DE1081566B - Compensation circuit for a current transformer used for distance protection purposes based on the principle of the magnetic voltmeter in maximum voltage networks - Google Patents

Description

GERMAN

As is known, instead of the usual Current transformers, advantageously the magnetic voltmeter, can be used. The application the magnetic voltmeter allows in particular to solve the voltage problem in the current transformer to solve in a simple way by the magnetic core with its measuring coil as a ring with enough large diameter can be placed around the conductor.

Such a current transformer works practically in no-load operation, which requires the use of an amplifier with a sufficiently high input resistance. A voltage is induced in the measuring coil which, in the steady state, leads the current to be measured by 90 °. For many applications, e.g. However, e.g. power measurement, distance protection, etc., it is important to have a secondary voltage in phase with the primary current. According to FIG. 1, this can be achieved by a capacitor with the capacitance C _{connected to the secondary winding 2 with the inductance L 2} via a resistor. If you tune the secondary circuit to the mains frequency by

Compensation circuit for a current transformer used for distance protection purposes

according to the principle of magnetic

Voltmeter in high voltage

networks

Applicant:

Public limited company Brown, Boveri & Cie., Baden (Switzerland)

Representative: Dr.-Ing. E. Sommerfeld, patent attorney, Munich 23, Dunantstr. 6th

Claimed priority: Switzerland of November 9, 1956

Dr.-Ing. Alexander Goldstein, Ennetbaden (Switzerland), has been named as the inventor

makes, the voltage across the capacitor becomes UT ^M

¹ ~ · * ^χ 'ΊΓΠϊ'

where U _{11 is} in phase with the current. L means the inductance of the measuring coil, I ₁ the current in the measuring coil and M the mutual inductance of the transducer.

Such a circuit also has the disadvantage that when switching operations on the line, non-network frequency Operations are transferred to the secondary side. It is z. B. to equalization processes resulting from a decaying direct current component in the event of a short circuit.

If you continue to make coC · Rp> 1, that is, if you dampen the tuned circuit very strongly aperiodically, the proportionality between U ₁₁ and I ₁ remains even with non-network frequency processes, e.g. B. equalization processes, are obtained and also applies to the instantaneous values M ₁₁ and I ₁ of U ₁₁ and I _1, respectively.

This process is of particular importance for distance protection circuits. In distance protection circuits the current transformers are switched to line simulation impedances. To get a correct distance measurement In the event of disturbances, even in the non-stationary state, should be made possible by these impedances in the event of short circuits, there is no voltage drop caused by the decaying direct current component of the Short-circuit current originates.

The invention relates to a compensation circuit for a current transformer used for distance protection purposes according to the principle of the magnetic voltmeter in high voltage systems, on whose An amplifier is connected to the measuring coil serving as the secondary winding.

The effect of a compensation process on the output side is rendered ineffective according to the invention in that the secondary winding is connected to a capacitor with the capacitance C via an ohmic resistor designed as a voltage divider with the division ratio R ₁ to R ₂ , that between the voltage divider tap and the opposite one Connection of the capacitor, the voltage controlling the amplifier is removed and that

R ₁ + R ₂ ^ - and CR ₂ = T ω C

T means the decay time constant of the direct current component of the short-circuit current in the network and ω means 2 π times the measuring frequency.

The voltage CZ ₁₁ (cf. FIG. 2) is free of compensation components under these conditions and can be used for further use in distance protection circuits, with one or more amplifiers being able to be interposed as required.

«09 509/177

If the time constant corresponding to the short-circuit phase angle φ of the line section to be protected

T - ^{tg <pk
h} ~~ ω

is different from the decay time constant T of the network short-circuit current, e.g. B. by the influence of the impedances of the feeding machines, a circuit according to FIG. 3 is appropriate. The outgoing voltage is additionally fed via a voltage divider made up of a resistor R ₃ and a capacitor C ₃ and the newly outgoing voltage U _{111 obtained} in this way is taken from the capacitor. This circuit makes additional phase angle corrections.

The time constant of the _{element formed from C 2} and R ₂ is here also chosen to be equal to the decay time T of the direct current component of the short-circuit current in the network, so that no corresponding direct voltage component can occur in the circuit. The time constant T _{k of} the line to be protected is usually smaller than the decay time constant T, i.e. H. that the phase angle 95 ^ is also smaller than the phase angle φ of the circle C ₂ · R ₂ . The alternating voltage CZ ₁₁₁ must therefore be turned back in relation to the alternating voltage U _n , which is done _{via C 3} and R _3. The individual sizes are then in the following context:

(QC ₂ - Cz (R ₂ + R ₃ ) C * + C _a

= ^ g (ψ - Ψι)

tgq> = ω · Τ.

The voltage CZ ₁₁₁ then leads the current I ₁ and the line phase angle φ ^ .

35

Claims (2)

Patent claims: 1. Compensation circuit for a current transformer serving for distance protection purposes according to the principle of the magnetic voltmeter in high voltage networks, to whose measuring coil serving as the secondary winding an amplifier is connected, characterized in that the secondary winding has an ohmic resistance designed as a voltage divider with the division ratio R ₁ + R ₂ is connected to a capacitor with the capacitance C, that between the voltage divider tap and the opposite terminal of the capacitor, the voltage controlling the amplifier (CZ ₁₁ ) is taken and R ₁ + coC and CR ₂ = T, d. H. is equal to the decay time constant of the direct current component of the network short-circuit current. 2. Compensating circuit according to claim 1, characterized in that its output voltage is additionally guided via a voltage divider consisting of a resistor (R ₃ ) and a capacitor (C ₃ ), that the voltage (CZ ₁₁₁ ) controlling the amplifier on the capacitor (C ₃₎ is removed and that the members of this voltage divider in the sense of obtaining the difference between the decay time constant T and the time constant T of the _k considered to be protected power supply Meßwertkorrektor are sized. Considered publications:
German Patent No. 609,486;
German patent application S 21030 VIIId / 21h (published on November 5, 1953). 1 sheet of drawings © 009 50W1'77 5.60