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Acoustic testing of instrument transformers

Acoustic testing of cable joints and bushings in the switchgears

Acoustic testing of the switchgears

Acoustic testing of power transformers

Acoustic testing of busducts

Implementation of the system of control of electrical insulation characteristics

New approaches to monitoring of the technical condition of the switchgear equipment



To detect insulation defects, accompanied by partial discharges in instrument transformers, acoustic method is the most effective non-invasive way of diagnostics that is performed under the operating voltage. Current instrument transformers of type ТФРМ-330, 500 and 750 are the most accidental in Russia at present.

Practice shows that existing methods of monitoring failed to detect emergency transformers. That’s the reason SPA "Technoservice-Electro" has designed an acoustic recorder with radio receiver and applies it in practice.

Reference point in which the sound of partial discharges is detected in insulation of ТФРМ-500, is located on the side of the transformer tank. This is due to the fact that the most probable location of the partial discharge - is the secondary winding at the top (Fig. 1).

Figure 1 Sketch of design of ТФРМ 500.

Acoustic tube with radio receiver, used to record discharge processes, was tested in the test station of ЗЗВА (a manufacturer of ТФРМ-500). For short discharge processes in a current measuring transformer insulation, it was found that the acoustic recorder tube with radio receiver, developed by SPA "TECHNOSERVICE-Electro", allows you to register discharges in insulation of current measuring transformers of type ТФРМ, not only at the alarm level, but also at a level allowed by factory tests of new products (several pC). This corresponds to the ignition of the first level indicator in the receiver of an acoustic recorder.

Accidental discharges process the ignition of all five levels of the indicator.

Installation of the acoustic discharge signal recorder with radio receiver is performed by the operational rod ШОУ 500 (Fig. 2).

Figure 2 Installation of the acoustic discharge signal recorder

View of the acoustic discharge signal recorder’s tube is shown in Figure 3. Constructively the recorder consists of two small portable devices – a sensor tube consisting of an acoustic recorder PD HRD with a radio transmitter and a magnetic holder (Fig.3), and a radio receiver that is connectable to your computer (Fig.4).


Figure 3. Acoustic discharge signal recorder’s sensor tube. View from the top (left) and bottom (right).

Signals from the acoustic recorder with radio receiver are taken (Fig. 4) and transmitted to the computer. Use of a computer helps to analyze the level of the ultrasonic signals, and in accordance with the standards the disturbances are defined. The level of detected ultrasonic radiation is displayed with five discrete lights. The minimum detectable level of the ultrasonic pressure of 0.04 Pa in the frequency band 60-130 kHz causes the ignition of the first indicator of the five in the signal processing program unit. Below there is a relative ratio of displayed indication levels to the sound pressure: Level 1 - 0.04 Pa, Level 2 - 0.08 Pa, Level 3 - 0.16 Pa, Level 4 - 0.32 Pa, Level 5 - 0.64 Pa. The approximate ratio of the displayed sound pressure and amount of spark charge:

- 0.04 - 0.4 Pa (low intensity discharges 20-300 pC)

- 0.2 - 2 Pa (high intensity discharges 300 pC-10 nC).


Figure 4 Radio receiver (left) and an example of the PC program with two sensors (right).

If an instrument transformer has a grounded tank, the acoustic survey is performed with the other device - "Dolphin" (Fig. 5). For example, in Serbia, it allowed to find about 80 pre-emergency current transformers.

Figure 5 The current transformers of type TPE 11 and their survey with "Dolphin"

Figure 6 Acoustic signals, the output results of disassembly and chromatographic analysis of dissolved gases in transformer oil, surveyed and rejected with "Dolphin"