Semiconductor analog excitation regulator units’ functions
(1) Measurement and comparison unit. Measures the generator voltage signal, converts it proportionally into a DC voltage signal, compares it with the set DC voltage, and sends out the generator voltage deviation signal. To ensure that the various units operating in parallel can reasonably and stably share reactive power, a correction unit should be set up.
(2) Comprehensive amplification unit. Composed of the comprehensive amplification section, the proportional-integral section, and the adapter section. The comprehensive amplification section combines and amplifies various basic measurement outputs, feedback and auxiliary limitations generated, as well as various stable and compensatory responses, and outputs them to the proportional-integral section. The proportional-integral section processes them according to the predetermined regulation law and outputs. The adapter section converts the signal voltage through amplification and processing into a phase-shifting control signal voltage to control the excitation voltage.
(3) Phase-shifting trigger unit. Receives the output signal voltage from the comprehensive amplification unit, changes the size of the thyristor trigger control angle, to control the excitation voltage.
(4) Voltage stabilizing power supply. Converts the input AC and DC power supplies into the required voltage-stable power supply for the excitation regulator. The AC and DC power supplies input should be able to be automatically switched in a timely manner.
(5) Various other auxiliary function units:
1) Maximum excitation current limiter. Limits the total current output by the thyristor rectifier bridge below the given excitation peak current.
2) Excitation overcurrent limiter. When strong excitation or excitation overcurrent reaches the allowed time, reduces the excitation current to the long-term allowable maximum value.
3) Under-excitation limiter. According to the needs of generator and power system stability calculation, limits the minimum current output by the thyristor rectifier bridge to the given value corresponding to the active power.
4) Voltage/frequency limiter. Mainly used during no-load operation of the generator disconnected from the grid, to prevent the unit from operating below the industrial frequency due to governor failure, causing incorrect strong excitation and over-excitation faults.
(6) Manual unit. In the early days, manual excitation regulation used an open-loop method, and later adopted a closed-loop regulation method using excitation current as the signal source.
(7) Tracking unit. At each moment when the regulator is in “automatic mode” and closed-loop regulating according to the generator terminal voltage as the signal, the tracking unit “automatically closely follows the corresponding aforementioned voltage signal” to ensure that there is no significant fluctuation in excitation when switching from “automatic” to “manual” mode. When the regulator “automatic” regulation mode has a main and backup dual-channel, it is necessary to ensure that the backup channel automatically tracks the signal of the main channel.
(8) Imbalance (pulse disappearance) protection. Monitors the main channel. When the pulse of the main channel disappears or becomes abnormal, it automatically switches to the standby channel.
(9) Voltage transformer open-circuit protection. When the voltage of the excitation measurement signal uses the voltage transformer voltage and it disappears due to a fault, the excitation regulator is switched from “automatic” to “manual” operation.
Functions of each unit of the microcomputer digital excitation regulator
(1) Analog input and output channels. The sampled quantities include generator terminal voltage, stator current, active power, reactive power, rotor current, and system voltage, etc. The sampling can be AC or DC. AC sampling can be done every 12 points per week.
(2) Switching quantity input and output channels. To ensure safety and prevent interference, the switching quantity input and output channels all need to be isolated by optoelectronics. It is mainly used for the input of signals such as on-site operation, parameter setting, generator status, protection, etc., as well as the operation instructions of the regulator for other excitation equipment on site and the output of various fault signals of the regulator.
(3) Digital phase-shifting trigger. Its function and structure are similar to the analog phase-shifting trigger, consisting of synchronous shaping, phase-shifting calculation, pulse formation, and pulse amplification sections.
Software functions of the microcomputer digital excitation regulator The key feature of the microcomputer digital excitation regulator is that it replaces the various functions of the analog excitation regulator, such as signal comparison, limitation, and integration, with software.