Instrumentation & Measurement Magazine 25-5 - 4

Reference Standard for the
Calibration of Transformer Loss
Measurement System in China
Wei Zhao, Huanghui Zhang, Li You, Jiafu Wang, and Haiming Shao
P
ower loss is unavoidable for transformers due to the
characteristics of the lossy electrical components and
magnetic materials used for manufacturing them.
Transformer loss can be roughly categorized into load loss and
no-load loss. Fig. 1 illustrates the circuit model of the non-ideal
transformer and the losses [1]. It is estimated that there are
more than 1.7 million power transformers in China, and the energy
loss of these transformers is approximately 250 TWh per
year. Such energy loss not only raises the total cost of the utilities
but also causes considerable impact to the environment.
Several government regulations have been issued by the
Chinese government in recent years. In 2020, the Transformer
Efficiency Improving Strategy was jointly released by the
Ministry of Industry and Information Technology, the State
Administration for Market Regulation and the National Energy
Administration. The national standard GB 20052-2020:
Minimum Allowable Values of Energy Efficiency and the
Energy Efficiency Grades for Power Transformers was implemented
since June 1, 2021. These regulations on the power
transformer efficiency require manufacturers of products to
comply with the requirements in these standards.
Transformer Loss Measurement
Systems
Measurement of the losses in power transformers is an
indispensable quality-verification process. Reliable loss measurement
with low uncertainty provides high quality evidence
to verify the transformer performance. Transformer Loss
Measurement Systems (TLMSs) are developed to measure the
load and no-load loss of power transformers. Fig. 2 illustrates
the setup of a TLMS consisting of a voltage transformer (VT),
wattmeter (WM) and current transformer (CT) [2]. The accuracy
of the TLMS is required to be better than 3%. Commercial
systems with an accuracy up to 1% are available for the testing
voltage of 100 kV, the current of 2000 A and the power factor
(PF) down to 0.01 from some companies with advanced manufacturing
capabilities.
Regular calibrations of TLMSs are required to ensure the
accuracy and stability of the systems. Generally, a TLMS can be
calibrated with two approaches: from the component level or
as a whole. One of the important benefits to calibrate a TLMS
as a whole system is that all possible systematic errors are
covered. E. So built a reference system based on current-comparator-bridge
and achieved the accuracy of 0.2% with PF of
0.01 [3]. O. Petersons also conducted relevant research in the
1980s. He built the standard system with error limit of 0.6%
Fig. 1. Circuit model of non-ideal transformers and the losses.
Fig. 2. Diagram of a transformer loss measurement system consisting of a
voltage transformer, wattmeter and current transformer.
4
IEEE Instrumentation & Measurement Magazine
1094-6969/22/$25.00©2022IEEE
August 2022
Instrumentation & Measurement Magazine 25-5

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