DE611411C - Device for measuring the zero point voltage of a network in which the zero point is not accessible, but two single-phase voltage converters are available in V-connection - Google Patents

Description

From the value of the zero point voltage of a three-phase network, valuable Conclusions about the operational status of the network, both in normal operation and in Malfunctions, can be derived. In cases where the network zero point is not accessible or not present (delta connection), circuits have been used at which the value of the zero point voltage ίο can be measured. To this end are z. B. three single-phase voltage converters have been used, their secondary windings are designed in an open delta connection, or a five-legged voltage converter with "'a winding on the fourth and fifth leg for measuring the zero point voltage.

In existing stations in which there are already transducers in V-connection, it is sufficient to install a third voltage converter of the same design as the two existing ones Add converters and now switch the three converters between the phases and earth. This solution has two disadvantages: i. the existing circuit must be changed;

2. the power is reduced to a third by switching, because the walls = i7 — a ² U "

U ₂ = a * U-aU

With the V connection, V ₃ = a * U + V ₀ ler only receive the phase voltage after the switchover and transition to star connection.

However, these drawbacks can be avoided if, according to the invention, the two existing a third voltage converter of the same design between the common Mains phase of the V-connection and earth is connected and each of the three voltage transformers one additional phase each D rdphaseri auxiliary converter s feeds its secondary windings are connected together in an open triangle, at whose terminals the zero point voltage is measured, the voltage ratio of the third phase of the Auxiliary Roadsfoiunators is three times larger than that of the other two phases. It then turns out that with the correct circuit sense the. Voltage at the terminals of the secondary open circuit of the auxiliary transformer three times the zero point voltage, as shown in the following:

Let Uχ, U _{2 be} the primary voltages of the two converters in a V connection, V ₃ the primary voltage of the third converter, V ₀ the zero point voltage, U, O- ² U ₁ UU the phase voltages of this network. Then

3 V ₃ = U— a * U— a ² U + aU + 3 a ² t7 + 3 = U + aU + a ² U + 3V ₀
-3F ₀ , because U + aU + cPU = o.

In Fig. Ι the circuit for a measuring device according to the invention is illustrated. The voltage converters b, C ₁ d , which feed the auxiliary transformer ^, are connected to the three-phase network g. There is then three times the zero point voltage at its secondary terminals /.

Fig. 2 shows a similar circuit, but at which the beginning and end of the windings of the middle column of the auxiliary transformer ^ are swapped.

Claims (1)

Claim: Device for measuring the zero point voltage of a network in which the Zero point is not accessible, but two single-phase voltage converters in V-connection are present, characterized in that a third voltage converter of the same design in addition to the two existing ones switched on between the common mains phase of the V-connection and earth is and each of the three voltage converters each 'one phase of an additional Three-phase auxiliary converter feeds whose secondary windings are interconnected in an open triangle at the terminals of which the zero point voltage is measured, the voltage ratio being the ■ third phase of the auxiliary transformer three times is greater than that of the other two phases. For this purpose ι sheet of drawings