DE966273C - Arrangement for testing contact converters - Google Patents

Description

It has recently been proposed to use contact converters for high voltage as well. in the In connection with this, several simultaneously actuated contacts are used for each anode, which are in series are switched in order to achieve the large opening distance caused by the high voltage. Furthermore is the subdivision into very many, for example 48 anodes, is necessary so that the effective current per contact is opposite the nominal current is reduced as much as possible. The consequence of this measure is that the contact time is extraordinary becomes low.

With such a construction of the contact converter it is necessary to carry out a careful To carry out a test that must cover various points, for example

a) Measurement of the contact time of the individual contact, consisting of a series of series-connected, contact bridges operated at the same time,

b) Measurement of the possible overlap of the contact time of consecutively actuated contacts,

c) Measurement of the dielectric strength of the contact opening during operation.

In detail, these measurements are carried out in the following way:

Each contact has four contact bridges, for example, which are connected in series and at the same time open and close. The contact completion time of the four bridges should be 15 el. Degrees. All four contact bridges must open at the same time and

709592/70

close, otherwise any shift in the opening time of a contact in the current passage through the series circuit is affected and causes difficulties in the passage of current.

In Fig. Ι the circuit for measuring the contact completion time of a contact is recorded. The measurement takes place with the contact rotating at normal speed. The four bridges of the same open and close during the measurement at a frequency of 50 per second. The constant voltage of an auxiliary direct current source is read on the instrument CZ _{1 , while the instrument CZ 2 shows} the effective voltage of the measuring current flowing over the contact bridge. For the full period of the alternating current, i.e. for the electrical time 2 π, there is no contact closing time of duration t. This time is calculated using the formula:

_{i =} St. _2π

or expressed in electrical degrees is: <° - £ -360.

The value ω = 2 % f corresponds to the duration of one second (f = number of periods of the alternating current). The measurement of the possible overlap in time of the contact closure duration of two successive contacts can be carried out approximately in the manner shown in FIG. Here, I denotes the series-connected contacts of one anode, and II denotes the series-connected contact bridges of the next following anode. The current profile of these contacts is shown in the diagram of FIG. As you can see, a time overlap can occur when the contact time t _t in one anode and the contact time i _{2 of} the other anode are together greater than the time t from the first zero crossing of the current of one to the second zero crossing of the current of the other Anode. In the test circuit, both contact arrangements are _{connected in series by means of switches S 1} , S ₂ , and the test voltage and the corresponding voltmeters CZ ₁ and CZ _{2 are applied} to their connection point.

After closing the switch S ₁ with the switch S ₂ open, the contact closure time is measured

St.

U ₁

2 π,

then by closing the switch S ₂ , with the switch S ₁ open, the contact _{closing time i 2} in the same way, and finally, after closing both switches S ₁ and S _2, the common contact closing time t. Is now

t = h + h,
then there is no coverage.

But if t < t _x + £ ₂ , then there is a contact time overlap

The contact time overlap, if any, can also be measured according to the diagram in FIG. 3. Here the contact sets I and II of successive anodes are connected in series _{via an ammeter U 2.} If there is no overlap, possibly even a contact time gap, the display of this instrument becomes zero. As long as there is an overlap, it is calculated from the equation:

t =

U ₁

2 31.

One of the most important tests concerns the measurement of the dielectric strength of the contact opening in the Operation.

To assess the quality of a contact converter, it is not sufficient that the contacts are free of switch-off fire, but it must also be ensured that the subsequently recurring Voltage — the so-called reverse voltage — between the contact surfaces does not increase faster than the dielectric strength of the separating distance that is being formed allows.

In contact converters for high voltage, the contacts work in compressed air chambers to improve the insulation value the opening point to increase.

First of all, the measurement should be carried out on the open contact in order to record all movement processes on the contact in a convenient way and to be able to study. From the knowledge of these processes one can then with sufficient certainty Draw conclusions about the closed and pressurized contact and the one described below Repeat measurement.

The measurement is made on each individual contact.

