alternator operation

Question 1

total (3 phase) power is

Answer 1

𝑃3𝜙 = 3𝑉𝑝ℎ𝐼𝑝ℎ cos𝜙 and 𝑄3𝜙 = 3𝑉𝑝ℎ𝐼𝑝ℎ sin 𝜙

Question 2

draw phasor dia for relationship between iph and vph

Answer 2

sjf

Question 3

Since 𝑋𝑠*𝐼𝑝ℎ is 90° leading 𝐼𝑝ℎ, what happens

Answer 3

𝑋𝑠𝐼𝑝ℎ cos𝜙 = 𝐸𝑝ℎ sin 𝜃
𝑋𝑠𝐼𝑝ℎ sin 𝜙 = 𝐸𝑝ℎ cos 𝜃 − 𝑉𝑝ℎ

Question 4

3 phase active and reactive is rewritten as (forms)

Answer 4

𝑃3𝜙 = 3 ( (𝑉𝑝ℎ𝐸𝑝ℎ sin 𝜃 / 𝑋𝑠)) and 𝑄3𝜙 = 3 ( (𝑉𝑝ℎ𝐸𝑝ℎ cos 𝜃−𝑉𝑝ℎ^2) / 𝑋𝑠)

relates power regulation to physical action becuase increased mech power input -> increased theta -> increased electrical output

Question 5

when load draws more active power

Answer 5

rotor tends to decelerate since kinetic energy strats converting to electrical energy to boost supplied active power

Question 6

why this bad

Answer 6

rotation speed of rotot must be kept constant becuase the frequency of the alternator V and I must be not changed

Question 7

what does governor and what is isochronous

Answer 7

regulates flow rate of inputted mechanical power, this amount of fuel being burnt , if there is this kind of speed regulation it is isochronous

Question 8

what is speed droop control

Answer 8

adjusts the rotor speed setpoint as power output changes, reducing speed as load increases to maintain stability and share load properly

Question 9

why do you need speed droop control

Answer 9

mech systems that drive alternator cant immediately repsond to changes so speed droop does it

Question 10

how does speed droop work

Answer 10

at no load runs at reference speed ω ref = ωnl (no-load speed). as the alternator starts supplying more active power, rotor slows down to a slightly new speed

Question 11

new speed droop formula (forms)

Answer 11

(forms)

ω = fl -> Speed at full-load power Prated

Question 12

to find speed ωdp when a certain 3phase power is delivered

Answer 12

f sheet

Question 13

what is voltage drrop control

Answer 13

reduces output voltage setpoint as reactive power increases to maintain V stability and allow the proper sharing of VARs along multiple alternators

Question 14

how does voltage droop happen

Answer 14

AVR (automatic V regulator) adjust field current to control V
reactive load increases, AVR reduces Vref to prevent instability

Question 15

how does V droop work

Answer 15

at no reactive power terminal V is no load V Vnl
at reactive power increases, V drops to a new values Vdp

Question 16

formulas for VD and reactive P-V equation (fshee)

Answer 16

f sheet

Question 17

if an alternator absorbs reactive power

Answer 17

Q would be negative so vdp>Vnl -> V rises

but can overlfux machine, overheat field winding, exceed machine ratings