SU1488909A2 - Device for compensating errors of instrument current transformers - Google Patents

Description

The invention relates to electrical engineering, in particular to relay protection. The purpose of the invention is to increase reliability by reducing po2

errors of the current transformer with an active-inductive load in a transient mode. At the moment of saturation of the current transformer magnetic circuit, a signal appears at the output of the block for identifying the moment of saturation.

This closes the keys 4, 10 and one of the keys 13 or 14. The nonlinearity unit 15 converts the input signal into a voltage proportional to the magnetizing current “It is fed to the input of the adder 16. At the output of the adder 16, the signal is proportional to the primary current. If the current transformer goes out of saturation mode, the keys 4, 10, 13 (or 14) open, and _β the output voltage of the device becomes ® proportional to the current again. * 1 il.

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1488909

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The invention relates to relay protection, is intended to compensate for the error of a transformer with an active-inductive load, due to the saturation of its magnetic circuit, and is an improvement of the invention according to ed. St. No. 1398014.

The aim of the invention is to improve reliability by reducing the error of the current transformer with active-inductive load in a transient mode.

The drawing shows a diagram of the device. 15

The device contains a measuring current transformer 1 connected to the primary winding of the intermediate transformer 2, parallel to the secondary winding of which a shunt is connected 3,20 one output of which is connected to the first semiconductor switch 4 and the saturation moment detection unit 5, the sample and storage unit 6, connected in series elements 7 and OR 8, integrator-adder 9, fourth semiconductor switch 10, voltage source 11 and 12, connected via the second 13 and third 14 semiconductor switches to the input of the block 15 are nonlinear spine connected to the adder 16.

The parameters of the integrator-resolver elements are chosen in such a way that its time constant equals the available time of the secondary circuit of the measuring TT, i.e. T =

= T _m , therefore, KS = b ₂ / K ₂ , where b ₂ , K ₂ is the inductance and resistance of the secondary circuit of the TT.

On the other hand, it is necessary that the equality IΖ ₂ Ι = k M (P) be fulfilled. ,

where Ζ ₂ = τΙ (h) b) ² + K ² is the resistance of the secondary circuit TT; Ινί (Ρ) (-. -Summatora transmission coefficient module integrator emf voltage references are selected proportionate to the saturation flux current, the output signal sampling and storage unit is proportional to L ₂ CH5> ΐ where _{g e} -. Tbk secondary CT saturation at the time.

The device works as follows.

Until the saturation of the magnetic core TT 1 managed keys 4, 10,

13 and 14 are open. There is no signal at the input and output of the nonlinearity block. At the first input of the adder 16, the signal is proportional to ί ₂ , the second is equal to zero, therefore at the output of the adder 16, the signal is equal to kg ₂ . This is true, since in this case the magnetization current of the measuring CT can be neglected and, therefore, ί., ~ ₂ .. The sampling and storage unit operates in the sampling mode and the output signal is also proportional to the secondary current.

At the moment of saturation (depending on the polarity ₂ ) of the CT 1 magnetic circuit, a signal appears from one of the outputs of the block 5 for identifying the moment of saturation. This closes the keys 4 and 10 and one of the keys 13 or 14, depending on the polarity of the secondary current. The signal at the control input of block 6 of sampling and storage becomes zero and, therefore, the value of the secondary current is remembered at the moment of saturation зап ^ ₅ . This value is maintained until the CT 1 magnetic core is in a saturated state.

After the closure of the keys 4, 10 and 13 (or 14) to the input of the nonlinear unit 15, the signal

u = k (+ ψ ₆ + - Ü ₂ 1 ₂₅ + 5 ί ₂ s / g)

where + c, is the saturation flux linkage modeled by + E and -E;

L ₂ ί is the flux linkage due to the presence of inductance of the secondary circuit, which is modeled with the power of the sampling and storage unit;

Ί L _{2 2} + K ² ₂ 5 ί <ίΓ - b ₂ 1 _GV - total flux linkage of the secondary winding ₍₅ g - point nasidi scheniya).

Block 15 of nonlinearity converts the input signal into a voltage proportional to the magnetizing current TT ΐ ₀ , which is fed to the second input 50 of adder 1b "The signal at the output of adder 16 is proportional to the reduced primary current

and _u = kt ₂ + kg „= kg /.

If the TT exits saturation mode, then the keys are 4, 10, and 13 (or 14)

open and output voltage

device (adder TB) is again proportional to ΐ ₂ , which is equal to ί ',.

⁵ 1488909

Thus, the device works only when the magnetic cores of the current transformer are in a saturated state.

Claims (1)

Claim Device to compensate for the error of the measuring current transformer auth.St. No. 1398014, characterized in that, in order to increase reliability by reducing the error of the transformer 6 current with active-inductive load in a transient mode, a semiconductor key, a sample and hold unit, an item NOT are added, with the ^5th sample and hold unit and a semiconductor key connected in series and included in the cut between the shunt and the nonlinearity block input and storage is connected to the output of the element OR through the element NOT, and the control input of the semiconductor key directly.