SD3-60 AIRCRAFT MAINTENANCE MANUAL SUPPLY ON GROUND DESCRIPTION & OPERATION

Transcription

1 AMM ELECTRICAL SUPPLY ON GROUND DESCRIPTION & OPERATION 1. General This section provides information about providing electrical power while the aircraft is on the ground. There are two ways in which the aircraft electrical circuits can be supplied with power, as follows:- A. External supply B. Aircraft internal supply (aircraft batteries) To preserve battery power always use an external supply whenever possible. The procedures for energiing the aircraft circuits are given under Servicing (page 301). 2. Electrical Shock - Vital Information The danger to life in the event of electrical shock, depends upon current passing through the body muscles, especially those of the heart, and whether or not the current is direct or alternating. Direct current (dc) is not as great a shock haard for a given voltage as alternating current. Since direct-current arcs are more persistent than those from alternating current (ac), direct-current arcs will burn more severely. Direct current potentials below 140 volts have never proved fatal, even when skin resistance is low. Under similar conditions, alternating currents can be fatal if the potential exceeds 35 volts. WARNING: ELECTRICAL SHOCK CAN DISRUPT NORMAL BODY FUNCTIONS, POSSIBLY RESULTING IN DEATH. THE VOLTAGE AND FREQUENCY USED TO ENERGIZE THE ELECTRICAL SYSTEMS ON MODERN AIRCRAFT MAKES IT NECESSARY TO CONSIDER THE HAZARDS OF ELECTRICAL SHOCK. THE PROCEDURES TO FOLLOW AND THE SEQUENCE IN WHICH THEY ARE FOLLOWED ARE EXTREMELY IMPORTANT IN CASE OF ELECTRICAL SHOCK. Except for mechanical injury which can result from sudden unpredictable muscle reflex or startle reaction, current is the damage-causing factor in electrical shock. Voltage is important only in that it determines the current which will flow through a given body resistance. Dry skin has a resistance between and ohms. Wet skin has a resistance of approximately 1000 ohms. Internal body resistance is between 100 and 600 ohms. The alternating current necessary to operate a 100 watt light bulb is 8 to 10 times the current required to kill a person. Alternating currents of 100 to 200 milliamperes can cause a fatal heart condition known as ventricular fibrillation. An alternating current of 3 amperes is not necessarily fatal unless prolonged over a minute. Such higher currents may result in loss of consciousness and severe burns on the skin. High currents also cause breathing to stop. Therefore, artificial respiration must be started immediately and continued until the victim is breathing normally. A. Procedure to follow in case of electrical shock (1) Act immediately, avoid all possible delay. Page 1 Jun 30/01

2 WARNING: USE SOME MEANS OF INSULATION BETWEEN VICTIM AND RESCUER. MOST DRY, NON-METALLIC MATERIALS ARE SATISFACTORY INSULATORS, USE EXTREME CARE IN REMOVING VICTIM FROM LIVE CONDUCTOR. (a) Free victim from current source, turn off power or remove victim from contact with any live conductor. (b) Start artificial respiration immediately if victim has stopped breathing. A delay of five to ten seconds may be fatal. (c) Call for a physician and an ambulance. Also obtain assistance of available personnel who have had first aid training. (2) Watch victim continuously. If victim is unconscious, breathing may stop. Start artificial respiration immediately to guarantee victim a supply of air. Breathing may resume in a short time if shock has not been too severe. (3) Administer artificial respiration at once if victim's breathing has stopped or is extremely laboured. Remember, a short delay may be fatal. Have someone else obtain medical assistance immediately and continue artificial respiration without ceasing until natural breathing is restored, unless advised otherwise by a physician. Three or four hours may be necessary. Often, when unconsciousness has resulted from electrical shock, the victim becomes stiff or rigid. This must never be a sign to stop artificial respiration. Many persons have been revived after this condition has developed. (4) Do not move victim until victim is breathing normally, except to position him for artificial respiration or to shift his position slightly for his comfort. ow the victim to relax and keep him warm and as comfortable as feasible until medical aid arrives. The time required to restore natural breathing is generally from one to thirty minutes, but may be as much as four hours. (5) A return of natural breathing is not a definite indication that the need for artificial respiration is ended. Do not leave the victim but watch him closely after normal breathing apparently is restored. Victims of electrical shock may stop breathing again after temporary recovery. If breathing stops, resume artificial respiration at once. Severe cuts and burns should be given first aid to stop bleeding and alleviate pain until aid arrives. 3. General Precautions A. Isolating circuits prior to component removal (1) To eliminate the possibility of injury, or damage to components, by shorting live terminals to ground before removing or working at electrical power or control panels and their electrical leads, ensure that all electrical power is off by disconnecting ground supplies and the aircraft batteries. Page 2 Jun 30/01

