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Testing Motor Drives of Disconnectors

Disconnectors and earthing switches are used to ensure that an energized part of certain substation disconnects and becomes de-energized providing safe access to certain elements which are needed to be serviced or replaced.

The main aim when diagnosing the disconnecting motor drive is to monitor and evaluate the following parameters:

  • Current and voltage,
  • Power consumption,
  • Operating time of the motor drive

DIS-H (disconnector analyzer) can measure all of the previously mentioned parameters and can start the recording according to a specific trigger. The trigger threshold value can be set according to the selected trigger source, either voltage or current. Moreover, it enables quick onsite analysis of the disconnecting motor drive and the possibility to evaluate the state of the motor drive and potential defects that may have occurred.

To perform the motor testing procedure the DC current clamps and DC voltage sense cables have to be connected as shown in Figure 1 below. The voltage sense cables are connected either to the substations battery or to an external power source.

Connection Diagram of DIS-H
Figure 1 – Connecting DIS-H to a motor

It is important to evaluate the motor state occasionally in order to determine the condition of the disconnecting motor drive and provide us with essential information on how would the disconnector operate in real-life situations in cases when a service or maintenance is needed. The DC current flowing through the motor is measured by a DC current clamp which provides the recordings of the motor current waveform, whereas the DC voltage is obtained by using sense cables and it provides the accurate measurement of the disconnecting motor drive DC voltage supply.

By initiating the start of the test the disconnector analyzer is going to await an external signal to start the measurement depending on the pre-defined test settings. When the motor begins the process of closing or opening, the disconnector motor current will start to flow and that will instantly trigger the timing measurement. The obtained results can be observed either graphically or numerically by using the intuitive touch-display, or by opening the test results through the DV-Win software. The representation of the graphical test results can be observed in Figure 2 and Figure 3 below.

Figure 3 – Test results in DV-Win software

Faults in motor-operated disconnectors are far more likely to occur than on the manually operated ones. Furthermore, the state of the motor operating drive of the disconnector can be assessed according to the obtained current waveform. The current waveform can indicate whether there are any defects within the mechanism of the disconnector and these problems can vary from dried lubrication of the bearings, exceeding rotational momentum as well as possible rusting and corrosion. The waveform can be investigated by observing four major points, these points can be observed in Figure 4 shown below.

Figure 4 – Motor current waveform

The labeled points on Figure 4 shown above are used to evaluate the state of the drive and they are as following:

  1. Starting (Inrush) current,
  2. Maximum operating current,
  3. Current when the sequence has been finished,
  4. Charging time

In terms of comparing the obtained test results, the DIS-H instrument can execute this function either with graphical or numerical comparison. When it comes to the graphical comparison the instrument can overlay up to 4 test results while in numerical form it can overlay up to 2 results.

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September 14, 2020

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