Automatic Voltage Regulator (AVR) (Essay Sample)

Automatic Voltage Regulator (AVR)
AVR or voltage stabilizer is meant for obtaining a stabilized AC supply from the fluctuating incoming mains. Also, they are used to provide constant rated voltage for sensitive electrical equipment such as transmitters, UPS and Process Control Equipment. They come in different sizes input/output voltage options. In KEMYA the Automatic Voltage Regulators are used to regulate either instrument supply or "By Pass Mains" in UPS system. See table 1
Table SEQ Table \* ARABIC 1 AVRs in KEMYA
Manufacturer

Function

BELOTTI

For stabilizing bypass power supply for GUTOR UPS systems.

SAFT (Claude Lyons)

For stabilizing instruments power supply. As well as bypass power supply for SAFT UPS systems.

CYBEREX (AC Line regulator)

For CYBEREX UPS systems in Substations 10-0 & 40-7
.

Power Protection Products

For CYBEREX UPS LDPE.

I will concentrate on BELOTTI one since it is used to stabilize the newest UPS system in KEMYA which is GUTOR UPS.
The operating principle of stabilizer is that an in-phase or out –phase voltage of variable magnitude is applied to the primary winding of the buck-and-boost transformer (TB) to control the voltage in the secondary winding, which is connected in series between the supply and the load. The variable transformer winding (AT) is connected across the controlled mains supply. The variable output is taken to the primary winding of the transformer (TB) via fixed and variable tapping that is provided by the brush (es) which pass through a specially prepared track on the winding. When the position of the brush (es) matches with the position of the fixed tapping, the output voltage from (AT) will be zero. The brush gear is rotated by the geared motor and the movement of the brush (es) in either direction from the zero position gives gradually increase output voltage. See figure 9
Figure SEQ Figure \* ARABIC 9 Single phase wiring of BELOTTI AVR
When the mains supply voltage falls, the servo amplifier supplies negative current with respect to earth to the motor armature. The motor then moves the brush gear of the variable transformer in such direction as to cause an in-phase voltage build-up in the secondary winding of transformer (TB). This voltage boosts the low mains and continues to build-up until the output voltage of the stabilizer is restored to normal. Then, the servo amplifier cuts the supply of negative current to the motor and the movement of the variable transformer brush gear ceases.
But, when the mains supply voltage rise, positive current is supplied to the motor, which drives the brush gear of the variable transformer in the opposite direction, reducing the voltage supplied to transformer (TB). As the brush gear passes the position of the fixed tapping, the voltage in the transformer is reduced to zero to build up 180 degree out-of-phase to the supply voltage. The voltage in the secondary winding of the transformer now opposes the increased input voltage and continues to build up until the stabilizer output voltage is again restored to normal, when the servo amplified again stops the motor.
If the variations in the supply voltage are greater than the acceptance range of the stabilizer, the brush gear of the variable transformer will be driven to one or other of its extremities without full correction being achieved. In order to prevent possible damage to the motor or variable transformer, limit switches are incorporated in the motor armature circuit, which break the motor supply when the limit reached. A rectifier is connected in series but in opposite polarity to each limit switch, and these two limit circuits are connected in parallel to the same motor brush. In addition, there are therefore separate paths for the supply of either positive or negative current to the motor. If the servo amplifier is supplying the motor from a positive source (the stabilizer is correcting for a rise in the supply voltage) when a limit is reached, the limit switch which operates break the positive current path and stop the motor. Current of the opposite polarity is able to reverse away from the limit when the supply voltage returns within the acceptance range of the stabilizer.
Transformer oil
Transformer oil or insulating oil is usually a highly-refined mineral oil that is stable at high temperatures and has excellent electrical insulating properties. It is used in oil-filled transformers and also for some types of high voltage capacitors, high voltage switches and circuit breakers. Its functions are to insulate, suppress corona and arcing, and to serve as a coolant. Large, high voltage transformers undergo prolonged drying processes,