1.1 Brief Introduction to WFB-800A series of protection devices
WFB-800A series of microcomputer-based protection devices for generator-transformer unit are applicable to the protection of generator-transformer units of 1,000MW-1,000KV and below with various capacities and voltage classes. They also can satisfy the protection of large-scale generator-transformer units in various connection types, and realize the totally independent configuration requirements for dual main protection and dual backup protection and non-electrical quantity protection. Meanwhile, such series of protection also can directly be connected to the comprehensive automation system of the power plant.
Such series of protection device include WFB-801A, WFB-802A, WFB-804A and WFB-805A, and they adopt the same software and hardware platform structure, but are slightly different from relevant hardware resources.
WFB-801A realizes the total electrical quantity protection of generator and exciting transformer (exciter) and can be used in the generator protection of large-scale thermal power, hydropower, nuclear power and gas turbine units, as well as the protection of synchronous phase modifiers.
WFB-802A realizes the total electrical quantity protection of transformers, and can be used in the protection for main transformer and station service transformer of large-scale units and startup/backup transformer of the power plant.
WFB-804A realizes the total non-electrical quantity protection of generator- transformer unit, and also can be used for the non-electrical quantity protection of startup/backup transformer.
WFB-805A realizes the total non-electrical quantity protection of generator-transformer unit and can realize the total electrical quantity protection of one generator and exciter (exciting transformer), one main transformer and one or two station service transformers.
In the engineering application, the corresponding protection devices can be chosen according to the capacity of generator sets, main connecting mode and operating mode, and the different protection configuration and panel configuration schemes are formed, as shown in Article 1.3. The protection software is subject to modular design in the principle of maximized configuration. The special configuration tool Prate-800A can be applied to conduct flexible configuration for protection modules according to different engineering requirements.
1.2 Performance characteristics
- Hardware structure with high performance and high reliability
The hardware structure of CPU management board, startup board and protection board working concurrently is applied. With 32-digit high-performance DSP processor, 32-digit logic processor and 16-digit high-speed AD, the protection exit tripping takes the method of “startup+ protection action” to avoid the false operation caused by the hardware fault of the protection device; the double-main double-rear configuration avoids the failure in operation caused by damage of the components.
- Strong anti-jamming ability
The adequate anti-jamming measures are taken for software and hardware design. The 6U fully-enclosed case, integral faceplate and strict separation of strong current and weak current make the anti-jamming ability of the protection device greatly increased. The external electromagnetic emission also satisfies related standards.
- Strong self-check function
The perfect self-check function of A/D sampling loop can avoid the false operation of the protection device incurred from A/D sampling malfunction; the self-check of switching-out loop can accurately detect the wire break or breakdown fault of any switching-out loop, and then give an alarm and reliably latch up the protection; the self-check of setting value can defect the malfunction of setting value storage area, off-limit of setting value, and unreasonable setting, etc.; it has the self-check function for the power supply of ＋5V and ±15V; when the voltage is abnormal, the protection device gives an alarm and latches up the protection.
- Advanced inrush current identification
When the transformer is closed without load, the inrush current can be identified by phase current, thereby avoiding the influence on the inrush current of this phase by the inrush current of other phases in the phase compensation process of the transformer and acquiring more distinct inrush current characteristics; the unique proprietary technology for fault identification in the no-load operation process of the main transformer is applied, so the differential protection can act instantaneously during faulty no-load operation according to the comprehensive phase opening criterion.
- Reliable TA satisfaction identification
The proprietary technology for TA anti-saturation identification “time lag method” + “virtual restraint current” is applied. When the external fault has TA saturation, the protection is reliably latched up. When the TA saturation of external fault is transformed into internal fault, the protection is opened instantaneously.
- Reliable ratio differential protection
The internal severe fault can be cleared fast by taking the multi-section and multi-broken line method, and at the same time the sensitivity of minor fault and complex fault can also be guaranteed. The multiple algorithms combining long data window with short data window can greatly improve the anti-jamming ability of the software.
- High-sensitivity incremental differential protection
The incremental differential protection is not affected by load current, but has high sensitivity and strong TA anti-saturation ability, and can sensitively reflect the minor turn-to-turn short circuit of the windings and the high resistance ground, and other faults.
- Perfect injection protection scheme for stator ground fault
The 20Hz power supply is used for injection. Considering the influence of the distribution transformer’s leakage impedance and exciting impedance, the calculation accuracy of the ground resistance can be improved. The abnormity warning function of cable loop is set, so as to enhance the reliability and sensitivity of protection.
- Flexible protection configuration
The modular design of the program can be truly realized, so the protection configuration satisfies the maximum requirement of generator-transformer unit. The special configuration tool Prate-800A can be utilized to conduct flexible configuration for protection according to different engineering requirements.
- Flexible setting of transformer coupling group
By setting the connecting method at each side of the transformer, the protection requirements for the transformers in different coupling groups on the site can be satisfied.
- Automatic calculation and setting of balance coefficient of each differential protection
By entering the device parameters, the balance coefficient of each differential protection can be automatically calculated by the device, and can be checked or printed and needn’t be calculated and set independently.
- Friendly human-computer interface
With large color liquid crystal screen display, it adopts the simulated Windows menu mode in full Chinese and displays the color main connection diagram and operating parameters, so it is simple for operation and convenient for use.
- Unique transmission test design
The two modes “transmission by channel” and “transmission by protection” can be selected, so as to inspect the connection of each exit loop on the site and also inspect the action tripping of each protection while the current and voltage are not applied.
- Convenient point-to-point communication function
If there are no test conditions for protection function, the point-to-point communication menu can make the device upload relevant protection action information and alarm information, etc. to the monitoring system, so it is very convenient to conduct point-to-point communication test.
- Perfect event recording function
100 times’ fault report, 10 times’ fault waveform and 200 times’ abnormal information can be recorded. The recorded wave data is compatible with COMTRADE.
- Strong communication function
Five serial ports working concurrently can be provided, and RS-485 or RS-232 can be flexibly selected. The function, Baud rate and verification mode of each port can be flexibly configured. These five ports are respectively used for the acceptance of GPS clock, testing of PC computer, local printing and communication with background of the dual networks. The two serial ports communicating with the background can be configured into Ethernet interfaces. The communication interface has strong compatibility and openness, and supports IEC60870-5-103 communication protocol and MODBUS protocol. It supports the configuration of the Industrial Personal Computer to be used as special managing machine, so as to manage relevant information of the protection device.
- Perfect printing function
The device is provided with two printing modes: automatic printing and manual printing, which can be selected flexibly. It can manually start up the recorded wave and has the printing function, so that the amplitude and phase position of current and voltage at each side can be printed out under normal circumstances, and the user can conveniently verify the polarity of TA and TV when the generator set is put into operation.
- Online modification of tripping ways
The users can set the tripping method of each protection, but needn’t modify the connection of the protection’s secondary loop, and the tripping contact can be directly connected to the tripping loop of the circuit breaker.
