Northeast – North China HVDC back-to-back interconnection project—Gaoling substation: big error between AC side and DC side power calculation. The experts from the State Grid analyzed the DC CT and decided to test the precision for accurate and reliable data. On 12th June, PONOVO engineers cooperated with the workers from State Grid to test at site with PDC4000A. For three days, PONOVO engineers complete the tasks and win praises from the owners and experts. The DC/AC power calculation error problems are solved in Gaoling Substation.

10th June: assemble equipment night and day
    
At 19:30 10th June, while engineer Li Zhibing was making supper, he got a call from Manager Chen informing him to go to Gaoling substation test the DC transformer with PDC400A the next afternoon.

There is a set of sample PDC4000A, but it is still not assembled well that can’t be sent to the test site. All the work is estimated to be finished about three day in normal situation. But now, all preparation should be done within less 24 hours.
After an emergency deployment, the Gaoling substation CT project team established: Li Zhibing-Power leader, be responsible for the whole work arrangement and staff coordination; Ren Zhijun-Project leader, be responsible for PDC4000A development, preparation and site test; Li Nan-structure designer, be responsible for structure design, adjustment and installation; be responsible for the test leads, claps installation at site; Lin Xiaoming-R&D assistant, be responsible for welding and installation circuit; be responsible for the test leads, claps installation at site; Ren Zeng, Men Yongzhi and Wang Wei-be responsible for technical support and logistical support.

Short time with heavy task

20:30: Li Zhibing, Ren Zhijun, Li Nan and Lin Xiaoming returned to company to prepare the equipment. In order to ensure the work, early in the morning 11th June, Manager Chen came to company check and instructed. His arrival greatly encouraged the staff. 2:30 in the morning, the circuit inspection and inner structure were inspected normal. All the staff came back home at about 4:00.

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DC CT test site paranoma | Picture for engineers in Gaoling substation

11th June: short rest, departure night and day

After short rest, the next day everyone came to work and started to install PDC4000A external structure. Li Nan and other colleagues were preparing the test leads and claps. At noon, engineers started to make power test. Hu Zhiling, Li Zhibing and Ren Zhijun etc solved the difficult problems. At 18:00, all the installation and adjustment work were finished. At 19:00, all staff set to the destination.

The drivers, Men Yongzhi and Wang Wei, drove smoothly to provide them a good journey for a short time rest.

The project group arrived in Qinhuandao at 1:00 in 12th June. They discussed with the experts from State Grid and got a solution. Engineer Ren Zhijun instructed the test operation process and get approval.

12th June: Skilled operation and precise test

The engineers arrived at the Gaoling substation at 9:30. Entering in the valve hall, the hall is 50m length, 20m height and 30m span. All wall floor were covered with metal plate avoiding electromagnetic interference. 6 groups of converter silicon valve and relevant equipments were hung under roof. There were two DC CT for test. The testers carefully checked the testing solution and reported to the leaders in substation. After getting approval at 14:30, our staff started to prepare the tests.

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CT wiring connection at aerial wrok | Complete wiring diagram by engineers

Accident situations occurred at site. Everyone thought and solved. Li Nan found the diameter of claps was bigger than the current busbar diameter. They couldn’t be connected well. After repeated comparison, they decided to change the structure of special claps. The claps after changed are not only applied the certain diameter current busbar, but also for the certain range diameter current busbar increasing the application range. During the test process, when the tester outputs current in a certain range, the output current would vibration and affected test results. This made engineers nervous. After the technical analysis, they got a conclusion: the tested object was complex with great capacitive and sensibility. If the current response time of the tester was in certain range, the vibration would be occurred. After relevant adjustment, the previous vibration disappeared. The engineers solved the problems one by one. It simultaneously proved PONOVO’s skill and responsive ability.

The DC CT’s rated current was 3000A, standard accuracy 0.2%. PDC4000A maximum outputs current 4000A and accuracy superior to 0.05%. From the primary test, DC CT error maximum arrived at 5.8%, and 200A-3000A non-linear was more than 2%. The accuracy and linear of DC CT had error. This error coincided with previous test result by workers in substation.

The PDC400A was the first time to test DC project CT accuracy and linearity. It provided accuracy data for DC CT and played a key role in excluding safety risks. Besides, PDC4000A outputed0.05% high accurate DC current with heavy current busbar claps to improve efficiency.

At about midnight, all the test work was completed. The results were approved by every party.

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PONOVO’s engineers test DC CT | Read test data

The next day, everyone journeyed home with morning sun. With sight of the DC substation in the high mountains and lofty peaks, everyone was proud. A s a ordinary worker in PONOVO, it was proud to contribute strength for the Northeast – North China HVDC back-to-back interconnection