EC135 P2+ Chp 2 Electrical Power System

What types of systems make up the electrical system?

DC (Direct Current) and AC (Alternating Current).

DC System

Main system

Operating at 24/28 VDC

Powered by batter and both engine driven starter generators, or EPU

AC System

Optional system

Converts DC power to 26 and 115 VAC using 1-2 solid state inverters 

What is the VEMD and what does it show?

Vehicle and Engine Monitoring Display

Shows DC voltage and amperage

What is the CAD and what does it show?

Cautions and Advisories Display

indicates malfunctions for both DC and AC systems

What does the WARNING panel show

Certain critical DC malfunctions

What do the starter-generators do

below 50% N1 RPM, starter

Above 50% N1 RPM, 200-amp DC generators

What kind of external power unit (EPU) can be used

24 VDC battery cart or 28 VDC EPU

how many positions does the BAT MSTR switch have

3, ON/OFF/RESET

GEN I & GEN II Switches - how many positions

3 - NORM/OFF/RESET

What Emergency Switches are there? where?

SHED BUS and BUS TIE I/II

Overhead panel

Inverters - how many and what do

2 solid state inverters

Switches on overhead console

convert 28 VDC from buses to 115 / 26 VAC at 400 Hz

INV SEL AC BUS SPLY Switch

used in case of an inverter failure to allow remaining inverter to power all AC buses

battery cold wx limitations

for engine starts in temps below -20 deg C aircraft batt must be preheated to at least -20 C

Max external power amps

max power flow 700 Amps

starter limitations with 2X battery

30 on 60 OFF x 2

30 sec on 30 min off

starter limitations with 40 AH batt/EPU

15 on, 30 off x 2 

then 15 sec on 30 min off

Generator max cont loads (normal, high alt, 2 min)

200 amps / gen

unless over 15000 ft PA - 126 Amps

2 minute 300

BAT TEMP (nicad batt): type of system malfunction, signs and procedure

DC Malfunction

BAT TEMP light on WARNING panel, audio GONG

1. turn BAT MSTR switch off

2. land as soon as possible

3. shut down engines

4. visual inspection may allow for continued flight in VMC only with BAT MSTR off but Land as soon as practicable is required

Dual Generator Failure: type of system malfunction, indications and procedures

DC Malfunction

GEN DISCON cautions for both SYS 1 and SYS II in CAD

BAT DISCH lights on WARNING panel and GONG

1. turn both GEN switch off

2. reduce electrical load 

3. move SHED BUS to EMER (will drain batt!!)

4. land within 30 min

should you reset generators in event of emergency?

NO could cause further damage or fire

single generator failure: type of system malfunction, indications and procedure

DC Malfunction

GEN DISCON caution on the CAD for either SYS I or II

1. move affected GEN switch off

2. Check VEMD for DC volts, rem. gen amps

3. Land as soon as practicable

electrical fire: type of system malfunction,indications and procedure

DC Malfunction

odor of burning insulation and or acrid smoke

procedure is a sequential process of isolating the source of the fire/smoke by turning off BUS TIEs, the BAT MSTR, and finally the individual generators, landing as soon as possible at each step if the condition persists. If both generators and the battery are switched off, all electrical systems will fail (black cockpit) except for standby instruments.

Single inverter failure: type of system malfunction, indication and procedure

AC Malfunction

INVERTER caution on the CAD for SYS I or II

1. move AC BUS SPLY switch from NORM to pos of operating inverter

2. move failed inverter switch to off

3. land as soon as practicable  to have unit repaired

dual inverter failure: type of system malfunction, indication and procedure

AC Malfunction

INVERTER cautions for both SYS I and II on CAD, loss of P/R SAS, and failure of AC powered flight instruments

1. maintain flight using standby instruments

2. if in IMC declare emergency, priority handling from ATC

loss of 26 VAC output from one inverter - indications of power loss from inverter no 1

failure of the signal from the No, 1 AHRS system

loss of 26 VAC output from one inverter - indications of power loss from inverter no 2

P/R SAS caution message in MISC column of CAD, MASTER CAUTION illumination

26 VAC power loss procedure

us AC BUS SPLY switch to select remaining inverter