Excitation systems for brush generators and compensators of up to 1000 MW

The SVTG series excitation systems (SVGG, SVGD, SVG, SVSK) (hereinafter the ES) are static, silicon-controlled, high-speed excitation systems.

General characteristics of ES Series

  • covered range of generator rated power:
    – up to 1000 MW;
  • types of generator excitation:
    – brush;
    – brushless;
  • range of rated excitation current and voltage:
    – excitation current: up to 7500 A;
    – excitation voltage: up to 700 V;
  • excitation transformer types:
    – oil- or dry-immersed transformer;
    – indoor or outdoor transformer;
    – one-group or two-group transformer;
  • power supply circuits:
    – one-group and two-group;
    – shunt-wound and separate excitation;
  • Automated Excitation controllers:
    – automatic (3 types) + system stabilizer (PSS);
    – manual;
  • Automated Excitation Control redundancy circuits:
    – redundancy according to 1+1 circuit: dual-channel full redundancy;
    – no redundancy – single channel with automated and manual controllers;
  • power converters redundancy circuits:
    – standby according to 1+1 circuit: dual-channel full redundancy of converters;
    – redundancy according to N-1 circuit: single-channel redundancy via one redundant converter;
    – no redundancy;
  • number of parallel thyristors on the converter arm:
    – 1;
    – 3 or 4;
  • number of parallel converters in one ES channel:
    – 1;
    – 2 or more;
  • power converter cooling:
    – natural air cooling;
    – forced air cooling;
    – combined air cooling;
  • excitation switching to standby station excitation system:
    – with excitation switching devices to the standby ES;
    – without excitation switching devices to the standby ES;
    – with digital “field-protective relay” (FPR);
  • completeness:
    – full completeness – without using former ES elements;
    – partial completeness – using former ES elements:
    – power transformer (one-group and two-group);
    – field suppression discharging resistance;
    – field suppression device (FSD);
    – devices for connection to standby station excitation system;
  • logging tools:
    – recorder embedded into the Automatic Excitation Controller;
    – stand-alone recorder (not included into Automatic Excitation Controller) for independent control over the Automatic Excitation Controller run;
    – event log file built into the AEC4 controller.
  • instruments for ES control, monitoring and diagnostics:
    – operator touch pad;
    – Computer workstation (a human-machine interface);
  • network interfaces for communication with Automated process control systems:
    – Profibus DP, Modbus RTU, Modbus TCP (Ethernet), CAN, etc.

Basic technical specifications

ES functions:

  • automatic excitation and suppression during generator start and shutdown;
  • initial excitation from the field flashing unit and from the generator residual voltage;
  • automatic adjustment of generator voltage to line voltage;
  • soft start with initial excitation;
  • cutting into mains by precision synchronization method in normal modes of the power system:
    – from the unit control desk/main control desk synchronizer;
    – from automatic excitation controller (AEC):
    * adjustment of generator voltage to the network voltage;
    * turbine frequency adjustment;
    * generator switch closing with control of level and difference in phases of generator and network voltages;
    *out-of-phase reclosing independent relay;
  • cutting in the network by the self-synchronization method in emergency modes of the power system;
  • excitation switching to a standby station excitation system according to standard rules without changing the generator operation mode;
  • rating of the generator short-circuit and no-load (when power is supplied from an external source for self-excitation system);
  • adjustable parameters in Automated Excitation Control:
    – generator voltage (main mode);
    – generator reactive power;
    – cos (?) generator.
  • control structure Automatic Excitation Control – “ARV-SD (stabilizing)”;
  • back-up manual controller of excitation current:
    – switching to a manual controller in case of automatic controller feedback malfunction;
    – switching to a manual controller with maintaining excitation setpoint;
    – excitation control through “More/Less” commands;
  • rotor electromechanical oscillations damping, securing stability of the generator and the power system;
  • droop (compounding) and voltage drop compensation in unit transformer for generator full and reactive current;
  • excitation boost;
  • electric braking mode;
  • line charging mode;
  • re-synchronization mode upon loss of field;
  • excitation winding temperature calculation;
  • generator active and reactive energy accounting;
  • password-protected change of settings.

