SU1737619A1 - Method of compensation for losses of voltage in feeding power network - Google Patents

Abstract

The essence of the invention: the adjustment of the current of the compensating device is carried out depending on the difference of the setpoint current, which is determined by the formula IP.O, + a (& b) / x, where la is the active current of the network; r0 is the network resistance at the calculated conductor temperature 0b; "- coefficient of temperature increase of active resistance; 0- temperature of conductors; x - inductive resistance of conductors, and the capacitive current network. Improving the accuracy of voltage loss compensation is achieved by correcting the reactive current of the compensating device depending on the temperature of the conductors. 3 il.

Description

The invention relates to electrical engineering and is intended for use in automatic control systems for compensating devices.

The purpose of the invention is to improve the accuracy of compensation when the temperature of the conductors changes.

Fig. 1 shows a voltage loss compensation circuit in a power supply network implementing the proposed method; Fig. 2 is an equivalent circuit for replacing a portion of the power supply system; FIG. 3 is a voltage vector diagram for this circuit.

The compensation circuit for the loss of voltage in the power supply network (FIG. 1) contains a power supply network 1, a measuring voltage transformer 2, a current measuring converter 3, a measuring current converter 4, a reactive current measuring converter 5, a temperature measuring sensor b, a functional unit 7, one-way rectifier 8, comparison element 9, regulating device 10, adjustable compensating device 11, electrical network load 12.

An equivalent circuit for replacing a portion of the power supply system shown in FIG. contains a supply line with active resistance g and inductive resistance x, load ZH and a compensating device xic. In the diagram (Fig. 2) and the vector diagram (Fig. 3), constructed for the case of the advance current (p 0), the following is denoted: E is the voltage at the beginning of the line; 0 - voltage at the end of the line (at the load node); I U + jlp is the network current containing the active U and reactive 1p components; AO - voltage drop in the supply network.

h (A) XJ Oh

h

Measuring transformers of voltage 2 and current 3 are connected to the supply network 1, the outputs of which generate signals proportional to the voltage U - 1) mz1p a) at the load node and the supply network current I 1m sin (on + (p). Current The mains supply is determined by the sum of the load currents and the compensating device and can be represented as the sum of the active and reactive 1p components.

The output of the transformer 3 current is connected to the combined information inputs of the measuring transducers active 4 and reactive 5 currents. The control inputs of the measuring transducers active 4 and reactive 5 currents are combined and connected to the output of the voltage transformer 2. The signal U at the output of the measuring transducer 4 of the active current is proportional to the active component of the current

IJ4 K lMSln 5COS (Wt,

and the us signal at the output of the reactive current measuring transducer 5 is proportional to the reactive component of the network current

L) 5 KslMSln CJSCUt.

where KA and KB are the transfer coefficients of the measuring transducers active 4 and reactive 5 currents.

The Us signal from the output of the reactive current measuring transducer 5 is fed to the input of a one-way rectifier 8, which generates a signal

Us)

I

Us Kslwislnpcos yipri 40 Oh at Us Oh,

0

five

0

five

0

five

0

reactive current network in accordance with the expression

(ea) 1a (1)

where r0 is the active resistance of the network at the calculated temperature 6b of the conductors;

a is the coefficient of temperature increase in the active resistance of conductors.

The 1p signal from the output of the functional unit 7 is fed to the summing input of the comparison element 9, to the subtracting input of which the output signal Ue of the one-way rectifier 8 arrives. The comparison element 9 generates a signal

Ug U - Us,

proportional to the difference of the setting 1p and the value of the capacitive current in the network. This signal is an error regulating the reactive current of the network. It is fed to the input of the regulating device 10, which, in accordance with the adopted regulation law, for example, proportional or proportional-integral, generates a control signal of the compensating device 11. As a result, the network establishes a capacitive current, the value of which is determined by the setting calculated by the formula ( one),

In accordance with the vector voltage diagram in the power supply system shown in FIG. 3, the voltage drop in the network is

AU AC + DC ag - 1 x 4- Jtax + Jlpr

The voltage module on the consumer is determined by the formula

capacitive and proportional to the supply current; at p 0, i.e. with lagging current. Us 0. The temperature measuring transducer 6 is designed to form a voltage Ue proportional to the temperature of the conductors ©:

Ue ke in,

where KB is the proportionality coefficient. The signals U4 and Ue from the outputs of the measuring transducers of the active current 4 and temperature 6 are fed to the inputs of the functional unit 7, which calculates the setpoint

U VEZ - (x1a + rip) - rla + xlp. (2)

Since the supply networks are designed from the condition of permissible voltage loss in the line, for real power supply systems the inequality is always satisfied

E2 (+ rip) 2

(3)

When changes in the temperature of the conductors occurring as a result of their heating by current and changes in the ambient temperature, their resistance changes in accordance with the expression r0 1 + a (0-Q)),

substituting which in formula (2), we obtain, taking into account inequality (3), an approximate equation for the voltage in the load node

U E - GoP + 0 (0 - 6b) la + xc1p. (4) 5

From equation (4) it follows that, if with the help of a compensating device connected in parallel with the load, the capacitive current of the network is adjusted so that the ratio

(0-a) Јla.

then the voltage loss in the power supply network will be almost completely compensated at any temperature of the conductors, i.e.

U "E.

In this case, the proposed method assumes the availability of information about the active la and reactive p components of the network current, the temperature of the conductors 0 and the ratio of the calculated active resistance of the Guo line to the inductive x, which is determined by the supply line characteristics and does not depend on its length. Consequently, information on the length of the supply line in the proposed method is not required. No information is required on the voltage values in the load node and the power center.

Thus, when using the proposed method of compensating for the loss of voltage in the supply network, the accuracy of compensating for the loss of voltage is increased by correcting the amount of reactive current during changes in temperature.

0

five

0

five

0

five

провод conductors that occur as a result of current heating as well as changes in the ambient temperature.

Using the proposed method of compensating for the loss of voltage in the supply network will improve the quality of electricity and reduce its losses in the electrical networks of industrial enterprises.

Claims (1)

Claims. A method for compensating for the loss of voltage in a power supply network using a compensating device connected in parallel with the load, consists in measuring the active and reactive currents of the network and regulating the capacitive current of the compensating device that differs from in order to improve the accuracy of compensation when the temperature of the conductors changes, the temperature of the conductors is measured, the current setting of the compensating device is calculated in accordance with the expression 1po + a (0-0o) / x, where is the active current of the network; r0 is the network resistance at the calculated conductor temperature 0b; a - coefficient of temperature increase of active resistance; 0-temperature conductors; x is the inductive impedance of the network, isolates the capacitive component of the reactive current of the network, compares it with the setpoint, and depending on the difference obtained, sets the current of the compensating device. laX 3 i: lg + jlf MD