CZ2013480A3 - Heavy-duty tester of power capacitors - Google Patents

Abstract

The load tester consists of a controllable network switched DC source (10) provided with a control input (11) for controlling the output current. The power supply output (10) powers the power switching bridge (20). The symmetrical rectangular voltage at the output of the bridge (20) is connected to the primary winding of the power transformer (40) via a surge protector block (30). To the secondary winding of the transformer (40) is connected a series combination of a separating capacitor (50) and a tested capacitor (70) forming a series resonant circuit with approximately sinusoidal current flow with the transformer inductance (40). The current information of the tested capacitor (70) is supplied via the transformer (80) to the input of the excitation and tuning block (90). The outputs (96) to (99) of the block (90) control the switching bridge (20). The output of the charging / discharging block (100) is connected to a decoupling capacitor (50) and allows the DC component of the voltage to be tested on the capacitor under test (70). The control unit (120) controls by its output (123) the activation of the blocks (10), (90) and (100) by the command from the input (122) or by switching them off either via the same command or emergency inputs on the inputs (124). ) and (126). The sockets (84) allow measurement of current parameters flowing through the test capacitor (70) via external meters. To measure the effective value of this current, the instrument is equipped with a pointer gauge (94), to measure the DC component of the voltage on the capacitor (70) by a pointer gauge (1010).

Description

There is a load tester of power capacitors, which allows simultaneous loading of power capacitors with alternating current up to 100 A and DC voltage up to 2 kV with the possibility of independent setting of values. The resonant principle is used to achieve high energy consumption at high kHz frequencies.

BACKGROUND OF THE INVENTION

Power capacitors in power equipment converters (eg DC-link DC link capacitors) are exposed to combined loads of DC voltages and higher frequency AC currents. The designers and manufacturers of these capacitors need to verify their properties and behavior in conditions close to actual operation during their design and manufacture. The present apparatus serves for this purpose.

At present, it is not known that anyone in the world offers a combined tester which allows simultaneous loading of the tested capacitor with alternating current of higher frequency and DC voltage with the possibility of their independent adjustment.

Capacitor manufacturers address these needs by a variety of partial methods or by deploying products in a trial run in one of the applications. The disadvantage of these procedures is often the inability to monitor the behavior of the tested capacitor in the test room by the same means available.

SUMMARY OF THE INVENTION

The above disadvantages are overcome by the load tester of the power capacitors of the present invention. This tester consists of a controllable mains DC power supply provided with a control input to control the output current, an input to set the output voltage limit, and an input to turn off the output voltage. The first output of the adjustable DC power supply is coupled to the first input of the power switching bridge, the second input of which is connected to the second output of the adjustable DC power supply. The first output of the power switching bridge is coupled to the first output of the surge protector block, the second output of which is coupled to the second output of the power switching bridge. Furthermore, the inputs of the overvoltage protection block are connected to the primary winding of the power transformer. One end of the secondary winding of the power transformer is connected to one end of the decoupling capacitor and to the first output of the charge / discharge block, which is provided with an input for adjusting the DC voltage on the power capacitor under test. The other end of the decoupling capacitor is connected to one terminal of the power socket and to the other output of the charge / discharge block. The other end of the secondary winding of the power transformer is passed through the current transformer and connected to the second terminal of the power socket. The power plug is fitted with a power plug with terminals for connecting the tested power capacitor. The power socket is further provided with a first safety contact terminal connected to a first input of the control unit and a second safety contact terminal connected to a second input of the control unit. The first secondary terminal of the measuring transformer is connected to one end of the load resistor, to one end of the surge protection circuit provided with external measurement sockets, and to the first input of the excitation and tuning block. The other terminal of the current transformer is connected to the other end of the load resistor, to the other end of the surge protection circuit, and to the second input of the excitation and tuning electronics block. The outputs of the excitation and tuning electronics block are connected to the corresponding inputs of the power switching bridge and its output is connected to the current meter. The third input of the excitation and tuning electronics block is coupled to the control unit output, and is also coupled to the input of an adjustable DC power supply and the charge / discharge block input. The third output of the charging / discharging block is connected to a DC voltage meter on the capacitor under test, its fourth and fifth outputs are bridged by the discharge resistor and the sixth output is connected via a charging protection block to the third input of the control unit.

