System for optimization of electricity consumption in thermal power plant Osijek

Why is energy efficiency important?

It is in the interest of every company to take care of the rational use of energy permanently. However, it is not easy to tame the consumption of a 40-year-old driver, especially when there is no consumption monitoring system at several points that gives us an overview at all times.

Even if we ignore the environmental consequences, reductions in the consumption of energy or materials are directly reflected in the profitability of the industry or plant itself. If we consume less power and get the same amount of electricity of the same quality, we do our job better.

And we are more environmentally friendly.

Consumption management begins with an overview of the situation in each step of production, continues with training employees to recognize problematic situations, and sets clear protocols for solving them.

How we defined the scope of the project

The total energy consumption is roughly divided into primary and secondary. Primary consumption is necessary for the normal functioning of the plant and the realization of the planned production. Secondary consumption is used for safety and auxiliary systems regardless of plant status, which regular production requires.

To better plan the system, we had to find out:

• What are the maximum loads during production?
• What are the costs of the so-called “cold drive” (no production)?
• Is it possible to reduce the consumption of “cold drive”?
• Is there a possibility of optimizing the maximum consumption during production cycles?
• How much energy is consumed in relation to the outside temperature?
• How much energy is used to produce a certain amount of the final product?
• Considering the amount of daylight and the day’s duration, how much electricity is used for plant lighting (interior and exterior)?

All this shows us exactly where more is being consumed than needed within the power plant, where own consumption includes numerous energy sources, so in this project, we focused exclusively on internal (own) consumption of electricity.

What was the situation at TE-TO Osijek?

When we first discussed this project, TE-TO Osijek did not have a system for recording the consumption of any engaged energy producers, including electricity.

Employees of the TE-TO Osijek facility, as well as their owner (HEP Proizvodnja d.o.o.), recognized the importance of intelligent management of available energy sources, so they ordered a comprehensive system for managing and optimizing consumption, which will initially rationalize their consumption.

Mapping of measurement locations

TE-TO Osijek was built in stages, so the self-consumption system has four locations and multiple power supply options.

1. Block 45MW
2. Gas turbine plant 2x25MW
3. Main administration building with workshop and SBK boiler room
4. Common plants (chemical water treatment)

The self-consumption system at low voltage for primary and secondary self-consumption has one LV drain for each technological consumer (pumps, valves, mixers…). In the case of tertiary consumption, one LV drain supplies a larger group of consumers (several sockets, a group of lighting fixtures, a group of heaters or air conditioners, etc.). Currently, the plant cannot register tertiary self-consumption on the local (power or energy meters) or the superior monitoring and control system (SPPA T3000).

Our first step was installing measuring equipment and creating a monitoring and control system that monitors and reports on the amount and location of tertiary energy consumed. Figure 2 shows the principle diagram of such a system. But that is only the first step.

The system is planned to expand to other energy sources.

We selected the measurement locations in cooperation with the competent service for electrical maintenance. The importance of consumers, their dimensions in terms of electrical power, the possibility of replacing existing or installing new measuring equipment, geographical location and the experience of the employed staff in terms of the relevance of the consumers in question for the optimization system were taken into account.

In addition to the selected consumables, the new system must also support the consumption of all existing benchmarks. As this is only the initial phase, after which the project is tailored to all levels of electricity consumption and other energy sources, LV distributors must be close to all locations where consumption will be measured in the present and future.

Five macro locations fit into the parameters: three in the ​​thermal power plant area and two in other locations. The central monitoring and control computer (main command room) is in the central control room.

The system is planned to be maximally flexible to meet the diversity of consumers within the circuit of the thermal power plant – and even outside it – one station is dislocated. The dislocated station communicates with the primary PLC device via the GSM/GPRS system, and the primary PLC device communicates with the monitoring and control system via the Industrial Ethernet protocol.

How we chose the measuring equipment and connected the old to the new system

Two-way working energy meters of the type SCHRACK MGDIZ were chosen for measurements on low-voltage drains of smaller dimensions and less importance. The voltage is measured directly on them, the current via the appropriate current measuring transformers, and the pulse output of the meter is used to collect data on the PLC device, the frequency and duration of which can be parameterized in different ways.
We use SENTRON PAC3200 two-way multi-tariff energy meters for more critical and more significant consumers. These more advanced devices measure working, reactive and apparent power in total and on each phase individually. Analogously, working, idle and apparent energy is recorded in both directions in a multi-tariff manner. Line and phase voltages, frequency, currents of all three phases, total and individual power factor, and total harmonic distortion of the voltage are also measured, and the minimum and maximum values ​​in the given interval are recorded. The meter can be read locally and is included in the system via the PFOFIBUS extension. Hence, all measured values ​​ read on the instrument are also available on the supervisory control system.

In addition to the new measuring equipment, we also included a Landis Gyr billing meter owned by HEP OPS d.o.o. and three Iskra MT851 meters owned by HEP ODS d.o.o. All the mentioned meters are equipped with impulse outputs, so we created a project to adapt the existing wiring by which the impulse outputs are introduced into the system. We protected them with galvanic isolation.

What does the system measures and at what intervals

Simplified, the input parameters are energy signals (pulses, analog value…), the weighting factor of the energy signal and the synchronization pulse, and the output parameters are the current power and energy, the forecasted power and energy at the end of the reference interval, the average power value, the accumulated energy value in the previous reference interval.

The reference interval is 15 minutes, but it can be changed for each drain.

In the case of the Power plant Osijek, the PLC device synchronizes the measurement data collection in 15-minute intervals, except for three dislocated meters whose internal clocks are synchronized with the grid frequency and which have their synchronization pulse.

At the end of each reference interval, the accumulated energy and average power are archived.

As the measurement records are sparse (the industry standard is continuous recording), it is essential not to lose measurements, even during regular monitoring and control computer maintenance. So, we implemented a buffer in the PLC computer that stores the archived values ​​until the archiving computer is available.