In order to ensure normal operation of the transmission system, grid network company EMS (TSO) has to rely on electricity producers, which provides EPS( Energy company of Serbia) and its power plants additional income. – Besides chosen hydro power units, some thermal power units in EPS are also equipped to work in the secondary regulation.
Recent statement of Mr. Zoran Božović, the director of EPS Head Office for electricity generation, that with emerging new, larger power producers independent of EPS, the need for keeping adequate reserves in the total power system in Serbia, and especially the need for system services, including voltage and frequency regulation, will rise. He added that the inclusion of thermal sector in the secondary regulation is something completely new for EPS, and that it is very possible. Then were tested the systems of regulation in the units in TENT and “Kostolac” and agreed with the EMS standards, and Mr. Božović has particularly emphasized that the goal of EPS is to make thermal units of capacity greater than 300 MW capable for operation in secondary regulation.
Only for the chosen ones
And what is, in fact, the secondary regulation in the power system?
In the conversation with Božović, we understood that the answer was much more complicated, prescribed network voltage of 230 volts and a frequency of 50 hertz may include. Previous reports covered extended meetings of ECC (Electricity Coordination Center of Serbia, Montenegro and Macedonia), where discussion was made for hours about how to maintain the frequency of 50 Hz, acknowledging the fact that during the bombing, the links with European interconnection(UCTE) were broken. Frequency less than specified, threatened the operation of the system as well as of systems in the neighboring countries, which was particularly harshly received by the Greeks who demanded strict adherence to standards, although, as they pointed out, they could grasp the difficult situation that EPS and others in the group were in.
The transmission system operator, today’s EMS was then the part of unified EPS and everything was agreed and governed within the unified electric power system. Both primary and secondary regulation operated, because how else the system could function. But back then, the system services were not considered for their market value. Nowadays is different. With the system services one can make profit, which EPS intends to use, and EMS, in turn, needs to purchase these services at certain prices, probably close to European prices, since it is about unique standards of European interconnection (ENTSO-E), in which the Serbian power system returned as soon as one of broken connection has been established. Electric power system of Serbia remained the sole regulatory area and an integral part of the Regulation unit of Serbia, Montenegro and Macedonia (CMM), in which EMS is responsible for the regulation of the entire unit. Hence is greater the need to explain to the general public what the secondary regulation is, especially because this service in power plants of EPS is seen as a novelty. For starters, it is important to understand that the need for secondary regulation will come to the fore when e.g. the wind or solar power plants of high power are attached to the transmission system.
For more detailed explanations, we approached Mr. Alexander Latinović, an independent engineer for turbine regulation, who with his colleague Mr.Milan Lukic, also an independent engineer, but for voltage regulation, prepared a technical paper for the needs of EPS Head Office for the energy generation, in which they both work.
Mr. Latinović said that we should make a difference between the primary and secondary regulation. The need for secondary regulation emerges when the primary regulation stops the frequency in the system with a frequency higher or less than 50 Hz.
– It will be necessary to bring the frequency to nominal value and to achieve the agreed exchange power with the surrounding regulation areas. Secondary regulation is only effective in areas where imbalance is reported. This is done in a way that the central network regulator adjusts the production of individual production units over which it has influence. This is the essence of this service. It should be noted, however, that in the secondary regulation only selected production units work that have a wide range of power regulation – Mr. Latinović said, adding that, in contrast to the secondary, in the primary regulation all machines in hydro and thermal power plants are participating.
Digitalization ensured services quality
– Thanks to the considerable capacities of hydro power sector, especially the reversible HPPs, EPS’s system has been very resilient and flexible, i.e. it reacts to any change in relationship between consumption and production. Simply put, the primary regulation is used to maintain a balance between production and consumption of electricity. Primary regulation works automatically and independently of where the disturbance has occurred. It is a part of each turbine regulator and acts when there is a change in frequency. If the frequency decreases (consumption exceeding the production), the primary regulation, linearly and proportionally to the drop, increases the power of all generating units until the production and consumption are equalized. The process is reversed with frequency growing, i.e. the consumption decrease – explained Mr. Latinović, mentioning the comparison because of the resemblance to pressing on the gas of the motor going uphill or releasing the gas when going downhill.
He said that there is a tertiary regulation as well, and this is a procedure when the planned operation of the production units is automatically or manually adjusted to ensure the necessary reserve for the secondary regulation in the power system. Besides the provision of such a reserve, the tertiary regulation serves to achieve greater efficiency and safety of production and power transmission within the regulation area by engaging new capacity or reallocation of existing ones.
Providing system services implies that there is a certain reserve in the production capacities, provided in a way that machines work with power less than nominal power. Since the reduction of power leads to more cost for production company, the cost of secondary regulation service shall include the value of kilowatt-hours non-produced for this reason. The system services, according Mr. Latinovic include voltage regulation, covering technical energy losses in the transmission network, as well as participation in restoring power system after the collapse (May that happen never again!).
When asked to assess the current readiness of the thermal power plants of EPS for secondary regulation, Mr. Latinović said that in the process of revitalization of thermal power units, new digital control systems were introduced, by which they can all be involved in the provision of certain system services.
– Turbine regulators and digital control systems have proven to be of very good quality during the tests, which is not surprising since they are the achievement of the renowned manufacturers, “Alstom” and “Siemens”, and part was made by our Institute “Mihajlo Pupin” with experts from EPS. New digital turbine regulators are built on aggregates of HPP “Đerdap 1 and 2” and on the HPP and RHPP “Bajina Bašta”, thus providing the most quality regulation of the speed and power of these machines. However, this is not all. The testing of all these systems and their compliance with the EMS standards is being worked on. Besides experts from EPS, the representatives of the Institute “Mihajlo Pupin” and “Nikola Tesla”, as well as competent persons in EMS are involved in this business. The test is done by recording the reaction of the unit to the simulated disturbance – Mr. Latinović said.
Our interviewee mentioned that development of a unique, comprehensive study is in progress, which refers to the state of the primary regulation. Preparation of the study is done by the Institute “Nikola Tesla”, and based on that insight, the need for further improvement in primary regulation of EPS’s power plants will be defined.
Voltage regulation
– The system services include voltage regulation of EMS network, to which the generators of EPS are attached. The transmission system operator (EMS) has the obligation to maintain the nominal voltage and to control the flows of active and reactive powers. The imbalance between the production and consumption of reactive power is the main cause of discrepancies in the nominal voltage value, because if there is a shortage of reactive power, a voltage drop occurs and vice versa. Early last decade, a lack of reactive power in the system was often reported, so it was quite difficult to maintain the proper voltage in the transmission. In addition to a large number of motors with the electricity consumers who “dragged” the reactive power, this problem often emerged due to outdated excitation regulators on generators in EPS’s power plants, which have since been replaced by digital microprocessor-based regulators. These modern devices, namely the excitation systems, have been made, almost all of them, by Institute “Nikola Tesla”. They are all tested and their full readiness was established for voltage regulation and for rendering system services – said Mr. Milan Lukić.
Source Serbia Energy
