THE BENEFITS OF U AND Q REGULATION

Through analysis of operation of the Regulatory systems of U and Q regulation on different voltage levels it was possible to detect and describe these benefits:

• Increased safety of the operation of the regulated power system – the system of U and Q regulation effectively uses to prevent voltage instability of the power system available reactive power of the action members (power plants) involved in this system. This makes it possible to respond immediately to the emergence of undervoltage in the system by increasing the supply of reactive power and vice versa by reduction of this supply in the case of overvoltage.

The way of benefits verification:
Comparison of the calculated safety factors of the unregulated and regulated system.

• Increasing the efficiency of operation of the regulated power system – the system of U and Q regulation continuously eliminates adverse reactive power transit in the power system, and thus is reducing the technical losses and improving economy of the power system.

The way of benefits verification
Calculation of savings of losses in the optimal flows distribution of reactive power in the regulated power system through the calculation functions OPF (Optimal Power Flow) application.

• Improving the quality of electricity supply to the end customer - the system of U and Q regulation continuously compensates the reactive power balance in the pilot node and thereby stabilizes voltage of the whole controlled power system and subsequently also in the sockets of the end customers of electricity at low and medium voltage.

The way of benefits verification
Comparison of standard deviations of the voltages in the selected nodes of the unregulated and regulated systems.

• Reduction of the number of tap changes on the transformers - the system of U and Q regulation eliminates the voltage changes before they trigger automatic or manually changing the taps of transformers and thus it is reducing the negative impact on the lifetime of the transformers as well as the risk of failure.

The way of benefits verification
Comparison of statistics of the transformer taps changes in the period considered of the unregulated and regulated systems.

• Compliance with the tolerance values of reactive power flow agreed with the neighboring power system - the system of U and Q regulation enables to maintain the tolerance of the reactive power flow for cross-border lines with neighboring transmission systems (TS), on the transformers TS/110kV and interconnectors between distribution systems and thus to comply with the agreements or applicable regulations.

Note:
Compliance with these set values may not to be specifically evaluated because the measurement of the flow of reactive power can be found on the user´s interface of the dispatcher, who can operatively react when breaching the agreed value occurs.

• Elimination of the negative reverse effect of the wind and photovoltaic power plants on the regulated power system - the system of U and Q regulation also enables the involvement of the wind and photovoltaic power plants into the regulatory process in favor of the regulated power system and thus to eliminate adverse voltage changes generated by the wind and solar power plants being not included into the regulatory system.

The way of benefits verification
Comparison of results of independent measurements of the voltage ratios of the concrete wind or solar power plants when switched on/off the system of U and Q regulation.

• Elimination of the reverse effect of industrial wholesale customers on the regulated power system - the system of U and Q regulation enables the involvement of factory power plants and compensation equipment of the wholesale electricity customers in the regulatory process in favor of the controlled power system and thus eliminate the negative voltage changes being generated by the heavy industrial technology (e.g. electric furnace).

The way of benefits verification
Comparison of results of independent measurements of the voltage ratios of the concrete industrial enterprise when switched on/off the system of U and Q regulation

• Reduction of the claims on the dispatcher of the regulated power system - the system of U and Q regulation functions as a fully automatic control process that requires minimal

co-operation of the regulated power system dispatcher or of the power plant operator.

Note:
The system of U and Q regulation is a dispatcher´s tool that practically when correctly triggered runs in automatic mode and so the best solution is just to let it working.

• The increase of the level of the diagnostics technology of the power plants involved in the regulation of U and Q - the system of U and Q regulation provides a set of pieces of diagnostic information about the power plant operation being generated due to their effect on this power system (accuracy of compliance ASRU).
• Elimination of reactive power dragging of the electrically close generators - the system of U and Q regulation eliminates by means of proper commanding the generators the adverse overflow of reactive power.

The way of benefits verification
Through the power lines between two power plants involved in the regulation of U and Q it shall flow the minimum reactive power.

• Reduction of the operating time of static and rotary compensators in the regulated power system.

Note:
Rotating compensator (overexcited synchronous motor) delivers and takes Q, but it consumes in the same time quite enough active power from the system. Thus it reduces its economic efficiency within the system of U and Q regulation when reducing the cost of electricity distribution, since for its operation it is necessary to spend special operating costs.

• Reduction of the operating time of power reactors in the regulated power system.

The switching the reactor on means a decrease of voltage, because the reactor is Q consumer (and P as well). The switching the reactor on also means, however, increased costs of operation of the network (similarly as the rotating compensator). Another disadvantage is that the switching the power reactor in the tertiary winding of the transformer TS/110kV means a significant step change of voltage 110kV and resulting in subsequent regulatory activity of electrically near transformers 110kV/Medium voltage.

• Prediction of anomalous operating conditions of the power system

The system of U and Q regulation provides a unique data to improve the technical level of the diagnostics tools of the regulated power system for the prevention of anomalous states of the that system. When increased the amount of ASRU regulatory interventions it can quickly be detected a change in the behavior of the system.

Note:
Practical use of this information is mainly a question of specific computational capabilities of the dispatching control system.

• Protection of the self-consumption of the power plants and of targeted power consumption of the wholesale consumers from voltage changes coming from the power system.

The system of U and Q regulation must be keeping a set of limiting conditions in the regulated power system and of the individual power plants. The keeping the specified voltage range of the self-consumption of the power plant and of the targeted power consumption of the wholesale consumers is one of the most important conditions.

Note:
A major contribution to widening the regulatory band of reactive power are the transformers of
self-consumption involved in the System of U and Q regulation equipped with the under loading tap control.