The contact closure time of the contact is equal to 15 el. Degrees with 48 anodes. If you think of one 50 periodic alternating current, the contact closure time has theoretically the duration

1000

50 360

= - ms. ο

The test proposal is based on the following basic idea:

A variable alternating voltage of 50 Hz is applied to the contact and it is ensured that the contact closure time is symmetrical around the point of the zero crossing of the alternating voltage curve. By means of a switching choke, as it is used for normal contact converters, a step of at least ⁵ Ie to ι millisecond duration is placed in the AC voltage curve. It then follows that the contact is closed exactly at the time of the step, i.e. in the de-energized part of the AC voltage curve, and that the voltage that starts after the step can be used to measure the dielectric strength of the opening path that is being formed. In Fig. 4, a diagram and the circuit of the test device is shown to illustrate the processes. 1 is the contact to be tested, to which a series circuit consisting of a resistor and a capacitor is connected in parallel. 2 is a current limiting resistor, 3 is a base load resistor. is a stretching circuit consisting of resistance and capacitance, which in connection with the premagnetic

ized throttle 5 for a corresponding widening of the zero crossing ensures. 6 is a test transformer through which the voltage is supplied.

It is advantageous to check each bridge of a contact individually. You can take the exam with perform relatively low voltage.

The graph, FIG. 4, shows the course of the contact movement in dashed lines. The synchronous run of the Contact with the periodicity of the alternating voltage is ensured by the fact that the synchronous motor of the gearbox and the test transformer have the same voltage generator.

The secondary winding of the test transformer receives appropriate taps to find the Limit voltage that the contact can block. The stretch circle that runs parallel to the winding of the Switching throttle is placed, the purpose of which is to create a step that is as sharp as possible.

The pre-magnetization forces the step to be shifted to the zero line; it would be without the premagnetization are below the zero line. The base load resistor 3 is used to control the magnetizing current to record the throttle. It is advantageously dimensioned so that the one in the excitation circuit flowing current is a certain amount above the magnetizing current, so that the desired length the level is secured. The following calculation provides information about the size of the currents mentioned here the switching throttle.

The current limiting resistor 2 limits the current that would arise if the contact as a result Voltage flashover or as a result of a possible shift in its movement phase during the test Current, it also limits the magnetic current for the time of the contact closure.

The capacitor, connected in parallel with the contact, protects the contact in the event of a current being conducted Switchfire, or - and this is another purpose of the test - · the extent to which it should be examined the capacitance connected in parallel to the contact protects it against voltage flashovers after opening and able to protect against closure.

The course of the strongly drawn voltage curve in FIG. 4 corresponds to the curve of the contact movement the actual operating conditions. Thereafter, the maximum of the reverse voltage does not fall in time the turning point of the contact opening distance together, but the two voltage maxima within of the period fall at the points in time - π / 2 and + π / 2. This means that not the entire contact opening distance can be used as an insulating section.

This fact must be taken into account when dimensioning the opening path. The contact converter can therefore only be operated with a voltage corresponding to the opening path.

Claims (1)

Claim: Arrangement for testing contact converters, especially those for high voltage, with a large number of anodes and several contacts connected in series per anode, with respect to the contact closure time of each anode, the time overlap of the contact times in succession actuated anodes and the dielectric strength during the opening movement of the Contacts, characterized in that as a measure of the contact closure time with normal Speed-driven contacts is the ratio of those occurring at the contacts Voltage pulses to a constant reference voltage that serves as the basis for the calculation of the temporal overlap of the contact times of successively activated anodes the sum or difference of the contacts connected to one another via a measuring circuit consecutively actuated anodes occurring voltages applies, or the ratio the voltage appearing in pulses at the contacts to a constant reference voltage is used as a measure for the coverage of the contact times, a measuring circuit being provided is that of the series connection of the contact bridges of successively actuated anodes with a current source and an ammeter, and that to test for dielectric strength one to the contact to be examined applied alternating voltage of such a phase position is used that the contact closure time is symmetrical to the zero crossing of this alternating voltage, where the zero crossing goes through a series with the AC voltage source switched, premagnetized switching throttle is slowed down and There are resistors in the test circuit for base load and current limitation. Publications considered: ETZ, Volume 62 (1941), Issue 1, p. 3. 1 sheet of drawings © 709 592/70 7.