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It is therefore a solution where the dissipation inductance of a power transformer forms a series resonant circuit determining the operating frequency of the tester with the capacitor to be tested and the isolation capacitor connected in series. The secondary winding of the power transformer is therefore connected to a series combination of the test and decoupling capacitor, the primary winding of the power transformer is connected to a bridge of semiconductor power switches, such as FET transistors, which provides power to the transformer with rectangular AC voltage. The necessary control of the power switches is provided by the excitation and tuning electronics block, which processes the current information flowing through the capacitor under test. This is obtained by a plug-in current transformer integrated into the secondary circuit of the power transformer. The winding of the plug-in current transformer is connected to the input of the excitation and tuning electronics block. This closes the feedback loop determining the operating frequency of the circuit. The power switching bridge is supplied from an adjustable mains switching power supply. The current through the capacitor being tested is controlled by means of the current control supplied by the power supply, i.e. it is a switched power supply in the current control mode. Directly to the capacitor to be tested is connected a controllable DC voltage source connected to the discharge circuit of the capacitors. Thereby, it is possible to set the required DC voltage on the tested capacitor, both when increasing the voltage when charging the tested capacitor and when decreasing it, ie when the tested capacitor is discharged. A controllable DC voltage source, together with the capacitor discharge circuit, is the essence of the charge / discharge block. The diode in the charge / discharge block output will prevent the AC circuit from loading the DC source, and the decoupling capacitor in the output circuit will prevent the DC source short-circuiting by the secondary winding of the power transformer.

This solution allows simultaneous loading of the capacitor to be tested with alternating current of higher frequency and DC voltage with the possibility of independent setting, monitoring and maintaining their values. To obtain higher values of alternating current the energy-saving resonance principle is used. The tester responds to the emergency conditions of the tested capacitor by interrupting the test. It also allows the connection of external meters to monitor the detailed testing process.

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An example of an arrangement of a load tester of power capacitors according to the invention is shown schematically in the attached drawing.

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Example / Embodiment of the invention

An example of a load capacitor load tester according to the present invention is shown in the attached drawing. The tester consists of a controllable DC power supply 10 provided with a control input 11 to control the output current, an input 14 to set the output voltage limit, and an input 15 to turn off the output voltage. The first output 12 of the controllable AC switching power supply 10 is coupled to the first input 21 of the power switching bridge 20, to the second input 22 of which the second output 13 of the controllable AC switching power supply 10 is connected. The first output 23 of the power switch bridge 20 is coupled to the first output 31 of the surge protector block 30, the second output 32 of which is coupled to the second output 24 of the power switch bridge 20. Furthermore, the first input 33 of the surge protector block 30 is connected to one end 41 the transformer 40 and the second input 34 of the overvoltage protection block 30 are connected to the other end of the primary winding 42 of the power transformer 40. One end 43 of the secondary winding of the power transformer 40 is connected to one end of the decoupling capacitor 50 and the first output 104 of the charge / discharge block 100 provided with an input 101 for adjusting the DC voltage on the power capacitor 70 under test. The other end of the decoupling capacitor 50 is connected to one terminal 61 of the power socket 60 and to the other output 105 of the charging / discharging block 100. The new transformer 40 is passed through a plug-in current transformer 80 and is connected to a second terminal 62 of the power socket 60, into which a power plug provided with a first terminal 63 and a second terminal 64 for connecting a test power capacitor 70 is inserted. 65 of the safety contact associated with the first input 126 of the control unit 120; · I 9 * · .. · · <

. '' »» · »• *> · · · .-. ·. Μ ·. The second safety contact terminal 66 coupled to the second input 125 of the control unit 120. The first secondary terminal 81 of the measuring device. the transformer 80 is connected to one end of the load resistor 83, to one end of the overvoltage protection circuit 85 provided with external measurement sockets 84 and to the first input 91 of the excitation and tuning block 90. The second terminal 82 of the transformer 80 is connected to the other end to the other end of the overvoltage protection circuit 85 and to the second input 92 of the driver block 90. The outputs 96, 97, 98, 99 of the driver block 90 are connected to the corresponding inputs 25, 26, 27, 28 of the power switching bridge 20. Output 93 the excitation and tuning block 90 is connected to the current meter 94 and its third input 95 is connected to the output 123 of the control unit 120, which is also connected to the The third output 106 of the charging / discharging block 100 is coupled to the DC meter 1010 on the capacitor 70 tested, the fourth output 107 and the fifth output 108 are bridged by the discharge resistor 109, and the sixth output 102 is connected via the charge protector block 110 to the third input 124 of the control unit 120 further provided with an input 122 for turning the tester on and off.

