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Power supply for thermal power plants 2017-02-22T13:11:01+00:00

Power supply for thermal power plants

For reliable operation of protection, monitoring and control in thermal power plants quality uninterrupted DC voltage is necessary. It can only be provided by power supply system which is appropriately, precisely designed, professionally manufactured, competently tested and professionally implemented in the plant. For the production of such power supply systems KONČAR uses only the highest quality components of renowned manufacturers (battery, special circuit breakers for DC distribution panels etc.). The numerous positive references from different thermal power plants confirm the soundness of the approach and practices.

Thermal power plants are among those power facilities which should have the highest possible reliability of power supply because the possible damage caused by a power supply failure at a critical moment can surpass by far the price of power supply.
The right choice for such facilities is redundant parallel connection of two completely independent power supplies. Thereby independent double supply of each load or a small group of loads is provided. Redundancy of cables themselves is often applied. High reliability is based on the requirement that the failure of one system does not in any way affect the operation of other system, which continues to supply all loads without interruption.
Voltage distribution must allow a safe connection of any load to the power supply system. They must be designed so that in the event of a short circuit only defective outgoing feeder or load is disconnected. In addition to the selectivity the ability to interrupt relatively high currents must be ensured. Short circuit current is limited only by very small resistance such as internal resistance of battery, cable resistance, contact resistance, etc. so that they typically reach several thousand amperes. The circuit breakers must be able to break those currents in the shortest possible time. Therefore only tested circuit breakers from high-quality manufacturers are applied.
For the smallest plants, with a small number of end loads, DC voltage distribution bord is designed with selectivity in two levels. In most other plants DC voltage distribution bord is designed with selectivity in three levels. There are very large plants with several hundred meters long cables by which the equipment is connected to the power supply. In their case the selectivity in three levels is unsatisfactory solution so DC voltage distribution bord is designed with selectivity in four levels.
It is necessary to carefully design DC voltage distribution bords in order for the selectivity to be ensured in all border situations. This is especially true for the most complex systems with DC distribution bords where it is necessary to achieve selectivity in four levels. Such configurations represent a real design challenge as only a very few circuit breakers are eligible for such applications, and the distribution bord itself inevitably has increased price.
In large plants with numerous and long cables, which connect various equipment to the power supply, earth faults due to weakening or insulation defects represent a serious threat to the reliability of a larger or smaller part of the power supply system. Usually both poles are isolated from the earth. When earth fault occurs in only one pole, it does not affect the operation of DC loads. If there is also earth fault of the second pole towards the earth, there is a short circuit between the poles. The equipment being supplied via these cables is disconnected. However, if there is the second earth fault in the same pole, the control logic of the of power facility will be compromised, so unwanted switching on or disabling of the desired manipulation of the primary equipment of the power facility can occur.
Isolation quality control and detection of earth-fault is a standard part of the power supply system. In major facilities a special system for monitoring and locating earth fault is applied which allows the determination of the outgoing feeder where earth-fault occurred even after its expiry.
In older transmission SS due to deterioration, end-of- life time and various reconstructions and adaptation, power supply quality often does not meet the minimum criteria of reliability, endangering the proper operation and security of the entire facility.
In such cases it is necessary to examine the actual state of power supply and implement appropriate reconstruction. Often it is necessary to redo the design and reconstruct a complete power supply system. It is a very delicate task, which requires a high skill and experience. KONČAR successfully reconstructed many substations, but because of the scope and complexity of the activities, the most important references are impeccable reconstruction of the largest hydro power plants and thermal power plants in Croatia.

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