currents induced by the current flowing to the motor for power, while the externally powered units contain an electronic power supply and require a separate source of control power to operate. The advantage of the setf-powered units is that they are sinyler, require no extra wiring, and are self-protected from short circuits. 

Neither this nor the sensitivity of the melting-alloy type to phase loss should be seen as true single-phasing protection. If single-phasing protection is a concern, complete protection may be provided by an electronic voltage monitor or solid-state overload relay. 

Each bay is responsible for (dis)connecting one element from the transmission network. This is achieved by a set of elements - relays and electronic devices of the following two types - either a protection device or a control device. The function of the protection devices is to disconnect the power elements from the transmission network, e.g. as a result of overloading of a line or of a generator. The control devices, on the other hand, are used to connect or disconnect the power elements from the network and are typically used by either the operators in the respective control centres or by special purpose software (SPS) designed to undertake some of the operators functions automatically. 

---