At present, external current transformer, voltage transformer is normally used to collect parameters when intelligent high voltage switchgear collect current and voltage electric parameters online, the biggest disadvantage of external voltage transformer is that fuse is easy to burn out, especially in lighting weather, the probability of damage is greater, which affects the reliability of voltage measurement. In addition, the cost of external voltage transformer is high, especially in distribution line, three external voltage transformer or three phase five column voltage transformers are needed to measure three phase voltage and zero sequence voltage. Users need to consider installation location and maintain them regularly.
Our company develops a kind of combined current and voltage transformer by ourselves which can collect three phase voltage and current signal online at the same time to replace the traditional current transformer and voltage transformer. Its characters are: use current transformer coil and copper foil; when working, the combined type current voltage transformer is fixed on the primary conductive part of high voltage switchgear. When AC current flows through the primary conductive part of high voltage switchgear, current transformer senses AC current, and output second side current which changes according to the values of first side current in lead-out line of current transformer to enable protective control equipment to collect current. When adding AC voltage to high voltage switchgear primary conductive part, copper foil ring will sense the value of AC voltage, shielding line will output second side voltage which changes according to the values of first side voltage to enable protective control equipment to collect voltage parameters.
This combined type current and voltage transformer has simple structure, stable mechanical performance, low maintenance cost, and relatively simple manufacturing and installation process.
At present, among the normal high voltage circuit breaker protection control systems, data collection and process unit normally input signal using more than one cycle(20ms) AC through FFT transformation(or DFT transformation, root mean square operation, ect) and calculation to extract all kinds of needed electrical characteristics. Then according to back of protection and setting value of action to make sure whether to send out protective action exit signal. Switch output circuit normally use output relay, intermediate relay to realize close and open drive. Because output relay, intermediate relay mechanical contact have a certain response time, normal output delay time for relay is more than 5ms, and delay time for intermediate relay is more than 8ms, which mean the fastest delay time from analog date of protection control system input circuit and fault current happens to send out close and open drive signal is at least more than 30.5ms(ignore software calculation time). This response time increases impact time of fault current on power grid and reduces lifetime of power grid operation, and is not conductive to fast fault isolation.
Our company develops a kind of high voltage circuit breaker fast protection control system with independent intellectual property rights, this system through reducing measurement and protection movement time to reduce delay time from analog date of protection control system input circuit and fault current happens to send out close and open drive signal, thus, the impact time of fault current on power grid is shortened, and the purpose of fast protection is achieved.
Open and close drive circuit in switch output circuit of fast protection control system use electronic open and close drive circuit to replace traditional mechanical contact relay, and construct switch fast output circuit. At the same time, use principle of half-wave symmetry and recursive operation, and calculate and extract all electrical parameters on every collecting point from the first half wave (10ms) time, so that reducing time of fault current measurement and sending protection control signal. When fault current exceed current setting value, delay time of protection movement signal will be less than 10ms+20ms/ every cycle collecting point, and use electronic open and close drive circuit to replace traditional mechanical contact relay to compose switch fast output circuit, thus shorten protection control delay time by reducing open and close delay time to less than 0.1ms. The slowest delay time of circuit breaker fast protection control system from analog date input circuit and fault current happens to sending out open drive signal is 10.4ms(when collecting point is 64). Therefore, the fault line can be isolated quickly, the holding time of fault current can be reduced, and the fast protection control will be realized.
Today's small current grounding wire choosing equipment mostly use external voltage transformer and current transformer to collect substation zero-sequence voltage and zero-sequence current of every outgoing switch. When single-phase grounding fault occurs in power grid, the fault line can be judged by using amplitude-comparison method, phase-comparison method or amplitude and phase comparison method. The correct rate of today's small current grounding wire choosing equipment is less than 50%, and many power supply departments are still using pull-wire method to determine fault line.
Our company develops a kind of high voltage circuit breaker single phase grounding protection measurement system with independent intellectual property rights, this protection measurement system use integrated design with circuit breaker main body. It collects three phase current, three phase voltage from distribution line switch, and extract fundamental wave, third and fifth harmonics and zero-sequence power from zero-sequence voltage and zero-sequence current. According to fault characteristics of single-phase grounding fault, use fundamental wave, third and fifth harmonics from zero-sequence voltage and zero-sequence current as activation value, use zero-sequence power direction as decision value to determine circuit breaker load fault, and send single phase grounding protection warning or protection trip order to realize single phase grounding warning and protection.
This single-phase grounding protection controller only needs to collect electrical characteristics of this line, rather than collect electrical characteristics of all outgoing lines in substation altogether. When this line load side occurs single phase grounding fault, single phase grounding protection controller can detect in time and issue alarm or protection trip order. While when this line power side occurs single phase grounding fault, circuit breaker will not move, so as to identify faults accurately and locate fault lines quickly.
Company Name: New Concept Electric Inc
Address: No. 7 Gujin Road, Kai Fa Qu, Yangzhou, Jiang Su Province, China