Protection capacitors

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

F = functional, ie, electiical, magnetic, thermal, mechanical, chemical, or optical function M = manufacturing aid and P = protective. Components such as capacitors and resistors. 

Electrical. The plant electrical system is sometimes more important than the steam system. The electrical system consists of the utihty company s entry substation, any ia-plant generating equipment, primary distribution feeders, secondary substations and transformers, final distribution cables, and various items of switch-gear, protective relays, motor starters, motors, lighting control panels, and capacitors to adjust power factor. 

The higher Ihe value of C. the lower will be the voltage overshoots in the rectified voltage and the inverter circuit would be fed by an almost cotistant voltage soitrce. The capacitor iti the circuit also provides an indirect protection from the voltage surges. 

X6/1987 Measuring voltage transformers Protective voltage transformers Capacitor voltage transformers. "1156-2/1992. 1156-3/1992 3156-4/1992 BS 7729/1995 BS 7625/1993 ... 

The characteristic shown also suggests that the MPCBs can withstand current transients up to 100 times the rated current (or the current setting) and hence are capable of switching a capacitor and protecting them against overloads. 

Table 15.6 Recommended limits of voltage and phase displacement errors, applicable for all types of protection VTs (electromagnetic, capacitor and residual VTs)...

With this particular arrester, the motor has to be specially designed for the higher level of FOW impulse voltage withstand. But the manufacturer can always modify the protective characteristics of the arrester, depending upon the system s requirements. The matter may therefore be referred to the manufacturer for recommendations. The arrester may be fitted with a 0.25, uF surge capacitor in parallel, to reduce the steepness of the FOW (for the arrester of example 17.5, it is 14/0.2 kV/jUS) to a safer value. 

Referring to the data available from experiments, as shi)wn in Table 23.1, it hits been estimated that a Vp, of I. Hj should be sufficient to account for the harmonic effects. For this dielectric strength is designed a capacitor unit and selected a switching or protective device. 

Based on the system studies carried out and Table 23.1, it has been assessed that in actual operation, effective current through a capacitor circuit may increase up to 1.3 limes its rated cunent, /,., i.e. = 1.3 /, to account for all the harmonic effects (V, - Jf. equation (23.4)). A capacitor unit is thus designed for at least M)9r continuous overload capacity (Section 25.6). Its switching and protective devices are selected along similar lines. 

It is desirable to contain the harmonic effects as far as practicable to protect the capacitors as well as inductive loads connected on the system and the communication network, if running in the vicinity. 

Coupling capacitor or CVT is used when it is required lor measurement and protection. For details on CVT refer to Section 15.4.1.3,... 

The above configuration or size of each unit is not mandatory and can be altered, depending upon the economics of capacitor voltage and size of units available. Protection for all types of configurations is easily available through various schemes discussed in Section 26.1. 

Since the line impedance, R + J (Xl - Xc), will reduce with a series compensation, the fault level of the system will rise. It should not matter if the fault level of the system is determined by the impedance of the source of supply, ignoring any other impedance of the circuit (Section 13.4.1 (5)). Moreover, such a situation is automatically averted through the protection of the series capacitors, as discussed below, by which the capacitors are bypassed during a line fault, the line restoring its original impedance, hence the original fault level. Nevertheless, when it is required to limit the system fault level, inductive coupling circuits may be provided to reduce the fault to the desired level. This is also discussed below ... 

A critical review of internally protected capacitor units 25/812... 

Shell rupture protection is a vital consideration in externally protected capacitor units. Since there is no control over small internal faults until they become major fault, protection can be provided only for the whole unit and the entire unit has to be dismantled after such a fault. In fact, the capacitor bank may have lo be shut down completely to replace the lost unit with a new one lo avoid an imbalance, besides making up for the lost capacitance. 

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. 

For loads, such as on motors where the capacitor unit is being switched with the machine, or where close monitoring of the capacitor health is a prerequisite to avoid an eventual outage of the capacitor unit by gradual depletion of its capacitance, internally protected capacitor units may be preferred. 

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