Distribution Transformers and Voltage Regulators
#Siemens invented the #voltage #regulator in 1932 and pioneered its use in the United States. Voltage Regulators have tapped step #autotransformers used to ensure that a desired level of voltage is maintained at all times. A voltage regulator comprises a tapped autotransformer and a #tapchanger.
The standard voltage regulator provides ± 10 % adjustment in thirty-two 0.625 % steps. Voltage Regulators with ± 15 % and ± 20 % regulation are available for some designs
!!! Voltage #regulators are liquid-immersed and can be 1-phase or 3-phase. They may be self-cooled or forced air-cooled. Available at 50 or 60 Hz and with 55 or 65 °C temperature rise, they can be used in any electrical system to improve #voltagequality.
Voltage regulator ratings are based on the percent of the regulation (i.e., 10 %).
For example, a set of three 1-phase 333 kVA regulators would be used with a 10 MVA transformer (e.g., 10 MVA 0.10/3 = 333 kVA). 1-phase voltage regulators are available in ratings ranging from 2.5 kV to 19.9 kV and from 38.1 kVA to 889 kVA.
3-phase voltage regulators are available at 13.2 kV or 34.5 kV and from 500 kVA to 4,000 kVA.
Voltage regulators can be partially or completely untanked for inspection and #maintenance without disconnecting any internal #electrical or #mechanical #connections. After the unit is untanked, it is possible to operate the voltage regulator mechanism and test the control panel from an external #voltagesource without any reconnections between the #control and the regulator.
Standard External Accessories
The standard accessories are as follows:
External metal-oxide varistor (MOV) bypass arrester
Cover-mounted terminal block with a removable gasketed cover. It allows easy #potentialtransformer reconnections for operation at different voltages
Oil sampling valve
Two laser-etched nameplates
External oil sight gauge that indicates oil level at 25 °C ambient air temperature and oil colour
External position indicator that shows the tap changer position Mounting bosses for the addition of lightning arresters to the source (S), load (L) and source-load (SL) bushings. They shall be fully welded around their circumference.
Accessories and Options
Remote mounting kit: Extra-long control cable shall be provided for remote mounting of the control cabinet at the base of the pole.
Sub-bases: To raise the voltage regulator to meet safe operating clearances from the ground to the lowest live part.
Auxiliary PT: Operation at different voltages.
Testing
All voltage regulators shall be tested in accordance with the latest #ANSI C57.15 standards.
Standard tests include:
#Resistance #measurements of all windings
Ratio tests on all tap locations
No-load loss at rated voltage and rated frequency Excitation current at rated voltage and rated frequency Impedance and load loss at rated current and rated frequency Applied potential
Induced potential
#Insulation #powerfactor test
