Methods of Regulating Input Voltage and Current (RADS 354)

Why do we need to regulate input voltage?

To permit the choice of a variety of kV

devices that can be used in regulating voltages and current

Autotransformer

Rheostat

Choke Coil

autotransformers are sometimes called?

variable transformer

with autotransformers, usually the step-up transformer (HT transformer) does what?

steps up volts to kilovolts (kV)

what is the voltage input fixed at for an autotransformer?

110 or 220 depending on power supply

What is the function of the autotransformer?

it modifies the fixed voltage input so we can have a range of kV

Where is the autotransformer located?

between the AC source and the primary coil of the high voltage transformer of HT transformer

Construction of the autotransformer

consists of a single coil of insulated wire, wrapped around a large iron core

at regular intervals along the core of the autotransformer the wire is interrupted, and the points are connected to...

electrical taps or metal buttons

Two of the taps of the autotransformer are connected to the ________________ and are called _______________

input power; primary taps that are fixed

The other taps of the autotransformer are called _______________

secondary taps and they are adjustable

Movable contactor is connected to which side of the high voltage transformer or HT transformer?

the primary side

Movable Contactor

varies the number of turns to include in the secondary circuit of the autotransformer and varies its output voltage

General Principle of Autotransformer

To vary the input voltage to the primary coil of the high voltage transformer of HT transformer (to select what kVp we want)

-want to control the amount of voltage to be stepped up from volts to kV

Scientific Principle of Autotransformer

Works on electromagnetic self-induction (1 coil and back EMF)

Autotransformer Law

The autotransformer secondary voltage is to the autotransformer primary voltage as the number of tapped turns is to the number of primary turns

Autotransformer Law Equation

ATVs/ATVp = # Tapped Turns (secondar turns)/ # Primary Turns

-direct

The autotransformer can be used as a...

step up or step down transformer

For an autotransformer it is much safer and easier to vary a ___________________, than to ___________________

low voltage and then increase it; increse a low voltage than vary it

For the autotransformer the primary side is ___________ and the secondary side is ____________

constant; adjustable

Autransformer varies voltage to primary side of HT and current and also serves as a...

mA Selector

Voltage from the mA selector is delivered to the primary side of the...

filament transformer

Filament Transformer

step down transformer that operates between 4-6 amps

-lowering incoming voltage

Rheostat

variable resistor used to regulate voltage to the HT transformer

The rheostat can work on either

a.c or d.c. current

Principle of Rheostat

based on the fact that according to Ohms law there will be a voltage drop across a resistor

-it converts more or less electrical energy into heat (wasteful process)

Construction of Rheostat

a series of resistors coils and a sliding tap, the tap is moved to increase or decrease the resistance in the circuit

-when placed in series with the primary side of the HT will vary voltage and current to it

Choke Coil

Consists of a coil of wire connected to an AC source and an iron core that is mechanically inserted into the coil (iron core goes up and down the coil)

Principle of Choke Coil

Self-Induction (1 coil of wire w/ back EMF)

The choke coil is primarily used to...

regulate filament current to permit control of mA, but has been largely replaced

The induction of the iron core into the coil of the choke coil intensifies the magnetic field and cuts across the coil itself, causing what effects?

a larger voltage decrease across the choke coil (goes down deeper), leaving a smaller remaining voltage for the rest of the of the circuit

-also a decrease in current due to large self inductance of the circuit

With the choke coil, the deeper the core inserted...

the more pronounced effects