Electric operation principle
The auxiliary winding, via the AVR’s control circuit, feeds electrical energy to the exciter winding of the exciter machine. This eliminates the need of additional auxiliary exciter machines or the often used current transformer assemblies. Power supply to the AVR of course is performed also in case of short circuit at the power terminals, so that a sufficiently high short circuit current is produced for granting selectivity of the power plant.
The exciter power, transformed to the 3-phase rotor winding of the exciter machine, is converted to DC power by means of a rotating diode bridge consisting of generously sized diodes and protective elements and then supplied to the rotor of the main generator. Permanent magnets that are located in the stator of the exciter machine ensure the self-excitation of the system.
The voltage control of the main generator at fluctuating loads is performed by changing the exciter current in the stator winding of the exciter machine via the power section of the automatic voltage regulator.
WKV alternators are produced according to international rules and regulations. For ensuring the best-possible operating reliability considering various operating conditions, our engineers have, based on long experience in building electric alternators, developed and adjusted the insulation system in close cooperation with notable manufacturers.
Thanks to our most-modern impregnation plant, WKV offers VPI impregnation (today our standard system) as well as Resin Rich impregnation. All coils are produced in our own plant, tested individually and later again in mounted condition. A sophisticated tape binding of the winding overhangs prevents movement or coil head deformation even at extreme loading. The complete insulation system is matching with temperature class “H” (all rotors and low voltage stators) resp. “F” (medium voltage stators).
Excitation and voltage regulation
Basically, a digital automatic voltage regulator (AVR) made by ABB or Basler or approved equal is used. The AVR shows, among others, the below listed functions:
- Voltage regulator with PID control algorithm
- Cos phi and Reactive power regulator with PID control algorithm
- Exciter current regulator (manual control) with PI control algorithm
- Various limiting and protection functions
- Commissioning and maintenance software is included
Optional functions are, among others:
- Reactive power sharing between parallel machines
- Voltage matching prior to synchronizing
- Automatic synchronizing
- Monitoring of rotating diodes
- Serial communication (MODBUS)
- Power System Stabilizer (IEEE 2A/2B)
On special request of customers, also analogue AVRs can be used.
The AVR is mounted into the alternator's auxiliary terminal box but can also be delivered lose for location into the control cubicle. If requested, we are of course prepared to use any other approved AVR system or to deliver a special exciter data sheet along with the alternator, to enable our customers to use their own AVR system.
Operating performance and alternator protection
Details regarding voltage setting and operation range, static and dynamic voltage performance, voltage wave form, asymmetrical loads and overload capability, parallel operation and taylored electrical design as well as regarding various protective devices can be learned from the Alternator Broshure.