Transformers Feeders

Active areas lighting 110 V outlets including feeder, transformer, panel, lights and receptacles - process, utilities and tank farm pumps areas 100 ft. 350 15... 

Inactive areas lighting, including feeder transformer panel lights - general yard tank farms 100 ft. 120 5... 

Misc. 110 V Identifiable loads, valve operators, solenoids, etc., including feeder, transformer, panel and wiring devices ea 180 10... 

Size of substations must be chosen with care. As size is reduced, more material is required for high-voltage feeders, transformers, and switches. However substations supplying too great an area will increase secondary circuitry costs. This is again an economic balance. Optimum power ratings for a three-phase substation are 400 to 600 kva with 208/120 or 230-volt secondaries and 600 to 1,000 kva with 460-volt secondaries. 

Moulded case circuit breakers are also available for incoming and busbar section purposes, with ratings up to 6000 A and service voltages between 220 V and 660 V. (At 415 V a 4000 A circuit breaker would satisfy the duty of a 2500 kVA feeder transformer with about 15% spare capacity.) These are also available as 4-pole units. Circuit breakers having ratings of 800 A and above are often provided with several adjustments that widely modify the shape of the complete protection curve, as described in Chapter 12. This enables the curve to coordinate with almost any other protective device or equipment that is immediately upstream or downstream of the circuit breaker. Some circuit breakers with the higher rated currents are also provided with integral earth fault protection facilities. 

Power systems for offshore platforms and onshore plants, which have their own generators seldom have feeder transformers with ratings greater than about 10 MVA. These transformers usually feed radially to the consumer switchboards. Several levels of operating voltages are used in these situations, for example ... 

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. 

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... 

Rated primary voltage The normal practice for an HT system is to provide a separate LT feeder for the auxiliary supplies. The primary voltage will be the normal system voltage, V, when the transformer is connected line to line or V,/ l3 when connected line to neutral. 

Figure 15.32 Phase and ground fault differential protection scheme for a transformer and feeder bus protection...

Bus bars of a transformer substation must not be directly grounded. They must be connected with rails by at least two insulated cables. Metal sheathing of feeder and return current cables must only then be connected with the rails or bus bar if an increase in anodic corrosion on other buried installations is absolutely excluded. The insulation of all return cables must therefore be monitored regularly. 

The standard approach for a secure supply system is to provide duplicated transformer supplies to a switchboard with each transformer rated to carry the total switchboard load. Both transformers are operated in parallel, and the loss of single incoming supply will not therefore affect the supply to the load feeders. With this configuration the... 

Such protection can be used on a power transformer, a motor or generator, or a single feeder. In addition, other types of relay are used for particular applications (e.g. transformer Buchholz gas, neutral voltage displacement and over-voltage). 

In some instances, it is required to measure the sum of the energy supplied along several feeders. This is the case, for example, when a factory site is fed by more than one cable and the tariff is based on the overall energy and maximum demand used. The usual method of doing this is to summate the currents in the individual feeders by installing separate current transformers in each and connecting their secondaries in parallel (Figure 17.3). 

The current transformers must have identical ratios. The assumption is that all the feeders have voltages which are equal in magnitude and phase. If the feeders are physically close together, it may be possible to use one current... 

Saxitoxin composition therefore originates as that of the local dinoflagellate population and evolves with time depending on the characteristics of the filter-feeders and subsequent consumers that accumulate and transform the toxins. 

One of the principal contributions of electronic data processing over the past several years in terms of chemical analysis is the saving of manual effort in interpreting analytical data. Special techniques, such as Fourier transform, have increased speed (as well as sensitivity) by orders of magnitude in connection with infrared, nuclear magnetic resonance, and mass spectroscopy, Of course, for on-line process analyses, essentially instantaneous interpretation is required to provide the proper error signal that is used to position the final control element (valve, feeder, damper, etc.). 

Distribution feeders, installed cost, / kVa main transformer capacity ... 

Centralized Control As mentioned previously, motor starters may be located either at the motor or at some remote point. Frequently they are grouped at a location convenient to the source of power. The feeders radiate from this point to the individual motor loads. A convenient method is the control-center modular structure for low-voltage control, into which are assembled motor starters and other control devices. The individual starters can be drawn out of the structure for rapid, easy maintenance and adjustment. With this construction it is easy to change starter size or add additional starters. All the starters are in one location, so that interwiring is simple and easy to check. Auxiliary relays, control transformers, and other special control devices can also be included. See Fig. 29-7. 

Identify and count 460 V electric heaters and treat them as motors. Other 460 V and higher loads such as heaters, lighting transformers, service feeders to building, etc., are also treated as motors. 

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