Contactors, coordination

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. 

A contactor must have full-load rating and be coordinated to proven capability with a selected fuse. 

The velocity readings are carried out by four probes whose radial and longitudinal position can be established at will inside the contactor by means of a displacement device controlled by computer, which established the coordinates... 

Note For small motors, e.g. 22 kW and below, the earth loop impedance inclnding the feeder cable armouring may be too high. When this is the situation a risk of electric shock exists dnring a short circnit at or near to the motor. To reduce the exposure to the risk it is necessary to nse a 51 N or a 50 N core balance current transformer and relay at the motor control centre. The choice of a 50 N is preferred subject to the contactor being properly coordinated with its upstream fuses. 

The necessity for an instantaneous tripping function is the same as for a high voltage motor. This function can be provided by a magnetic repulsion device within the moulded case circuit breaker, by a (50) relay or by upstream fuses. If fuses are used then the contactor must be capable of carrying the duty until the fuse completes its function. To minimise the stressing of the contactor it should be coordinated with the fuses as recommended in IEC60947 Part 2, as a Type 2 requirement. 

Cocalia, V. A., Jensen, M. P., Holbrey, J. D., Spear, S. K., Stepinski, D. C. Rogers, R. D. (2005). Identical extraction behavior and coordination of trivalent or hexavalent f-element cations using ionic liquid and molecular solvents. Dalton Transactions, 2005, 1966-1971. de Menech, M., Garstecki, P., Jousse, F., Stone, H. (2008). Transition from squeezing to dripping in a microfluidic T-shaped junction. Journal of Fluid Mechanics, 595, 141-161. Dehkordi, A. M. (2001). Novel type of impinging streams contactor for liquid-liquid extraction. 

The components are closely coordinated to work together, and the unit is rated for a particular value of short-circuit interrupting current. The unit may contain a thermal-magnetic or magnetic-only circuit breaker and a starter, or a fusible or nonfusible switch and a contactor or starter. The suitability of the enclosure (either provided with the combination starter or into which the combination starter is mounted) to its environment is an important consideration. 

In a combination starter, the magnetic or sohd-state contactor or starter is coordinated with a circuit breaker or set of fuses so that the equipment will successfully complete a fault interruption up to its pubhshed rating. The same coordination is built into the self-protected combination controller. 

---