3 NOTE: Prominently tag the external supply socket with: NOTE: Prominently tag the batteries with: (2) Before removing, or working at, electrical components remote from power and control panels, render the circuit inoperative by opening the relevant circuit breaker. Refer to Wiring Diagram Manual. NOTE: Prominently tag the circuit breaker with: B. Rendering aircraft safe (1) Where replacements have not been fitted, ensure that the aircraft is electrically safe, as outlined in para A.(2), before re-connecting electrical supplies. 4. External Source - Requirements CAUTION: DO NOT CONNECT EXTERNAL POWER MAINTENANCE IN PROGRESS CAUTION: DO NOT CONNECT BATTERY. MAINTENANCE IN PROGRESS CAUTION: DO NOT CLOSE THIS CIRCUIT BREAKER. MAINTENANCE IN PROGRESS The requirements for the external source are summaried as follows:- A. Nominal 28V dc output with steady state variation of 24 to 29V. B. Socket outlet must correspond to the aircraft ground supply plug (Cannon GCB/3LV/14). Page 3 Jun 30/01

4 AMM ELECTRICAL SUPPLY ON GROUND - SERVICING 1. General WARNING: ALWAYS OBSERVE THE SAFETY PRECAUTIONS REFERRED TO IN DESCRIPTION AND OPERATION. Use an external source, whenever possible, to conserve the aircraft batteries. 2. Provision of external power on ground A. General The aircraft electrical circuits can be energised from an external power source or from the internal batteries as respectively detailed in para 2.B. and 2.C. The requirements for an external power source are summarised as follows:- (1) It should meet requirements of ISO6858 (BS 2G219). (2) Nominal 28V dc output with steady state variation of 24 to 29V. (3) Overvoltage protection is essential to prevent a steady state voltage exceeding 32V. (4) Ripple content is critical. Maximum permissible is ± 2 volts. (5) Starter supply characteristics as follows:- Peak current Min. supply characteristic Max. supply characteristic 1000A (with power supply IV/150A/28V) IV/60A/24V UNLIMITED (6) Socket outlet must conform to ISO 461/2 style 1 B (BS 4G173), Cannon GCB/3LV/14. B. Supply aircraft with external electrical power. (1) Check that all circuit breakers are closed. (2) Check that the undernoted switches on panel 4P are as follows: LEFT and RIGHT SHEDDING BUS switches NORMal LEFT and RIGHT GENerator control switches ELECTRICAL MASTER switch LEFT and RIGHT BATTERY switches LEFT and RIGHT ESSENTIAL SERVICES switch/indicators Normal ('out') Page 301