The output voltage of the controllable power supply 10 is applied from its first output 12 to the first input of the power switch bridge 20 and from its second output 13 to the second input of the power switch bridge 20. The power switch bridge 20 interconnects its first output 23 alternately with its first input 21 and with its second input 22 and its second output 24 with its second input 22 and its first input 21. This results in a rectangular voltage waveform with an inter-peak value equal to twice the output voltage of the controllable mains power supply 10 between its first output 23 and the second output 24. This voltage is then used to supply other function blocks, namely the overvoltage protection block 30, the power transformer 40, the decoupling capacitor 50, and the power socket 60, to achieve the required shape and size for The frequency of the rectangular voltage waveform and the switching bridge switching times 20 are controlled by the excitation and tuning block 90 based on the current waveform feedback information in the test capacitor 70, which is obtained through a plug-in current transformer 80.

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The third terminal 33 of the overvoltage protection block 30 is directly connected to the first terminal 31 inside the block and the fourth terminal 34 of the overvoltage protection block 30 is directly connected to the second terminal 32 inside the block 32. The rectangular voltage from the first output 23 and the second output 24 of the power switching bridge 20 30 overvoltage protections without interference. Overvoltage pulses of higher amplitude that may occur when the isolation capacitor 50 or test capacitor 70 break through are limited in amplitude and power in the overvoltage protection block 30 to prevent damage to the power switching bridge 20, the controllable power supply 10 and possibly the drive / tuning block. 90.

Thus, the test capacitor 70 connected in series to the decoupling capacitor 50 forms, together with the dissipation inductance of the power transformer 40, a series resonant circuit connected to a rectangular voltage between the ends 41 and 42 of the primary winding of the power transformer 40. the capacitor is approximately sinusoidal. This current is sensed by a plug-in current transformer 80 with an appropriate load resistor 83 and a surge protection circuit 85. The output voltage at terminals 81 and 82 of the secondary winding of the plug-in current transformer 80, proportional to the current flowing through the test capacitor 70, is then applied to both the external meter connection terminals 84 and to the first input 91 and the second input 92 of the excitation and tuning block 90.

In the drive and tuning block 90, the drive signals 20 of the power switch bridge 20 at outputs 96, 97, 98, 99 of this drive and tuning block 90 are derived from the voltage between the first input 91 and the second input 92 to provide switching with frequency and phase determined resonant circuit and switching at zero current. The excitation signals also contain the necessary time delays to prevent the bridging of the half bridge transistors simultaneously. By amplifying and rectifying the voltages from the first input 91 and the second input 92, a voltage meter is also provided at the output 93 for the pointer 94 of the current flowing through the capacitor 70 to be tested.

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The described circuit configuration makes it possible to control the alternating current flowing through the capacitor 70 through the control input 11 of the output current of the controllable mains switched DC power supply W. The output voltage of the controllable mains switched power supply 10 is limited in current control mode by setting from input 14 so that inside the power switching bridge 20.

The charge / discharge block 100 serves to adjust the DC voltage component of the capacitor 70 tested. Therefore, it includes a controllable DC voltage source controlled from the DC input 101 to adjust the DC capacitor on the test capacitor 70 and circuits that set the source voltage to less than the current. the DC voltage component of the tested power capacitor 70, diverts the excess charge through the fourth output 107 and the fifth output 108 to the discharge resistor 109 so that the DC voltage component approaches the desired set point. The charge / discharge block 100 further provides adequate voltage at its third output 106 for the DC voltage meter 1010 on the capacitor 70 under test, and at its sixth output 102 overload and abnormal status information for the charge protection block 110.

The charge protector block 110 provides error information at its output 112 when either the current overload of the charge / discharge block 100 has been charged while the capacitor 70 and the decoupling capacitor 50 are being charged, or when the voltage at these capacitors is constantly lower than the desired set point. Based on this error information, the control unit 120 then deactivates the self-test

The decoupling capacitor 50 prevents the DC voltage on the test capacitor 70 from being shorted by the secondary winding of the power transformer 40. When the test capacitor 70 is charged, the decoupling capacitor 50 is simultaneously charged to the same voltage in this circuit configuration.

The control unit 120 mediates switching on and off of the actual test process in which the set capacitor 70 flows through the set value.

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• 4 alternating current and at the same time the DC voltage setting is applied. The control, that is to say the on and off at the operator's request, is done by the buttons 121 connected to the input 122 of the control unit 120. The test can also be switched off at error states at inputs 124, 125 and 126 of the control unit 120. are described above in the description of the function of the charge protection block 110.

