Da Nang Power Company: to put automatic voltage regulator of 110kV transformer into operation
On 09/2016, the Control center for 110kV unmanned substations of Da Nang city was officially put into operation, performing the function of operation management and remote control of equipment for 09 unmanned substations within the municipal area.
After more than 03 years of operation, the Control center has brought substantial efficiency in operation, has contributed to enhancement of labor productivity and automation level in power system operation, has played a part in safe operation and in increasingly meeting power quality supplied to customers.
Currently at 110kV unmanned substations, 110kV transformers are always equipped with automatic voltage regulator system (AVR), with the function to automatically regulate tap changers of the transformers under given voltage range, however, this system is still operating under manual mode (physically controlled). Under this mode, operators will manually alter tap changers of transformers on HMI screen of Control center via SCADA system. Meanwhile, with 15 transformers, it will take a lot of time and effort for this job; and also trigger delays in controlling as well as interfering in the system during fault event. Specifically, if low voltage level is maintained for a long time, reliability in power supply will be reduced and power losses will be increased. But if high voltage level is kept for a long time, lifetime of equipment will be decreased, which causes financial loss.
Control center of Da Nang
Therefore, in order to enhance automation level of control center, to reduce time for regulating, workload of operators and human supervision towards the system during operation, engineers came up with the idea to introduce AVR function into actual operation, converting from conventional “Manual mode” to “Atuto mode”. In order to ensure operation quality, engineers checked control-protection circuits, set protection relays relating to AVR, calculated the modified voltage range appropriate for load characteristics of each transformer, for voltage diagram which had been published according to regulation. From that, proposals can be submitted to Central Region Load Dispatch Center for issuing adjustment order appropriate to calculated voltage range. In order to ensure that the system can run automatically and efficiently, the Control Center operated a pilot run and evaluated the responsiveness and safety of AVR system of T2 transformer at Xuan Ha substation. Based on the result of this pilot run, AVR system applied for the other transformers.
Auto mode at Lien Tri substation
As mentioned above, turning into auto control mode will help operators reduce a substantial amount of work and time for supervising the system. However, to ensure safe and reliable operation, especially during abnormal events of the power system such as: flicker, voltage fluctuation, over voltage, under voltage and other abnormal cases during operation of tap changers such as: gear slipping, over/under stroke-length of contactors… engineers programmed via Survalent program of Control Center for minimizing unnecessary adjustment, risks towards the system such as locking Auto mode, turning into Manual mode, for installing operational alerts on HMI interface, urgent stoppage of AVR, ensuring safe operation of transformers.
With the above-said improvement, this is the first time on central region power system that regulating output voltage of 110kV transformers of unmanned substations is performed automatically via SCADA system at Control center, without interference of operators. This solution has brought many significant benefits in operating power system and was recognized under the innovation “Improvement of operational level of 110kV unmanned substation via automatic voltage regulation” by Committee of Innovation and Scientific research of Da Nang Power Company in 04/2019, which contributed to realization of EVN 2019 target “Enhance operational efficiency of power system and power market”. In the upcoming period, with accrued experience, engineers of the Control center will continue to master the equipped automation technology in order to improve operational efficiency of the Control center and 110kV unmanned substation, to ensure safe, stable power supply in the city.
Author: Kim Sơn - Anh Chương