Governor and controlling:
1. Turbine generators speed/load control
Electrical generator is in the manifestation of synchronized air conditioning electrical force, making the generator and driving turbine to turn at precisely the same speed (or recurrence) as other synchronized generators joined into the regular system. Essential speed/load legislating gear is intended to permit every unit to hold its own particular load relentless at consistent recurrence, or to acknowledge its impart of burden varieties, as the normal load climbs and falls. Extremely minor machines might use immediate mechanical governors, however the greater part of the units will utilize either mechanical-water powered administering frameworks or electrohydraulic frameworks. Non-warm gathering units 5000 kw and bigger and back force units without immediate extraction will be outfitted with mechanical-water driven representing. Forimmediate extraction units bigger than 20,000 kw, legislating will be specified either with a mechanicalhydraulic then again an electro-water driven framework.
2. Overspeed governors.
All turbines require separate safety or overspeed governing frameworks to insure inlet steam interruption if the machine surpasses a safe speed for any reason. The emergency governor closes a specially designed stop valve which not just close off stream and yet treks different security apparatuses to counteract overspeed by blaze steam prompting through the turbine drain (extraction) focuses.
c. Single and multi-valve arrangements.
Whatever type of governor is used, it will modulate the turbine inlet valves to regulate steam flow and turbine output. For machines expected to operate extensively at low or partial loads, multi-valve arrangements improve economy. Single valve turbines,in general, have equal economy and efficiency at rated load, but lower part load efficiencies
CONDENSER AND CIRCULATING WATER SYSTEM
(1) The primary purpose of a condenser and circulating water system is to remove the latent heat
from the steam exhausted from the exhaust end of the steam turbine prime mover, and to transfer the latent heat so removed to the circulating water which is the medium for dissipating this heat to the atmosphere. A secondary purpose is to recover the condensate resulting from the phase change in the exhaust steam and to recirculate it as the working fluid in the cycle.
(2) Practically, these purposes are accomplished in two steps. In the first step, the condenser
is supplied with circulating water which serves as a medium for absorbing the latent heat in the condensing exhaust steam. The source of this circulating water can be a natural body of water such as an ocean, a river, or a lake, or it can be from a recirculated source such as a cooling tower or cooling pond.In the second step, the heated circulating water is rejected to the natural body of water or recirculated source which, in turn, transfers the heat to the atmosphere, principally by evaporative cooling effect.
EMERGENCY POWER SYSTEM
The dc system, consisting of a station battery, chargers and dc distribution panels, provides a continuous and reliable source of dc control voltage for system protection during normal operation and for emergency shutdown of the power plant. Battery will be nominal 125 volts,mounted on wooden racks or metal racks with PVC covers on the metal supporting surfaces. Lead calciurncells having pasted plates Plante or other suitable cells will be considered for use.
.
Battery chargers.
Two chargers capable of maintaining the proper float and equalizing voltage on the battery will be provided. Each charger will be capable of restoring the station battery to full charge in 12
hours after emergency service discharge. Also, each unit will be capable of meeting 50 percent of the total
dc demand including charging current taken by the discharged battery during normal conditions..
.
Appurtenances.
The following instruments and devices will be supplied for each charger:
(a) Relay to recognize loss of ac supply.
(b) Ac voltage with selector switch.
(c) Dc ground detection system with test device.
(d) Relay to recognize loss of dc output.
(e) Relay to alarm on high dc voltage.
(f) Relay to alarm on low dc voltage.
(g) Dc voltmeter.
(h) Dc ammeter with shunt.
.
DC distribution panel
The distribution panel will utilize molded case circuit breakers or fuses selected to coordinate with dc breakers furnished in control panels and switchgear. The breakers will be equipped with thermal magnetic trip devices, and for 20 kA dc interrupting rating.
4-25. Emergency ac system
Those portions of the station service load that must be operable for a safe shutdown of the unit, or that are required for protection of the unit during shutdown, will be fed from a separate 480-volt unit emergency power bus. A suitable emergency diesel engine driven generator will be installed and arranged to start automatically and carry these loads of the normal source of power to this bus is lost. The loads fed from this bus might include such things as emergency lighting, communication system, battery charger, boiler control system, burner control system, control boards, annunciator, recorders and instrumentation. Design of these systems will provide for them to return to operation after a brief power outage.
Excitation systems
Rotating commutator exciters as a source of dc power for the ac generator field generally have been replaced by silicon diode power rectifier systems of the static or brushless type.. A typical brushless system includes a rotating permanent magnet pilot exciter with the stator connected
through the excitation switchgear to the stationary field of an ac exciter with rotating armature
and a rotating silicon diode rectifier assembly, which in turn is connected to the rotating field of the generator. This arrangement eliminates both the .commutator and the collector rings. Also, part of the system is a solid state automatic voltage regulator, a means of manual voltage regulation, and necessary control devices for mounting on a remote panel. The exciter rotating parts and the diodes are mounted on the generator shaft.
0 comments:
Post a Comment