1.
POWER – MEASUREMENT for balanced THREE-PHASE LOAD
Task: To measure the input power of asynchronous motor by no–load test – using
ONE – Wattmeter Method – the artificial Neutral wire, with.
To compute with respect to the wattmeter consumption P´.
Diagram (lab 107):
Diagram for lab 57:
Instruments:
VAC…ferromagnetic voltmeter 250V
Rn … resistance multiplier for wattmeter
AAC…ferromagnetic ammeter 5A
ASM … asynchronous motor
W… ferrodynamic wattmeter cos φ 0,2
The measuring Current transformer is used in lab 57 ( the transformer secondary winding has
to be shortened – during the as. motor start).
Measured and computed values:
VL1L2
kW
IL1
αW
[V]
[A]
[W/d]
[d]
RW
[Ω]
RV
[Ω]
P1
[W]
P'W
[W]
P'V
[W]
P3
[W]
cos ϕ
[-]
Wattmeter reading:
P1 = k W α W
Wattmeter and voltmeter consumption:
PW′ =
Three phase input power:
P3 = 3 ( P1 − PW′ − PV′ ) = 3 PL1
Power factor:
cos ϕ =
U L21
RW
kW =
PV′ =
U L21L 2
RV
rV .rA
cos φw
d
U
U L1 = L1L 2
3
PL1
U L1 I L1
2. POWER MEASUREMENT for Unbalanced FOUR-WIRE, WYE-Connected
Load (the neutral conductor, with).
Task:
Having been realized, the 3 – PHASE-WYE connected LOAD (the three various
resistors); by the electronic wattmeter using, to measure:
- either the average power in each phase;
and either the total average power, too.
Diagram:
Instruments:
PMP3 … the electronic programmable ELKO ŠŤOVÍČEK
RZ1 … load resistor 250 Ω (lab 57 … 400 Ω)
RZ2 … load resistor 450 Ω (lab 57 … 600 Ω)
RZ3 … load resistor 600 Ω (lab 57 … 1200 Ω)
Measured and computed values:
VL1
IL1
PL1
VL2
IL2
[V]
[A]
[W]
[V]
[A]
PL2
[W]
VL3
[V]
IL2
[A]
PL3
[W]
P3
[W]
cos ϕ
[-]
Note:
The electronic wattmeter has to be controlled in agreement the enclosed instructions, with.
3. TWO WATTMETER METHOD (Aron´s Method)
- for the TOTAL POWER MEASUREMENT in a THREE-PHASE
system (no-neutral conductor, with).
Task:
Two Wattmeter Method - being applied to the THREE resistors DELTA -connected
LOAD; to measure the input power.
To compute – being respected – the instruments consumptions.
Instruments:
VAC…ferromagnetic voltmeter 500V
AAC…ferromagnetic ammeter 2A
W… ferrodynamic wattmeter 360V/2A
RZ1 … load resistor 410 Ω
RZ2 … load resistor 600 Ω
RZ3 … load resistor 1200 Ω
Diagram:
L1
A
W1
V1 V3 RZ1
RP
L2
A
RP
L3
RZ2
A
Measured and computed values:
V L1L2 I L1 αW1 kW1 VL2L3 I L3
[V] [A] [d] [W/d] [V] [A]
V2
RZ3
W2
αW2
[d]
kW2
[W/d]
I2 VL1L3
[A] [V]
Calculation:
wattmeter consumption; and voltmeter consumption:
2
U L2L
U L21L2
U2
3
P´W 1 =
P´W 2 =
P´V 1 = L1L2
RV1
( RW1 + RP )
( RW2 + RP )
RW
[Ω]
P´V 2 =
RV
[Ω]
P'
[W]
2
U L2L
3
RV2
3 – phase input power:
P3 = k W 1 α W1 + k W 2 α W 2 − P′
P ′ = PW′ 1 + PW′ 2 + PV′1 + PV′2
P3
[W]
4. REACTIVE POWER MEASUREMENT in a THREE-PHASE
system
Task: To measure the reactive input power Q of asynchronous motor by no–load test –
using ONE – Wattmeter Method.
To sketch the phasor diagram – the measured voltages, for.
Diagram:
L1
A
W
ASM
L2
V
RP
L3
Note:
To be measured the reactive power (by the average power wattmeter using) – the voltage coil
has to be connected the voltage lags 90˚, on – with respect to the corresponding voltage.
These one voltage is the line – to line voltage:
- (between line L2 and L3), if it’s measured in line L1;
- (between L3 and L1), if measured in L2;
- (between L1 and L2), if measured in L3;
Instruments:
VAC…ferromagnetic voltmeter 500V
AAC…ferromagnetic ammeter 2A
Measured and computed values:
k W1
α W1
α W2
[VAr/d]
[d]
[d]
W… ferrodynamic wattmeter 360V/2A
k W2
[VAr/d]
Calculation:
Q=
1
( k W 1 α W1 + k W 2 α W 2 + k W 3 α W 3 )
3
Simplification – for the one – phase measurement, only:.
Q=3
1
( k W1 α W1)
3
α W3
[d]
k W3
[VAr/d]
Q
[VAr]