The measurement of electric power and energy at high-voltages and currents at low power factors is becoming increasingly important economically as a way to reduce costs in an ever-growing industrial economy. Today the transformer purchaser subjects the transformer manufacturer to an economic penalty for losses that occur in load and no-load conditions. To keep these penalties as low as possible, it is important that the manufacturer accurately measure these losses. Failure to do so can result in the manufacturer losing important contract awards to their competitors who may be utilizing a more accurate system.
Using “State-of-the-Art” proven two-stage-current comparator technology, the AccuLoss® series of Transformer Loss Measurement Systems is designed to meet the needs of today’s transformer manufacturer by providing the most accurate power loss measurement system in the world. Designed for power frequency testing and calibration, the AccuLoss® system can be used for testing small, medium and large power transformers as well as motors and turbines up to 400 Hz. The system is also ideal for R & D facilities. The AccuLoss® system can also be used to measure losses in single and three-phase reactors.
The AccuLoss® series of Transformer Loss Measurement Systems has been accepted and installed by transformer manufacturers around the world and distinguished itself in the rugged transformer manufacturing environment. There are two types of bushings available for the AccuLoss® system, Vertical for systems at and above 100 kV L-N and Horizontal for systems below 100 kV L-N.
The AccuLoss® system includes a powerful “operator friendly” software. Included are voltage and current waveform analysis, manual and fully automatic time-saving range selection and over voltage and over current protection.
The AccuLoss® system controller can be directly connected to the plant LAN for transferring data to a host computer for backup and further processing including generating customer reports. As an option, AccuLoss® can be controlled remotely from a separate program running on another computer. This is very helpful in those situations when the power generator, which is not part of the loss measurement system, has to be controlled automatically and from a different location.
The AccuLoss® system is a complete transformer loss measuring system and complies with the latest standards and specifications dealing with the calibration of test systems to measure transformer losses.
A capacitive divider consisting of three (3) shielded gas-filled (SF6) High-Voltage Standard Capacitors and three model 2500A Voltage Dividers are used for measuring the phase to ground voltage in each phase. The output of the High-Voltage Standard Capacitor is connected to the voltage input of the instrument rack and then directly into the voltage input of the model 2500A Voltage Divider.
The output of the voltage divider is connected to the input of the power analyzer where the voltage (input/range) is displayed. System input voltage is displayed on the controller screen as RMS or AVG value.
The model 2500A Divider uses a two-stage compensated current comparator to correct for magnitude and phase errors within the divider. As a result, calibration does not drift from year to year. The recommended calibration for the dividers is every three to five years.
For in-house calibration, the dividers can be calibrated using the MIL model 7010A or 7010B High-Voltage Capacitance Bridge, two Low-Voltage 1000 pF Standard Capacitors and two of the High-Voltage Standard Capacitors. Both the High-Voltage Standard Capacitors and Voltage Dividers can be calibrated over the full range.
Current: A current divider consisting of three (3) model 7021U (100 kV or 200 kV) precision two-stage-compensated current-transformers are supplied as part of the current measurement system in each phase. The output and compensation of the model 7021U current transformer are connected to the current input of the instrument rack and then directly to the current and compensation input of the model 2020A Power Analyzer.
The model 7021U and model 7022 Precision Current Transformer have only one range of 2000:1. The linearity of the current transformer is less than 10 ppm, so measurements as low as one hundred milliamperes (100 mA) can be made with ease. Subsequent current ranging is provided on the power analyzer which has 10 current ranges in stages of 5, 2, 1, 0.5, 0.2, 0.1, 0.05, 0.02, 0.01 and 0.005 A.
The two-stage current transformers’ accuracy is not affected by age. As a result, annual calibration is not necessary. Calibration for the 7021U current transformers is recommended every three to five years.
The model 2020A Power Analyzer uses a multi tapped two-stage-compensated CT to perform the switching on its input to measure the current. The current value is displayed on the power analyzer and the control screen. The two-stage-compensated CT within the power analyzer reduces the error of the High-Voltage Current Transformer.
Power: The model 2020A Power Analyzer displays the power of all three phases at the input to the power analyzer. The sum of the three phases is calculated and displayed on the controller screen. Automatic ranging of the model 2500A High-Voltage Dividers and the model 2020A Power Analyzer ensures that each component measures in the best range. The values are calculated and displayed with 5-digit numbers on the screen.
Accuracy and Uncertainty: The maximum power measurement accuracy and uncertainty of the AccuLoss® series of loss measurement systems are shown below as a function of the power factor. This accuracy can further be improved by asking for a National Measurement Institute (NMI) calibration of the components. An optional system calibration is also available.
Control Cabinet: The control cabinet houses the electronics and is protected against impulse through the input and ground connections. The model 2500A Voltage Dividers, model 2020A Power Analyzer and industrial-grade PC controller are housed in the cabinet.
All connections are made at the rear of the control cabinet. Channels include the three current channels and the three voltage channels. The inputs to the power analyzer are updated every one (1) second. The controller reads each power analyzer and displays the input voltage and current and calculates the real power, the apparent power and the power factor.
PC/Controller: The AccuLoss® system is controlled and monitored by an industrial-grade PC/controller. The keyboard and monitor are external to the control rack where they can be easily placed near the generator control.
Laser Printer: As an option, a quality laser printer can be supplied with the system.
Cable Leads: Interconnection cables between the Current Transformer, High-Voltage Capacitor and the electronic rack are included. Systems have been installed with cable lead lengths up to 50 metres.
Software for the AccuLoss® series of Loss Measurement Systems utilizes the globally recognized LabVIEW interface from National Instruments. The software runs in a Windows operating environment and is fast, easy and intuitive. Large buttons on the Main screen are used to ensure correct settings for the measurements. All measurement data is displayed on the Measurement screen as well as waveforms for the voltage and current channels. Measurement data is stored to an ASCII file which can be exported over the ethernet to the main computer for analyzing and producing calibration reports.
The software can be modified to meet the specific needs of the user prior to shipment of the system.
Main Screen: The Main screen provides easily recognized icons for entry into the UUT data, test GPIB and calibration data entry screens. Test configuration selectors are also available.
The Main Menu screen is divided into four (4) sections:
The Measurement screen allows the operator to quickly review the measurement data. Included on this screen is the Hold [F6] and Save button for saving the data to an ASCII file. The Hold and Save button toggle back and forth depending on which is selected.
Scrolling down to the bottom of the screen reveals the Waveform Analyzer showing the waveforms for both current and voltage on all three phases including the even and odd harmonics up to the 25th harmonic. These waveforms can be printed.