Editing Avro Vulcan (section)

===Electrical and hydraulic systems===
The main electrical system on the B.1/B.1A was 112 V [[Direct current|DC]] supplied by four 22.5[[Watt#Kilowatt|kW]] engine-driven [[starter-generators]]. Backup power was provided by four 24 V 40 [[Ampere hour|Ah]] batteries connected in series providing 96 V. Secondary electrical systems were 28 V DC, [[Single-phase electric power|single-phase]] 115 V [[Alternating current|AC]] at 1600&nbsp;Hz, and [[Three-phase electric power|three-phase]] 115 V AC at 400&nbsp;Hz, driven by [[transformer]]s and [[Inverter (electrical)|inverters]] from the main system. The 28 V DC system was backed up by a single 24 V battery.<ref>''Pilot's Notes'', ch. 7.</ref>

For greater efficiency and higher reliability,<ref name='blackman100101'>Blackman 2007, pp. 100, 101.</ref> the main system on the B.2 was changed to three-phase 200 V AC at 400&nbsp;Hz supplied by four 40 [[Volt-ampere|kVA]] engine-driven [[Constant Speed Drive|constant-speed]] [[alternator]]s. Engine starting was then by air-starters supplied from a [[Turbomeca Palouste|Palouste]] compressor on the ground. Standby supplies in the event of a main AC failure were provided by two primary systems: A [[ram air turbine]]  driving a 17 kVA alternator was stowed in the underside of the port wing and could operate from high altitudes down to {{convert|20000|ft|m|abbr=on}}. In addition an [[Auxiliary power unit|airborne auxiliary power plant]],<ref name='ACMch4'/> a [[Rover Company|Rover]]<ref name="laming p62"/> gas turbine driving a 40kVA alternator was fitted within the starboard wing, and could be started once the aircraft was below an altitude of {{convert|30000|ft|m|abbr=on}}. Secondary electrical supplies were by transformer-rectifier units for 28 V DC and rotary frequency converters for the 115 V 1600&nbsp;Hz single-phase supplies.<ref name='ACMch4'>''Aircrew Manual'', ch. 4.</ref>

The change to an AC system was a significant improvement. Each PFCU had a hydraulic pump that was driven by an electric motor, in modern terminology, this is an [[electro-hydraulic actuator]].<ref>''Aircrew Manual'', ch. 7.</ref> Because no manual reversion existed, a total electrical failure would result in a loss of control. The standby batteries on the B.1 were designed to give enough power for 20 minutes of flying time, but this proved to be optimistic and two aircraft, XA891 and XA908, crashed as a result.<ref name="lamingp60"/>

The main hydraulic system provided pressure for undercarriage raising and lowering and bogie trim; nosewheel centring and steering; wheel brakes (fitted with [[Maxaret]]s); bomb doors opening and closing; and (B.2 only) AAPP air scoop lowering. Hydraulic pressure was provided by three hydraulic pumps fitted to Nos. 1, 2 and 3 engines. An electrically operated [[Pump|hydraulic power pack]] (EHPP) could be used to operate the bomb doors and recharge the [[Hydraulic accumulator#Compressed gas (or gas-charged) closed accumulator|brake accumulators]]. A compressed air (later nitrogen) system was provided for emergency undercarriage lowering.<ref>''Aircrew Manual'' pt. 1, ch. 10, paras. 1–3, 48.</ref>