The ES parameters control accuracy:

  • generator voltage – 0.2%;
  • generator reactive power – 0.5%;
  • cos (?) generator – 0.5%;
  • excitation current in the manual mode – 0.5%.

The ES parameter control range (adjustable):

  • generator voltage:
    – no load mode – from 5% to 110%;
    – network mode – from 95% to 110%.
  • excitation current manual control:
    – no load mode – from 5% to 110% of the generator rated no-load current;
    – network mode – from the minimum limit of 20 … 40% to 110% of the rated generator current.

Control system

All CS tasks are fulfilled by a software and hardware approach.

The control structure of the Automatic Excitation Control – “ARV-SDPK” with the following control channels (see figure down):

  • PID voltage controller:
    – by voltage deviation – dUs (proportional-integral section);
    – by the generator voltage derivative – Us’ (differential section);
  • PSS – power system stabilizer:
    – by the excitation current derivative – If`;
    – by the generator frequency derivative – Fs`;
    – by the generator frequency deviation – dFs.
  • DF – direct feedback on rotor voltage for brushless excitation systems;

Note: the control structure for generators of up to 60 MW can be switched from the “Power System Stabilizer” mode to the PID-controller mode.

Additional functions of Automatic Excitation Control for Generator/motor at Pumped Storage Power Plants:

  • supported starting circuits:
    – direct-on-line and inductor start;
    – auxiliary motor start;
    – start with a soft starter;
  • start with a frequency converter and excitation current control over the “4-20mA” channel from frequency converter.

Structural design of ARV-SDPK control system

Automatic excitation control limiters:

  • minimum and maximum generator voltage;
  • minimum and maximum excitation current;
  • maximum no-load excitation current with power off and generator overfrequency;
  • minimum excitation – limitation of generator reactive power subject to active power («Q=f(P)»);
  • generator overvoltage during its frequency drop («V/Hz=const»);
  • stator overload limiter by time-dependent characteristic;
  • rotor overload limiter by time-dependent characteristic;
  • forcing time by rotor overvoltage characteristic;

Protection system

Protection types for operation on thyristor excitation system:

  • generator overvoltage;
  • generator overcurrent;
  • loss of excitation;
  • internal short circuits in thyristor converters;
  • short circuits in excitation circuit;
  • overvoltage in arrester excitation circuit;
  • loss of conduction on the converter arm;
  • loss of conduction in parallel thyristors on arms;
  • no signal from voltage transformer during field flashing;
  • no signal from voltage transformer and current transformer for the generator in operation mode with switching to manual mode maintaining the excitation setpoint;
  • against forcing excessive duration limiter failure and excitation overcurrent limiter failure;
  • against the “P/Q” minimum excitation limiter failure and transfer to a manual mode with set excitation that ensures over-excitation mode;
  • excitation circuits insulation resistance decrease protection:
    – built-in insulation control device with resistance indication on the console terminal, operator touch-panel, AWS;
    – protection unit “BENDER” with resistance display panel on the UPS cabinet door or on AWS (optional);
  • against resistance increase of excitation circuit “cable-brush rig-rotor”;
  • design excitation winding temperature protection;
  • protection against the stator circuit breaker a-contacts malfunction through redundancy on the stator current;
  • overcurrent and overtemperature protection of power rectifier transformer:
    – basic current protection – ensured independently from ES by using a block incorporate into the generator protection panel;
    – basic temperature protection – secured independently from the ES by using tinternal protection block built into the transformer;
    – backup current and temperature protection – provided by the ES built-in protection;

Protection for operation on the backup station ES:

  • protection against excitation circuits insulation resistance decrease;
  • protection unit “Rotor Protection Relay (RPR)”:
    – protection types:
    • against forcing excessive duration and excitation overcurrent;
    • for short circuits in the excitation circuit;
    – the RPR block consists of:
    • RPR controller;
    • Warning (If> 1.05 * Inom) relay – combined signal of overload starting point and RPR non-readiness.
    • De-excitation relay – a signal informing about the request to decrease the excitation upon overload time expiration;
    • Shutdown relay – a signal to shut down if excitation overcurrent fails to decrease upon overcurrent time expiration or upon the short-circuit current.

Note: The RPR unit serves as the basic protection for operation on the backup excitation system and as the backup protection for operation on the thyristor excitation system.

Callback form