5 (3) Connect the external power supply and check on panel 4P that GROUND SUPPLY PLUG upper indicator displays connection to GROUND SERVICES BUS. NOTE: Those services powered by the ground services busbar are now available. CAUTION: AFTER ELECTRICAL POWER IS CONNECTED TO THE AIRCRAFT AND THE REQUIRED BUSBARS ARE ENERGISED, CONFIRM THAT ALL CONTROL SWITCHES ARE IN THE POSITION AND THAT THE CONTROL PANEL INDICATIONS ARE CONSISTENT WITH THE SELECTED SWITCH POSITIONS. PARTICULAR ATTENTION SHOULD BE GIVEN TO THE ICE PROTECTION SYSTEMS SUPPLIED FROM THE SHEDDING BUSBARS. (4) If it is further required to energise the LEFT and RIGHT MAIN DC BUSbars and the ESSENTIAL SERVICES busbars:- (a) Set ELECTRICAL MASTER switch to EXTERNAL (b) Check that appropriate indicators on panel 4P line diagram confirm: 1 the GROUND SUPPLY PLUG is connected to the GROUND SERVICES BUSbar and the RIGHT MAIN DC BUSbar. 2 the RIGHT and LEFT MAIN DC BUSbars are coupled, and each is connected to the corresponding ESSENTIAL SERVICES busbar. (5) If it is further required to energise the LEFT and RIGHT SHEDDING BUSbars, select associated switches to EMGY (emergency) and check that related indicators confirm connection with corresponding MAIN DC BUS. (6) If A.C. power is required:- (a) Press L, R & STANDBY INVerter switches. Check integral display goes out and line indicators confirm left and right inverters connected to associated AC BUS (standby in reserve). (b) Check indicated inverter voltages and frequencies are in respective ranges V and H. (7) If avionics busbar power is required, set ganged AVIONICS MASTER SWITCH (panel 2P) to ON. C. Supply aircraft with internal electrical power. (1) Check that all circuit breakers are closed. (2) To provide power for ground services only:- Page 302

6 (a) check/set undernoted switches on panel 4P as referred. LEFT & RIGHT SHEDDING BUS switches LEFT & RIGHT GENerator control switches LEFT & RIGHT BATTERY switches LEFT & RIGHT ESSENTIAL SERVICES switch/indicators ELECTRICAL MASTER switch NORMal Normal ('out') INTERNAL (b) check that RIGHT BATTERY to GROUND SERVICES BUS indicator displays 'in line'. NOTE: The services powered by the Ground Services busbar are now available. CAUTION: AFTER ELECTRICAL POWER IS CONNECTED TO THE AIRCRAFT AND THE REQUIRED BUSBARS ARE ENERGISED, CONFIRM THAT ALL CONTROL SWITCHES ARE IN THE POSITION AND THAT THE CONTROL PANEL INDICATIONS ARE CONSISTENT WITH THE SELECTED SWITCH POSITIONS. PARTICULAR ATTENTION SHOULD BE GIVEN TO THE ICE PROTECTION SYSTEMS SUPPLIED FROM THE SHEDDING BUSBARS. (3) If it is further required to energise the LEFT and RIGHT MAIN DC BUSbars and the ESSENTIAL SERVICES busbars:- (a) Select LEFT and RIGHT BATTERY switches ON. (b) Check appropriate indicators on panel 4P, confirm:- 1 RIGHT BATTERY connected to GROUND SERVICES BUS and to RIGHT MAIN DC BUS. 2 LEFT BATTERY connected to LEFT MAIN DC BUS. 3 LEFT & RIGHT MAIN DC BUSbars are connected to respective ESSENTIAL SERVICES busbars. (4) If it is further required to energise the LEFT and RIGHT SHEDDING BUSbars, select associated switches to EMGY (emergency) and check that related indicators confirm connection with corresponding MAIN DC BUS. (5) If A.C. power is required: (a) Press L, R & STANDBY INVerter switches. Check integral display goes out and line indicators confirm left and right inverters connected to associated AC BUS (standby in reserve). Page 303

7 (b) Check indicated inverter voltages and frequencies are in respective ranges, V and H. (6) If avionics busbar power is required, set ganged AVIONICS MASTER SWITCH (panel 1P) to ON. Page 304