4.1 ALTERNATOR AND EXCITER
The alternator shall be of screen protected, drip-proof, revolving fields, self regulating, brushless, salient pole type, directly coupled to the engine and fitted with exciter compliance to relevant parts of IEC 60034 and IEC 60034-22 as minimum requirements. The alternator shall be of 415 V, three phase, four wire, 50 Hz and duty type S1 in accordance with IEC 60034-1. The alternator shall be capable of delivering its basic continuous rating not less than the rated kVA specified at 0.8 power factor lagging over the whole range of operating conditions. The principal characteristics of
the alternator shall be within the operating limit values compliance to ISO 8528-3 for the performance class specified
Insulation shall be of Class ‘H’ conforming with IEC 60085 and the alternator shall operate up to the temperature rise limits of Class ‘F’ complying to IEC 60034-1. The rotor or armature shall be of one piece, four pole type with lamination pressed and keyed to the shaft. The stator shall be of the multiplicity type for high or low voltages in Star or Delta
connections. Damper windings shall be provided in the pole faces. For alternator of rated capacity at and exceeding 1000 kVA, the alternator shall be fitted with winding heaters to prevent moisture in the winding. The winding heaters
shall complete with automatic thermostat control, maintaining the winding temperature at 5 0C above ambient temperature when the alternator is at stand-still. The winding heaters shall be arranged for automatic disconnection when the alternator is in operation. Two winding heaters per phase shall be provided – one winding heater shall be
connected for operation and the other is for replacement in case the first heater fails. In addition resistance temperature devices (RTD) of Pt100 type shall be provided to monitor the winding temperatures during operation. Two RTD per phase shall be provided. For parallel operation the alternators and their voltage regulations shall comply
with the requirements of BS 4999-140 and relevant parts of ISO 8528.
4.2 VOLTAGE REGULATIONS AND WAVEFORM
The voltage regulation shall be of solid-state transistor amplified type capable of providing voltage regulation conforming to performance class G2 within the operating limit values compliance to ISO 8528-3. The alternator, when driven its rated speed and operating with its normal excitation control system, shall be capable of maintaining the voltage under steady state conditions within ± 2.5 % (± 1 % for parallel operation) of rated voltage for all loads between no-load and rated load at rated power factor. Following transient changes the voltage shall restore to within these limits in less than 1.5 seconds. When alternator driven at rated speed and giving its rated voltage on no load under its normal excitation control system is switched on to a sudden load application, the initial voltage drop shall be limited to 20% of rated voltage and the voltage shall recover to rated voltage in less than 1.5 seconds. The transient rise in voltage after a sudden rated load rejection at rated power factor and constant speed shall not exceed 25%. Normal voltage shall be variable by means of voltage trimmer within ±5% of rated voltage. The voltage waveform shall approximate closely to a sine wave both at no load and full load with a lagging power factor of 0.8 and shall not exceed the limits as stated in ISO 8528-3. The automatic voltage regulator (AVR) shall be of three phase sensing electronic
type equipped with radio frequency interference (RFI) suppressor to electromagnetic compatibility (EMC) compliance and encapsulated to provide protection against moisture and salt-spray. The AVR shall be mounted on anti-vibration mounts for mechanical protection from engine vibrations. Separate voltage trimmer shall be provided. Protection against over-excitation, loss of excitation, alternator overload protection and rotating diode failure shall also be
incorporated. Triggering or activation of any of these protection device shall cause an alarm and shutdown the generator set. For parallel operation, AVR shall be of same made and type to ensure stable operation and correct sharing of reactive power. The voltage unbalance shall be 0.5% of the rated voltage.