METHOD FOR MEASURING VOLTAGE QUALITY PARAMETERS

V. V. Litvak, V. V. Prokopchik

(Presented by the Department of Electrical Systems and Networks)

The quality of electric power, together with the reliability of power supply and its economy, is one of the most important requirements imposed on the system for generating and transmitting electric power to consumers. Quality parameters are strictly regulated by the special technical law—GOST 13109–67. However, fulfillment of the requirements of the state standard for power quality is currently hindered by the lack in the power industry of a sufficient quantity of the necessary equipment for regulating and monitoring the parameters [1]. The methodology itself for measuring and recording the regulated parameters of electric-power quality also remains insufficiently developed.

It is generally accepted, nevertheless, that the assessment of whether a parameter conforms to its standard should be carried out integrally, over a sufficiently long period of time.

In the present work, it is proposed to assess one of the most important quality parameters—deviations of voltages from the optimal value—by the amount of electric power transmitted to consumers in regimes in which the voltage deviations exceed the permissible values.

At present, the quantitative assessment of voltage quality is performed, as a rule, with the aid of probabilistic characteristics of voltage deviations.

However, such an assessment is incomplete, since the result proves to be “weighted” in time [2]. One could agree with such an approach to the determination of quality criteria if the consumers’ load remained unchanged, while the voltage varied arbitrarily with time.

In order to assess the influence of voltage deviations on the economy of operation of electrical receivers and the production mechanisms associated with them, it is far more important to know not the probability of the appearance of voltage deviations above limiting values, but the amount of electric power consumed at one or another deviation of the voltage from the optimal level. If, in addition to this, the operating time of the consumer at different voltage levels is also known, then such data are quite sufficient for selecting expedient methods of readjusting the voltage-control system.

Such a method is the most effective and can be implemented quite simply in the following manner.

Three electric energy meters are connected in the load circuit. The first meter (1) records all the energy received by the consumer. The second meter (2) records the energy received at a voltage lower than the limit specified by the state standard. The third meter (3) records the energy received at a voltage higher than the specified limit.

The block diagram of the instrument is shown in Fig. 1. The measuring elements of the channels responding to voltage increase and decrease are continuously in operation and, if the voltage exceeds the set point, give a start signal to “their” electricity meters and timing devices, which count the time during which the voltage deviations remain beyond the set points.

Fig. 1. Block diagram of the instrument: IO—measuring element; ZAPRET—inhibit-start element; PUSK—starting device; 1, 2, 3—electric energy meters; BP—power supply unit; EP—electric receiver.

Starting and stopping of the meters is carried out by switching the supply circuits of the voltage windings, while the current circuits are loaded continuously. The timing devices are started by supplying power to a synchronous motor. At the same time, starting for the channel responding to a voltage decrease can be performed only on condition that the measuring element with the higher voltage set point (in this case \(IO_2\)) is in the non-operated state. If it operates, then its signal is sent to the inhibit element, which breaks the connection between the measuring element and the starting device.

Thus, by changing the operating set points of the measuring elements, one can obtain a complete picture of the character of voltage-deviation variation, since the amount of electric energy consumed beyond the set points of each of the channels, and the time during which the consumer remains under such voltage, will be known.

It is more convenient to monitor voltage quality at those points of the network where billing or control meters of electric energy are installed. Transferring the measurement point from the terminals of the electric receiver to such a nodal point of the network can be carried out by a simple recalculation of the permissible voltage deviations and its losses in the network, with a corresponding change in the instrument set points.

A prototype of the instrument was developed and manufactured, in which the measuring elements are built on tunnel diodes, and the timing devices on DSD60-L1 synchronous motors, for counting whose number of revolutions counting mechanisms from electric meters were used. The dimensions and weight of the instrument depend strongly on the number and type of electric meters used. If the assessment is required to be made only

in time, operation of the instrument is simplified, since there is no need to connect meters. The timing devices are made as a separate unit together with the measuring elements and can be used independently.

Technical Data of the Instrument

1. Rated line voltage: \(3 \times 380/220\) or \(100\ \text{V}\) alternating current, \(50\ \text{Hz}\).

2. Limits of stepwise or smooth adjustment of the operating setpoints:

\[ U_{\text{n}} - 15\% \leq U \leq U_{\text{n}} + 15\%. \]

1. The error in measuring time depends on the frequency of the supply network and does not exceed \(0.2\%\).

2. Power consumption: not more than \(40\ \text{VA}\).

3. Weight: up to \(14\ \text{kg}\) (when three SA4U—I1672M electric meters are used).

Trial operation of the instrument at the Tomsk Electric-Lamp Plant demonstrated the effectiveness and accuracy of its operation, the simplicity of servicing it, and the possibility of using the information obtained with its aid without additional processing.

REFERENCES

1. Voltage Regulation in Electrical Networks. Moscow, “Energiya,” 1968.

2. Ya. D. Barkan, N. S. Markushevich. Statistical instruments as a means of obtaining information on the voltage conditions of distribution networks. — Elektricheskie stantsii, 1968, No. 4.