Some factors used in electrical supply industry:

ECONOMIC LOADING OF POWER PLANTS

Before synchronizing and loading a new steam power plant, the following steps must be gone through very carefully:

•Before any large auxiliary units are run, the auxiliary electric supply system and the service water supply system must be put into operation.•Next, it should be checked if the electric system for the remote control of dampers or other boiler controls are in working order.•Then most of the boiler auxiliaries can be checked for rotation, tried out and given enough operation to furnish some certainty about their performance.•Now the fuel supply system and fuel preparation system and the chemical feed system must be readied and tested.•Next items on the programme are usually:

• Boiler dryout and cleaning.• Setting of safety valves.• Blow down of steam lines.

•The ash disposal system should also be completed and tried out.

• While the above steps are being carried out, the condenser cooling water system and the turbine generator is run for balance check, overspeed test, and dryout of the generator.

• At this time, the feed water pumps and heaters are brought into partial operation.• After this, the switches are tried out and a check is made of electrical circuits and relay

settings, of generator phasing and of phase rotation.• By this time, all the instruments, automatic control and lighting and communication system

should be installed and seen that they are working reasonably well.

Synchronizing and Loading

•After the above initial run ups and check ups, the generator is then brought to speed and phased in on the line.•The load is usually brought to about 10% of the rating at once and is then increased over a period of several days, while the feed water and other auxiliaries are placed in operation, at one time.•After half the load is reached on the turbine, a short shutdown is often made for checking turbine bearings, filling the generator with H2 and checking the other difficulties which might have appeared.•The plant is then started again and gradually brought to full load.•After few days of running at normal load and after correcting the various troubles which are more than likely to arise, the plant should be operating fairly smoothly.

METHOD OF LOADING A HYDRO-ELECTRIC POWER PLANT

A supply of current should be made available to check and try out the station auxiliaries. All wiring and equipment should be meggertested. The direction of rotation of every motor should be checked. The overload protection should be checked and its setting adjusted to the correct value.

All the large plants have a battery and motor generator charging sets for supplying current to operate tripping circuits remote control systems and emergency lighting. Therefore, to try out the main switchgear, the battery should be commissioned, first.

After this, the next step is to dry out the generator. For this, the generator terminal are short circuited and the generator is run at a speed below the normal. Sufficient field resistance is applied so that full load current flows through the windings. These will warm up and initially their insulation resistance rapidly falls. Drying out will continue until the insulation resistance is sufficiently high and remains steady under conditions of constant temperature.

Next, the phase rotation of the generator is checked with the help of phase rotation indicator. This is connected across the secondaries of potential transformers. The instrument should show the same direction of rotation when connected in turn across the incoming and the existing supplies. After this the phasing is checked with a volt meter.

Next, the tests are applied on protective gear and overload relays to see that these are properly working.

After the above check ups, sequence of operations to parallel an alternator on the bus bars is as follows:

The water turbine is run up to normal speed. For this, the guide vanes of the reaction turbine, or the needle valve of a pelton turbine are opened to admit water. Then the automatic governor is put into service. The field switch of the alternator is then closed and the incoming voltmeter is then switched on. The exciter field rheostat is operated and the alternator voltage is increased slowly until it is equal to that of the bus bars. The synchroscope is connected in circuit and the direction of rotation relative to the bus bars is noted, whether it is slow or fast. The governor control motor can be operated from the control panel to adjust the speed of the turbine, so that the frequency of the incoming alternator is almost equal to that of the plant on the bus bars.

The generator circuit breaker control is operated just before the synchroscope pointer reaches its top vertical position so that the breaker contacts will actually make circuit when the pointer is on 12 o’ clock. After the synchronization, the synchroscope and the incoming voltmeter are switched out of the circuit.

METHOD FOR LOADING A DIESEL POWER PLANT

The following procedure is usually followed for loading of a diesel power plant:

•Be certain that the starting air pressure is sufficient.•Check the possible leaks of starting air into the cylinder. Don’t start the engine if the high pressure air is leaking into the system.•Start cooling water circulation through the engine before starting the engine.•Observe precautions and checks for fuel oil, gas fuel, lubricating oil, and starting air required by the starting instructions for the particular make and type of the engine.•Start the engine according to manufacturers instructions.•Run at reduced speed while checking the operation of fuel pumps, lubrication system, fuel oil and lubricating oil pressure. Check the lubrication of generator and exciter bearings.•Check the generator voltage to ensure that it is equal to the bus voltage.•Adjust the engine speed until the alternator comes into synchronization with the station bus. This is done by the use of a synchroscope or synchronizing lamps or both.•Now close the switch connecting the generator to bus.•Increase the engine speed until the alternator is delivering the amount of electricity desired.

For unloading and stopping of the engine, the following steps are required:

•Reduce the engine speed until practically no power is delivered by the alternator.•Open the switch connecting the alternator to bus.•Idle the engine at no load for a short time before stopping.•Stop the engine according to manufacturers instructions.•After engine has shut down, it is very urgent to continue circulating the cooling water and lubricating oil until it has been cooled to a value set by the engine manufacturer.

METHOD OF LOADING A NUCLEAR POWER PLANT

•After assembling a reactor, the next step is to make the calculations of the circumstances under which it should become critical.•For this, the uranium fuel elements are loaded one by one into the channels. The measurement of the neutron flux is continuously takes.

• After making the reactor critical, the next step is to take various measurements such as flux distribution throughout the core, the effects of control rods and the effect of temperature, by heating the coolant can be noted.

• Running up to power may now be effected by careful withdrawal of control rods.• A close watch is kept on the neutron flux measurements, operation of coolant circulators

and steam plant.• Control rods movement are to be carried out to compensate for any slight change in

reactivity that may occur and for varying the load in accordance with the demand.• The movement is generally done automatically.• To shut down the plant, the power is reduced slowly by gradually inserting the control

rods.• In case of emergency, it is done quickly by dropping in the safety valves.• Radioactive decay of the fission products continues at a high level for several hours and

may generate 5 to 10% of the full rated amount of heat.• Some coolant circulation must therefore be maintained.

• To start up after shut down, the steam plant and coolant are prepared by heating the latter.

• After this the control rods are gradually removed and the neutron flux measurements and the reactor period are closely observed.

• After the shut down, the xenon poisoning builds up a considerable negative reactivity which reaches a maximum after 20 or 30 hours.

• Therefore, the reactor should be started within an hour or two before poison has the time to build up or after a few days when the poison has died down.

• For this reason, the nuclear reactor should not be run intermittently.