Voltage regulators Flashcards
How is generator voltage regulated?
Generator output voltage results from the cutting of flux lines by a conductor. The number of flux lines cut can be varied easily by changing the amplitude of the DC exciter field current, which in turn varies the voltage at the generator terminals.
How do you excite large generators.
Because the field current is greater, it is easier to connect the output of the exciter directly to the generator field and put the regulating rheostat in the field of the exciter.
What is the essential function of the voltage regulators?
To use the generated AC voltage , which is now the controller,, as a sensing influence to automatically vary the main exciter field rheostat which in turn supplies the required generator field strength to maintain a constant generator voltage.
Name the 4 types of voltage generators used today?
Vibrating contact type in which a resistance in the field circuit is periodically short circuited.
Rheostat type in which the value of the resistance in the field circuit is varied directly by suitable control devices.
Indirect acting type in which the regulation is effected through the opening and closing of contacts by a voltage sensing device.
Dynamic voltage regulator in which feedback and electronic components are used.
The difference between them is the way they alter the field current.
Describe vibrating type contact rheostat.
*the voltage held by the regulator as determined by the voltage adjusting rheostat can be adjusted by varying the weight and adjusting the tension of the DC solenoid spring.
Describe rheostat type regulators.
Horizontal plates on a shaft are pulled together with a motor. Silver shorting contacts on the ends touch as plates come together and add resistance once shorted through the high resistance plates.
Describe whetstone bridge rheostats?
Whetstone Bridge rheostats are widely used in the main exciter field circuit on large generators using separately excited main exciter and having line charging requirements. This type of rheostat providesa wider range of excitation control and has the additional advantage of providing better protection against excessive over voltage from overspending due to loss of load.
Describe dynamic voltage regulators.
They differ from the others in that they have a feedback control and electronically controlled separate motor or shaft-driven rotating machine. Systems equipped with this equipment enjoys greater system stability or make and break contacts or other styles.
Regulation with the amplidyne.
Amplidyne is a
With the amplidyne turned on, the regulator will supply control field current to the amplidyne, so that the amplidyne voltage will oppose ( or buck ) the exciter voltage impressed across the exciter field circuit. This will tend to reduce the exciter field current, lower the exciter voltage, and decrease the field current and terminal voltage of the ac machine.
What is cross current compensation.
In order to obtain successful parallel operation of two or more generators with individual voltage regulating control, they must perform two function; must hold voltage constant, and provide proper division of reactive KVA load among the generators. Most generators hold constant voltage regardless of reactive load or power factor of regulated machines. It is therefore necessary to bias the voltage element of the regulators with reactive current or some equivalent effect, so as to obtain proper division of reactive current between paralleled machines for all load conditions. This tends to prevent the flow of cross currents between paralleled AC machines as well as to insure stable operation of regulators in parallel.
What is line drop compensation?
It is voltage regulation of transmission lines. A current transformer is located in the outgoing feeder or transformer bank and the current is fed through a compensator consisting of a variable reactor and a variable resistor.
How do you regulate voltage for synchronous condensor?
Large power systems need voltage control near the load center as well as at the source. Constructed similar to ana ac generator. The excitation range used on synchronous condesor is greater that that used on generators in order to give a wider range of voltages. Under weak field conditions, the machine consumes VARS like a large induction motor, lowering voltage and presenting lagging power factor. When the field is strong, the synchronous condensor produces VARS, raises voltage, and presents a leading power factor. Cross current compensation may be used where synchronous condensers are used in parallel.
