Protection circuits

Fig. 10. Exploded view of a monolithic multicomponent ceramic substrate. Layers (a) signal distribution (b) resistor (c) capacitor (d) circuit protection ...

In other designs, a diffused siUcon sensor is mounted in a meter body that is designed to permit caUbration, convenient installation in pressure systems and electrical circuits, protection against overload, protection from weather, isolation from corrosive or conductive process fluids, and in some cases to meet standards requirements, eg, of Factory Mutual. A typical process pressure meter body is shown in Figure 10. Pressure measurement from 0—746 Pa (0—3 in. H2O) to 0—69 MPa (0—10,000 psi) is available for process temperatures in the range —40 to 125°C. Differential pressure- and absolute pressure-measuring meter bodies are also available. As transmitters, the output of these devices is typically 4—20 m A dc with 25-V-dc supply voltage. 

High-voltage contactor-type motor controls depend on power fuses for short-circuit protection. The fuses are coordinated with the overload relays to protect the motor circuit over the full range of fault conditions from overload conditions to solid maximum-current short circmts. 

The starting of an induction motor does not relate to simple switching alone. It also involves its switchgears to control its starting inrush current, starting torque, or both, and its overload and short-circuit protection. 

The selection should be such as to provide proper discrimination at the various levels of a multi-distribution network. Our discussions generally take account of the recommendations in lEC 60947-4-1 regarding coordination between the short-circuit protection and the main components such as switching devices [switch, breaker. 

Short-circuit protection. To provide an instantaneous tripping on a short-circuit delay of, say, one or two cycles may be introduced into the tripping circuit to bypass any transient currents and avoid an unwanted trip. 

Thermal capacity to perform the required switching duties and sustain the fault conditions, at least up to the cut-off time of the short-circuit protective device, say, the HRC fuses. 

Role of an OCR this is only an overcurrent protection device and does not provide short-circuit protection. 

Testing of the main circuits (with short-circuit protective devices)... 

The current element of a relay is wound for a wide range of current settings in terms of the rated secondary current of the CT, such as 10-80% for a ground fault protection, 50-200% for an overcurrent and 300-800% for a short-circuit protection. At lower current settings, while the VA requirement for the operation of the relay will remain the same, the VA capacity of the CT will decrease in a square proportion of the current. A CT of a correspondingly higher VA level would therefore be necessary to obtain the reduced VA level. 

For circuits protected by HRC fuses for short-circuit conditions, the G/F relay must be a back-up to the fuses, and trip first on a ground fault. In other words, 1 1 (relay) < rt fuses. 

Nevertheless, unbalance is a major occurrence in either case and an unbalanced protection, in addition to short-circuit protection is imperative in all types of capacitor units. Hence it is also possible to design series protected capacitor units in larger sizes and for higher voltages, which are more economical, compared to smaller units. 

The electrical distribution system design and equipment selection must consider requirements of the utility company for protection and metering. Available short circuit currents from the utility distribution network to the primary of the facility s main transfoiTner must be considered in selecting circuit protection devices for the facility distribution system. 

The engineer providing the initial design of major facilities is faced with the decision of providing a motor control center building or indi id-ual (usually rack-mounted) motor starters and corresponding branch circuit protection devices. For installations using only several motors it fre-... 

Underwriters Laboratories (UL) requires that consumer batteries pass a number of safety tests [3]. UL requires that a battery withstand a short circuit without fire or explosion. A positive temperature coefficient (PTC) device [4] is used for external short-circuit protection. The resistance of a PTC placed in series with the cell increases by orders of magnitude at high currents and resulting high temperatures. However, in the case of an internal short, e.g., if the positive tab comes lose and contacts the interior of the negative metal can, the separator could act as a fuse. That is, the impedance of the separator increases by two to three orders of magnitude due to an increase in cell temperature. 

Jovalusky, J., Integrating Circuit-Protection Functions Reduces Power Source Costs, ECN, Jun. 2003. 

Due to the high breaking capacity of the contactor (20 kA rms), fuses for short-circuit protection are unnecessary. 

As applicable, short-circuit protection of the power supply is in accordance with the documentation X ... 

Electrochemical machining (ECM) is a method of metal machining that aims at producing parts of specified shape, dimensions, and surface finish. The process is based on the removal of metal by electrochemical dissolution ([1-15] and references cited therein). Special machines have been developed to realize this aim. A complete ECM installation (Fig. 1) consists of the machine, the power supply, the electrolyte circulation system (tank, pump, heat exchanger, and sludge removal unit), and the control system (control of current, voltage, feed rate, gap width, and electrolyte temperature, pH value, pressure, and concentration short-circuit protection). 

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