Automatic Mains Failure Panel
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AMF panel and generator packages are designed to provide emergency power during mains supply failure. During operation, the control panel of the AMF monitors the mains entering the building. If a mains failure occurs, the panel will disconnect the mains from the load, the generator is started and its output connected to the load. (The load being appliances, lights, etc in use within the house/office/factory at the time of mains failure). The generator continues to supply the building until the mains supply returns. The generator then automatically disconnects, stops and the mains is re-connected to the load. The AMF panel reverts to the standby mode ready to respond in case of another mains failure. Operation With the generator in 'Auto' mode, the incoming main is monitored continuously. If the mains voltage falls outside the preset limits, a 'mains failure' has occurred and the process of starting the generator set is initiated. Once the mains failure is recognised, the contacts are released to disconnect the load from the mains. The 'mains available' and 'mains on load' lamps extinguish. There is a pre-set and adjustable time delay before the generator is started. This avoids unnecessary starting of the generator when very short duration mains breaks occur e.g. 2 or 3 second breaks due to lightning strikes. After the delay, the engine fuel solenoid / ignition system is energised. A pre-heat period begins for generators fitted with indirect injection diesel engines. The choke is operated on petrol-engined sets. The starter motor relay energises and the engine is cranked for a pre-set period (typically 10 seconds). If the engine fires up and the speed increases through the 'crank-cut' threshold, then the starter motor is dis-engaged. Alternatively, if the engine does not start during the first crank period then the starter de-energises for an equal rest period before energising for another attempt. If the engine has not started after the last 'crank' period, then the engine fuel solenoid / ignition is de-energised and the generator is deemed to have failed to start and the appropriate annunciator is illuminated. Assuming that the generator has started during one of the attempts, the alternator output is checked to ensure that it is within specification. If so, then the generator contactor is energised and the load is supplied from the generator. In normal circumstances, the period from mains failure occurring to generator supply being connected is about 20 seconds. During generator operation, the engine oil pressure and temperatures are monitored and should an abnormality occur, the generator will immediately be shutdown and the appropriate annunciator illuminated. When the mains supply returns, the mains available lamp is illuminated within specified limits. The main is then monitored for a pre-set time to ensure that the supply is stable. The generator contactor is then de-energised and the mains contactor energised so that the mains supply is restored to the load. The 'alternator available' and 'alternator on-load' lamps extinguish and 'mains on load' lamp is illuminated. A short break in approximately 1 second occurs whilst the changeover is complete. The generator is 'run-on' for a cooling down period (adjustable up to 30 minutes) before the fuel solenoid / ignition system is de-energised and the engine stops. The operational cycle is then complete and the generator returns to a standby condition. During this time the starter battery is maintained in a charged condition by a 'trickle' charger supplied from the mains.Â
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