Synchronous generators excitation system

Excitation system provides:

• generator startup according to the set algorithm;
• generator operation in standalone mode and in power system with loads from no-load up to rated operation, as well as with overloads accepted for turbogenerator;
• stable operation of turbogenerator in transient and emergency modes, upon load relief and rise, in underexcitation modes accepted for generator according to the stability and heating conditions;
• forced excitation or de-excitation upon power system failures, which cause decreasing or increasing of generator voltage;
• suppression of generator excitation winding field upon normal generator stop by switching of thyristor converter into inverter mode, and in generator emergency modes — by automatic field suppression deactivation;
• automatic regulation of generator excitation current in reactive power, stator voltage, as well as cosφ functions.

• remote generator voltage setting change in the range of 80 % to 110 % of rated value;
• manual excitation current regulation in the range of 0 % to 200 % (set);
• generator excitation current limitation by double value in relation to rated current, as well as generator rotor current overload limitation by time-current characteristic;
• generator stator current overload control by time-current characteristic;
• control and limitation of generator reactive power depending on active power value;
• adjustment of turbogenerator voltage setting according to network voltage with accuracy of 0.3 % of network steady-state voltage;
• accuracy of voltage maintenance at the turbogenerator outputs in the range of 0.5% of set static characteristic;
• constant control of rotor circuits insulation resistance;
• initial generator excitation from DC voltage network 220 V or 110 V;
• control of feeding transformer primary winding phases current.

Generator excitation system consists of the following functional systems:

• main circuit;
• automatic regulators;
• protections;
• control system.

Power part of SVG is a parallel self-excitation circuit with one thyristor converter.

Thyristor converter rectification circuit is irreversible three-phase bridge. Thyristor protection against switching overvoltages is provided by RC-circuits, protection against external overvoltages is provided by varistors.

Internal short circuit protection is provided by reed sensors, which open input automatic circuit breaker via shunt tripping device. Protection of thyristor converter and rotor against overvoltages is provided by thyristor discharger.

Control system provides thyristor converter control, protection and signaling, excitation automatic regulation.

Control system excitation automatic regulator provides voltage maintenance at the generator output with set accuracy upon load change in static and transient modes.

The following protections and limitations channels are implemented in excitation system:

• limitation of excitation current;
• monitoring of excitation current availability;
• monitoring and limitation of generator reactive power;
• generator protection against stator overvoltage higher than 1.2 Ur;
• generator protection against magnetic system saturation upon decrease of generator voltage frequency;
• protection of thyristor converters upon internal and external short circuits;
• protection of thyristor converter and generator rotor against overvoltage;
• control of rotor circuits insulation;
• generator excitation forcing upon generator voltage decrease lower than 0.8 Ur.

All tasks of control system are performed by means of software and hardware. Control system output signals are phase regulated control pulses of thyristor converter. Besides, control system indicates operation modes and causes of emergency trippings, as well as forms signals for Customer’s equipment.

Output signals form into functions of external tasks and values of excitation system output parameters.

Control system is a set of devices and main and peripheral printed-circuit boards. Main printed-circuit boards include control board, output stages board and control terminal with display. Peripheral boards include output current sensor and output voltage sensor, discrete input board, input current sensors, etc.