Instrumentation & Measurement Magazine 25-5 - 8

Fig. 11. The interface of the analysis software for TLMS calibration.
u u I  u UI

PU
   


cosu U cos 
 

22 2
I
 sin 
(3)
The relative measurement uncertainty model of active power
P to apparent power S is:
uuu  PIU
cos 
SU I
22
    
 
u  sin 
 cos  (4)

2
The uncertainty budget is listed in Table 2. The expanded uncertainty
of uP
/S is evaluated to be better than 30 μW/VA, k=2
with power factor ranging from 0.1 to 0.001.
Summary
To meet the requirements for calibrating transformer loss
measurement systems, National Institute of Metrology
China developed a reference system that was able to provide
the measurement accuracy of 30 μW/VA, k=2, i.e.,
the accuracy of the system is 0.3% when power factor is
0.01. Future research will utilize the system on-site and
overcome the challenge of field noise and interference. In
addition, international comparisons with other National
Measurement Institutes will be planned for global equivalence
of transformer loss measurement, which can benefit
transformer manufacturers in exporting the products to
global markets.
Table 1 - A group of testing results at 50 kV, 500 A conditions

Power
factor
0.1
0.05
0.01
0.005
0.001
8
Reference System
Voltage
(V)
Current
(A)
Power
(W)
Voltage
(V)
Unit Under Test
Current
(A)
PP
S
50.0804k 500.238 2.5003M 50.0853k 500.272 2.50125M
50.0825k 500.130 1.24855M 50.0868k 500.166 1.24915M
50.0803k 500.032 245.329k 50.0857k 500.040 245.736k
50.0805k 499.915 122.003k 50.0868k 499.952 123.194k
50.0820k 499.824 22.458k 50.0869k 499.857
22.985k
IEEE Instrumentation & Measurement Magazine
Power (W) Avg.
62
50
42
34
35
BA
A
(μW/VA)
uA
3
3
3
3
3
Avg.
0.06
0.10
0.42
0.68
3.50
PP
P

BA
A
(%)
uA
0.0
0.0
0.0
0.1
0.3
August 2022

Instrumentation & Measurement Magazine 25-5

Table of Contents for the Digital Edition of Instrumentation & Measurement Magazine 25-5

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