The error condition at the first inlet 126 and the second inlet 125 is caused by a slight extension or complete absence of the plug for connecting the capacitor 70 to be tested in the power socket 60 and are therefore connected to the first terminal 65 and the second terminal 66 of the safety contact of the power socket 60.

The control unit 120 is switched on and off by an output 123 through which the operation of the adjustable power supply W, the charge / discharge block 100 and the drive / tuning block 90 can be blocked or unblocked. The charge / discharge block 100 starts to discharge the test capacitor 70 and a separating capacitor 50.

During testing, external meters connected to sockets 84 and test capacitor 70 can determine whether the capacitance of test capacitor 70 changes during loading. For this purpose, it is sufficient to monitor the operating frequency during the test, for example with a counter connected to sockets 84. the leakage resistance of the test capacitor 70 has dropped, this will result in a drop in the actual value of the DC voltage on the test capacitor 70 below the value initially set, as identified by the DC voltage meter 1010. If this drop reaches about 20j%, they will affect the internal protections and deactivate the test. Further, it can be ascertained whether the equivalent series resistance of the test capacitor 70 increases during loading by measuring the magnitude of the alternating current AC component on the test capacitor 70 and the magnitude of the current flowing therethrough. The current is proportional to the signal at sockets 84. It is also possible to find out whether a potential tester interruption was caused by a fault in the capacitor 70 being tested. In this case, most tester internal protections will not allow the test to be reactivated or can be reactivated and * ♦ í 'i «« «?. '. »· ·, *. (i); 4 «'. r _f

J f »4,. t> * t t t t t 2 · napětí Another possibility is to determine if the temperature of the capacitor 70 under test does not exceed a specified limit. The capacitor development samples to be tested are usually provided with a built-in thermocouple for this purpose. After the capacitor has been removed from the test with external gauges, any permanent changes in the parameters of the capacitor under test due to previous loading are detected.

Industrial applicability

Said load capacitor load tester is useful in the development and manufacture of power capacitors to verify their behavior under conditions close to real operation conditions.

Claims (1)

Power capacitor load tester _; characterized in that it comprises a controllable DC power supply (10) provided with a control input (11) for controlling the output current, an input (14) for adjusting the output voltage limit and an input (15) for switching off the output voltage and having a first output (12) coupled to a first input (21) of a power switching bridge (20), to the second input (22) of which is connected a second output (13) of an adjustable DC power supply (10); (20) is coupled to the first output (31) of the surge protector block (30), the second output (32) of which is coupled to the second output (24) of the power switching bridge (20), further being the first input (33) of the block (30) the overvoltage protections are connected to one end (41) of the primary winding of the power transformer (40) and the other input (34) of the overvoltage protector block (30) is connected to the other a transformer primary winding (42), wherein one end (43) of the transformer secondary winding (40) is connected to one end of the decoupling capacitors (50) and to the first output (104) of the charge / discharge block (100), is provided with an input (101) for adjusting the DC voltage on the power capacitors (70) under test, and the other end of the decoupling capacitors (50) is connected to one terminal (61) of the power outlet (60) and the other output (105) of the charging / discharging block ), wherein the second end (44) of the secondary winding of the power transformer (40) is passed through a plug-in current transformer (80) and is connected to a second terminal (62) of the power socket (60) into which a power plug provided with the first terminal (63) is inserted. ) and a second terminal (64) for connecting the tested power capacitors (70) and the power socket (60) is further provided with a first terminal (64) 65) a safety contact coupled to the first input (126) of the control unit (120) and a second safety contact terminal (66) coupled to the second input (125) of the control unit (120), the first secondary terminal (81) of the plug-in measuring transformer (80) the current is connected to one end of the load resistor (83), to one end of the overvoltage protection circuit (85) provided with external measurement sockets (84) and to the first input (91) of the excitation and tuning block (90) and the second terminal (82) the transformer (80) is connected to the other end of the load resistor (83), to the other end of the overvoltage protection circuit (85) and to the second input (92) of the excitation and tuning block (90) whose outputs (96, 97, 98, 99) are connected to corresponding inputs (25, 26, 27, 28) of the power switching bridge (20) and whose output (93) is connected to the current meter (94) and whose third input (95) is connected to the output (123) of the control unit (120), which it is also connected to the input (15) of an adjustable DC power supply (10) and to the input (103) of the charging / discharging block (100), whose third output (106) is connected to the DC meter (1010) on the capacitor ( 70), the fourth output (107) and the fifth output (108) are bridged by a discharge resistor (109) and the sixth output (102) is connected via a charging protection block (110) to a third input (124) of the control unit (120) (122) for turning the tester on and off.