Current breakers

Since current leakage through an electrolyte depends on the existence of a continuous path, another technique for the prevention of leakage currents is the use of current breakers at the cells. Their purpose is to physically break the electrolyte stream in order to interrupt the electrical path. Figure 8.10 shows the design used with some diaphragm cells. The liquor from each cell is collected in a cup (C). The demister... 

FIGURE 8.10. Diaphragm-cell current breaker. (With pmmission of ELTECH Systems Corporation.)... 

Active metal targets in electrolyte headers can intercept leakage currents and prevent corrosion of piping and equipment. Leakage can also be prevented at its source by installing current breakers that actually disrupt the continuous stream of liquid (Fig. 8.10). 

RCBO residual current breaker with overcurrent device... 

Even without the combined capacity or power loss, the effect of gas generation might then limit the life of cells submitted to long-term high-voltage and high temperature storage, especially if they are equipped for pressure sensitive current breaker or low pressure vent. 

Line Starters and Combination Starters A line starter consists of a contactor (motor-starting switch) and motor-overload relays, (Contactors are capable of canving and interrupting normal motor-starting and -running currents they are not, hovv ever, normally capable of interrupting short-circuit currents. They must be backed up by fuses or a circuit breaker for this function,... 

Fault condition particularly when the LT distribution is fed through a large transformer and the outgoing feeders tre protected by a current limiting device, HRC fuses or breakers. In the event of a fault, on a large... 

To achieve the above the characteristic of the fuses should lie well above the characteristic of the overcurrent and short-circuit releases of the breaker for the lower region of currents, such that only the breaker operates. However, it should lie well below the eharacteristic of the breaker in the higher region of currents to ensure that the fuses operate sufficiently quickly and long before the in-built releases. The breaker is thus prevented from operating at currents that are in excess of its breaking capacity. Figure 12.22 illustrates such a coordination. 

To make a proper selection of HRC fuses it is essential that the current-time characteristic curves for Ihe releases of the breaker and the fuses are available from their manufacturers. 

They will make and break, without damage, all currents falling even outside the protected zone of a thermal overcurrenl relay or the built-in overcurrent (o/c) and short circuit (s/c) relea,ses of a breaker, but within the protected region of the HRC fuses, as illustrated by the hatched portion, of the overcurrenl and short-circuit,... 

The relays and the breaker will operate only during the transient state, hence the significance of transient state values to set the current and the time of the protective and isolating devices. 

The mechanical endurance of the current-carrying parts of all the equipment, bus system, deviees and components, used in a particular circuit as well as the load-bearing members and supports on which they are mounted. The electrical parts of a device (breakers and switches, etc.) are the responsibility of the component manufacturers. The manufacturer of the switchgear assembly is responsible for the busbar systems, metallic links and wires. 

A breaker, usually an MCCB or an MCB on an LT system, can be provided with backup HRC fuses to enhance their short-time rating. This may be done when the available MCCBs or MCBs possess a lower short-time rating than the fault level of the circuit they are required to protect, and make them suitable for the fault level of the circuit. But this is not a preferred practice and is seldom used. As a rule of thumb, the device that is protecting must be suitable to withstand electrically and endure mechanically the system fault current for a duration of one or three seconds, according to the system design. 

To isolate the circuit after the lest is over and to also interrupt the test in between, in case the test piece fails. The breaker must possess an instantaneous capacity of more than the test current and the short-circuit MVA of the feeding generator. To achieve the desired voltage it must be suitable to perform the duties of repeated short-circuit tests. 

Electrical accessories circuit breakers for over current protection for household and similar installations 8828/1996 BSEN 60898/1991... 

High voliage alternating current circuit breakers 13118/1991 BS 5311/1996... 

Such breakers are normally produced for use on an LT system only. At higher voltages, while interrupting heavy currents (such as on a fault) the arc energy may be so high that a disproportionate size of arc chutes may be required to arrest and extinguish the arc, leading to disproportionate size of ACB. 

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