“Offload” Test Part 1

To test Energy Meters, AMT Transducer & Meter room can be used. On “Start” page, the “AMT Transducer & Meter” room software is opened. This room is comprised of the two main windows of “Test View” and “Transducer Characteristic”; in “Test View” window, it is possible to perform a “Shot Test” for various quantities and compare the results with the meter characteristic.

To begin the test, after completing the information in “Device” in “General Test Object” window, double click on “Transducer” option. On “Transducer Properties” page, it is possible to view a set of functions. To test the meter, two functions of “Wh” and “Varh” are used; here, “Wh” is selected. By selecting “Injection” option in “Input” section, it is possible to perform the “Offload” test of the meter by injection from the device. The other option is “Read from Binary” which is used to perform an “On Load” test of the meter. By selecting this option, it is necessary to enter the values into the inputs of the device using the clamps and interface cables.

In “Output” section, it is possible to specify the type of the output received from the meter. To test transducers and their corresponding outputs, by selecting “Current” or “Voltage” options, it is possible to take the output current and voltage values to the inputs 9 and 10 for measurement. To test the meter, if only the output values are being displayed on the screen, “Open Loop” option can be used. Here, “Pulse” option is used so that using the light sensor which comes with the device, the number of the output pulses of the meter is recorded.

In „CT Star point Connection“ section, the connection related to the current transformers are specified. Usually and since the active power flows from the busbar toward the line, "Toward Line” option is selected. Selecting “Toward Line” is in accordance with the injection of the active power from the device to the equipment. If “Toward Busbar” is selected, 180 degrees are added to the angle of the current.

In “Full Scale Error Reference” section it is possible to specify the error recording reference which can be selected from a range of zero to the maximum or negative to the positive maximum. If the characteristic is asymmetrical the range is from zero to the maximum while if the characteristic is symmetrical, it is possible to select both options for error measurement. As for error measurement, suppose that for a transducer with a characteristic with the maximum input of 1 amp and output of 33 milliamperes, for a 0/5 amp current, the output of the transducer equals 16 milliamperes. In such a case, the error percentage is calculated as follows.

This means that ideally, for a 480 milliamperes input, the output equals 16 milliamperes. Therefore, the absolute error value equals 20 milliamperes and the error percentage equals -4 percent:

Also, the “Full-Scale” error value of the transducer equals -2 percent.

This method is used for cases where “Full Scale Error Reference” is set at “0…+max”. If the characteristic is “Symmetrical”, the error calculation method should be selected from among “0..+max” and “-max…+max”. For the previous example, if the characteristic was symmetrical and “-max..+max” was selected, the following relation is used for “Full Scale Error” calculation.

In "Tolerance” section, it is possible to enter the error value as an absolute or a relative value; the default values are 1 milli pulse and 0/25 percent. Finally, a comparison is made between these two values and the larger value is selected as the allowed error value. In “Number of phases” section, it is possible to specify whether the meter is single-phase or three-phase.

The test characteristic is specified in "Characteristic Definition” section. Since the meter characteristic is linear, “Linear” option is selected as the “Characteristic Type” and it is uneditable.

To specify the energy “Import” and “Export” values, it is possible to check the “Symmetrical” option so that there is a Symmetrical characteristic in both sides available. The “Minimum Value”, “Knee Point” and “Saturation range” fields are disabled for meter test but in “Maximum Value” section, it is possible to enter the amount of power and the number of pulses received in exchange for that amount of power. Usually, the meter factor or “c/r” is entered in this section. For example, the factor for a edmi mk6e meter equals 5000 Wh per pulse.

Note that by using “Primary” and “Secondary” options at the top of the screen, it is possible to enter the values as primary or secondary in accordance with the meter type which needs to be done considering the CT and PT conversion ratios.

"Relative” and “Absolute” options are used for displaying the absolute or relative amount of the values. After entering the values, “Ok” is selected to continue with the test.

After completing the information in "Transducer Properties” section, the “Hardware Configuration” settings need to be examined. By opening this window, you can see that the current and voltage outputs are set by default.

In "Binary/Analog Input” tab, you see that the Binary number 8 is selected to record the pulses of the meter by default. However, it is possible for the user to use any other binary if necessary. By clicking on “Ok”, the applied changes are saved.

To perform a test, a point on the characteristic must be selected which can be done using two methods:

1- Entering the values in the fields of “Test Point” section which means entering the related parameters including Wh value, number of pulses, test performance time and frequency. Then, by selecting “Add”, this point is added to the test table.

2- Holding down the “CTRL” key and then clicking on the meter characteristic curve.

On “Test View” page, by clicking on “Advanced View”, a page opens where it is possible to enter the voltage, current and their angle as well as the